Nd-Sr-Mn-O钙态矿锰氧化物的低场磁电阻效应

采用固相烧结法和脉冲激光沉积法分别制备了钙态矿型锰氧化物Nd1-xSrxMnO3(x=0．1，0．2，0．3，0．4，0．5)大块多晶和Nd0．7Sr0．3MnO3在(100)LaAlO3基片上的单取向薄膜样品，分别研究了这些样品的磁电阻效应。研究表明，在多晶样品中，x=0．3时具有最大的磁电阻比，其值在240K和1T磁场下可达24．2％。对于同一成分的外延薄膜，发现磁电阻随着沉积时基片温度Ts的升高而下降，当Ts=500℃时的制备态薄膜在同样条件下的磁电阻可达84％，随着外加磁场增大到5T，磁电阻将线性增大到275％。并讨论了造成单取向膜和块材磁电阻不同的原因。     

IrO_2掺杂对La_(0.7)Ca_(0.2)Sr_(0.1)MnO_3室温磁电阻效应的增强

将IrO2掺杂到固相反应法制备的La0.7Ca0.2Sr0.1MnO3(LCSMO)微粉中,制备了(1-x)La0.7Ca0.2Sr0.1MnO3+xIrO2(LCSMO/IrO2)复合体系。通过X射线衍射(XRD)、振动样品磁强计(VSM)以及直流四探针法测试,对复合材料的结构及性能进行了研究。结果发现,在复合体系中,一部分Ir4+离子取代了B位的Mn4+离子,另一部分以IrO2氧化物的形式存在于颗粒的边界处。随着IrO2掺杂量的增加,样品的比饱和磁化强度(σs)快速下降,而居里温度(TC)先下降后上升,电阻率也发生显著变化。与此同时,IrO2的掺杂使样品的低场磁电阻效应(LFMR)和高场磁电阻效应(HFMR)都有所增强,在H=3 kOe,T=307 K,x=5%的样品磁电阻达到11.65%;同样对于x=5%的样品,在H=2 T,T=295 K,磁电阻达到28%,室温磁电阻得到显著增强,这可能与本征磁电阻效应的特点及材料的TC和相变温度接近室温有关,另外掺杂物本身的特性对磁电阻的增强也有一定的影响。     

钙钛矿型稀土锰氧化物La_(0.7)Sr_(0.3)Fe_xMn_(1-x)O_3的磁性和巨磁电阻效应

采用溶胶 凝胶工艺制备了La0 .7Sr0 .3FexMn1 -xO3化合物 ,研究Fe掺杂对材料的导电性能、磁性能、磁电阻性能的影响。发现随Fe含量的增加 ,材料的电阻率提高 ,铁磁居里温度 (TC)下降 ,巨磁电阻效应增强。观察到x =0 0 5和x =0 0 8的样品的电阻率随温度变化曲线出现双峰。对于x =0 0 8的样品 ,在室温附近磁电阻达到 18% (8× 10 5 A·m- 1 外场 )。对于x >0 0 8的样品 ,金属 绝缘体转变温度均比相应的铁磁 顺磁转变温度低 5 0～ 80K     

稀土(Sm,Gd,Dy)代换镧对La0.7Sr0.3MnO3磁电性质的影响及室温CMR的增强

用固相反应法制备了La0.7-xSm,Sr0.3MnO3,La0.7-x,GdxSr0.3MnO3和La0.7-xDyxSr0.3MnO3(x=0.00,0.10,0.20,0.30)系列样品.通过M-T'曲线,ρ-T曲线,研究了用稀土离子代换La对La0.7Sr0.3MnO3磁电性质和磁电阻的影响.结果表明:稀土离子代换La引起的晶格畸变和稀土离子的额外磁性对钙钛矿锰氧化物的磁电性质影响很大;稀土离子代换La是改变钙钛矿锰氧化物居里温度和增强MR的有效途径;适量稀土离子代换La可以在室温附近产生大的磁电阻.     

有效介质模型对La0.67-xYxCa0.33MnO3化合物多孔陶瓷样品ρ-T曲线的拟合分析

介绍并采用有效介质模型对钙钛矿型氧化物La0．670xYxCa0.l33MnO3(x=0．1，0．2)多孔陶瓷样品的ρ-T曲线进行了拟合分析。结果显示，在磁场作用下，样品中的铁磁相和顺磁相随机分布的温度范围变宽，自旋极化子的激活能减小。描述这些样品的ρ-T曲线需要建立更加复杂的模型。     

(La1-xREx)2/3Sr1/3MnO3(RE=Y,Sm,Eu,Tb;x=0.1～0.5)的晶体结构及磁性质研究

采用空气中固相反应烧结法制备了一系列钙钛矿结构的(La1-xREx)2/3Sr1/3MnO3(RE=Y,Sm,Eu,Tb;x=0.1～0.5)稀土锰氧化物多晶样品.X射线衍射(XRD)分析表明掺杂RE部分替代La以后,样品的晶体结构为正交结构,空间群为Pbmm.在室温(300K)和液氮温度(77K)下分别测试了样品的磁性质,发现磁性质的改变与RE的掺入量以及RE的离子半径有关.在掺Tb的样品中明显存在巨磁电阻效应,磁场为2 T,温度为300和77 K分别测得(La0.6Tb0.4)2/3Sr1/3MnO3和(La0.7Tb0.3)2/3Sr1/3MnO3的磁电阻(MR)为80%和85%.随着Tb掺杂量的增加,在不同的磁场下,样品电阻-温度关系曲线的峰均向高温方向移动.     

La_(0.67)Sr_(0.33)Fe_xMn_(1-x)O_3制备和奇特磁电阻效应

系列陶瓷氧化物La0.67Sr0.33FexMn1-xO3（0.055x0.33）通过共沉淀法工艺合成获得.经X射线衍射分析表明，所得氧化物均为单相，属三方结构.在零场和外加磁场下的四极法电阻测试结果表明：所有样品都具有较大的磁电阻效应，当x<0.13时，样品的电阻率-温度曲线中均出现电阻率峰（电阻率出现从半导体性向金属性的转变），该电阻率峰处的温度（Tp）随x的增大而向低温区移动，磁电阻效应是负值;x＝0.23时，样品已呈半导体性，磁电阻效应仍是负值;然而x＝0.33时，样品虽也表现为半导体性，但其中的磁电阻效应出现奇特的正负交替转换.     

稀土空位庞磁电阻材料La(1-x)2/3Ca1/3MnO3的结构变化和输运性质

利用标准的固相反应法制备了La（1-x）2/3Ca（1/3）MnO3（x〈0.1）系列具有稀土La空位的庞磁电阻锰氧化物多晶样品.X射线粉末衍射（XRD）测量分析表明所有的样品均为单相,单胞具有正交对称性（Pnma）.分析了不同浓度的La空位对磁电输运性质的影响： 随着空位浓度的增大,绝缘体-金属的转变温度（TMI）几乎不变（约为267 K）,这表明少量的稀土空位不会破坏双交换作用;但当La空位浓度x〉0.04时,零场电阻率增大,但磁电阻（MR）值减小;在x=0.04时MR值在转变温度TMI处达到最大值约为220%（8 T）.     

La0.6Sr0.4Co1-yFeyO3(y=0.2,0.8)复合氧化物混合导电性能研究

采用甘氨酸-硝酸盐（GNP）法制备了La0．6Sr0．4Co1-yFeyO3（y=0．2，0．8）g合氧化物，研究了材料的结构、电子-离子混合导电性能及其相关性。结果表明，La0.6Sr0.4Co1-yFeyO3（y=0．2，0．8）合成粉料的颗粒细小均匀（～100nm），陶瓷形成菱形六面体钙钛矿结构。与La0．6Sr0．4Co0．2Fe0．8O3（y=0．8）陶瓷相比，La0.6Sr0.4Co0．8Fe0．2O3（y=0．2）陶瓷的晶粒尺寸大、致密度较高。在La0.6Sr0.4Co0．8Fe0．2O3（y=0．2）陶瓷中观察到Co^3＋离子歧化对电子导电性能的影响。与La0.6Sr0.4Co0.2Fe0.8O3（y=0．8）陶瓷相比，La0.6Sr0.4Co0.8Fe0．2O3（y=0．2）陶瓷具有更优异的电子-离子混合导电性能，材料在混合导电性能上的差异与其电子结构和显微结构紧密相关。     

稀土锰氧化物La0.7Ca0.3Mn1-xCuxO3低场磁电阻及电传输特性研究

采用溶胶-凝胶法制备了系列多晶CMR材料La0.7Ca0.3Mn1-xCuxO3（x=0%,1%,5%,10%,15%,20%）。在77-350 K温度范围内测量了样品的电阻率及磁电阻大小。实验结果发现：系列样品TC随掺杂量增加而递减;系列样品的电阻率峰及磁电阻峰在整个测温范围内随掺杂量的增加均依次被展宽直至消失,当掺杂量为x≥10%时,电阻率随温度的变化在整个测温范围内呈现绝缘相行为;同时还发现,掺杂量为x≥10%时,样品的磁电阻在整个测温区内基本表现为隧穿磁电阻。基于我们采用蒙特卡罗模拟方法提出的逾渗模型及隧穿磁电阻模型,对样品的磁电阻行为进行了很好的解释。对系列样品的ρ-T曲线进行lnρ-T^-（1/4）系拟合,发现掺杂量为x=10%样品在整个温区内的lnρ-T^-（1/4）系基本呈线性。     

超晶格多层膜的电化学制备、表征及其GMR特性的研究

以半导体Si为衬底,电化学沉积Cu/Co超晶格多层膜,用SEM表征多层膜的断面形貌.XRD研究表明,多层膜的调制波长为20～160 nm时,膜层间发生外延生长.随着调制波长的减小,外延生长对膜层结构的影响越来越明显.当调制波长小于20 nm时,在XRD强衍射峰的两侧出现卫星峰,表明多层膜形成超晶格结构.根据卫星峰位置计算的调制波长与由法拉第定律估算的结果非常接近.多层膜的巨磁电阻(GMR)性能随多层膜周期数的增加而增大;当周期数大于300时,GMR性能基本上不再随周期数变化,说明基体的导电性质对GMR的影响可以忽略.     

Analytical investigations of tunnel magnetoresistance layers

The basic elements of tunnel magnetoresists are two magnetic layers separated by an insulating barrier layer. The uniformity of this only 1–2 nm thick barrier layer up to dot edges and the chemical composition of the layers are properties important for the efficiency of tunnel magnetoresistance devices. These key-properties have been investigated by analytical TEM methods like high resolution TEM imaging and energy-filtered imaging. With regard to the chemical composition the TEM results have been confirmed by XPS investigations. The subsequent oxidation of the barrier is one of the most critical steps of the deposition procedure of the layer stacks. An undersized oxygen dose leads to an incomplete oxidation of the barrier layer with uncontrollable tunnel behaviour. An overdose of oxygen leads to oxygen diffusion in the layers beneath the barrier and uncontrollable magnetic hardness of the lower magnetic electrode.     

自掺杂La1-δMn1-δO3化合物的晶体结构和巨磁电阻效应

采用溶胶-凝胶工艺制备了La1-δMn1-δO3化合物.研究了烧结条件的改变对材料的结构、磁性、导电性、磁电阻效应的影响.首次发现La1-δMn1-δO3化合物的电阻-温度曲线的双峰现象.     

Giant magnetoresistance in electrodeposited Ni-Cu/Cu multilayers and anisotropic magnetoresistance in pulse-plated Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> alloy films

Ni-Cu/Cu multilayers and Ni_xCu_1–x alloy films were electrodeposited on Au-coated glass substrates from a sulfamate-based electrolyte. The room-temperature magnetoresistance of the multilayers was studied as a function of the ferromagnetic Ni-Cu layer thickness. Giant magnetoresistance was observed, which peaked at about 1% for a Ni-Cu layer thickness around 15 Å. Magnetoresistance measurements of Ni_xCu_1–x films of different composition were obtained at both room temperature and 77 K. Anisotropic magnetoresistance of up to 1.1% and 1.7% was observed at room temperature and 77 K, respectively.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany     

电沉积Co-Cu颗粒膜的巨磁电阻效应

从１９８８年Ｂａｉｂｉｃｈ首先在磁性Ｆｅ／Ｃｒ多层膜中发现巨磁电阻效应（ＧＭＲ）以来 ［１］,由于ＧＭＲ本身的科研价值和在磁记录、磁性传感器等方面的广泛应用前景 ,引起了人们的极大关注．继多层膜之后 ,人们在金属颗粒膜如Ｃｏ Ａｇ［２］,Ｃｏ Ｃｕ［３,４］等中也相继发现了巨磁电阻效应．颗粒膜是微颗粒镶嵌于薄膜中所构成的复合材料体系．原则上 ,颗粒的组成与薄膜的组成在制备条件上应互不固溶 ,因此颗粒膜区别于合金、化合物 ,属于非均匀相组成的材料．磁性颗粒膜是磁性粒子分布在非磁性金属材料薄膜中．在磁性颗粒与非…     

Crystal Structure and Magnetic Properties of SrCaMnGaO5+δ

The room-temperature crystal structure of the brownmillerite SrCaMnGaO_5+δ (δ=0.035) has been refined from neutron powder diffraction data; space group Ima2, a=15.7817(6), b=5.4925(2), c=5.3196(2)> Å. Mn and Ga occupy 99.0(2)% of the 6- and 4-coordinate sites, respectively. A combination of magnetometry, neutron diffraction and μSR spectroscopy has shown that the compound orders magnetically at 180 K, and that the low-temperature phase has a G-type antiferromagnetic structure, with an ordered magnetic moment of 3.30(2) μ_B per Mn at 2 K. Displaced hysteresis loops provide evidence that the atomic moment has an additional, glassy component. Magnetometry shows that significant short-range magnetic interactions persist above 180 K, and μSR that the spin fluctuations are thermally activated in this temperature region. The compound is an electrical insulator which at 159 K shows an unusually large magnetoresistance of 85% in 6 T, increasing to 90% in 13 T.     

Properties of CMR composites

Colossal magnetoresistance (CMR) composites form an interesting field of study. The intrinsic CMR, governed by the intragrain transport of the conduction electrons through the double exchange, limits its application owing to the high field requirement and generally low transition temperatures. Extrinsic CMR, a function of the intergrain transport between ferromagnetic (FM) particles, plays a crucial role in enhancing low field magnetoresistance (LFMR) or increasing room temperature magnetoresistance. Since extrinsic CMR is a grain boundary controlled phenomena, magnetically dirty grain boundaries in the virgin state of the sample help in achieving a high LFMR or increase the field sensitivity. In this article, we give the properties of different composites of magnetoresistive LCMO or LSMO where the second component is (a) an insulating phase, (b) a conducting phase, (c) a nonmagnetic phase and (d) a magnetic phase. We present here some of our recent work on CMR composites where the CMR phase is chosen as LCMO and SiO₂, ZnO, ZrO₂ and SiCN have been used as the different second phase of the composites. We summarise some of the salient features of the results. Dedicated to Professor C N R Rao on his 70th birthday     

(La0.67Ca0.33MnO3)x/(ZrO2)1-x复合体系的磁性和传输特性

将用溶胶-凝胶法得到的La0.67Ca0.33MnO3(LCMO)微粉与ZrO2的颗粒进行复合,制备了(LCMO)x/(ZrO2)1-x渗流复合体系.当LCMO的体积分数为40%时,复合体系达到渗流阈值,此时材料在低温下的磁电阻得到显著增强.77 K时在10 mT的磁场下,(LCMO)0.4/(ZrO2)0.6的磁电阻比为7.8%,相对于LCMO增加了712%.低场磁电阻(LFMR)的增强是由于载流子在二者界面处发生的自旋相关隧穿效应.由于界面反应,不可避免地产生了Zr离子对Mn离子的B位替代,从而引起材料磁性M和居里温度Tc的下降.在x＜60%时,Tc保持在220 K附近基本不变,说明该B位替代是有限的.     

Enhanced magnetoresistance in La07Sr03MnO3 nanoscaledgranular composites

By soft chemical processing, two kinds of nanoscaled lanthanum manganite granular composites, La₀₇Sr₀₃Mn₃ / CoFe_2O4 (LSMO/CF) and La₀₇Sr_0.3Mn₃ / Nd₀₇Sr₀₃Mn_O3(LSMO/NSMO), were fabricated. Enhancement in magnetoresistance is observed in both of the composites. Different magnetic compounds, CF and NSMO, embedded in LSMO matrix, result in different temperature ranges where the enhancement occurs. It is considered that the phenomenon is associate with electron tunneling between sorts of grains as well as spin-dependent scattering.