钙钛矿锰氧化物La0.7Sr0.3MxMn1-xO3(M=Cr,Fe)的巨磁电阻效应与磁性

研究了溶胶-凝胶法制备氧化物巨磁电阻材料的工艺,制备了La_0.7Sr_{0.3< /sub>CrxMn1-xO3(x=0,0.10,0.15)和La0.7Sr0.3FexMn1-xO3(x=0.05,0.10,0.16)两 系列的单相钙钛矿锰氧化物多晶样品,并研究了Cr,Fe替代La0.7Sr0.3MnO3中部分Mn后对其结构、磁性和巨磁电阻性质的影响.观察到La0.7 Sr0.3Cr0.15Mn0.85O3和La0. 7Sr0.3Fe0.05Mn0.95O3两个样品的 电阻-温度曲线都出现了双峰.定性讨论了可能产生双峰的机制.随Cr(或Fe)替代量的增加, 材料的居里温度很快下降,铁磁性减弱,导电性降低,巨磁电阻效应增强.但与Fe掺杂相比 ,相同数量的Cr掺杂对材料的影响要小. 关键词： 巨磁电阻效应 溶胶-凝胶工艺 电阻-温度曲线 金属绝缘体转变}     

用激光分子束外延在玻璃衬底上生长La0.67Sr0.33MnO3薄膜

采用激光分子束外延技术,在玻璃衬底上制备了La_067Sr_033MnO₃ （LSMO） 薄膜,X射线衍射测量结果表明在玻璃衬底上生长的LSMO薄膜沿c轴择优取向生长.在外磁场3 T和88, 220, 300 K条件下,LSMO薄膜的磁电阻变化率分别达到-378%, -268%和-607%.实验结果表明,在廉价的玻璃衬底上制备大面积和具有应用价值的锰氧化物薄膜是可行的. 关键词： 锰氧化物薄膜 玻璃衬底 外延生长     

La0.67Ba0.33MnO3薄膜的激光辐照效应研究

利用脉冲激光沉积技术在LaAlO₃（00l）单晶衬底上制备了La_067Ba_033MnO₃薄膜,研究了CO₂激光辐照对La_067Ba_033MnO₃薄膜的微结构和磁电性能的影响.结果表明,经激光辐照后,La_067Ba_033MnO₃薄膜的结晶性增强,薄膜应变减小;薄膜表面形貌由“岛状”结构变为“平原"结构,且粗糙度大大降低;同时,薄膜的饱和磁化强度、铁磁居里温度、金属—绝缘态转变温度和磁电阻增大,而矫顽场和电阻率减小.根据对传统退火效应的分析和理论计算,认为激光辐照导致的表面微结构的变化以及薄膜的氧含量和均匀性的提高对La_067Ba_033MnO₃薄膜的磁电性能的改善与优化密切相关. 关键词： 庞磁电阻 激光辐照 脉冲激光溅射沉积     

磁电双层膜层间耦合的弹性力学研究

基于磁致伸缩相与压电相的本构方程,应用弹性力学模型,简要介绍了如何推导自由状态的磁电双层膜纵向、横向磁电(ME)电压系数. 并采用相应的材料参数计算了La_07Sr_03MnO₃-Pb(Zr,Ti)O₃ (LSMO-PZT),Tb_1-xDy_xFe_2-y(TDF)-PZT双层膜中的磁电电压系数,具体分析了其与压电相 关键词： 磁电效应 双层膜 TDF LSMO PZT     

La0.9Sr0.1MnO3薄膜中电流效应研究

用直流磁控溅射法在(100)LaAlO₃衬底上制备了La_0.9Sr_0.1MnO₃薄膜.经退火处理后薄膜的原子力显微镜形貌观测和X射线衍射分析显示具有比较好的质量.电阻率-温度关系表明La_0.9Sr_0.1MnO₃薄膜在281 K处发生金属绝缘体转变.电流在0.01—4 mA范围内，薄膜的峰值电阻率随电流增大而减小，在4 mA下获得了30.5%的峰值电阻率变 关键词： 掺杂锰氧化合物 0.9Sr_0.1MnO₃薄膜')" href="#">La_0.9Sr_0.1MnO₃薄膜 电流诱导效应 相分离理论     

多晶La0.7Sr0.3MnO3的低温输运性质和磁电阻效应

详细研究了由纳米晶粒组成的块体多晶La_0.7Sr_0.3MnO₃(LSM)的电阻率和磁电阻效应,以及它们的温度依赖性.随着温度从室温降低,电阻率(ρ)在250K附近存在一最大值,低于该温度后,样品表现为金属导电特性,随后在50K附近存在一极小值.也就是说在低于50K的温度范围内,随着温度降低ρ反而升高,表现为绝缘体性的导电特性.经研究发现,这种随温度降低ρ反而增加的现象与隧穿效应的理论模型(lnρ∝T^-1/2)符合得很好 关键词： 0.7Sr_0.3MnO₃')" href="#">多晶La_0.7Sr_0.3MnO₃ 隧道效应 隧道磁电阻效应     

La0.4Ca0.6MnO3系统中Mn位Fe和Cr掺杂效应的比较性研究

利用固相反应法制备了Mn位Fe³⁺和Cr³⁺掺杂的系列锰氧化物La_0.4Ca_0.6(Mn_1-x(y)B_x(y))O₃ (B=Fe³⁺ (0≤x≤0.1); Cr³⁺ (0≤y≤0.1)) 多晶样品,研究了掺杂对样品输运性质的影响.实验结果表明两种离子具有截 关键词： 锰氧化物 反铁磁 磁电阻效应     

成分调制的La1－xSrxMnO3复合隧道结

利用磁控溅射和Sr成分的调制以及原位热处理方法，在10mm×10mm大小的(001) 取向SrTiO_３单晶衬底上制备出三明治结构为La_0.7Sr_0.3MnO３(100nm)/La_0.96Sr_0.04MnO_３ (5nm)/ La0.7Sr_0.3MnO_３ (100nm) 的隧道结外延薄膜，然后再次 利用磁控溅射方法，在三层单晶膜上方继续沉积Ir_２２Mn_７８(15n m)/Ni_７９Fe_２１(5nm)/Pt(20nm)等金属三层膜.最后利用深紫外曝 光和Ar离子束刻蚀等微加工技术，制备出长短轴分别为12和6μm或者8和4μm大小的椭圆形L a_１-xSr_xMnO_３成分调制的复合磁性隧道结.在4.2K和 外加磁场8 T的测试下，La_１-xSr_xMnO_３成分调制的复 合磁性隧道结其隧穿磁电阻(TMR)比值达到3270%, 直接从实验上证实了铁磁性La_{0.7Sr0.3MnO３金属氧化物的自旋极化率（97%）可接近100％，具 有很好的半金属性质. 关键词： １-x}Sr_xMnO_３')" href="#">La_１-xSr_xMnO_３ 半金属 成分调制 复合磁性隧道 结 隧穿磁电阻     

La1－xPrxMnO3(x=0.1，0.2)薄膜庞磁电阻性质的研究

一种新的庞磁电阻氧化物薄膜La_1-xPr_xMnO₃(x=0.1，0 .2)薄膜用脉冲激光沉积(PLD)方法生长在(100)SrTiO₃单晶基底上.XRD结果显示 薄膜具有很好的外延单晶取向.电输运和磁性质的研究表明薄膜具有显著的庞磁电阻效应(CM R)效应，其中磁电阻比率达95％(在5T的磁场下).X射线光电子能谱(XPS)的结果表明薄膜体 系中Pr离子的价态为+4价，因此该薄膜很可能是电子掺杂的庞磁电阻体系. 关键词： 脉冲激光沉积 1-xPr_xMnO₃')" href="#">La_1-xPr_xMnO₃ 电子 掺杂 庞磁电阻     

钙钛矿结构La0.9Sb0.1MnO3的庞磁电阻性质

一种新的钙钛矿结构的庞磁电阻氧化物La_0.9Sb_0.1MnO₃已用固态反应方法制 成，通过超导量子干涉器件(SQUID)装置测量研究了它的电输运性质和磁性质.x射线光电子 能谱分析证明，该氧化物中Sb的价态是+5价，因此该氧化物是一种新的电子掺杂型庞磁电阻 材料. 关键词： 钙钛矿结构 0.9Sb_0.1MnO₃')" href="#">La_0.9Sb_0.1MnO₃ 电子掺杂 庞磁电阻     

Giant positive magnetoresistance in heterostructure (La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>) coated with YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript> composites

(La_0.7Sr_0.3MnO₃) _x /(YBa₂Cu₃O₇) _y composites were prepared by mixing La_0.7Sr_0.3MnO₃ powders and the sol–gel-derived YBa₂Cu₃O₇ matrix, followed by high-temperature calcinations. Their structural, magnetic properties and magnetoresistance effect have been investigated systematically. A giant positive magnetoresistance (PMR) at low magnetic field is observed at low temperatures. In the case of (La_0.7Sr_0.3MnO₃)₁/(YBa₂Cu₃O₇)₉ composite, the PMR achieves 260% under a magnetic field of 5800 Oe. However, the PMR value sharply decreases with increasing temperature and no magnetoresistance effects are found above metal-insulator transition temperature. The enhancement of spin-dependent scattering at the grain boundaries should be responsible for the observed PMR. In addition, the temperature dependence of resistance under magnetic field could be explained by the competition between diamagnetism and paramagnetism in YBCO phase. At low temperature, the diamagnetism is predominant over paramagnetism and the interface scattering between LSMO grains is enhanced correspondingly. As a result, the low-temperature resistance increases and large PMR appears.     

Simultaneous observation of positive and negative giant magnetoresistances in composite (La0.83Sr0.17MnO3)1－x(ITO)x

We have studied the transport property of the composites （La0.83Sr0.17 MnO3）1-x（ITO）x [ITO=（In2O3）0.95 （SNO2）0.05], which were fabricated by mechanically mixing La0.83Sr0.17MnO3 and ITO grains. A giant positive magnetoresistance （PMR） has been observed above the Curie temperature Tc for samples with x around 0.40, in addition to the negative magnetoresistanee related to spin-dependent interracial tunnelling below To. For （La0.83Sr0.17MnO3）0.6（ITO）0.4, the magnetoresistive ratio for the PMR can reach 39.3% under a magnetic field H=2.24×10^5A/m. Theoretical analysis suggests that the magnetic-field-induced broadening of the p-n barrier between both kinds of grains and the density of the p-n heterostructures should be responsible for the PMR behaviour.     

Electrical properties and enhanced room temperature magnetoresistance in La0.7Ca0.2Sr0.1MnO3/Pd composites prepared by chemical plating

A series of bulk polycrystalline La_0.7Ca_0.2Sr_0.1MnO₃ (LCSMO)/Pd composites were prepared by chemical plating and structural, electrical, magnetic, and magnetoresistance (MR) properties were investigated. It is found that Pd additions are uniformly distributed on the grain boundaries of the LCSMO grains, which decrease the resistivity and the saturation magnetic moment of the matrix. An interesting phenomenon is observed that at a given field, when the plating time increases, the MR increases at low addition level (0>t (plating time)<40 min) and decreases at high addition level (t>40 min), indicating an optimal plating time of 40 min, at which the MR value is maximum. Our analysis suggests that the improvement of grain boundaries originating from Pd addition plays an important role in enhancing the MR.     

Influence of annealing atmosphere on the properties of La0.5Sr0.5MnO3

The structure, magnetic and electrical transport properties of La_0.5Sr_0.5MnO₃ annealed in different atmosphere have been investigated. No evident change of structural symmetry and the Curie temperature is observed for the samples. The resistivity at zero magnetic field of the samples annealed in air and nitrogen exhibits a metal–insulator transition, while no metal–insulator transition is observed for the sample annealed in oxygen, and for which the resistivity decreases monotonously with increasing temperature. Surprisingly, when an external magnetic field is applied, a metal–insulator transition appears for the sample annealed in oxygen. It is suggested that the annealing atmosphere affects the competition between FM and AFM phases due to the change of Mn⁴⁺/Mn³⁺ ratio and the oxygen/cation vacancies, and has a great influence on the electrical transport properties of La_0.5Sr_0.5MnO₃.     

Large magnetoresistance induced by surface ferromagnetism in A-type antiferromagnetic La0.4Sr0.6MnO3 nanoparticles

Grain size effects on magnetic and transport properties for heavily Sr-doped A-type antiferromagnetic La_0.4Sr_0.6MnO₃ ceramics were studied. It was observed that with decrease in grain size, surface ferromagnetism could be introduced due to bond-breaking at surfaces. With decrease in grain size, the surface ferromagnetism was enhanced, and the phase transition order distinguished from the Arrott plot was a second one. The surface-induced ferromagnetism was insulating as judged from transport properties. With decrease in grain size, magnetoresistance was largely improved for both high magnetic and low magnetic fields. Under a 500 Oe magnetic field, the magnetoresistance is improved from 0.2%, 0.1%, 0.03% and 0.02% for the sample with grain size of 150 nm at 10, 100, 200 and 300 K, respectively, to 3%, 2.3%, 0.43% and 0.12% for the sample with grain size of 20 nm at 10, 100, 200 and 300 K. It was interesting to find that large magnetoresistance could be induced due to the surface ferromagnetism in A-type antiferromagnetic La_0.4Sr_0.6MnO₃ nanoparticles, which suggested that it was possible to search for manganites with relatively high low-field magnetoresistance in nanostructured A-type antiferromagnetic materials.     

Prediction of thermomagnetic properties of La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3

The dependence of magnetization on the variation of temperature for La_0.67Ca_0.33MnO₃ and La_0.67Sr_0.33MnO₃ perovskite-type ceramic materials under an external magnetic field was modelled. Application of phenomenological model was performed, showing a good agreement with the experimental data. Temperature dependence of change of both magnetic entropy and specific heat under magnetic field 0.05?T was predicted for La_0.67Ca_0.33MnO₃ and La_0.67Sr_0.33MnO₃. Predicted values of maximum magnetic entropy change, full-width at half-maximum, relative cooling power and maximum specific heat under 0.05 T were evaluated.     

Effect of Sr content on structure and electrical properties of La1−x Sr x MnO3 from ITSOFC cathode view point

The samples belonging to La_1−x Sr _x MnO₃ series, prepared by combustion route without using fuel, exhibit crystal structural phase transition with the change in Sr content. Less than 40 mol% Sr is partially substituted in the crystal structure of LaMnO₃. The structural phase transition from rhombohedral to cubic, cubic to tetragonal, and tetragonal to orthorhombic takes place on 40, 60, and 80 mol% addition of Sr. The highest electrical conductivity in La_0.4Sr_0.6MnO₃ is understood to be due to the maximum concentration of polaron. The polarons are formed due to the conversion of Mn³⁺ to Mn⁴⁺ so as to achieve electroneutrality after substitution of Sr²⁺ for La³⁺.     

Effects of ZnO film thickness on electrical and magnetoresistance characteristics of La0.8Sr0.2MnO3/ZnO heterostructures

The La_0.8Sr_0.2MnO₃/ZnO heterostructures with different thicknesses of ZnO films are fabricated by using RF magnetron sputtering technique. The heterojunctions exhibit excellent rectifying properties at 300 K. At low temperatures the temperature dependent junction resistance exhibits a metal-insulator transition like behavior. A magnetic field strongly impacts on electrical characteristics of La_0.8Sr_0.2MnO₃/ZnO p-n junctions, i.e., depressing the junction resistance greatly and driving the metal-insulator transition temperature (T_MI) towards higher temperatures. Large magnetoresistance is observed below T_MI, and it increases with increasing magnetic field and almost saturates at 5 T, i.e., above −90% at 100 K and 5 T.     

Phase separation of the spin system in the La<Subscript>0.93</Subscript>Sr<Subscript>0.07</Subscript>MnO<Subscript>3</Subscript> crystal

The magnetic state of the manganite La_0.93Sr_0.07MnO₃ in the range 4.2–290 K was studied using elastic neutron scattering. The magnetic state of this compound was found to occupy a particular place in the La_1?xSr_xMnO₃ solid-solution system, in which the antiferromagnetic type of order (LaMnO₃, T_N=139.5 K) switches to ferromagnetic ordering (La_0.9Sr_0.1MnO₃, T_C=152 K) with increasing x. In the transition state, this compound contains large-scale spin configurations of two types. A fractional crystal volume of about 10% is occupied by regions of the ferromagnetic phase with an average linear size of 200 Å, while the remainder of the crystal is a phase with a nonuniform canted magnetic structure. Arguments are presented for the phase separation of the La_0.93Sr_0.07MnO₃ spin system being accounted for by Mn⁴⁺ ion ordering.