In this paper, the magnetocaloric in La0.5Sm0.2Sr0.3Mn1-xFexO3 compounds with x = 0 (LSSMO) and x = 0.05 (LSSMFO) were simulated using mean field model theory. A strong consistency was observed between the theoretical...In this paper, the magnetocaloric in La0.5Sm0.2Sr0.3Mn1-xFexO3 compounds with x = 0 (LSSMO) and x = 0.05 (LSSMFO) were simulated using mean field model theory. A strong consistency was observed between the theoretical and experimental curves of magnetizations and magnetic entropy changes, −ΔSM(T). Based on the mean-field generated −ΔSM(T), the substantial Temperature-averaged Entropy Change (TEC) values reinforce the appropriateness of these materials for use in magnetic refrigeration technology within TEC (10) values of 1 and 0.57 J∙kg−1∙K−1under 1 T applied magnetic field.展开更多
Electrical properties and magnetoresistance have been studied in two series of xAg-La0.67(Ca0.65Ba0.35)0.33MnO3 and xPd-La0.67(Ca0.65Ba0.35)0.33MnO3 (abbreviated by xAg-LCBMO and xPd-LCBMO) composites. Both Pd a...Electrical properties and magnetoresistance have been studied in two series of xAg-La0.67(Ca0.65Ba0.35)0.33MnO3 and xPd-La0.67(Ca0.65Ba0.35)0.33MnO3 (abbreviated by xAg-LCBMO and xPd-LCBMO) composites. Both Pd and Ag addition induce a decrease in resistivity and an increase in temperature at which the resistivity reaches its maximum. This is mainly due to the improvement of grain boundaries caused by the segregation of good conductive metal grains on the grain boundaries/surfaces. In addition, both Pd and Ag addition induce a large enhancement of room temperature magnetoresistance (RTMR). Note that 27% molar ratio of Ag addition induces a large RTMR of about 70%, about ten times larger than pure LCBMO, whereas 27% molar ratio Pd addition brings a much larger RTMR of about 170%. The large enhancements of MR can be attributed to the decrease in resistivity of the samples caused by the good conductive metal. On the other hand, the polarization of Pd atoms near the Mn ions on the grain surfaces/boundaries plays a very im-portant role in the increase in MR, which induces a large number of spin clusters in Pd-added samples.展开更多
Thermal-annealing has been widely used in modulating the oxygen content of manganites. In this work, we have studied the effect of annealing on the transport properties and magnetoresistance of junctions composed of a...Thermal-annealing has been widely used in modulating the oxygen content of manganites. In this work, we have studied the effect of annealing on the transport properties and magnetoresistance of junctions composed of a La0.9Ca0.1MnO3+6 film and a Nb-doped SrTiO3 substrate. We have demonstrated that the magnetoresistance of junctions is strongly dependent on the annealing conditions: Prom the junction annealed-in-air to the junction annealedin-vacuum, the magnetoresistance near 0-V bias can vary from ~-60% to N~0. A possible mechanism accounting for this phenomenon is discussed.展开更多
Owing to the inhomogeneous state resulting from the doping of a small number of Eu ions into Laa/3Sr5/3Mn2O7, from the resulting single crystal (La0.8Eu0.2)a/3Sr5/3Mn2O7 we have observed the magnetization jump, the ...Owing to the inhomogeneous state resulting from the doping of a small number of Eu ions into Laa/3Sr5/3Mn2O7, from the resulting single crystal (La0.8Eu0.2)a/3Sr5/3Mn2O7 we have observed the magnetization jump, the resistivity jump, as well as the relaxation phenomena. For (Lao.sEuo.2)a/3Sr5/3Mn2O7, it has a very delicate ground state due to the interplays among spin, charge, orbital, lattice degrees of freedom. Consequently, the magnetization state is sensitive to temperature, magnetic field, as well as time. Meanwhile, the evolution of the magnetization with time shows a spontaneous jump when both the temperature and the magnetic field are constant. Similar step-like behaviours are also observed in resistivity. All these results suggest that Eu doping can greatly modulate the physical properties of Laa/3Sr5/3Mn2O7 and cause such interesting behaviours.展开更多
Powder samples with nominal composition La0.6Sr0.1TexMnO3 (x = 0.00, 0.05, 0.10, 0.15, 0.20) were prepared using the sol-gel method with thermal treatment up to 1473 K. On the basis of powder X-ray diffraction (XRD...Powder samples with nominal composition La0.6Sr0.1TexMnO3 (x = 0.00, 0.05, 0.10, 0.15, 0.20) were prepared using the sol-gel method with thermal treatment up to 1473 K. On the basis of powder X-ray diffraction (XRD), thermogravimetric and magnetic measurements, it was found that almost all of the Te and a few of the Mn ions were lost from the samples when they were calcined at 1473 K. The reason for the Te loss and a quantitative phase analysis for the samples calcined at 1473 K are discussed in detail.展开更多
We review colossal magnetoresistance in single phase manganites, as related to the field sensitive spin-charge interactions and phase separation; the rectifying property and negative/positive magnetoresistance in mang...We review colossal magnetoresistance in single phase manganites, as related to the field sensitive spin-charge interactions and phase separation; the rectifying property and negative/positive magnetoresistance in manganite/Nb:SrTio3 p-n junctions in relation to the special interface electronic structure; magnetoelectric coupling in manganite/ferroelectric structures that takes advantage of strain, carrier density, and magnetic field sensitivity; tunneling magnetoresistance in tunnel junctions with dielectric, ferroelectric, and organic semiconductor spacers using the fully spin polarized nature of manganites; and the effect of particle size on magnetic properties in manganite nanoparticles.展开更多
We have performed magnetization measurements and electron spin resonance (ESR) on polycrystalline manganites of Nd0.5Sr0.5-xBaxMnO3 (x = 0.1). Phase separation and phase transitions are observed from the susceptib...We have performed magnetization measurements and electron spin resonance (ESR) on polycrystalline manganites of Nd0.5Sr0.5-xBaxMnO3 (x = 0.1). Phase separation and phase transitions are observed from the susceptibility and the ESR spectra data. Between 260 K (~ Tc) and 185 K (~ TN), the system coexists of the paramagnetic phase and the ferromagnetic (FM) phase. Between 185 K and 140 K, the system coexists of the FM phase and the antiferromagnetic (AFM) phase. These results indicate that the system has a very complex magnetic state due to the origin of the instability stemming from manganite Nd0.5Sr0.4Ba0.1MnO3 by partially substituting the larger Ba^2+ ions for the smaller Sr^2+ ions.展开更多
Phase structures, the transport ana magnetic properties of the Perovskite-type manganite (La0.8-x CexSr0.2)0.97 MnO3(x = 0 - 0. 26) prepared by La2O3 containing CeO2 with different contents were studied. Experimen...Phase structures, the transport ana magnetic properties of the Perovskite-type manganite (La0.8-x CexSr0.2)0.97 MnO3(x = 0 - 0. 26) prepared by La2O3 containing CeO2 with different contents were studied. Experiments show that the compounds consist of a magnetic perovskite phase and non-magnetic CeO2 and Mn3O4. The resistivity and magnetoresistance ratio (MR) of the samples vary with changing x. Their room-temperature MR reaches -3% - - 14% at the magnetic field of 1 T. For x =0; x =0.037 and x = 0.26 samples, the conductance keeps unchanged basically in a relatively wide temperature range above 600 K, and the result shows that it is feasible for producing SOFC cathode materials with these samples.展开更多
It is becoming increasingly clear that the exotic properties displayed by correlated electronic materials such as high- Tc superconductivity in cuprates, colossal magnetoresistance (CMR) in manganites, and heavy-fer...It is becoming increasingly clear that the exotic properties displayed by correlated electronic materials such as high- Tc superconductivity in cuprates, colossal magnetoresistance (CMR) in manganites, and heavy-fermion compounds are intimately related to the coexistence of competing nearly degenerate states which couple simultaneously active degrees of freedom---charge, lattice, orbital, and spin states. The striking phenomena associated with these materials are due in a large part to spatial electronic inhomogeneities, or electronic phase separation (EPS). In many of these hard materials, the functionality is a result of the soft electronic component that leads to self-organization. In this paper, we review our recent work on a novel spatial confinement technique that has led to some fascinating new discoveries about the role of EPS in manganites. Using lithographic techniques to confine manganite thin films to length scales of the EPS domains that reside within them, it is possible to simultaneously probe EPS domains with different electronic states. This method allows for a much more complete view of the phases residing in a material and gives vital information on phase formation, movement, and fluctuation. Pushing this trend to its limit, we propose to control the formation process of the EPS using external local fields, which include magnetic exchange field, strain field, and electric field. We term the ability to pattern EPS "electronic nanofabrication." This method allows us to control the global physical properties of the system at a very fundamental level, and greatly enhances the potential for realizing true oxide electronics.展开更多
In the present paper, we continue our investigation on the antiferromagneticorigin of the charge order observed in the halt-doped manganese. By introducing aSu-Schrieffer-Heeger (SSH) type of perturbation interaction ...In the present paper, we continue our investigation on the antiferromagneticorigin of the charge order observed in the halt-doped manganese. By introducing aSu-Schrieffer-Heeger (SSH) type of perturbation interaction to the double-exchange Hamiltonian, wecalculate again its ground-state phase diagram at Glling x = 0.5 by the unrestricted real-spaceHartree-Fock approximation method. We find that, as the SSH electron-phonon interaction increases,the charge order parameter decreases to zero rapidly but the CE-type antiferromagnetic order becomesmore stable. In other words, the charge order is much more fragile than the CE-type or theNeel-type antiferromagnetic orders under the electron-phonon perturbation. These results support theproposed theory in the recent publications that the charge order in these systems is induced by theantiferromagnetic correlations.展开更多
Manganites are very complex systems because of interplay among charge, spin, orbital and lattice degrees of freedom. To come closer to the understanding of its nature, we discuss its three important features: 1) corre...Manganites are very complex systems because of interplay among charge, spin, orbital and lattice degrees of freedom. To come closer to the understanding of its nature, we discuss its three important features: 1) correlation between magnetization and electrical resistivity in the same temperature range;2) detection of chemical constitution and the arrangement of Mn3+ and Mn4+ ions at different hole concentrations;and 3) how electrical current flows through double exchange in manganites. The first feature will be discussed for three-dimensional manganies. The features 2 and 3 are inscrutable in three-dimensional manganites. So they will be discussed for one-dimensional manganites and then generalized. One-dimensional solid has been discussed because it may give a see-through picture of various aspects of manganites. All the discussions will be done through a representative example of La1-xCaxMnO3, because it is the intermediate bandwidth manganite;has been most widely investigated and has the highest magnetoresistance. If two things: 1) magnetization and resistivity as a function of temperature at various magnetic fields;and 2) phase diagrams of other manganites are known, their properties can be understood by the discussion of the three features mentioned above.展开更多
We develop a new electrospinning method to prepare ultra-long ordered La1-xSrxMnO3 (LSMO) nanowires. The length is up to several centimeters and is only limited by the size of the collector. The well-ordered straigh...We develop a new electrospinning method to prepare ultra-long ordered La1-xSrxMnO3 (LSMO) nanowires. The length is up to several centimeters and is only limited by the size of the collector. The well-ordered straight-line structure ensures the transport measurement, which is impossible to be carried out for the random nanowires fabricated by the traditional electrospinning method. Magnetic and transport measurements indicate that the physical properties of the LSMO nanowires depend sensitively on the doping concentration. At the optimum doping, the LSMO wires are ferromagnetic at room temperature with a metal-insulator transition temperature close to room temperature. Magnetic force microscopy studies are also performed to provide a microscopic view of these ultra-long nanowires.展开更多
The temperature evolution of the crystal structure for Nd_(0.5)Sr_(0.5)MnO_3 has been investigated by powder XRD between 125 Kand 725K.The structure can be described with a monoclinic symmetry(space group P21/m)in the...The temperature evolution of the crystal structure for Nd_(0.5)Sr_(0.5)MnO_3 has been investigated by powder XRD between 125 Kand 725K.The structure can be described with a monoclinic symmetry(space group P21/m)in the temperature range of 125—175 K,while with the increase in temperature between 175 Kand 575 Kthe structure involves a higher orthorhombic symmetry(space group Imma).The rhombohedral structure with space group R-3cis observed at high temperature region of 575—725K.The increase in the magnetization at low temperatures can be ascribed to the field-induced short-range magnetic order of the Nd3+ions.The dc and ac susceptibility data show some anomalies around the FM-PM transition region which can be attributed to the glass behavior and magnetic relaxation.展开更多
The fact that there are Mn^(2+) at the A sites in the ABO_3 perovskite phase of manganites with the nominal composition La_(0.6-x)Nd_xSr_(0.1)MnO_3 showed by detailed experimental study and theoretical calculations.Th...The fact that there are Mn^(2+) at the A sites in the ABO_3 perovskite phase of manganites with the nominal composition La_(0.6-x)Nd_xSr_(0.1)MnO_3 showed by detailed experimental study and theoretical calculations.The magnetic moments of these Mn^(2+) are antiparallel to those of the Mn ions at the B sites.The content of the Mn^(2+) increases as the average ionic radius,<r_A>,of the ions at A sites decreases,resulting in the experimentally observed phenomenon that the content of the Mn_3O_4 phase in the manganites decreases with decreasing <r_A>.展开更多
The effect of sintering temperature on the structure, magnetic transition and magnetic entropy of La0.6Ca0.4MnO3 manganite was studied. It was observed that this compound belongs to the orthorhombic structure with the...The effect of sintering temperature on the structure, magnetic transition and magnetic entropy of La0.6Ca0.4MnO3 manganite was studied. It was observed that this compound belongs to the orthorhombic structure with the Pnma space group without any impurity phase. The effect of sintering temperature on the Curie temperature(TC) was studied. The small increment in TC is found with increasing the sintering temperature. The magnetocaloric study exposes a quite large change of the magnetic entropy, which varies with sintering temperature. For an applied magnetic field of 3 T and sintering temperature of 1300 °C, the relative cooling power(RCP) is 89 J/kg. As a result, the studied compound can be considered as potential material for magnetic refrigeration near and below room temperature.展开更多
Ag-doped manganite powder samples, La0.7Sr0.1AgxMnO3 6 (x = 0.00, 0.025, 0.05, 0.075, and 0.10) were synthesized using the sol-gel method. X-ray diffraction patterns indicated that the samples had two phases with th...Ag-doped manganite powder samples, La0.7Sr0.1AgxMnO3 6 (x = 0.00, 0.025, 0.05, 0.075, and 0.10) were synthesized using the sol-gel method. X-ray diffraction patterns indicated that the samples had two phases with the R-3c perovskite being the dominant phase and Mn3O4 being the second phase. X-ray energy dispersive spectra indicated that the ratio of Ag to La was very close to that of the nominal composition in the samples. The specific saturation magnetizations at 300 K increased from 32.0 A.mZ/kg when x = 0.00 to 46.8 A-mZ/kg when x = 0.10. The Curie temperature, TC, of the samples increased from 310 K when x = 0.00 to 328 K when x = 0.10. Because the atomic concentration ratios of La, Sr, and Mn in the five samples were all the same and only the Ag concentration changed, the variations of the specific saturation magnetizations at 300 K and the Curie temperatures suggested that the Ag cations have been doped into the A sites of the perovskite phase in the samples.展开更多
Interracial barrier is a key factor that determines the performances of heterojunctions. In this work, we study the effect of manganite film thickness on the effective interracial barrier for La0.67Sr0.33MnO3/Nb:SrTi...Interracial barrier is a key factor that determines the performances of heterojunctions. In this work, we study the effect of manganite film thickness on the effective interracial barrier for La0.67Sr0.33MnO3/Nb:SrTiO3 junctions, The barrier is extracted from the forward current-voltage characteristics. Our results demonstrate that the barrier decreases gradually from -0.85 eV to -0.60 eV when the film thickness decreases from 150 nm to 2 nm. The overall value of the barrier is only about 50% of the corresponding one determined from the photovoltaic effect.展开更多
A manganite p-n heterojunction composed of Lao.67Sro.33MnO3 film and 0.05 wt% Nb-doped SrTiO3 substrate is fabricated. Rectifying behavior of the junction well described by the Shockley equation is observed, and the t...A manganite p-n heterojunction composed of Lao.67Sro.33MnO3 film and 0.05 wt% Nb-doped SrTiO3 substrate is fabricated. Rectifying behavior of the junction well described by the Shockley equation is observed, and the transport properties of the interface are experimentally studied. A satisfactorily logarithmic linear dependence of resistance on temperature is observed in a temperature range of 150 K-380 K, and the linear relation between bias and activation energies deduced from the R - lIT curves is observed. According to activation energy, the interfacial barrier of the heterojunction is obtained, which is 0.91 eV.展开更多
An oxide p-n heterojunction composed of a 150-nm La0.67Ca0.33 MnO3(LCMO) film, 0.05 wt% Nb doped SrTiO3 substrate(STON), and sandwiched 5-nm LaAlO3(LAO) thin film is fabricated with the pulsed laser deposition t...An oxide p-n heterojunction composed of a 150-nm La0.67Ca0.33 MnO3(LCMO) film, 0.05 wt% Nb doped SrTiO3 substrate(STON), and sandwiched 5-nm LaAlO3(LAO) thin film is fabricated with the pulsed laser deposition technique and the interfacial transport properties are experimentally studied. The rectifying behavior of the junction is in agreement with Newman's equation, indicating that tunneling is the dominant process for the carriers to pass through the interface while thermal emission is the dominant transport model of an LCMO/STON heterojunction with no LAO buffer layer.展开更多
文摘In this paper, the magnetocaloric in La0.5Sm0.2Sr0.3Mn1-xFexO3 compounds with x = 0 (LSSMO) and x = 0.05 (LSSMFO) were simulated using mean field model theory. A strong consistency was observed between the theoretical and experimental curves of magnetizations and magnetic entropy changes, −ΔSM(T). Based on the mean-field generated −ΔSM(T), the substantial Temperature-averaged Entropy Change (TEC) values reinforce the appropriateness of these materials for use in magnetic refrigeration technology within TEC (10) values of 1 and 0.57 J∙kg−1∙K−1under 1 T applied magnetic field.
文摘Electrical properties and magnetoresistance have been studied in two series of xAg-La0.67(Ca0.65Ba0.35)0.33MnO3 and xPd-La0.67(Ca0.65Ba0.35)0.33MnO3 (abbreviated by xAg-LCBMO and xPd-LCBMO) composites. Both Pd and Ag addition induce a decrease in resistivity and an increase in temperature at which the resistivity reaches its maximum. This is mainly due to the improvement of grain boundaries caused by the segregation of good conductive metal grains on the grain boundaries/surfaces. In addition, both Pd and Ag addition induce a large enhancement of room temperature magnetoresistance (RTMR). Note that 27% molar ratio of Ag addition induces a large RTMR of about 70%, about ten times larger than pure LCBMO, whereas 27% molar ratio Pd addition brings a much larger RTMR of about 170%. The large enhancements of MR can be attributed to the decrease in resistivity of the samples caused by the good conductive metal. On the other hand, the polarization of Pd atoms near the Mn ions on the grain surfaces/boundaries plays a very im-portant role in the increase in MR, which induces a large number of spin clusters in Pd-added samples.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10474133 and 10674169)the National Fundamental Research of China (Grant No 2007CB925002)
文摘Thermal-annealing has been widely used in modulating the oxygen content of manganites. In this work, we have studied the effect of annealing on the transport properties and magnetoresistance of junctions composed of a La0.9Ca0.1MnO3+6 film and a Nb-doped SrTiO3 substrate. We have demonstrated that the magnetoresistance of junctions is strongly dependent on the annealing conditions: Prom the junction annealed-in-air to the junction annealedin-vacuum, the magnetoresistance near 0-V bias can vary from ~-60% to N~0. A possible mechanism accounting for this phenomenon is discussed.
基金supported by the National Natural Science Foundation of China (Grant No 50672126)the Inner Mongolia Natural Science Foundation,China (Grant No 200607010102)
文摘Owing to the inhomogeneous state resulting from the doping of a small number of Eu ions into Laa/3Sr5/3Mn2O7, from the resulting single crystal (La0.8Eu0.2)a/3Sr5/3Mn2O7 we have observed the magnetization jump, the resistivity jump, as well as the relaxation phenomena. For (Lao.sEuo.2)a/3Sr5/3Mn2O7, it has a very delicate ground state due to the interplays among spin, charge, orbital, lattice degrees of freedom. Consequently, the magnetization state is sensitive to temperature, magnetic field, as well as time. Meanwhile, the evolution of the magnetization with time shows a spontaneous jump when both the temperature and the magnetic field are constant. Similar step-like behaviours are also observed in resistivity. All these results suggest that Eu doping can greatly modulate the physical properties of Laa/3Sr5/3Mn2O7 and cause such interesting behaviours.
基金supported by the Natural Science Foundation of Hebei Province (No. E2011205083)the Key Item Science Foundation of Hebei Province, China (No.10965125D+3 种基金 No.08965108D)the National Natural Science Foundation of China (No.NSF-10774037No.10074013)the National High Technology Research and Development Program of China (No. 2007AA03Z100)
文摘Powder samples with nominal composition La0.6Sr0.1TexMnO3 (x = 0.00, 0.05, 0.10, 0.15, 0.20) were prepared using the sol-gel method with thermal treatment up to 1473 K. On the basis of powder X-ray diffraction (XRD), thermogravimetric and magnetic measurements, it was found that almost all of the Te and a few of the Mn ions were lost from the samples when they were calcined at 1473 K. The reason for the Te loss and a quantitative phase analysis for the samples calcined at 1473 K are discussed in detail.
基金supported by the National Natural Science Foundation of Chinathe National Basic Research Program of China(Grant Nos.2012CB922003,2011CBA00102,and 2009CB929502)
文摘We review colossal magnetoresistance in single phase manganites, as related to the field sensitive spin-charge interactions and phase separation; the rectifying property and negative/positive magnetoresistance in manganite/Nb:SrTio3 p-n junctions in relation to the special interface electronic structure; magnetoelectric coupling in manganite/ferroelectric structures that takes advantage of strain, carrier density, and magnetic field sensitivity; tunneling magnetoresistance in tunnel junctions with dielectric, ferroelectric, and organic semiconductor spacers using the fully spin polarized nature of manganites; and the effect of particle size on magnetic properties in manganite nanoparticles.
基金supported by the National Natural Science Foundation of China (Grant No 50672126)the Inner Mongolia Natural Science Foundation of China (Grant No 200607010102)
文摘We have performed magnetization measurements and electron spin resonance (ESR) on polycrystalline manganites of Nd0.5Sr0.5-xBaxMnO3 (x = 0.1). Phase separation and phase transitions are observed from the susceptibility and the ESR spectra data. Between 260 K (~ Tc) and 185 K (~ TN), the system coexists of the paramagnetic phase and the ferromagnetic (FM) phase. Between 185 K and 140 K, the system coexists of the FM phase and the antiferromagnetic (AFM) phase. These results indicate that the system has a very complex magnetic state due to the origin of the instability stemming from manganite Nd0.5Sr0.4Ba0.1MnO3 by partially substituting the larger Ba^2+ ions for the smaller Sr^2+ ions.
文摘Phase structures, the transport ana magnetic properties of the Perovskite-type manganite (La0.8-x CexSr0.2)0.97 MnO3(x = 0 - 0. 26) prepared by La2O3 containing CeO2 with different contents were studied. Experiments show that the compounds consist of a magnetic perovskite phase and non-magnetic CeO2 and Mn3O4. The resistivity and magnetoresistance ratio (MR) of the samples vary with changing x. Their room-temperature MR reaches -3% - - 14% at the magnetic field of 1 T. For x =0; x =0.037 and x = 0.26 samples, the conductance keeps unchanged basically in a relatively wide temperature range above 600 K, and the result shows that it is feasible for producing SOFC cathode materials with these samples.
基金Project supported by the National Basic Research Program of China(Grant No.2011CB921801)the National Natural Science Foundation of China(Grant Nos.91121002and11274071)+1 种基金US DOE Office of Basic Energy Sciences,Scientific User Facilities Division,and the US DOE grant DE-SC0002136the US DOE Office of Basic Energy Sciences,Materials Sciences and Engineering Division,through the Oak Ridge National Laboratory
文摘It is becoming increasingly clear that the exotic properties displayed by correlated electronic materials such as high- Tc superconductivity in cuprates, colossal magnetoresistance (CMR) in manganites, and heavy-fermion compounds are intimately related to the coexistence of competing nearly degenerate states which couple simultaneously active degrees of freedom---charge, lattice, orbital, and spin states. The striking phenomena associated with these materials are due in a large part to spatial electronic inhomogeneities, or electronic phase separation (EPS). In many of these hard materials, the functionality is a result of the soft electronic component that leads to self-organization. In this paper, we review our recent work on a novel spatial confinement technique that has led to some fascinating new discoveries about the role of EPS in manganites. Using lithographic techniques to confine manganite thin films to length scales of the EPS domains that reside within them, it is possible to simultaneously probe EPS domains with different electronic states. This method allows for a much more complete view of the phases residing in a material and gives vital information on phase formation, movement, and fluctuation. Pushing this trend to its limit, we propose to control the formation process of the EPS using external local fields, which include magnetic exchange field, strain field, and electric field. We term the ability to pattern EPS "electronic nanofabrication." This method allows us to control the global physical properties of the system at a very fundamental level, and greatly enhances the potential for realizing true oxide electronics.
文摘In the present paper, we continue our investigation on the antiferromagneticorigin of the charge order observed in the halt-doped manganese. By introducing aSu-Schrieffer-Heeger (SSH) type of perturbation interaction to the double-exchange Hamiltonian, wecalculate again its ground-state phase diagram at Glling x = 0.5 by the unrestricted real-spaceHartree-Fock approximation method. We find that, as the SSH electron-phonon interaction increases,the charge order parameter decreases to zero rapidly but the CE-type antiferromagnetic order becomesmore stable. In other words, the charge order is much more fragile than the CE-type or theNeel-type antiferromagnetic orders under the electron-phonon perturbation. These results support theproposed theory in the recent publications that the charge order in these systems is induced by theantiferromagnetic correlations.
文摘Manganites are very complex systems because of interplay among charge, spin, orbital and lattice degrees of freedom. To come closer to the understanding of its nature, we discuss its three important features: 1) correlation between magnetization and electrical resistivity in the same temperature range;2) detection of chemical constitution and the arrangement of Mn3+ and Mn4+ ions at different hole concentrations;and 3) how electrical current flows through double exchange in manganites. The first feature will be discussed for three-dimensional manganies. The features 2 and 3 are inscrutable in three-dimensional manganites. So they will be discussed for one-dimensional manganites and then generalized. One-dimensional solid has been discussed because it may give a see-through picture of various aspects of manganites. All the discussions will be done through a representative example of La1-xCaxMnO3, because it is the intermediate bandwidth manganite;has been most widely investigated and has the highest magnetoresistance. If two things: 1) magnetization and resistivity as a function of temperature at various magnetic fields;and 2) phase diagrams of other manganites are known, their properties can be understood by the discussion of the three features mentioned above.
基金Supported by the National Basic Research Program of China under Grant Nos 2016YFA0300700,2013CB932901 and2014CB921104the National Natural Science Foundation of China under Grant Nos 11274071 and 11504053the Shanghai Municipal Natural Science Foundation under Grant No 11ZR140260
文摘We develop a new electrospinning method to prepare ultra-long ordered La1-xSrxMnO3 (LSMO) nanowires. The length is up to several centimeters and is only limited by the size of the collector. The well-ordered straight-line structure ensures the transport measurement, which is impossible to be carried out for the random nanowires fabricated by the traditional electrospinning method. Magnetic and transport measurements indicate that the physical properties of the LSMO nanowires depend sensitively on the doping concentration. At the optimum doping, the LSMO wires are ferromagnetic at room temperature with a metal-insulator transition temperature close to room temperature. Magnetic force microscopy studies are also performed to provide a microscopic view of these ultra-long nanowires.
基金supported by the Jiangsu Provincial Natural Science Foundation(No.BK20141411)
文摘The temperature evolution of the crystal structure for Nd_(0.5)Sr_(0.5)MnO_3 has been investigated by powder XRD between 125 Kand 725K.The structure can be described with a monoclinic symmetry(space group P21/m)in the temperature range of 125—175 K,while with the increase in temperature between 175 Kand 575 Kthe structure involves a higher orthorhombic symmetry(space group Imma).The rhombohedral structure with space group R-3cis observed at high temperature region of 575—725K.The increase in the magnetization at low temperatures can be ascribed to the field-induced short-range magnetic order of the Nd3+ions.The dc and ac susceptibility data show some anomalies around the FM-PM transition region which can be attributed to the glass behavior and magnetic relaxation.
基金supported by the National Natural Science Foundation of China (No. NSF-11174069)the Natural Science Foundation of Hebei Province (No.E2011205083)+2 种基金the Key Item Science Foundation of Hebei Province (No. 10965125D)the Key Item Science Foundation of Education Department of Hebei Province (No.ZD2010129)the National High Technology Research and Development Program of China (863 Program,No.2007AA03Z100)
文摘The fact that there are Mn^(2+) at the A sites in the ABO_3 perovskite phase of manganites with the nominal composition La_(0.6-x)Nd_xSr_(0.1)MnO_3 showed by detailed experimental study and theoretical calculations.The magnetic moments of these Mn^(2+) are antiparallel to those of the Mn ions at the B sites.The content of the Mn^(2+) increases as the average ionic radius,<r_A>,of the ions at A sites decreases,resulting in the experimentally observed phenomenon that the content of the Mn_3O_4 phase in the manganites decreases with decreasing <r_A>.
基金Project(2012-RIAIB300784) supported by Basic Science Research Program through the NRF of Korea funded by the MESTProject(2012HIB8A2026212) supported by the MEST and NRF of Korea the Human Training Project for Regional Innovation
文摘The effect of sintering temperature on the structure, magnetic transition and magnetic entropy of La0.6Ca0.4MnO3 manganite was studied. It was observed that this compound belongs to the orthorhombic structure with the Pnma space group without any impurity phase. The effect of sintering temperature on the Curie temperature(TC) was studied. The small increment in TC is found with increasing the sintering temperature. The magnetocaloric study exposes a quite large change of the magnetic entropy, which varies with sintering temperature. For an applied magnetic field of 3 T and sintering temperature of 1300 °C, the relative cooling power(RCP) is 89 J/kg. As a result, the studied compound can be considered as potential material for magnetic refrigeration near and below room temperature.
基金supported by the National Natural Science Foundation of China(Grant No.NSF-11174069)the Natural Science Foundation of Hebei Province,China(Grant No.E2011205083)+2 种基金the Key Item Science Foundation of Hebei Province,China(Grant No.10965125D)the Key Item Science Foundation of the Education Department of Hebei Province,China(Grant No.ZD2010129)the Young Scholar Science Foundation of the Education Department of Hebei Province,China(Grant No.QN20131008)
文摘Ag-doped manganite powder samples, La0.7Sr0.1AgxMnO3 6 (x = 0.00, 0.025, 0.05, 0.075, and 0.10) were synthesized using the sol-gel method. X-ray diffraction patterns indicated that the samples had two phases with the R-3c perovskite being the dominant phase and Mn3O4 being the second phase. X-ray energy dispersive spectra indicated that the ratio of Ag to La was very close to that of the nominal composition in the samples. The specific saturation magnetizations at 300 K increased from 32.0 A.mZ/kg when x = 0.00 to 46.8 A-mZ/kg when x = 0.10. The Curie temperature, TC, of the samples increased from 310 K when x = 0.00 to 328 K when x = 0.10. Because the atomic concentration ratios of La, Sr, and Mn in the five samples were all the same and only the Ag concentration changed, the variations of the specific saturation magnetizations at 300 K and the Curie temperatures suggested that the Ag cations have been doped into the A sites of the perovskite phase in the samples.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10804094,50832007,50721001 and 50821001)the Natural Science Foundation of Hebei Province,China (Grant No. A2009000339)
文摘Interracial barrier is a key factor that determines the performances of heterojunctions. In this work, we study the effect of manganite film thickness on the effective interracial barrier for La0.67Sr0.33MnO3/Nb:SrTiO3 junctions, The barrier is extracted from the forward current-voltage characteristics. Our results demonstrate that the barrier decreases gradually from -0.85 eV to -0.60 eV when the film thickness decreases from 150 nm to 2 nm. The overall value of the barrier is only about 50% of the corresponding one determined from the photovoltaic effect.
基金Project supported by the National Natural Science Foundation of China(Grant No.10804089)
文摘A manganite p-n heterojunction composed of Lao.67Sro.33MnO3 film and 0.05 wt% Nb-doped SrTiO3 substrate is fabricated. Rectifying behavior of the junction well described by the Shockley equation is observed, and the transport properties of the interface are experimentally studied. A satisfactorily logarithmic linear dependence of resistance on temperature is observed in a temperature range of 150 K-380 K, and the linear relation between bias and activation energies deduced from the R - lIT curves is observed. According to activation energy, the interfacial barrier of the heterojunction is obtained, which is 0.91 eV.
基金Project supported by the National Natural Science Foundation of China(Grant No.10804089)
文摘An oxide p-n heterojunction composed of a 150-nm La0.67Ca0.33 MnO3(LCMO) film, 0.05 wt% Nb doped SrTiO3 substrate(STON), and sandwiched 5-nm LaAlO3(LAO) thin film is fabricated with the pulsed laser deposition technique and the interfacial transport properties are experimentally studied. The rectifying behavior of the junction is in agreement with Newman's equation, indicating that tunneling is the dominant process for the carriers to pass through the interface while thermal emission is the dominant transport model of an LCMO/STON heterojunction with no LAO buffer layer.
基金the National Natural Science Foundation of China,the Project of Chinese National High Magnetic Field Facilities,the Major Program of Development Foundation of Hefei Center for Physical Science and Technology,the Scientific Research Grant of Hefei Science Center of Chinese Academy of Sciences