Cubic Mn_(2)Ru_(x)Ga Heusler compound is a typical example of compensated ferrimagnet with attractive potential for high-density,ultrafast,and low-power spintronic applications.In the form of epitaxial thin films,Mn_(...Cubic Mn_(2)Ru_(x)Ga Heusler compound is a typical example of compensated ferrimagnet with attractive potential for high-density,ultrafast,and low-power spintronic applications.In the form of epitaxial thin films,Mn_(2)Ru_(x)Ga exhibits high spin polarization and high tunability of compensation temperature by freely changing the Ru content x in a broad range(0.3<x<1.0).Herein Mn-Ru-Ga-based polycrystalline bulk buttons prepared by arc melting are systematically studied and it is found that in equilibrium bulk form,the cubic structure is unstable when x<0.75.To overcome this limitation,Mn-Ru-Ga is alloyed with a fourth element V.By adjusting the content of V in the By adjusting the content of V in the Mn_(2)Ru_(0.75)V_(y)Ga and Mn_(2.25-y)Ru_(0.75)V_(y)Ga quaternary systems the magnetic compensation temperature is tuned.Compensation is achieved near 300 K which is confirmed by both the magnetic measurement and anomalous Hall effect measurement.The analyses of the anomalous Hall effect scaling in quaternary Mn-Ru-V-Ga alloy reveal the dominant role of skew scattering,notably that contributed caused by the thermally excited phonons,in contrast to the dominant intrinsic mechanism found in many other 3d ferromagnets and Heusler compounds.It is further shown that the Ga antisites and V content can simultaneously control the residual resistivity ratio(RRR)as well as the relative contribution of phonon and defect to the anomalous Hall effect a"/a0'in Mn-Ru-V-Ga,resulting in a scaling relation a"/a0'∝RRR^(1.8).展开更多
We conducted a comparative study of the magnetic and transport properties of single-crystalline LaCo_(2)As_(2) and NdCo_(2)As_(2).LaCo_(2)As_(2) is a soft metallic ferromagnet which exhibits purely intrinsic anomalous...We conducted a comparative study of the magnetic and transport properties of single-crystalline LaCo_(2)As_(2) and NdCo_(2)As_(2).LaCo_(2)As_(2) is a soft metallic ferromagnet which exhibits purely intrinsic anomalous Hall effect(AHE) due to Co-3d electrons. With Nd-4f electronic magnetism, ferrimagnetic NdCo_(2)As_(2) manifests pronounced sign reversal and multiple hysteresis loops in temperature-and field-dependent magnetization, Hall resistivity, and magnetoresistance, due to complicated magnetic structural changes. We reveal that the AHE for NdCo_(2)As_(2) is stemming from the Co sub-lattice and deduce its phase diagram which includes magnetic compensation and two meta-magnetic phase transitions. The sensitivity of the Hall effect on the details of the magnetic structures in ferrimagnetic NdCo_(2)As_(2) provides a unique opportunity to explore the magnetic interaction between 4f and 3d electrons and its impact on the electronic structure.展开更多
Rare earth iron garnets R3Fe5-xMnxO12(R=Pr, Nd, Sm, Eu) were prepared through mild hydrothermal me- thod. The initial alkalinity of solutions was thought to play an important role in governing the content of Mn. The...Rare earth iron garnets R3Fe5-xMnxO12(R=Pr, Nd, Sm, Eu) were prepared through mild hydrothermal me- thod. The initial alkalinity of solutions was thought to play an important role in governing the content of Mn. The effect of substitution Fe^3+ ions by Mn^3+ ions on magnetic properties was investigated. The saturation magnetizations of Mn-doped samples are larger than that of corresponding parent compounds due to the moment of Mn^3+ ion being smaller than that of Fe^3+. It is clearly shown that incorporation of Mn^3+ gives rise to significant variations in the Curie temperature. With increasing of Mn content x, Curie temperatures reduced sharply for the garnets, which could be explained by the exchange interaction between a-d Fe^3+ being reduced in these compounds.展开更多
We use the mean-field approximation of Dyson–Maleev representation to study an XXZ Heisenberg ferrimagnetic spin chain with single-ion anisotropy. By solving the self-consistent equations with different anisotropies,...We use the mean-field approximation of Dyson–Maleev representation to study an XXZ Heisenberg ferrimagnetic spin chain with single-ion anisotropy. By solving the self-consistent equations with different anisotropies, λ and D respectively,the energy spectrums, internal energy, static susceptibility and specific heat are calculated. Especially, the quantum phase transition of the magnetization plateau induced by single-ion anisotropy D is obtained in the model of the ferrimagnetic spin chain by using Dyson–Maleev mean-field theory.展开更多
Magnetic hyperthermia is a fast emerging, non-invasive cancer treatment method which is used synergistically with the existing cancer therapeutics. We have attempted to address the current challenges in clinical magne...Magnetic hyperthermia is a fast emerging, non-invasive cancer treatment method which is used synergistically with the existing cancer therapeutics. We have attempted to address the current challenges in clinical magnetic hyperthermia-improved biocompatibility and enhanced heating characteristics, through a single combinatorial approach. Both superparamagnetic iron oxide nanoparticles(SPIONs) of size 10 nm and ferrimagnetic iron oxide nanoparticles(FIONs) of size 30 nm were synthesized by thermal decomposition method for comparison studies. Two different surface modifying agents, viz, Cetyl Trimethyl Ammonium Bromide and 3-Aminopropyltrimethoxysilane, were used to conjugate Bovine Serum Albumin(BSA) over the iron oxide nanoparticles via two different methods—surface charge adsorption and covalent amide bonding, respectively. The preliminary haemolysis and cell viability experiments show that BSA conjugation mitigates the haemolytic effect of the iron oxide nanoparticles on erythrocytes and is non-cytotoxic to the healthy Baby Hamster Kidney cells. It was observed from the results that due to better colloidal stability, the SAR value of the BSA-iron oxide nanoparticles is higher than the iron oxide nanoparticles without BSA, irrespective of the size of the iron oxide nanoparticles and method of conjugation. The BSA-FIONs seem to show improved biocompatibility, as the haemolytic index is less than 2 % and cell viability is up to 120 %, when normalized with the control. The SAR value of BSAFIONs is 2300 Wg^(-1) when compared to 1700 Wg^(-1) of FIONs without BSA conjugation. Thus, we report here that BSA conjugation over FIONs(with a high saturation magnetization of 87 emug^(-1)) provide a single combinatorial approach to improve the biocompatibility and enhance the SAR value for magnetic hyperthermia, thus addressing both the current challenges of the same.展开更多
Magnetic properties of a two sublattice ferrimagnet with antiferromagnetic exchange interaction inside one of the sublattices are calculated within the framework of the molecular field theory taking into account the a...Magnetic properties of a two sublattice ferrimagnet with antiferromagnetic exchange interaction inside one of the sublattices are calculated within the framework of the molecular field theory taking into account the anisotropy of unstable sublattice. The magnetization curves of single crystal GdMn 2Ge 2 for the magnetic field parallel and perpendicular to the c axis at different temperatures are calculated. Field induced magnetic phase transitions in GdMn 2Ge 2 are discussed. Calculated H T magnetic phase diagrams are in fair agreement with experimental data.展开更多
We use the Schwinger-boson approach to study the anisotropy ferrimagnetic spin-(1/2,1) chain with bond alternation.Based on the effect of bond alternation δ,we obtain energy gap,free energy,and specific heat,respec...We use the Schwinger-boson approach to study the anisotropy ferrimagnetic spin-(1/2,1) chain with bond alternation.Based on the effect of bond alternation δ,we obtain energy gap,free energy,and specific heat,respectively.The specific heat with larger bond alternation(δ 〉 0.7) displays a peak at low temperature.Based on the effect of XXZ anisotropy parameter Δ,we present excited spectrums,free energy,and specific heat,respectively.展开更多
We have investigated the low-temperature magnetism and spin-lattice coupling in (Bio.46Nao.46Bao.os)TiO3 :Co in order to understand the magnetoelectric effect in such artificially synthesized dilute magnetic ferroe...We have investigated the low-temperature magnetism and spin-lattice coupling in (Bio.46Nao.46Bao.os)TiO3 :Co in order to understand the magnetoelectric effect in such artificially synthesized dilute magnetic ferroelectrics. It is revealed that the as-prepared (Bio.46Nao.46Bao.os)TiO3:Co at Co content of 20%~30% exhibits fascinating ferrimagnetism which is robust against magnetic field, the abnormal spin lattice coupling characterized by a negative magnetostriction effect; and the suppressed magnetic moment within the temperature range of 30 K-50 K is identified. These magnetic behaviours at low temperatures can be explained by the competition between the ferrimagnetic response and the magnetic moment suppression induced by the abnormal spin lattice coupling effect. Finally, the ferroelectric and magnetodielectric properties are also discussed.展开更多
The ferrimagnetism and quantum phase transition of a bipartite lozenge periodic Anderson-like organic polymer, in which the localized f electrons hybridize with the odd site conduction orbitals, are investigated by me...The ferrimagnetism and quantum phase transition of a bipartite lozenge periodic Anderson-like organic polymer, in which the localized f electrons hybridize with the odd site conduction orbitals, are investigated by means of Green's function theory. The ground state turns out to be gapless ferrimagnetism. At a finite temperature, the ferrimagnetic-to- paramagnetic phase transition takes place. The Kondo screenings and Ruderman-Kittel-Kasuya-Yosida (RKKY) inter- action can reduce and increase the transition temperature, respectively. Two Kondo screenings compete with each other, giving rise to the localized f electron spin screened antiferromagnetically. Accordingly, in a magnetic field, all spins are aligned along the chain easily, which is associated with metal-insulator transition. Furthermore, in a temperature-field plane, we reveal the gapless and spin polarized phases, which are characterized by susceptibility and specific heat, and whose behaviours are determined by the competition between the up-spin and down-spin hole excitations.展开更多
The magnetic properties of an antiferromagnetic bond alternating spin-l/2 zigzag chain with asymmetrical ferro- magnetic next-nearest-neighbour exchange interactions at finite temperature are investigated by using the...The magnetic properties of an antiferromagnetic bond alternating spin-l/2 zigzag chain with asymmetrical ferro- magnetic next-nearest-neighbour exchange interactions at finite temperature are investigated by using the many-body Green's function theory. It is found that the ferrimagnetic ordering does not appear in the symmetrical next-nearest- neighbour coupling case, and takes place only for the asymmetrical next-nearest-neighbour case at finite temperature rather than the ground state. Furthermore, as the asymmetry degree of the next-nearest-neighbour exchange inter- actions increases, the ferrimagnetism becomes more and more dominant. It is shown that the elementary excitation spectra are responsible for the observed magnetic behaviour.展开更多
The electronic structures of Ti_2NbSb with Hg_2CuTi structure and TiZrNbSb with LiMgPdSn structure are investigated using first-principles calculations.The results indicate that Ti_2NbSb is a fully compensated ferrima...The electronic structures of Ti_2NbSb with Hg_2CuTi structure and TiZrNbSb with LiMgPdSn structure are investigated using first-principles calculations.The results indicate that Ti_2NbSb is a fully compensated ferrimagnetic spin-gapless semiconductor with an energy gap of 0.13 e V,and TiZrNbSb is a half-metallic fully compensated ferrimagnet with a half-metallic gap of 0.17 e V.For Ti_2NbSb,the total energy of the Hg_2CuTi structure is0.62 e V/f.u.higher than that of the L2_(1) structure,which is the ground state,and for TiZrNbSb,the total energy of the structure considered in this work is only 0.15 e V/f.u.larger than that of the ground state.Thus both of them may be good candidates for spintronic applications.展开更多
The spin Hall magnetoresistance(SMR)effect in Pt/Gd_(3)Fe_(5)O_(12)(Gd IG)bilayers was systematically investigated.The sign of SMR changes twice with increasing magnetic field in the vicinity of the magnetization comp...The spin Hall magnetoresistance(SMR)effect in Pt/Gd_(3)Fe_(5)O_(12)(Gd IG)bilayers was systematically investigated.The sign of SMR changes twice with increasing magnetic field in the vicinity of the magnetization compensation point(TM)of Gd IG.However,conventional SMR theory predicts the invariant SMR sign in the heterostructure composed of a heavy metal film in contact with a ferromagnetic or antiferromagnetic film.We conclude that this is because of the significant enhancement of the magnetic moment of the Gd sub-lattice and the unchanged moment of the Fe sub-lattice with a relatively large field,meaning that a small net magnetic moment is induced at TM.As a result,the Néel vector aligns with the field after the spin-flop transition,meaning that a bi-reorientation of the Néel vector is produced.Theoretical calculations based on the Néel’s theory and SMR theory also support our conclusions.Our findings indicate that the Néel-vector direction of a ferrimagnet can be tuned across a wide range by a relatively low external field around TM.展开更多
Compensated ferrimagnetic insulators are particularly interesting for enabling functional spintronic,optical,and microwave devices.Among many different garnets,Gd_(3)Fe_(5)O_(12)(GdIG)is a representative compensated f...Compensated ferrimagnetic insulators are particularly interesting for enabling functional spintronic,optical,and microwave devices.Among many different garnets,Gd_(3)Fe_(5)O_(12)(GdIG)is a representative compensated ferrimagnetic insulator.In this paper,we will study the evolution of the surface morphology,the magnetic properties,and the magnetization compensation through changing the following parameters:the annealing temperature,the growth temperature,the annealing duration,and the choice of different single crystalline garnet substrates.Our objective is to find the optimized growth condition of the GdIG films,for the purpose of achieving a strong perpendicular magnetic anisotropy(PMA)and a flat surface,together with a small effective damping parameter.Through our experiments,we have found that the surface roughness approaching 0.15 nm can be obtained by choosing the growth temperature around 700℃,together with an enhanced PMA.We have also found the modulation of magnetic anisotropy by choosing different single crystalline garnet substrates which change the tensile strain to the compressive strain.A measure of the effective magnetic damping parameter(α_(eff)=0.04±0.01)through a spin pumping experiment in a GdIG/Pt bilayer is also made.Through optimizing the growth dynamics of GdIG films,our results could be useful for synthesizing garnet films with a PMA,which could be beneficial for the future development of ferrimagnetic spintronics.展开更多
Current-induced multilevel magnetization switching in ferrimagnetic spintronic devices is highly pursued for the application in neuromorphic computing.In this work,we demonstrate the switching plasticity in Co/Gd ferr...Current-induced multilevel magnetization switching in ferrimagnetic spintronic devices is highly pursued for the application in neuromorphic computing.In this work,we demonstrate the switching plasticity in Co/Gd ferrimagnetic multilayers where the binary states magnetization switching induced by spin–orbit toque can be tuned into a multistate one as decreasing the domain nucleation barrier.Therefore,the switching plasticity can be tuned by the perpendicular magnetic anisotropy of the multilayers and the in-plane magnetic field.Moreover,we used the switching plasticity of Co/Gd multilayers for demonstrating spike timing-dependent plasticity and sigmoid-like activation behavior.This work gives useful guidance to design multilevel spintronic devices which could be applied in high-performance neuromorphic computing.展开更多
We further calculate the dependence of xT on T in high magnetic fields,where X denotes susceptibility and T is temperature,using our previous research work - Green function's decoupling approximate approach,for th...We further calculate the dependence of xT on T in high magnetic fields,where X denotes susceptibility and T is temperature,using our previous research work - Green function's decoupling approximate approach,for the one-dimensional ferrimagnetic chain with alternating spins 1 and 1/2.We find a linear correlation in certain range of magnetic field between the temperature of xT maximum and the magnetic field.Moreover,we simply analyze its physical meaning by our approach.展开更多
Ferroelectric and magnetic properties of Fe1-xMnxV2O4 (0 ≤ x ≤ 0.5) spinels are investigated on the basis of dielectric, polarization, and susceptibility measurements. Ferroeleetric polarization is discovered in c...Ferroelectric and magnetic properties of Fe1-xMnxV2O4 (0 ≤ x ≤ 0.5) spinels are investigated on the basis of dielectric, polarization, and susceptibility measurements. Ferroeleetric polarization is discovered in collinear ferrimagnetic and Yafet-Kittel magnetic phases for 0.1 ≤ x ≤ 0.4, which can be tuned by a magnetic field. As orbital-active FJ+ is substituted with Mn2+, ferroeleetric polarization decreases for 0 ≤ x ≤ 0.4 and disappears for x=0.5. We propose that the two polar components in ferroelectric polarization originate from the exchange striction mechanism and the spin-current model, respectively.展开更多
The mixed spin-2 and spin-5/2 Ising ferrimagnetic system with different anisotropies (DA/z|J|) for the spin-2 and (DB/z|J|) for the spin-5/2 is studied by the use of the mean-field theory based on the Bogoliubov inequ...The mixed spin-2 and spin-5/2 Ising ferrimagnetic system with different anisotropies (DA/z|J|) for the spin-2 and (DB/z|J|) for the spin-5/2 is studied by the use of the mean-field theory based on the Bogoliubov inequality for the free energy. First, the ground state phase diagram of the system at zero temperature is obtained on the (DA/z|J|,DB/z|J|) plane. Topologically, different kinds of phase diagrams are achieved by changing the temperature and the values of the single ion anisotropies DA/z|J| and DB/z|J|. Besides second-order transition lines, first order phase transition lines terminating at tricritical points, are found. The existence and dependence of a compensation temperature on single-ion anisotropies is also investigated.展开更多
A first-principles study of structure property correlation and the origin of ferrimagnetism is presented based on LSDA+U method. In particular, the results for the ground state structure, electronic band structure, de...A first-principles study of structure property correlation and the origin of ferrimagnetism is presented based on LSDA+U method. In particular, the results for the ground state structure, electronic band structure, density of states, Born effective charges, spontaneous polarization and cationic disorder are discussed. The calculations were done using Vienna ab-initio simulation package (VASP) with projector augmented wave method. We find that the ground state structure is orthorhombic and insulating having A-type antiferromagnetic spin configuration. The cationic disorder is found to play an important role. Although the cationic site disorder is not spontaneous in the ground state, interchange of octahedrally coordinated Ga2 and Fe2 sites is most favored. We find that ferrimagnetism? in gallium ferrite is primarily due to this exchange between Ga-Fe sites? such that Fe spins at Ga1 and Ga2 sites are antiferromagnetically aligned? while maintaining ferromagnetic coupling between Fe spins at Ga1 and Fe1? sites as well as between Fe spins at Ga2 and Fe2 sites. Further, the partial density of states shows noticeable hybridization of Fe 3d, Ga 4s,? Ga 4p and O 2p states indicating some covalent character of Ga/Fe-O bonds.? However, the charge density and electron localization functions show largely the ionic character of these bonds. Our calculation predicts spontaneous polarization of ~59 μC/cm2 along b-axis.展开更多
The heat capacity of some ferrimagnets has additional structures like a shoulder in the Schottky-like peak, or emergence of a second peak when an external magnetic field is applied. It is shown here that the ferromagn...The heat capacity of some ferrimagnets has additional structures like a shoulder in the Schottky-like peak, or emergence of a second peak when an external magnetic field is applied. It is shown here that the ferromagnetic and anti-ferromagnetic elementary excitation spectra give rise to two independent heat capacity peaks, one enveloped by the other, which add up to give the peak for the total system. Taking this into account helps understand the additional structures in the peaks. Moreover, the classification of ferrimagnets into predominantly antiferromagnetic, ferromagnetic, or a mixture of the two is shown to be validated by studying them under additional influences like dimerization and frustration. Because these two are shown to influence the ferromagnetic and antiferromagnetic dispersion rela tions—and hence the quantities like heat capacity and magnetic susceptibility—by different amounts, the characterization of ferrimagnetic systems (1,1/2), (3/2,1) and (3/2,1/2) is brought out more clearly. Both these influences enhance antiferromagnetic character. PACS numbers: 75.10.Jm, 75.50.Ge.展开更多
To improve microwave hyperthevmia in cancer therapy, the thermal effect of fer-rimagnetic resonance (FMR) during microwave irradiation was studied. Resonant temperatureelevation (RTE) of single crystal grain and polyc...To improve microwave hyperthevmia in cancer therapy, the thermal effect of fer-rimagnetic resonance (FMR) during microwave irradiation was studied. Resonant temperatureelevation (RTE) of single crystal grain and polycrystal powder of resonant media was measuredalone and in imitative muscle and egg white and in mice. The results indicated that the RTE produced by FMR could be used to improve penetrationdeepness, heating selectivity and temperature distribution of microwave hyperthermia in cancertreatment. It was expected that the potential function of the FMR heating system would be ex-ploited greatly for cancer therapy, and then magnetically guided microwave hyperthermia thera-py, chemotherapy, radiotherapy and immunotherapy might he combined multiply within this sys-tem by means of the static magnetic field (SMF) and magnetic microcarrier. Limitation of reso-nant heating was also discussed in this paper.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFA1402600)the National Natural Science Foundation of China(Grant No.12274438)the Beijing Natural Science Foundation,China(Grant No.Z230006)。
文摘Cubic Mn_(2)Ru_(x)Ga Heusler compound is a typical example of compensated ferrimagnet with attractive potential for high-density,ultrafast,and low-power spintronic applications.In the form of epitaxial thin films,Mn_(2)Ru_(x)Ga exhibits high spin polarization and high tunability of compensation temperature by freely changing the Ru content x in a broad range(0.3<x<1.0).Herein Mn-Ru-Ga-based polycrystalline bulk buttons prepared by arc melting are systematically studied and it is found that in equilibrium bulk form,the cubic structure is unstable when x<0.75.To overcome this limitation,Mn-Ru-Ga is alloyed with a fourth element V.By adjusting the content of V in the By adjusting the content of V in the Mn_(2)Ru_(0.75)V_(y)Ga and Mn_(2.25-y)Ru_(0.75)V_(y)Ga quaternary systems the magnetic compensation temperature is tuned.Compensation is achieved near 300 K which is confirmed by both the magnetic measurement and anomalous Hall effect measurement.The analyses of the anomalous Hall effect scaling in quaternary Mn-Ru-V-Ga alloy reveal the dominant role of skew scattering,notably that contributed caused by the thermally excited phonons,in contrast to the dominant intrinsic mechanism found in many other 3d ferromagnets and Heusler compounds.It is further shown that the Ga antisites and V content can simultaneously control the residual resistivity ratio(RRR)as well as the relative contribution of phonon and defect to the anomalous Hall effect a"/a0'in Mn-Ru-V-Ga,resulting in a scaling relation a"/a0'∝RRR^(1.8).
基金Project supported by the National Key Research and Development Program of China(Grant No.2018YFB1502502)the National Natural Science Foundation of China(Grant Nos.12141002 and 12225401)+6 种基金the Fund from Foshan Xianhu Laboratory of the Advanced Energy Science and Technology Guangdong Laboratorysupported by the Interdisciplinary Program of Wuhan National High Magnetic Field Center(Grant No.WHMFC202123)Huazhong University of Science and Technologysupported by the National Natural Science Foundation of China(Grant Nos.12074041 and 11674030)the Foundation of the National Key Laboratory of Shock Wave and Detonation Physics(Grant No.6142A03191005)the National Key Research and Development Program of China(Grant No.2016YFA0302300)the startup funding of Beijing Normal University。
文摘We conducted a comparative study of the magnetic and transport properties of single-crystalline LaCo_(2)As_(2) and NdCo_(2)As_(2).LaCo_(2)As_(2) is a soft metallic ferromagnet which exhibits purely intrinsic anomalous Hall effect(AHE) due to Co-3d electrons. With Nd-4f electronic magnetism, ferrimagnetic NdCo_(2)As_(2) manifests pronounced sign reversal and multiple hysteresis loops in temperature-and field-dependent magnetization, Hall resistivity, and magnetoresistance, due to complicated magnetic structural changes. We reveal that the AHE for NdCo_(2)As_(2) is stemming from the Co sub-lattice and deduce its phase diagram which includes magnetic compensation and two meta-magnetic phase transitions. The sensitivity of the Hall effect on the details of the magnetic structures in ferrimagnetic NdCo_(2)As_(2) provides a unique opportunity to explore the magnetic interaction between 4f and 3d electrons and its impact on the electronic structure.
基金Supported by the National Natural Science Foundation of China(Nos.90922034,20771042)
文摘Rare earth iron garnets R3Fe5-xMnxO12(R=Pr, Nd, Sm, Eu) were prepared through mild hydrothermal me- thod. The initial alkalinity of solutions was thought to play an important role in governing the content of Mn. The effect of substitution Fe^3+ ions by Mn^3+ ions on magnetic properties was investigated. The saturation magnetizations of Mn-doped samples are larger than that of corresponding parent compounds due to the moment of Mn^3+ ion being smaller than that of Fe^3+. It is clearly shown that incorporation of Mn^3+ gives rise to significant variations in the Curie temperature. With increasing of Mn content x, Curie temperatures reduced sharply for the garnets, which could be explained by the exchange interaction between a-d Fe^3+ being reduced in these compounds.
基金Project supported by the National Natural Science Foundation of China(Grant No.10774035)the Qianjiang RenCai Program of Zhejiang Province,China(Grant No.2007R0010)
文摘We use the mean-field approximation of Dyson–Maleev representation to study an XXZ Heisenberg ferrimagnetic spin chain with single-ion anisotropy. By solving the self-consistent equations with different anisotropies, λ and D respectively,the energy spectrums, internal energy, static susceptibility and specific heat are calculated. Especially, the quantum phase transition of the magnetization plateau induced by single-ion anisotropy D is obtained in the model of the ferrimagnetic spin chain by using Dyson–Maleev mean-field theory.
文摘Magnetic hyperthermia is a fast emerging, non-invasive cancer treatment method which is used synergistically with the existing cancer therapeutics. We have attempted to address the current challenges in clinical magnetic hyperthermia-improved biocompatibility and enhanced heating characteristics, through a single combinatorial approach. Both superparamagnetic iron oxide nanoparticles(SPIONs) of size 10 nm and ferrimagnetic iron oxide nanoparticles(FIONs) of size 30 nm were synthesized by thermal decomposition method for comparison studies. Two different surface modifying agents, viz, Cetyl Trimethyl Ammonium Bromide and 3-Aminopropyltrimethoxysilane, were used to conjugate Bovine Serum Albumin(BSA) over the iron oxide nanoparticles via two different methods—surface charge adsorption and covalent amide bonding, respectively. The preliminary haemolysis and cell viability experiments show that BSA conjugation mitigates the haemolytic effect of the iron oxide nanoparticles on erythrocytes and is non-cytotoxic to the healthy Baby Hamster Kidney cells. It was observed from the results that due to better colloidal stability, the SAR value of the BSA-iron oxide nanoparticles is higher than the iron oxide nanoparticles without BSA, irrespective of the size of the iron oxide nanoparticles and method of conjugation. The BSA-FIONs seem to show improved biocompatibility, as the haemolytic index is less than 2 % and cell viability is up to 120 %, when normalized with the control. The SAR value of BSAFIONs is 2300 Wg^(-1) when compared to 1700 Wg^(-1) of FIONs without BSA conjugation. Thus, we report here that BSA conjugation over FIONs(with a high saturation magnetization of 87 emug^(-1)) provide a single combinatorial approach to improve the biocompatibility and enhance the SAR value for magnetic hyperthermia, thus addressing both the current challenges of the same.
文摘Magnetic properties of a two sublattice ferrimagnet with antiferromagnetic exchange interaction inside one of the sublattices are calculated within the framework of the molecular field theory taking into account the anisotropy of unstable sublattice. The magnetization curves of single crystal GdMn 2Ge 2 for the magnetic field parallel and perpendicular to the c axis at different temperatures are calculated. Field induced magnetic phase transitions in GdMn 2Ge 2 are discussed. Calculated H T magnetic phase diagrams are in fair agreement with experimental data.
基金supported by the National Natural Science Foundation of China(Grant No.10774035)the Qianjiang RenCai Program of Zhejiang Province,China(Grant No.2007R0010)
文摘We use the Schwinger-boson approach to study the anisotropy ferrimagnetic spin-(1/2,1) chain with bond alternation.Based on the effect of bond alternation δ,we obtain energy gap,free energy,and specific heat,respectively.The specific heat with larger bond alternation(δ 〉 0.7) displays a peak at low temperature.Based on the effect of XXZ anisotropy parameter Δ,we present excited spectrums,free energy,and specific heat,respectively.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50832002 and 10874075)the National Basic Research Program of China (Grant Nos. 2009CB613303 and 2009CB929501)the Natural Science Foundation of Jiangsu Province,China (Grant No. BK2008024)
文摘We have investigated the low-temperature magnetism and spin-lattice coupling in (Bio.46Nao.46Bao.os)TiO3 :Co in order to understand the magnetoelectric effect in such artificially synthesized dilute magnetic ferroelectrics. It is revealed that the as-prepared (Bio.46Nao.46Bao.os)TiO3:Co at Co content of 20%~30% exhibits fascinating ferrimagnetism which is robust against magnetic field, the abnormal spin lattice coupling characterized by a negative magnetostriction effect; and the suppressed magnetic moment within the temperature range of 30 K-50 K is identified. These magnetic behaviours at low temperatures can be explained by the competition between the ferrimagnetic response and the magnetic moment suppression induced by the abnormal spin lattice coupling effect. Finally, the ferroelectric and magnetodielectric properties are also discussed.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.11204157 and 11174179)the China Three Gorges University Project (Grant No.KJ2011B068)the Yichang City Project,China (Grant No.A201230229)
文摘The ferrimagnetism and quantum phase transition of a bipartite lozenge periodic Anderson-like organic polymer, in which the localized f electrons hybridize with the odd site conduction orbitals, are investigated by means of Green's function theory. The ground state turns out to be gapless ferrimagnetism. At a finite temperature, the ferrimagnetic-to- paramagnetic phase transition takes place. The Kondo screenings and Ruderman-Kittel-Kasuya-Yosida (RKKY) inter- action can reduce and increase the transition temperature, respectively. Two Kondo screenings compete with each other, giving rise to the localized f electron spin screened antiferromagnetically. Accordingly, in a magnetic field, all spins are aligned along the chain easily, which is associated with metal-insulator transition. Furthermore, in a temperature-field plane, we reveal the gapless and spin polarized phases, which are characterized by susceptibility and specific heat, and whose behaviours are determined by the competition between the up-spin and down-spin hole excitations.
基金Project supported by the National Natural Science Foundation of China (Grant No.1010804034)the Science Foundation of China for Three Gorges University (Grant No.KJ2009B012)
文摘The magnetic properties of an antiferromagnetic bond alternating spin-l/2 zigzag chain with asymmetrical ferro- magnetic next-nearest-neighbour exchange interactions at finite temperature are investigated by using the many-body Green's function theory. It is found that the ferrimagnetic ordering does not appear in the symmetrical next-nearest- neighbour coupling case, and takes place only for the asymmetrical next-nearest-neighbour case at finite temperature rather than the ground state. Furthermore, as the asymmetry degree of the next-nearest-neighbour exchange inter- actions increases, the ferrimagnetism becomes more and more dominant. It is shown that the elementary excitation spectra are responsible for the observed magnetic behaviour.
基金Supported by the National Natural Science Foundation of China under Grant No 51301119the Natural Science Foundation for Young Scientists of Shanxi Province under Grant No 2013021010-1the Scientific and Technological Innovation Programs of Higher Education Institutions of Shanxi Province under Grant No 201802023
文摘The electronic structures of Ti_2NbSb with Hg_2CuTi structure and TiZrNbSb with LiMgPdSn structure are investigated using first-principles calculations.The results indicate that Ti_2NbSb is a fully compensated ferrimagnetic spin-gapless semiconductor with an energy gap of 0.13 e V,and TiZrNbSb is a half-metallic fully compensated ferrimagnet with a half-metallic gap of 0.17 e V.For Ti_2NbSb,the total energy of the Hg_2CuTi structure is0.62 e V/f.u.higher than that of the L2_(1) structure,which is the ground state,and for TiZrNbSb,the total energy of the structure considered in this work is only 0.15 e V/f.u.larger than that of the ground state.Thus both of them may be good candidates for spintronic applications.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0303202 and 2016YFA0300803)the National Natural Science Foundation of China(Grant Nos.11904194,11727808,and 11674159)the Fundamental Research Funds for the Central Universities,China(Grant No.020414380121)。
文摘The spin Hall magnetoresistance(SMR)effect in Pt/Gd_(3)Fe_(5)O_(12)(Gd IG)bilayers was systematically investigated.The sign of SMR changes twice with increasing magnetic field in the vicinity of the magnetization compensation point(TM)of Gd IG.However,conventional SMR theory predicts the invariant SMR sign in the heterostructure composed of a heavy metal film in contact with a ferromagnetic or antiferromagnetic film.We conclude that this is because of the significant enhancement of the magnetic moment of the Gd sub-lattice and the unchanged moment of the Fe sub-lattice with a relatively large field,meaning that a small net magnetic moment is induced at TM.As a result,the Néel vector aligns with the field after the spin-flop transition,meaning that a bi-reorientation of the Néel vector is produced.Theoretical calculations based on the Néel’s theory and SMR theory also support our conclusions.Our findings indicate that the Néel-vector direction of a ferrimagnet can be tuned across a wide range by a relatively low external field around TM.
基金Project supported by the National Key R&D Program of China(Grant Nos.2017YFA0206200 and 2016YFA0302300)the Basic Science Center Project of the National Natural Science Foundation of China(Grant No.51788104)+2 种基金the National Natural Science Foundation of China(Grant Nos.11774194,11804182,51831005,and 11811082)Beijing Natural Science Foundation(Grant No.Z190009)the Beijing Advanced Innovation Center for Future Chip(ICFC).
文摘Compensated ferrimagnetic insulators are particularly interesting for enabling functional spintronic,optical,and microwave devices.Among many different garnets,Gd_(3)Fe_(5)O_(12)(GdIG)is a representative compensated ferrimagnetic insulator.In this paper,we will study the evolution of the surface morphology,the magnetic properties,and the magnetization compensation through changing the following parameters:the annealing temperature,the growth temperature,the annealing duration,and the choice of different single crystalline garnet substrates.Our objective is to find the optimized growth condition of the GdIG films,for the purpose of achieving a strong perpendicular magnetic anisotropy(PMA)and a flat surface,together with a small effective damping parameter.Through our experiments,we have found that the surface roughness approaching 0.15 nm can be obtained by choosing the growth temperature around 700℃,together with an enhanced PMA.We have also found the modulation of magnetic anisotropy by choosing different single crystalline garnet substrates which change the tensile strain to the compressive strain.A measure of the effective magnetic damping parameter(α_(eff)=0.04±0.01)through a spin pumping experiment in a GdIG/Pt bilayer is also made.Through optimizing the growth dynamics of GdIG films,our results could be useful for synthesizing garnet films with a PMA,which could be beneficial for the future development of ferrimagnetic spintronics.
基金supported by Beijing Natural Science Foundation Key Program(Grant No.Z190007)Beijing Natural Science Foundation(Grant No.2212048)+1 种基金the National Natural Science Foundation of China(Grant Nos.11474272,61774144,and 12004212)the Chinese Academy of Sciences(Grant Nos.QYZDY-SSW-JSC020,XDB28000000,and XDB44000000)。
文摘Current-induced multilevel magnetization switching in ferrimagnetic spintronic devices is highly pursued for the application in neuromorphic computing.In this work,we demonstrate the switching plasticity in Co/Gd ferrimagnetic multilayers where the binary states magnetization switching induced by spin–orbit toque can be tuned into a multistate one as decreasing the domain nucleation barrier.Therefore,the switching plasticity can be tuned by the perpendicular magnetic anisotropy of the multilayers and the in-plane magnetic field.Moreover,we used the switching plasticity of Co/Gd multilayers for demonstrating spike timing-dependent plasticity and sigmoid-like activation behavior.This work gives useful guidance to design multilevel spintronic devices which could be applied in high-performance neuromorphic computing.
文摘We further calculate the dependence of xT on T in high magnetic fields,where X denotes susceptibility and T is temperature,using our previous research work - Green function's decoupling approximate approach,for the one-dimensional ferrimagnetic chain with alternating spins 1 and 1/2.We find a linear correlation in certain range of magnetic field between the temperature of xT maximum and the magnetic field.Moreover,we simply analyze its physical meaning by our approach.
基金Supported by the National Basic Research Program of China under Grant Nos 2011CB921904 and 2012CB927402the National Natural Science Foundation of China under Grant Nos 11074142 and 11021464+1 种基金the Key Project of the Ministry of Education of China under Grant No 309003the Tsinghua TNList Cross-discipline Foundation
文摘Ferroelectric and magnetic properties of Fe1-xMnxV2O4 (0 ≤ x ≤ 0.5) spinels are investigated on the basis of dielectric, polarization, and susceptibility measurements. Ferroeleetric polarization is discovered in collinear ferrimagnetic and Yafet-Kittel magnetic phases for 0.1 ≤ x ≤ 0.4, which can be tuned by a magnetic field. As orbital-active FJ+ is substituted with Mn2+, ferroeleetric polarization decreases for 0 ≤ x ≤ 0.4 and disappears for x=0.5. We propose that the two polar components in ferroelectric polarization originate from the exchange striction mechanism and the spin-current model, respectively.
文摘The mixed spin-2 and spin-5/2 Ising ferrimagnetic system with different anisotropies (DA/z|J|) for the spin-2 and (DB/z|J|) for the spin-5/2 is studied by the use of the mean-field theory based on the Bogoliubov inequality for the free energy. First, the ground state phase diagram of the system at zero temperature is obtained on the (DA/z|J|,DB/z|J|) plane. Topologically, different kinds of phase diagrams are achieved by changing the temperature and the values of the single ion anisotropies DA/z|J| and DB/z|J|. Besides second-order transition lines, first order phase transition lines terminating at tricritical points, are found. The existence and dependence of a compensation temperature on single-ion anisotropies is also investigated.
文摘A first-principles study of structure property correlation and the origin of ferrimagnetism is presented based on LSDA+U method. In particular, the results for the ground state structure, electronic band structure, density of states, Born effective charges, spontaneous polarization and cationic disorder are discussed. The calculations were done using Vienna ab-initio simulation package (VASP) with projector augmented wave method. We find that the ground state structure is orthorhombic and insulating having A-type antiferromagnetic spin configuration. The cationic disorder is found to play an important role. Although the cationic site disorder is not spontaneous in the ground state, interchange of octahedrally coordinated Ga2 and Fe2 sites is most favored. We find that ferrimagnetism? in gallium ferrite is primarily due to this exchange between Ga-Fe sites? such that Fe spins at Ga1 and Ga2 sites are antiferromagnetically aligned? while maintaining ferromagnetic coupling between Fe spins at Ga1 and Fe1? sites as well as between Fe spins at Ga2 and Fe2 sites. Further, the partial density of states shows noticeable hybridization of Fe 3d, Ga 4s,? Ga 4p and O 2p states indicating some covalent character of Ga/Fe-O bonds.? However, the charge density and electron localization functions show largely the ionic character of these bonds. Our calculation predicts spontaneous polarization of ~59 μC/cm2 along b-axis.
文摘The heat capacity of some ferrimagnets has additional structures like a shoulder in the Schottky-like peak, or emergence of a second peak when an external magnetic field is applied. It is shown here that the ferromagnetic and anti-ferromagnetic elementary excitation spectra give rise to two independent heat capacity peaks, one enveloped by the other, which add up to give the peak for the total system. Taking this into account helps understand the additional structures in the peaks. Moreover, the classification of ferrimagnets into predominantly antiferromagnetic, ferromagnetic, or a mixture of the two is shown to be validated by studying them under additional influences like dimerization and frustration. Because these two are shown to influence the ferromagnetic and antiferromagnetic dispersion rela tions—and hence the quantities like heat capacity and magnetic susceptibility—by different amounts, the characterization of ferrimagnetic systems (1,1/2), (3/2,1) and (3/2,1/2) is brought out more clearly. Both these influences enhance antiferromagnetic character. PACS numbers: 75.10.Jm, 75.50.Ge.
文摘To improve microwave hyperthevmia in cancer therapy, the thermal effect of fer-rimagnetic resonance (FMR) during microwave irradiation was studied. Resonant temperatureelevation (RTE) of single crystal grain and polycrystal powder of resonant media was measuredalone and in imitative muscle and egg white and in mice. The results indicated that the RTE produced by FMR could be used to improve penetrationdeepness, heating selectivity and temperature distribution of microwave hyperthermia in cancertreatment. It was expected that the potential function of the FMR heating system would be ex-ploited greatly for cancer therapy, and then magnetically guided microwave hyperthermia thera-py, chemotherapy, radiotherapy and immunotherapy might he combined multiply within this sys-tem by means of the static magnetic field (SMF) and magnetic microcarrier. Limitation of reso-nant heating was also discussed in this paper.