Zhensheng Peng

Influence of the substitution of Sm, Gd, and Dy for La in La0.7Sr0.3MnO3 on its magnetic and electric properties and strengthening effect on room-temperature CMR

Abstract A series of La0.7–xSmxSr0.3MnO3, La0.7–xGdxSr0.3MnO3, and La0.7–xDyxSr0.3MnO3 (x=0.00, 0.10, 0.20, 0.30) samples were prepared by the solid-state reaction method. The influence of the substitution of Sm, Gd, and Dy for La on the magnetic and electric properties and on the magnetoresistance (MR) was studied through measurements of M-T curves and ρ-T curves. The results showed that: lattice distortion induced by substitution of Sm, Gd, and Dy for La and extra magnetism of substitution had great influence on the magnetic and electric properties of perovskite manganites; substitution of magnetic rare earth element for La was an effective way to change Curie temperature and to strengthen MR in perovskite manganites; and appropriate substitution proportion would generate large MR near room temperature.

Magneto-Electric Properties of LaMnO3 with Monovalent Na Element Doping at A Site

Abstract By measuring M-T curves and R-T curves of the samples La 1- x Na x MnO 3 ( x =0.05, 0.10, 0.15, 0.20, 0. 25, 0.33), the influence of Na doping at La site on the magneto-electric properties was investigated. Results show that, Curie temperature T C increases and paramagnetic-ferromagnetic transition becomes steeper with increasing of Na content; all samples exhibit a paramagnetic-ferromagnetic transition associated with metal-insulator transition whereas the values of resistance decrease with the doping concentration increasing. The change of the magneto-electric properties originates from double-exchange function in Mn 3+ -O-Mn 4+ and static Jahn-Teller distortion as well as the change of tolerance factor caused by increasing of the doping concentration.

Magnetoresistance enhancement and temperature stability of magnetoresistance in La1−x(Sr1−yNay)xMnO3

A series of the samples La1−x(Sr1−yNay)xMnO3 (y=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were prepared by the solid-state reaction method. Magnetoresistance enhancement and temperature stability of magnetoresistance in the system La1−x(Sr1−yNay)xMnO3 with unchanged Mn3+/Mn4+ ratio through the doping of both monovalent and divalent elements at A site were studied through the measurements of X-ray diffraction (XRD) patterns, resistivity-temperature (ρ-T) curves and magnetoresistance-temperature (MR-T) curves. The results indicate that with the increase of Na doping amount, the peak value of MR increases, and it increases from 12.4% for y=0.2 to 50.6% for y=1.0 in the magnetic field B=0.8 T; ρ-T curves exhibit the double-peak phenomenon, which comes from the competition between the resistivity of surface phase and that of body phase; for the sample of y=0.8, MR increases slowly from 8.3% to 9.4% in the temperature range from 259 to 179 K, and MR is so stable in such a wide temperature range, which provides reference for the research on the temperature stability of MR.

Low-field magnetoresistance of (1−x)La0.6Dy0.1Sr0.3MnO3/0.5x (Sb2O3) composite system under different sintering temperatures of matrix

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, low-field 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 magnetoresistance 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 magnetoresistance (TMR) induced by grain boundary effect. The temperature stability of magnetoresistance is beneficial to the practical applications of MR.

Research on charge ordering and magnetic properties in La0.3Ca0.7Mn1-xWxO3 system

Abstract The perovskite manganite sample La 0.3 Ca 0.7 Mn 1-x W x O 3 ( x = 0.08, 0.12) was prepared by the solid-state reaction method. The effect of W doping on the Mn site to La 0.3 Ca 0.7 MnO 3 charge ordering phase and the changing process of magnetic properties were studied through the measurement of the M-T curve, M-H curves, and ESR curves of the sample. The results showed that when x = 0.08, the charge ordering (CO) phase exists in the system, the transition temperature T CO = 275 K, and the system exhibits PM when T > 275 K. The system transforms from spin-disordering paramagnetism to spin-ordering antiferromagnetism in the charge ordering state with the temperature decreasing from 275 K to 230 K. The long-range antiferromagnetism forms and AFM/CO states coexist between 230 K and 5 K. There is a little ferromagnetic component in the AFM/CO background in a low temperature range. When x = 0.12, the CO phase in the system has almost melted completely. There is a little remnant of the CO phase below 150 K. The system exhibits paramagnetism when T > 150 K and transforms from paramagnetism to ferromagnetism when T