A series of Mn-doped ZnO films have been prepared in different sputtering plasmas by using the inductively coupled plasma enhanced physical vapour deposition. The films show paramagnetic behaviour when they are deposi...A series of Mn-doped ZnO films have been prepared in different sputtering plasmas by using the inductively coupled plasma enhanced physical vapour deposition. The films show paramagnetic behaviour when they are deposited in an argon plasma. The Hall measurement indicates that ferromagnetism cannot be realized by increasing the electron concentration. However, the room-temperature ferromagnetism is obtained when the films are deposited in a mixed argon-nitrogen plasma. The first-principles calculations reveal that antiferromagnetic ordering is favoured in the case of the substitution of Mn^2+ for Zn^2+ without additional acceptor doping. The substitution of N for O (NO^-) is necessary to induce ferromagnetic couplings in the Zn-Mn-O system. The hybridization between N 2p and Mn 3d provides an empty orbit around the Fermi level. The hopping of Mn 3d electrons through the empty orbit can induce the ferromagnetic coupling. The ferromagnetism in the N-doped Zn-Mn-O system possibly originates from the charge transfer between Mn^2+ and Mn^3+ via NO^-, The key factor is the empty orbit provided by substituting N for O, rather than the conductivity type or the carrier concentration.展开更多
First principle calculations have been performed to study the electron structures and magnetic properties of transition metal doped ruilles in order to predict room temperature diluted magnetic semiconductors. Differe...First principle calculations have been performed to study the electron structures and magnetic properties of transition metal doped ruilles in order to predict room temperature diluted magnetic semiconductors. Different doping configurailons have been calculated to find the preferred doping site. The ground state energies of both FM and AFM states have been calculated to study the magnetic coupling between the dopants. The calculation results show the Co doped mutile has a Curie temperature of 1438 K. Co doped mille films have been prepared on Si substrate by magnetron sputtering. X-ray diffraction results show that the deposited film is ruille. Hysteresis loop curves measured by vibration sample magnetization show that the film is ferromagnetic at root temperature.展开更多
The layered semiconductor BaFZnAs with the tetragonal ZrCuSiAs-type structure has been successfully synthesized.Both the in-situ high-pressure synchrotron x-ray diffraction and the high-pressure Raman scattering measu...The layered semiconductor BaFZnAs with the tetragonal ZrCuSiAs-type structure has been successfully synthesized.Both the in-situ high-pressure synchrotron x-ray diffraction and the high-pressure Raman scattering measurements demonstrate that the structure of BaFZnAs is stable under pressure up to 17.5 GPa at room temperature. The resistivity and the magnetic susceptibility data show that BaFZnAs is a non-magnetic semiconductor. BaFZnAs is recommended as a candidate of the host material of diluted magnetic semiconductor.展开更多
Lattice constants and electronic structures of diluted magnetic semiconductors ( In, Mn ) As were investigated using the first principles LMTO-ASA band calculation by assuming supercell structures. Three concentrati...Lattice constants and electronic structures of diluted magnetic semiconductors ( In, Mn ) As were investigated using the first principles LMTO-ASA band calculation by assuming supercell structures. Three concentrations of the 3 d impurities were studied ( x = 1/2, 1/4, 1/8). The effect of varying Mn coucentrations on the lattice constants and the electronic structures are shown.展开更多
We study (Ga, Mn)As diluted magnetic semiconductors in terms of the Ruderman-Kittel-Kasuya-Yosida quantum spin model in Green's function approach. Random distributions of the magnetic atoms are treated by using an ...We study (Ga, Mn)As diluted magnetic semiconductors in terms of the Ruderman-Kittel-Kasuya-Yosida quantum spin model in Green's function approach. Random distributions of the magnetic atoms are treated by using an analytical average of magnetic configurations. Average magnetic moments and spin excitation spectra as functions of temperature can be obtained by solving self-consistent equations, and the Curie temperature TC is given explicitly. Tc is proportional to magnetic atomic concentration, and there exists a maximum for Tc as a function of carrier concentration. Applied to (Ga, Mn)As, the theoretical results are consistent with experiment and the experimental TC can be obtained with reasonable parameters. This modelling can also be applied to other diluted magnetic semiconductors.展开更多
Tuning of the magnetic interaction plays the vital role in reducing the clustering of magnetic dopant in diluted magnetic semiconductors(DMS).Due to the not well understood magnetic mechanism and the interplay between...Tuning of the magnetic interaction plays the vital role in reducing the clustering of magnetic dopant in diluted magnetic semiconductors(DMS).Due to the not well understood magnetic mechanism and the interplay between different magnetic mechanisms,no efficient and universal tuning strategy is proposed at present.Here,the magnetic interactions and formation energies of isovalent-doped(Mn) and aliovalent(Cr)-doped LiZnAs are studied based on density functional theory(DFT).It is found that the dopant–dopant distance-dependent magnetic interaction is highly sensitive to the carrier concentration and carrier type and can only be explained by the interplay between two magnetic mechanisms,i.e.,superexchange and Zener’s p–d exchange model.Thus,the magnetic behavior and clustering of magnetic dopant can be tuned by the interplay between two magnetic mechanisms.The insensitivity of the tuning effect to U parameter suggests that our strategy could be universal to other DMS.展开更多
The electronic and optical properties of zincblende ZnX(X=S, Se, Te) and ZnX:Co are studied from density functional theory (DFT) based first principles calculations. The local crystal structure changes around the...The electronic and optical properties of zincblende ZnX(X=S, Se, Te) and ZnX:Co are studied from density functional theory (DFT) based first principles calculations. The local crystal structure changes around the Co atoms in the lattice are studied after Co atoms are doped. It is shown that the Co-doped materials have smaller lattice constant (about 0.6%-0.9%). This is mainly due to the shortened Co-X bond length. The (partial) density of states (DOS) is calculated and differences between the pure and doped materials are studied. Results show that for the Co-doped materials, the valence bands are moving upward due to the existence of Co 3d electron states while the conductance bands are moving downward due to the reduced lattice constants. This results in the narrowed band gap of the doped materials. The complex dielectric indices and the absorption coefficients are calculated to examine the influences of the Co atoms on the optical properties. Results show that for the Co-doped materials, the absorption peaks in the high wavelength region are not as sharp and distinct as the undoped materials, and the absorption ranges are extended to even higher wavelength region.展开更多
This paper reports that the (Ga, Co)-codoped ZnO thin films have been grown by inductively coupled plasma enhanced physical vapour deposition. Room-temperature ferromagnetism is observed for the as-grown thin films....This paper reports that the (Ga, Co)-codoped ZnO thin films have been grown by inductively coupled plasma enhanced physical vapour deposition. Room-temperature ferromagnetism is observed for the as-grown thin films. The x-ray absorption fine structure characterization reveals that Co2+ and Ga3+ ions substitute for Zn2+ ions in the ZnO lattice and exclude the possibility of extrinsic ferromagnetism origin. The ferromagnetic (Ga, Co)-codoped ZnO thin films exhibit carrier concentration dependent anomalous Hall effect and positive magnetoresistance at room tempera- ture. The mechanism of anomalous Hall effect and magneto-transport in ferromagnetic ZnO-based diluted magnetic semiconductors is discussed.展开更多
Zn1-xCoxO diluted magnetic semiconductor bulks were prepared by hot pressing.Mixed powders of pure ZnO and CoO were compacted under pressure of 10 MPa at the temperature of 1 073 K.Then the samples were annealed in va...Zn1-xCoxO diluted magnetic semiconductor bulks were prepared by hot pressing.Mixed powders of pure ZnO and CoO were compacted under pressure of 10 MPa at the temperature of 1 073 K.Then the samples were annealed in vacuum at the temperature from 673 K to 873 K for 10 h.The crystal structure and magnetic properties of Zn1-xCoxO bulks have been investigated by X-ray diffraction(XRD) and vibrating sample magnetometer(VSM).X-ray photoelectron spectroscopy(XPS) was used to study chemical valence of zinc and cobalt in the samples.The results showed that Zn1-xCoxO samples had c-axis oriented wurtzite symmetry,neither cobalt or cobalt oxide phase was found in the samples if x was less than 0.15.Zn and Co existed in Zn0.9Co0.1O sample in Zn2+ and Co2+ states.The results of VSM experiment proved the room temperature ferromagnetic properties(RTFP) of Co-doped ZnO samples.The saturation magnetization and the coercivity of Zn0.9Co0.1O sample,observed in the M-H curve,were about 0.20 emu/g and 200 Oe,respectively.展开更多
The interplay of magnetic and semiconducting properties has been in the focus for more than a half of the century. In this introductory article we briefly review the key properties and functionalities of various magne...The interplay of magnetic and semiconducting properties has been in the focus for more than a half of the century. In this introductory article we briefly review the key properties and functionalities of various magnetic semiconductor families, including europium chalcogenides, chromium spinels, dilute magnetic semiconductors, dilute ferromagnetic semiconductors and insulators, mentioning also sources of non-uniformities in the magnetization distribution, accounting for an apparent high Curie temperature ferromagnetism in many systems. Our survey is carried out from today's perspective of ferromagnetic and antiferromagnetic spintronics as well as of the emerging fields of magnetic topological materials and atomically thin 2D layers.展开更多
In this paper, we report the growth of single crystals of Co_x Zn_(1-x)S and Co_x Zn_(1-x)Se (0<x<0.3) by the method of chemical transport, using iodine as a transport agent. The light green color of single crys...In this paper, we report the growth of single crystals of Co_x Zn_(1-x)S and Co_x Zn_(1-x)Se (0<x<0.3) by the method of chemical transport, using iodine as a transport agent. The light green color of single crystal Co_xZn_(1-x)S as well as the light brown color of Co_xZn_(1-x)Se become deep with an increase in x. The compositions of the single crystals were nearly stoichiometric. The transfer rate decreases with an increase of the x value. The growth rate was related to the temperature difference. The large temperature difference speed up the growth rate, but the size of crystal obtained was small. In general, the optimal temperature difference was 15℃. From X-ray diffraction measurements, the structures of crystals Co_xZn_(1-x)S and Co_xZn_(1-x)Se (0<x<0.1) were identified to be zinc blende structure similar to that of ZnS and ZnSe.展开更多
The magnetization of Hg0.89Mn0.11 Te single crystal grown by vertical Bridgman method was studied by using superconducting quantum interference device magnetometer(SQUID Magnetometer). First, magnetization measureme...The magnetization of Hg0.89Mn0.11 Te single crystal grown by vertical Bridgman method was studied by using superconducting quantum interference device magnetometer(SQUID Magnetometer). First, magnetization measurements were done under various magnetic fi eld strengths from-20 kOe to 20 kOe at 5 K, 15 K, and 77 K, respectively. Then, the magnetizations were measured with continuous changes of temperature in the range from 5 K to 300 K under the magnetic field of 0.1 kOe and 10 kOe, respectively. The modifi ed Brillouin function was well fitted with the data of magnetization vs. magnetic field strength. The analysis indicated that there was an antiferromagnetic exchange coupling among Mn^2+ ions. The results of reciprocal susceptibility vs. temperature fi t Curie-Weiss law very well at the temperatures above 40 K, but deviate from the law from 5 Kto 40 K, which shows that the antiferromagnetic exchange coupling among Mn^2+ ions increases in the lower temperature range below 40 K. The experimental result was explained by extending higher-order terms in the calculation of susceptibility and fitted by a power law function. The measurements reveal that Hg0.89Mn0.11 Te possesses paramagnetic properties at temperatures from 5 K to 300 K.展开更多
In order to search for promising candidates for spintronic applications, this paper systematically studies three ternary compounds based on Mn5Ce3 by using a full-potential linearized augmented plane wave method withi...In order to search for promising candidates for spintronic applications, this paper systematically studies three ternary compounds based on Mn5Ce3 by using a full-potential linearized augmented plane wave method within the density functional theory. Through structure optimization and electronic structure calculations, it finds that Mn4FeCe3 and MnaCoCe3 have much higher spin-polarization than original intermetallic compound Mn5Ce3, although the spin polarization of MnaNiCe3 is lower than that of Mn5Ce3. The calculated result is in agreement with experiment in the case of Mn4FeCe3. Both of them can be taken as promising candidates for spintronics applications because of their high spin-polarization and compatibility with semiconductors.展开更多
First-principles calculations based on density functional theory are performed to study the origin of ferromagnetism in boron-doped ZnO. It is found that boron atoms tend to reside at Zn sites. The induced Zn vacancy ...First-principles calculations based on density functional theory are performed to study the origin of ferromagnetism in boron-doped ZnO. It is found that boron atoms tend to reside at Zn sites. The induced Zn vacancy is a key factor for ferromagnetism in Znl-xBxO (0 〈 x 〈 1) systems. The nearest oxygen atoms coordinated with the B Zn vacancy pair show a few hole states in the 2p orbitals and induce magnetic moments. However, the configuration of two boron atoms inducing one Zn vacancy is nonmagnetic, with a lower formation energy than that of the B-Zn vacancy pair. This explains the difference between the theoretical and experimental magnetic moments.展开更多
We have successfully synthesized a novel diluted magnetic semiconductor(Ca_(1−2x)K_(2x))(Zn_(1−x)Mn_(x))_(2)As_(2) with decoupled charge and spin doping.The substitutions of(Ca^(2+),K^(+))and(Zn^(2+),Mn^(2+))in the pa...We have successfully synthesized a novel diluted magnetic semiconductor(Ca_(1−2x)K_(2x))(Zn_(1−x)Mn_(x))_(2)As_(2) with decoupled charge and spin doping.The substitutions of(Ca^(2+),K^(+))and(Zn^(2+),Mn^(2+))in the parent compound CaZn_(2)As_(2)(space group P m1(No.164))introduce carriers and magnetic moments,respectively.Doping only Mn into CaZn_(2)As_(2) does not induce any type of long range magnetic ordering.The ferromagnetic ordering arise can only when K^(+)and Mn^(2+)are simultaneously doped.The res-ulted maximum Curie temperature reaches~7 K,and the corresponding coercive field is~60 Oe.The transport measurements confirm that samples with K and Mn co-doping still behave like a semiconductor.展开更多
According to first-principles density functional calculations, we have investigated the magnetic properties of Mn- doped GaN with defects, Ga1-x-yVGxMny N1-z-tVNzOt with Mn substituted at Ga sites, nitrogen vacancies ...According to first-principles density functional calculations, we have investigated the magnetic properties of Mn- doped GaN with defects, Ga1-x-yVGxMny N1-z-tVNzOt with Mn substituted at Ga sites, nitrogen vacancies VN, gallium vacancies VG and oxygen substituted at nitrogen sites. The magnetic interaction in Mn-doped GaN favours the ferromagnetic coupling via the double exchange mechanism. The ground state is found to be well described by a model based on a Mn3+-d5 in a high spin state coupled via a double exchange to a partially delocalized hole accommodated in the 2p states of neighbouring nitrogen ions. The effect of defects on ferromagnetic coupling is investigated. It is found that in the presence of donor defects, such as oxygen substituted at nitrogen sites, nitrogen vacancy antiferromagnetic interactions appear, while in the case of Ga vacancies, the interactions remain ferromagnetic; in the case of acceptor defects like Mg and Zn codoping, ferromagnetism is stabilized. The formation energies of these defects are computed. Furthermore, the half-metallic behaviours appear in some studied compounds.展开更多
Ni-doped ZnO nanopowder (Zn0.98Ni0.2O) was synthesized by improved coprecipitation method. The average particle size of the powder was estimated to be 50 nm. The powder was then processed by thermal treatment. Sampl...Ni-doped ZnO nanopowder (Zn0.98Ni0.2O) was synthesized by improved coprecipitation method. The average particle size of the powder was estimated to be 50 nm. The powder was then processed by thermal treatment. Samples were annealed at 1 073, 1 273, and 1 473 K, respectively. The solubility of NiO in ZnO and the lattice parameters of ZnO both increased with the temperature. The magnetic property of the doped samples was examined, and hysteresis loops were got. The results showed all the samples were ferromagnetic, while powder processed at 1 273 K for 4 h got a highest saturation magnetization (Ms) of 0.0457 emu/g. Also, magnetic properties were related to the grain size of the powder.展开更多
Zn0.75Co0.25O films are fabricated via reactive electron beam evaporation. The influence of growth temperature on the microstructural, optical and magnetic properties of Zn0.75Co0.25O films is investigated by using x-...Zn0.75Co0.25O films are fabricated via reactive electron beam evaporation. The influence of growth temperature on the microstructural, optical and magnetic properties of Zn0.75Co0.25O films is investigated by using x-ray diffraction, selected area electron diffraction, field emission scanning electron microscope, high resolution transmitting electron microscope, photoluminescence (PL), field dependent and temperature dependent DC magnetization, and x-ray photoelectron spectroscopy (XPS). It is shown that Zn0.75Co0.25O films grown at low temperatures (250-350℃) are of single-phase wurtzite structure. Films synthesized at 300 or 350℃ reveal room temperature (RT) ferromagnetism (FM), while su for 250℃ fabricated films is found above 56 K. PL and XPS investigations show favour towards the perspective that the O-vacancy induced spin-split impurity band mechanism is responsible for the formation of RT FM of Zn0.75Co0.25O film, while the superparamagnetism of 250℃ fabricated film is attributed to the small size effect of nanoparticles in Zn0.75Co0.25O film.展开更多
Variations in magnetic and electronic properties as a function of uniaxial strain in wurtzite (Ga,Mn)As nanowires (NWs) grown along the [0001] direction were investigated based on density functional theory (DFT)...Variations in magnetic and electronic properties as a function of uniaxial strain in wurtzite (Ga,Mn)As nanowires (NWs) grown along the [0001] direction were investigated based on density functional theory (DFT). We found that (Ga,Mn)As NWs are half-metal, and the ferromagnetic state is their stable ground state. The magnetism of the NWs is significantly affected by the strain and by the substituent position of Mn impurities. By examining charge densities near the Fermi level, we found that strain can regulate the conductive region of the N-Ws. More interestingly, the size of spin-down band gap of the NWs is tunable by adjusting uniaxial stress, and the NWs can be converted from indirect to direct band gap under tension.展开更多
基金Project supported by the Shanghai Nanotechnology Promotion Center (Grant No 0452nm071)the National Natural Science Foundation of China (Grant Nos 50702071 and 50772122)
文摘A series of Mn-doped ZnO films have been prepared in different sputtering plasmas by using the inductively coupled plasma enhanced physical vapour deposition. The films show paramagnetic behaviour when they are deposited in an argon plasma. The Hall measurement indicates that ferromagnetism cannot be realized by increasing the electron concentration. However, the room-temperature ferromagnetism is obtained when the films are deposited in a mixed argon-nitrogen plasma. The first-principles calculations reveal that antiferromagnetic ordering is favoured in the case of the substitution of Mn^2+ for Zn^2+ without additional acceptor doping. The substitution of N for O (NO^-) is necessary to induce ferromagnetic couplings in the Zn-Mn-O system. The hybridization between N 2p and Mn 3d provides an empty orbit around the Fermi level. The hopping of Mn 3d electrons through the empty orbit can induce the ferromagnetic coupling. The ferromagnetism in the N-doped Zn-Mn-O system possibly originates from the charge transfer between Mn^2+ and Mn^3+ via NO^-, The key factor is the empty orbit provided by substituting N for O, rather than the conductivity type or the carrier concentration.
基金This project was financially supported by the National Natural Science Foundation of China (Nos. 50325209, 50232030, and 50572005).
文摘First principle calculations have been performed to study the electron structures and magnetic properties of transition metal doped ruilles in order to predict room temperature diluted magnetic semiconductors. Different doping configurailons have been calculated to find the preferred doping site. The ground state energies of both FM and AFM states have been calculated to study the magnetic coupling between the dopants. The calculation results show the Co doped mutile has a Curie temperature of 1438 K. Co doped mille films have been prepared on Si substrate by magnetron sputtering. X-ray diffraction results show that the deposited film is ruille. Hysteresis loop curves measured by vibration sample magnetization show that the film is ferromagnetic at root temperature.
基金Project supported by the National Natural Science Foundation of ChinaProject of Ministry of Science and Technology of China
文摘The layered semiconductor BaFZnAs with the tetragonal ZrCuSiAs-type structure has been successfully synthesized.Both the in-situ high-pressure synchrotron x-ray diffraction and the high-pressure Raman scattering measurements demonstrate that the structure of BaFZnAs is stable under pressure up to 17.5 GPa at room temperature. The resistivity and the magnetic susceptibility data show that BaFZnAs is a non-magnetic semiconductor. BaFZnAs is recommended as a candidate of the host material of diluted magnetic semiconductor.
基金Funded by the National Natural Science Foundation of China(No.60476047) ,the Key Teacher Foundation of the EducationalBureau of Henan Province ,and the Natural Science Foundation ofthe Educational Bureau of Henan Province , China ( No:2003140027 ,2004140004)
文摘Lattice constants and electronic structures of diluted magnetic semiconductors ( In, Mn ) As were investigated using the first principles LMTO-ASA band calculation by assuming supercell structures. Three concentrations of the 3 d impurities were studied ( x = 1/2, 1/4, 1/8). The effect of varying Mn coucentrations on the lattice constants and the electronic structures are shown.
基金Project supported by the National Nature Science Foundation of China (Grant Nos 10774180, 90406010 and 6062109)Funds of the Chinese Academy of Sciences for Key Topics in Innovation Engineering (Grant No KJCX2.YW.W09-5)the National Basic Research Program of China (Grant No 2005CB623602)
文摘We study (Ga, Mn)As diluted magnetic semiconductors in terms of the Ruderman-Kittel-Kasuya-Yosida quantum spin model in Green's function approach. Random distributions of the magnetic atoms are treated by using an analytical average of magnetic configurations. Average magnetic moments and spin excitation spectra as functions of temperature can be obtained by solving self-consistent equations, and the Curie temperature TC is given explicitly. Tc is proportional to magnetic atomic concentration, and there exists a maximum for Tc as a function of carrier concentration. Applied to (Ga, Mn)As, the theoretical results are consistent with experiment and the experimental TC can be obtained with reasonable parameters. This modelling can also be applied to other diluted magnetic semiconductors.
基金Project supported by the Natural Science Foundation of Shaanxi Province of China(Grant No.2013JQ1018)the Natural Science Foundation of Department of Education of Shaanxi Province of China(Grant No.15JK1759)+3 种基金the Double First-class University Construction Project of Northwest Universitythe financial support of Chinese University of Hong Kong(CUHK)(Grant No.4053084)University Grants Committee of Hong Kong,China(Grant No.24300814)start-up funding of CUHK。
文摘Tuning of the magnetic interaction plays the vital role in reducing the clustering of magnetic dopant in diluted magnetic semiconductors(DMS).Due to the not well understood magnetic mechanism and the interplay between different magnetic mechanisms,no efficient and universal tuning strategy is proposed at present.Here,the magnetic interactions and formation energies of isovalent-doped(Mn) and aliovalent(Cr)-doped LiZnAs are studied based on density functional theory(DFT).It is found that the dopant–dopant distance-dependent magnetic interaction is highly sensitive to the carrier concentration and carrier type and can only be explained by the interplay between two magnetic mechanisms,i.e.,superexchange and Zener’s p–d exchange model.Thus,the magnetic behavior and clustering of magnetic dopant can be tuned by the interplay between two magnetic mechanisms.The insensitivity of the tuning effect to U parameter suggests that our strategy could be universal to other DMS.
基金Project supported by the National Natural Science Foundation of China (Grant No 10564002) and the 0pen Foundations of Key Laboratory for 0pto-electronics of Jiangxi Province, China (Grant Nos 2004003 and 2004008), the Natural Science Foundation of Jiangxi Province, China (Grant No 0512017) and the Youth Science Program of Jiangxi Normal University, China(Grant No 1075).
文摘The electronic and optical properties of zincblende ZnX(X=S, Se, Te) and ZnX:Co are studied from density functional theory (DFT) based first principles calculations. The local crystal structure changes around the Co atoms in the lattice are studied after Co atoms are doped. It is shown that the Co-doped materials have smaller lattice constant (about 0.6%-0.9%). This is mainly due to the shortened Co-X bond length. The (partial) density of states (DOS) is calculated and differences between the pure and doped materials are studied. Results show that for the Co-doped materials, the valence bands are moving upward due to the existence of Co 3d electron states while the conductance bands are moving downward due to the reduced lattice constants. This results in the narrowed band gap of the doped materials. The complex dielectric indices and the absorption coefficients are calculated to examine the influences of the Co atoms on the optical properties. Results show that for the Co-doped materials, the absorption peaks in the high wavelength region are not as sharp and distinct as the undoped materials, and the absorption ranges are extended to even higher wavelength region.
基金supported by the National Natural Science Foundation of China (Grant No. 50772122)the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 51002176)
文摘This paper reports that the (Ga, Co)-codoped ZnO thin films have been grown by inductively coupled plasma enhanced physical vapour deposition. Room-temperature ferromagnetism is observed for the as-grown thin films. The x-ray absorption fine structure characterization reveals that Co2+ and Ga3+ ions substitute for Zn2+ ions in the ZnO lattice and exclude the possibility of extrinsic ferromagnetism origin. The ferromagnetic (Ga, Co)-codoped ZnO thin films exhibit carrier concentration dependent anomalous Hall effect and positive magnetoresistance at room tempera- ture. The mechanism of anomalous Hall effect and magneto-transport in ferromagnetic ZnO-based diluted magnetic semiconductors is discussed.
基金Funded by the Innovative Scientific Research Foundation of Shanghai Education Committee (No.09YZ367)
文摘Zn1-xCoxO diluted magnetic semiconductor bulks were prepared by hot pressing.Mixed powders of pure ZnO and CoO were compacted under pressure of 10 MPa at the temperature of 1 073 K.Then the samples were annealed in vacuum at the temperature from 673 K to 873 K for 10 h.The crystal structure and magnetic properties of Zn1-xCoxO bulks have been investigated by X-ray diffraction(XRD) and vibrating sample magnetometer(VSM).X-ray photoelectron spectroscopy(XPS) was used to study chemical valence of zinc and cobalt in the samples.The results showed that Zn1-xCoxO samples had c-axis oriented wurtzite symmetry,neither cobalt or cobalt oxide phase was found in the samples if x was less than 0.15.Zn and Co existed in Zn0.9Co0.1O sample in Zn2+ and Co2+ states.The results of VSM experiment proved the room temperature ferromagnetic properties(RTFP) of Co-doped ZnO samples.The saturation magnetization and the coercivity of Zn0.9Co0.1O sample,observed in the M-H curve,were about 0.20 emu/g and 200 Oe,respectively.
基金supported by the Foundation for Polish Science through the IRA Programme financed by EU within SG OP Programmesupport by the Austrian Science Foundation-FWF (P31423 and P26830)the Austrian Exchange Service (OAD) Project PL-01/2017
文摘The interplay of magnetic and semiconducting properties has been in the focus for more than a half of the century. In this introductory article we briefly review the key properties and functionalities of various magnetic semiconductor families, including europium chalcogenides, chromium spinels, dilute magnetic semiconductors, dilute ferromagnetic semiconductors and insulators, mentioning also sources of non-uniformities in the magnetization distribution, accounting for an apparent high Curie temperature ferromagnetism in many systems. Our survey is carried out from today's perspective of ferromagnetic and antiferromagnetic spintronics as well as of the emerging fields of magnetic topological materials and atomically thin 2D layers.
文摘In this paper, we report the growth of single crystals of Co_x Zn_(1-x)S and Co_x Zn_(1-x)Se (0<x<0.3) by the method of chemical transport, using iodine as a transport agent. The light green color of single crystal Co_xZn_(1-x)S as well as the light brown color of Co_xZn_(1-x)Se become deep with an increase in x. The compositions of the single crystals were nearly stoichiometric. The transfer rate decreases with an increase of the x value. The growth rate was related to the temperature difference. The large temperature difference speed up the growth rate, but the size of crystal obtained was small. In general, the optimal temperature difference was 15℃. From X-ray diffraction measurements, the structures of crystals Co_xZn_(1-x)S and Co_xZn_(1-x)Se (0<x<0.1) were identified to be zinc blende structure similar to that of ZnS and ZnSe.
基金Funded by the National Natural Science Foundation of China(50336040)
文摘The magnetization of Hg0.89Mn0.11 Te single crystal grown by vertical Bridgman method was studied by using superconducting quantum interference device magnetometer(SQUID Magnetometer). First, magnetization measurements were done under various magnetic fi eld strengths from-20 kOe to 20 kOe at 5 K, 15 K, and 77 K, respectively. Then, the magnetizations were measured with continuous changes of temperature in the range from 5 K to 300 K under the magnetic field of 0.1 kOe and 10 kOe, respectively. The modifi ed Brillouin function was well fitted with the data of magnetization vs. magnetic field strength. The analysis indicated that there was an antiferromagnetic exchange coupling among Mn^2+ ions. The results of reciprocal susceptibility vs. temperature fi t Curie-Weiss law very well at the temperatures above 40 K, but deviate from the law from 5 Kto 40 K, which shows that the antiferromagnetic exchange coupling among Mn^2+ ions increases in the lower temperature range below 40 K. The experimental result was explained by extending higher-order terms in the calculation of susceptibility and fitted by a power law function. The measurements reveal that Hg0.89Mn0.11 Te possesses paramagnetic properties at temperatures from 5 K to 300 K.
基金financially supported by the National Natural Foundation of China (Nos. 50831002, 50971025,11174031, 51071022)Program for Changjiang Scholars and Innovative Research Team in University, Beijing NovaProgram (No. 2011031)+1 种基金Beijing Natural Science Foundation (No. 2102032)the National Basic Research Program of China (No. 2012CB932702)
基金supported by the National Natural Science Foundation of China (Grant Nos 10774180,90406010 and 60621091)Chinese Department of Science and Technology under National Basic Research Program (973) (Grant No 2005CB623602)
文摘In order to search for promising candidates for spintronic applications, this paper systematically studies three ternary compounds based on Mn5Ce3 by using a full-potential linearized augmented plane wave method within the density functional theory. Through structure optimization and electronic structure calculations, it finds that Mn4FeCe3 and MnaCoCe3 have much higher spin-polarization than original intermetallic compound Mn5Ce3, although the spin polarization of MnaNiCe3 is lower than that of Mn5Ce3. The calculated result is in agreement with experiment in the case of Mn4FeCe3. Both of them can be taken as promising candidates for spintronics applications because of their high spin-polarization and compatibility with semiconductors.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50831002, 50971025, 51071022, and 11174031)Beijing Nova Program, China (Grant No. 2011031)+1 种基金Beijing Natural Science Foundation, China (Grant No. 2102032)the National Basic Research Program of China (Grant No. 2012CB932702)
文摘First-principles calculations based on density functional theory are performed to study the origin of ferromagnetism in boron-doped ZnO. It is found that boron atoms tend to reside at Zn sites. The induced Zn vacancy is a key factor for ferromagnetism in Znl-xBxO (0 〈 x 〈 1) systems. The nearest oxygen atoms coordinated with the B Zn vacancy pair show a few hole states in the 2p orbitals and induce magnetic moments. However, the configuration of two boron atoms inducing one Zn vacancy is nonmagnetic, with a lower formation energy than that of the B-Zn vacancy pair. This explains the difference between the theoretical and experimental magnetic moments.
基金supported by the Key R&D Program of Zhejiang Province, China (2021C01002)NSF of China (No. 12074333)。
文摘We have successfully synthesized a novel diluted magnetic semiconductor(Ca_(1−2x)K_(2x))(Zn_(1−x)Mn_(x))_(2)As_(2) with decoupled charge and spin doping.The substitutions of(Ca^(2+),K^(+))and(Zn^(2+),Mn^(2+))in the parent compound CaZn_(2)As_(2)(space group P m1(No.164))introduce carriers and magnetic moments,respectively.Doping only Mn into CaZn_(2)As_(2) does not induce any type of long range magnetic ordering.The ferromagnetic ordering arise can only when K^(+)and Mn^(2+)are simultaneously doped.The res-ulted maximum Curie temperature reaches~7 K,and the corresponding coercive field is~60 Oe.The transport measurements confirm that samples with K and Mn co-doping still behave like a semiconductor.
文摘According to first-principles density functional calculations, we have investigated the magnetic properties of Mn- doped GaN with defects, Ga1-x-yVGxMny N1-z-tVNzOt with Mn substituted at Ga sites, nitrogen vacancies VN, gallium vacancies VG and oxygen substituted at nitrogen sites. The magnetic interaction in Mn-doped GaN favours the ferromagnetic coupling via the double exchange mechanism. The ground state is found to be well described by a model based on a Mn3+-d5 in a high spin state coupled via a double exchange to a partially delocalized hole accommodated in the 2p states of neighbouring nitrogen ions. The effect of defects on ferromagnetic coupling is investigated. It is found that in the presence of donor defects, such as oxygen substituted at nitrogen sites, nitrogen vacancy antiferromagnetic interactions appear, while in the case of Ga vacancies, the interactions remain ferromagnetic; in the case of acceptor defects like Mg and Zn codoping, ferromagnetism is stabilized. The formation energies of these defects are computed. Furthermore, the half-metallic behaviours appear in some studied compounds.
文摘Ni-doped ZnO nanopowder (Zn0.98Ni0.2O) was synthesized by improved coprecipitation method. The average particle size of the powder was estimated to be 50 nm. The powder was then processed by thermal treatment. Samples were annealed at 1 073, 1 273, and 1 473 K, respectively. The solubility of NiO in ZnO and the lattice parameters of ZnO both increased with the temperature. The magnetic property of the doped samples was examined, and hysteresis loops were got. The results showed all the samples were ferromagnetic, while powder processed at 1 273 K for 4 h got a highest saturation magnetization (Ms) of 0.0457 emu/g. Also, magnetic properties were related to the grain size of the powder.
基金Project supported by the National Natural Science Foundation of China (Grant No 50472058)
文摘Zn0.75Co0.25O films are fabricated via reactive electron beam evaporation. The influence of growth temperature on the microstructural, optical and magnetic properties of Zn0.75Co0.25O films is investigated by using x-ray diffraction, selected area electron diffraction, field emission scanning electron microscope, high resolution transmitting electron microscope, photoluminescence (PL), field dependent and temperature dependent DC magnetization, and x-ray photoelectron spectroscopy (XPS). It is shown that Zn0.75Co0.25O films grown at low temperatures (250-350℃) are of single-phase wurtzite structure. Films synthesized at 300 or 350℃ reveal room temperature (RT) ferromagnetism (FM), while su for 250℃ fabricated films is found above 56 K. PL and XPS investigations show favour towards the perspective that the O-vacancy induced spin-split impurity band mechanism is responsible for the formation of RT FM of Zn0.75Co0.25O film, while the superparamagnetism of 250℃ fabricated film is attributed to the small size effect of nanoparticles in Zn0.75Co0.25O film.
基金supported by the National Natural Science Foundation of China(Grant Nos.11004141 and 11174212)the Program for New Century Excellent Talents in University of Ministry of Education of China(Grant No.11-0351)the Scientific Research Starting Foundation for the Returned Overseas Chinese Scholars,Ministry of Education of China
文摘Variations in magnetic and electronic properties as a function of uniaxial strain in wurtzite (Ga,Mn)As nanowires (NWs) grown along the [0001] direction were investigated based on density functional theory (DFT). We found that (Ga,Mn)As NWs are half-metal, and the ferromagnetic state is their stable ground state. The magnetism of the NWs is significantly affected by the strain and by the substituent position of Mn impurities. By examining charge densities near the Fermi level, we found that strain can regulate the conductive region of the N-Ws. More interestingly, the size of spin-down band gap of the NWs is tunable by adjusting uniaxial stress, and the NWs can be converted from indirect to direct band gap under tension.