La0.5Sm0.2Sr0.3MnO3/（Ag2O）x/2 （x = 0.00, 0.04, 0.08, 0.25, 0.30） samples were prepared by the solid-state reaction method, and their transport behaviors, transport mechanism, and magnetoresistance effect were stud...La0.5Sm0.2Sr0.3MnO3/（Ag2O）x/2 （x = 0.00, 0.04, 0.08, 0.25, 0.30） samples were prepared by the solid-state reaction method, and their transport behaviors, transport mechanism, and magnetoresistance effect were studied through the measurement and fitting of p-T curves. The results show that the element Ag takes part in reaction when the doping amount is small. Ag is mainly distributed at the grain boundary of the host material and is in metallic state when the doping amount is relatively large; then the system becomes a two-phase composite. A small amount of Ag doping can apparently increase grain-boundary magnetoresistance induced by the spin-dependent scattering. The resistivity of the sample doped with 30 mol% Ag is one order of magnitude smaller than that of low-doped samples, and its magnetoresistance in the magnetic field of 0.5 T and at 300 K is strengthened apparently reaching 9.4%, which is connected not only with the improvement of the grain-boundary structure of the host material but also with the decrease of material resistivity.展开更多
A series of (1-x)La0.6Dy0.1Sr0.3MnO3/0.5x(Sb2O3)(x=0.15) samples were prepared by the solid-state reaction method, and the influence of sintering temperature of the matrix on low-field magnetoresistance of (1-x)La0.6D...A series of (1-x)La0.6Dy0.1Sr0.3MnO3/0.5x(Sb2O3)(x=0.15) samples were prepared by the solid-state reaction method, and the influence of sintering temperature of the matrix on low-field magnetoresistance of (1-x)La0.6Dy0.1Sr0.3MnO3/0.5x (Sb2O3) was studied through the measurements of X-ray diffraction (XRD) patterns, scanning electron microscope (SEM) image, resistivity-temperature (ρ-T) curves, and magnetoresistance-temperature (MR-T) curves. The results indicate that for the samples with low sintering temperature of the matrix, lowfield magnetoresistance effect appears on the whole temperature range and can be explained by grain boundary effect; for the sample with high sintering temperature of the matrix, intrinsic magnetoresistance peak appears on the high-temperature range, low-field magnetore-sistance effect appears on low temperature range, and the magnetoresistance in the magnetic field of 0.2 T and on the comparatively large temperature range between 280 K and 225 K hardly changes with temperature and remains at 4.8%, which can be explained by the competition between the intrinsic magnetoresistance induced by double-exchange function inside grains and the tunneling magnetoresis-tance (TMR) induced by grain boundary effect. The temperature stability of magnetoresistance is beneficial to the practical applications of MR.展开更多
La_(0.67)Ca_(0.33)MnO_3)_x /(ZrO_2)_(1-x) (x is the volume fraction ratio) percolated composites were fabricated by combining La_(0.67)Ca_(0.33)MnO_3 (LCMO) powders with ZrO_2 particles, where LCMO powders were prepar...La_(0.67)Ca_(0.33)MnO_3)_x /(ZrO_2)_(1-x) (x is the volume fraction ratio) percolated composites were fabricated by combining La_(0.67)Ca_(0.33)MnO_3 (LCMO) powders with ZrO_2 particles, where LCMO powders were prepared by sol-gel process. Low field magnetoresistance ( LFMR ) is greatly enhanced at low temperature when the system is close to the metallic percolation threshold of x=0.4. The magnetoresistance ratio of ( LCMO)_(0.4) /( ZrO_2 )_(0.6) in a 10 mT magnetic field at 77 K is 7.8 %, about 7.12 times larger than that of pure LCMO compound. The enhancement of spin-dependent tunneling of electrons at the interfaces between LCMO and ZrO_2 grains is responsible for the enhanced LFMR. With increasing ZrO_2 addition, Curie temperature T_C decreases firstly and then remains constant at about 220 K when (x<60%), showing limited substitution effect of Zr ions on B sites.展开更多
Samples with nominal composition of （1 - x）La0.67Ca0.33MnO3 （LCMO）/xCuO （x = 0%, 2%, 4% and 20% ） were made using a special experimental method. The temperature dependence of the resistivity （ρ） of the compos...Samples with nominal composition of （1 - x）La0.67Ca0.33MnO3 （LCMO）/xCuO （x = 0%, 2%, 4% and 20% ） were made using a special experimental method. The temperature dependence of the resistivity （ρ） of the composites was investigated in the temperature range of 10 - 300 K and different magnetic fields of H = 0, 0.1, 0.3, 0.5, 1.0 and 3.0 T. The results showed that CuO percentage x had important effects on metal-insulator transition temperature （Tp）, zero field peak resistivity （ρmax）, and magnetoresistance （MR） properties of the composites. Tp shifted sharply towards low temperature with the increase of x in the range of x ≤4%, but was almost independent of x at high level of CuO content. Composites with x = 4 % and 20 % exhibited similar electrical transmission behavior. Compared with pure LCMO, enhanced magnetoresistance could be clearly observed even in a quite low magnetic field of 0.3 T. For x =4% and 20% samples, the MR value at 0.3 T could reach as high as - 88% and - 90%, respectively. XRD and SEM analysis showed that the substantial enhancement of MR, especially near Tp, was because of local spin disorder between contiguous LCMO ferromagnetic particles caused by the addition of CuO.展开更多
The Cr O2 micro rod powder was synthesized by decomposing the Cr O3 flakes at a specific temperature to yield precursor and annealing such a precursor in a sealed glass tube. The magneto-transport properties have been...The Cr O2 micro rod powder was synthesized by decomposing the Cr O3 flakes at a specific temperature to yield precursor and annealing such a precursor in a sealed glass tube. The magneto-transport properties have been measured by a direct current four-probe method using a Cu/Cr O2rods/colloidal silver liquid electrode sandwich device. The largest magnetoresistance(MR) around *72 % was observed at 77 K with applied current of 0.05 l A. The non-linear I–V curve indicates a tunneling type transport properties and the tunneling barrier height is around 2.2 ± 0.04 e V at 77 K, which is obtained with fitting the non-linear I–V curves using Simmons' equation. A mixing of Cr oxides on the surface of Cr O2 rod observed by X-ray photoemission spectroscopy provides a tunneling barrier rather than a single phase of Cr2O3 insulating barrier. The MR shows strong bias voltage dependence and is ascribed to the two-step tunneling process.展开更多
基金supported by the Key Program of the National Natural Science Foundation of China (No. 19934003)the Grand Program of Natural Science Research of Anhui Education Department (No. ZD2007003-1)the Natural Science Research Program of Universities and Colleges of Anhui Province, China (Nos. KJ2008A19ZC, KJ2009B281Z, and KJ2009A053Z)
文摘La0.5Sm0.2Sr0.3MnO3/（Ag2O）x/2 （x = 0.00, 0.04, 0.08, 0.25, 0.30） samples were prepared by the solid-state reaction method, and their transport behaviors, transport mechanism, and magnetoresistance effect were studied through the measurement and fitting of p-T curves. The results show that the element Ag takes part in reaction when the doping amount is small. Ag is mainly distributed at the grain boundary of the host material and is in metallic state when the doping amount is relatively large; then the system becomes a two-phase composite. A small amount of Ag doping can apparently increase grain-boundary magnetoresistance induced by the spin-dependent scattering. The resistivity of the sample doped with 30 mol% Ag is one order of magnitude smaller than that of low-doped samples, and its magnetoresistance in the magnetic field of 0.5 T and at 300 K is strengthened apparently reaching 9.4%, which is connected not only with the improvement of the grain-boundary structure of the host material but also with the decrease of material resistivity.
基金supported by the National Natural Foundation of China (No. 19934003) the Natural Science Research Key Program of Anhui Educational Committee (No. KJ2011A259)+3 种基金the Opening Program of Cultivating Base of Anhui Key Laboratory of Spintronics and Nanomaterials (Nos. 2010YKF04 2011YKF05)the Professors’and Doctors’Research Startup Foundation of Suzhou University (Nos. 2011jb01 2011jb02)
文摘A series of (1-x)La0.6Dy0.1Sr0.3MnO3/0.5x(Sb2O3)(x=0.15) samples were prepared by the solid-state reaction method, and the influence of sintering temperature of the matrix on low-field magnetoresistance of (1-x)La0.6Dy0.1Sr0.3MnO3/0.5x (Sb2O3) was studied through the measurements of X-ray diffraction (XRD) patterns, scanning electron microscope (SEM) image, resistivity-temperature (ρ-T) curves, and magnetoresistance-temperature (MR-T) curves. The results indicate that for the samples with low sintering temperature of the matrix, lowfield magnetoresistance effect appears on the whole temperature range and can be explained by grain boundary effect; for the sample with high sintering temperature of the matrix, intrinsic magnetoresistance peak appears on the high-temperature range, low-field magnetore-sistance effect appears on low temperature range, and the magnetoresistance in the magnetic field of 0.2 T and on the comparatively large temperature range between 280 K and 225 K hardly changes with temperature and remains at 4.8%, which can be explained by the competition between the intrinsic magnetoresistance induced by double-exchange function inside grains and the tunneling magnetoresis-tance (TMR) induced by grain boundary effect. The temperature stability of magnetoresistance is beneficial to the practical applications of MR.
文摘La_(0.67)Ca_(0.33)MnO_3)_x /(ZrO_2)_(1-x) (x is the volume fraction ratio) percolated composites were fabricated by combining La_(0.67)Ca_(0.33)MnO_3 (LCMO) powders with ZrO_2 particles, where LCMO powders were prepared by sol-gel process. Low field magnetoresistance ( LFMR ) is greatly enhanced at low temperature when the system is close to the metallic percolation threshold of x=0.4. The magnetoresistance ratio of ( LCMO)_(0.4) /( ZrO_2 )_(0.6) in a 10 mT magnetic field at 77 K is 7.8 %, about 7.12 times larger than that of pure LCMO compound. The enhancement of spin-dependent tunneling of electrons at the interfaces between LCMO and ZrO_2 grains is responsible for the enhanced LFMR. With increasing ZrO_2 addition, Curie temperature T_C decreases firstly and then remains constant at about 220 K when (x<60%), showing limited substitution effect of Zr ions on B sites.
基金Project supported by the National Natural Science Foundation of China (10374032)
文摘Samples with nominal composition of （1 - x）La0.67Ca0.33MnO3 （LCMO）/xCuO （x = 0%, 2%, 4% and 20% ） were made using a special experimental method. The temperature dependence of the resistivity （ρ） of the composites was investigated in the temperature range of 10 - 300 K and different magnetic fields of H = 0, 0.1, 0.3, 0.5, 1.0 and 3.0 T. The results showed that CuO percentage x had important effects on metal-insulator transition temperature （Tp）, zero field peak resistivity （ρmax）, and magnetoresistance （MR） properties of the composites. Tp shifted sharply towards low temperature with the increase of x in the range of x ≤4%, but was almost independent of x at high level of CuO content. Composites with x = 4 % and 20 % exhibited similar electrical transmission behavior. Compared with pure LCMO, enhanced magnetoresistance could be clearly observed even in a quite low magnetic field of 0.3 T. For x =4% and 20% samples, the MR value at 0.3 T could reach as high as - 88% and - 90%, respectively. XRD and SEM analysis showed that the substantial enhancement of MR, especially near Tp, was because of local spin disorder between contiguous LCMO ferromagnetic particles caused by the addition of CuO.
基金supported by the NNSF of China (Nos. 51171076, 51101079)the Natural Science Foundation of Gansu Province (No. 145RJZA154)+1 种基金the Fundamental Research Funds for the Central Universities (No. Lzujbky-2012-27, Lzujbky-2010172)the CERS of China (No. CERS-1-89)
文摘The Cr O2 micro rod powder was synthesized by decomposing the Cr O3 flakes at a specific temperature to yield precursor and annealing such a precursor in a sealed glass tube. The magneto-transport properties have been measured by a direct current four-probe method using a Cu/Cr O2rods/colloidal silver liquid electrode sandwich device. The largest magnetoresistance(MR) around *72 % was observed at 77 K with applied current of 0.05 l A. The non-linear I–V curve indicates a tunneling type transport properties and the tunneling barrier height is around 2.2 ± 0.04 e V at 77 K, which is obtained with fitting the non-linear I–V curves using Simmons' equation. A mixing of Cr oxides on the surface of Cr O2 rod observed by X-ray photoemission spectroscopy provides a tunneling barrier rather than a single phase of Cr2O3 insulating barrier. The MR shows strong bias voltage dependence and is ascribed to the two-step tunneling process.
