Magnetic Properties of Interacting La0.67Sr0.33MnO3 Nanoparticles

Magnetic nanoparticles of La_0.67Sr_0.33MnO₃ (LSMO) with mean particle sizes of 13, 16, 18, and 21 nm were prepared by the sol?Cgel method. The samples were characterized by X-ray diffraction (XRD) using Rietveld refinement and transmission electron microscope (TEM). Fourier transform infrared (FTIR) transmission spectroscopy revealed that stretching and bending modes are influenced by annealing temperature. Dc magnetization versus magnetic field of the samples was carried out at room temperature. Magnetic dynamics of the samples was studied by the measurement of ac magnetic susceptibility versus temperature at different frequencies and ac magnetic fields. A frequency-dependent peak was observed in ac magnetic susceptibility versus temperature which is well described by Vogel?CFulcher and critical slowing down laws, and empirical $c_{1} = \frac{\Delta T_{f}}{T_{f}\Delta (\log _{10}f)}$ and $c_{2} = \frac{T_{f} -T_{0}}{T_{f}}$ parameters. By fitting the experimental data with Vogel?CFulcher magnetic anisotropy energy and an effective magnetic anisotropy constant have been estimated. The obtained values support the presence of strong interaction between magnetic nanoparticles of LSMO.     

High-Field Magnetoresistance of La0.67Sr0.33MnO3 Thin Films Deposited on LiNbO3 Substrates

Colossal magnetoresistive manganites have been widely studied due to their potential use in sensor and device applications. In this work, La_0.67Sr_0.33MnO₃ thin films were deposited by pulsed laser ablation on LiNbO₃ substrates and magnetoresistance measurements were performed using pulsed magnetic fields up to 25 T. The corresponding magnetoconductance of the films was fitted in order to obtain the grain boundary (GB) contribution to the transport properties. The observed temperature dependence of the fitting parameters was indicative of antiferromagnetism across GB spins and reflected the progressive reduction of magnetic ordering with increasing temperature.     

PLZST陶瓷衬底上La0.7Sr0.3MnO3薄膜生长及其磁性能和电输运特性研究

采用磁控溅射法在PLZST陶瓷衬底上制备了不同厚度的LSMO薄膜, 并对其微结构、磁性能及电输运特性进行了研究。结果表明, LSMO薄膜具有单一钙钛矿结构, 晶粒均匀, 表面平整, 其中20 nm厚LSMO薄膜粗糙度仅为2.93 nm。在10~300 K温度范围内, LSMO薄膜均具有大的磁电阻效应, 20 nm厚的LSMO薄膜磁电阻温度稳定性优异。随着薄膜厚度的增加, 薄膜的居里温度、金属绝缘体转变温度、磁化强度和导电性能降低。这可能是由于Pb、Sn、Zr等离子扩散进入LSMO薄膜中, 导致MnO₆八面体畸变造成的。     

La0.67Sr0.33MnO3中Ag-Ti的掺杂效应

将La0.67Sr0.33MnO3（LSMO）、Ag2O及TiO2粉混合经高温烧结后制备了钙钛矿相/xAg两相复合体系（x是Ag与钙钛矿材料的物质的量比）,系统地研究了Ag-Ti的共掺杂对LSMO电性和磁电阻效应的影响.0.07摩尔比Ti4＋离子的B位掺杂使LSMO的居里温度降至室温.Ag的掺入对Tc影响不大,Tp逐渐升高.由于钙钛矿颗粒属性的改善和金属导电通道的出现,材料的电阻率明显下降.Ag掺杂使室温磁电阻得到显著增强,室温下从x=0.30样品中得到最大的磁电阻,约为32%,是La0.67Sr0.33MnO3样品的8倍,La0.67Sr0.33Mn0.93Ti0.07O3样品的1.6倍.     

Relaxation of La0.67Ca0.33MnO3 Films Resistance in Pulsed High Magnetic Fields

The resistance relaxation after switch-off of high magnetic field pulses of 20-40 T was studied for two series of La _0.67 Ca _0.33 MnO ₃ thin films. The response dynamics was obtained for temperature range 77-300 K. It is shown that the relaxation time is sensitive to the temperature of the resistivity maximum and to magnetoresistive properties of a film. The observed relaxation times are assumed to be related to existence of magnetic domains or intergrain material.     

衬底温度和生长氧压对La0.67Sr0.33MnO3:Ag0.08薄膜激光感生电压效应的影响

通过化学共沉淀法制备了La_0.67Sr_0.33MnO₃:Ag_0.08 (LSMO:Ag_0.08)多晶材料, 然后采用脉冲激光沉积(PLD)技术在LaAlO₃ (LAO)倾斜衬底上制备了LSMO:Ag_0.08薄膜。研究了衬底温度和生长氧压对薄膜结构、电输运特性及激光感生电压(LIV)效应的影响。结果表明: 当衬底温度为790℃、生长氧压为45 Pa时, 薄膜具有最大峰值电压(U_p)、优值(F_m)和各向异性Seebeck系数(ΔS); 在优化的衬底温度和生长氧压条件下, 长程Jahn-Teller协变引起ΔS数值提高, 这是LIV信号增强的主要原因。     

Fabrication and Magnetic Properties of Electrospun La0.7Sr0.3MnO3 Nanostructures

La_0.7Sr_0.3MnO₃ (abbreviated as LSMO) nanostructures were fabricated by a simple electrospinning using a solution that contained poly(vinylpyrrolidone) (PVP), lanthanum, strontium and manganese nitrates. The LSMO nanostructures were successfully obtained from calcination of the as-spun LSMO/PVP composite nanofibers at 500–900 °C in air for 7 h. The as-spun and calcined LSMO/PVP composite nanofibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Analysis of phase composition by XRD revealed that all the calcined samples have a single rhombohedral LSMO phase. The SEM results showed that the crystal structure and morphology of the LSMO nanofibers were affected by the calcination temperature. Crystallite size of the nanoparticles contained in nanofibers increased with an increase in calcination temperature. The specific saturation magnetization (M _s ) values were obtained to be 1.23, 28.61, and 40.52 emu/g at 10 kOe for the LSMO samples calcined respectively at 500, 700, and 900 °C. It is found that the increase of the tendency of M _s is consistent with the enhancement of crystallinity, and the values of M _s for the calcined LSMO samples were observed to increase with increasing crystallite size. This increase in M _s for the calcined LSMO samples with increasing crystallite size may be explained by considering a magnetic domain of the samples.     

Effects of Transition-Metal V-Doping on the Structural, Magnetic and Transport Properties in La0.67Sr0.33MnO3 Manganite Oxide

We have investigated the structural, magnetic, and electrical transport properties of a series of ABO₃-type perovskite compounds, La_0.67Sr_0.33Mn_1?x V _x O₃ (0≤x≤0.15). The samples were characterized by X-ray diffraction and data were analyzed using Rietveld refinement technique, it has been concluded that these materials have the rhombohedral structure with $\mathrm{R}\overline{3}\mathrm{C}$ space group. The magnetization and resistivity measurements versus temperature proved that all our samples exhibit a ferromagnetic to paramagnetic transition and a metallic to semiconductor one when the temperature increases. Both the Curie temperature T _C and the resistivity transition temperature T _P of the composites decrease, while the resistance increases as the V content increases. It has been concluded that the electrical conduction mechanism in the metallic regime at low temperatures (T<T _P) can be explained on the basis of grain boundary effects and the single electron-magnon scattering process. Resistivity data were well fitted with the relation ρ=ρ ₀+ρ ₂ T ²+ρ _4.5 T ^4.5, whereas the adiabatic Small Polaron Hopping (SPH) and Variable Range Hopping (VRH) models are found to fit well in the paramagnetic semiconducting regime at the high temperature (T>T _P).     

Study of Structural, Magnetic and Electrical Properties of the Rare-Earth Manganite La0.2235Pr0.2235Nd0.2235Sr0.33MnO3

The perovskite-type La_0.2235Pr_0.2235Nd_0.2235Sr_0.33MnO₃ (LPNSM) ceramic sample was prepared using the solid-state reaction at high temperature. The material was subjected to X-ray diffraction and found to crystallize in rhombohedral structure with space group $\mathrm{R}\bar{3}\mathrm{c}$ . Physical characterization of this compound was carried out using magnetization and dielectric properties. From the magnetic characterization of this compound, the existence of a transition from ferromagnetic to paramagnetic at the Curie temperature T _C=289?K was deduced. This T _C-value is in good agreement with the ones obtained from the Curie?CWeiss law (1/???? vs. T). After characterizing this material, a systematic investigation of dielectric properties as a function of temperature was undertaken. It has been found that the sample shows high dielectric constant and diffuse phase transition (DPT) above room temperature. The scaling behavior of the imaginary part of electric modulus, M?? suggests that the relaxation describes the same mechanism at various temperatures in LPNSM.     

用溶胶－凝法制备锆钛铅铁电薄膜

利用溶胶－凝胶法在镀铂硅片上制备了ＰＺＴ铁电薄膜。利用ＸＲＤ、ＳＥＭ和ＴＥＭ观察了ＰＺＴ薄膜的组成与形貌，测定ＰＺＴ薄膜的电学性能。为防止薄膜发生龟裂，在前体溶液中加入了干燥控制化学添加剂，并采用慢速变温的热处理过程。ＰｂＴｉＯ３过渡层保证了ＰＺＴ薄膜结晶完好。     

La0.67Sr0.33MnO3中Bi的掺杂效应

将Bi2O3掺杂到用溶胶—凝胶法制备的La0.6Sr0．33MnO3(LSMO)微粉中,XRD测量结果证实有过量的Bi析出。随着Bi掺杂量的增加,LSMO／(Bi2O3)x/2材料电阻率发生明显变化,在x=(0—0．10)摩尔比的掺杂范围内,电阻率先上升后突然下降。当X=0．1时,电阻率比未掺杂样品下降了一个数量级。Bi掺杂对低温和室温磁电阻有着完全不同的影响。低温下,随掺杂量增加,磁电阻下降;室温下Bi的微量掺杂可以使磁电阻增大,掺入x=0.03Bi使室温磁电阻由-4.4％提高到-5．6％。     

La0.67 Sr0.33 MnO3外延薄膜的电脉冲诱发可逆变阻效应

采用脉冲激光沉积技术在SrTiO3,(001)单晶衬底上制备出钙钛矿结构La0.67 Sr0.33 MnO3,(LSMO)外延薄膜,通过X射线衍射仪和原子力显微镜表征其晶体取向与表面形貌,并对Ag-LSMO结构的室温电脉冲诱发可逆变阻效应进行研究.结果表明,在±4V、50ns对称脉冲作用下,LSMO膜层电阻发生高低转变,且变阻范围随脉冲幅值电压、脉冲宽度、脉冲数日等参数的变化而变化.该效应表现出良好的疲劳特性与非挥发存储特性,有望应用于新型不挥发存储器、传感器、可变电阻等电子元器件的研制.     

Nb5+的掺杂引起La0.67Sr0.33MnO3增强的磁电阻效应

将Nb2O5掺杂到用溶胶-凝胶法制备的La0.67Sr0.33MnO3(LSMO)微粉中,XRD测量结果表明所有样品均为单相菱面结构.随着Nb5 掺杂量的增加,材料电阻率发生显著变化.在x=0.06的掺杂样品中得到最高为1110Ω·cm电阻率(x是掺入的Nb离子与母体材料的摩尔比),比LSMO高5个数量级,这是由于晶界处以及颗粒内部增加的自旋相关的散射和隧穿效应所致.Nb5 离子的掺杂使样品的低场磁电阻(LFMR)和高场磁电阻(HFMR)效应都有所增强.77K下,0.1和1T磁场下在x=0.07样品中分别得到25%和42%的磁电阻效应,分别是LSMO样品的2倍和1.7倍.室温下x=0.03样品的磁电阻最大,为7%.其中,LFMR来源于颗粒晶界处电子的自旋相关隧穿及散射作用,而HFMR来源于表面层的自旋非共线结构.