Atom States and Interatomic Interactions in Complex Perovskite-Like Oxides: XIX. Magnetic Dilution in the La0.67Ba0.33MnO3-LaAlO3 System

Barium-doped solid solutions of lanthanum manganites in lanthanum aluminate were studied. In barium-containing magnetoresisting manganites, complete disaggregation of paramagnetic atoms does not occur even at infinite dilution, and clusters of ferromagnetically coupled manganese atoms remain in the structure.     

Magnetic Susceptibility of Dilute La0.67Sr0.33MnO3-LaAlO3 Solid Solutions

Russian Journal of General Chemistry -     

State of Atoms and Interatomic Distances in Complex Perovskite-like Oxides: XVII.1 Magnetic Dilution of La0.67Ca0.33MnO3 in LaGaO3

A magnetic susceptibility study of solid solutions of calcium-doped lanthanum manganite inlanthanum gallate showed that exchange interactions in clusters of manganese atoms do not change theircharacter with increasing temperature, unlike what is observed with solid solutions on the basis of lanthanumaluminate.     

(La1-xDyx)0.67Ca0.33MnO3的磁性和磁电阻特性

在La0.67Ca0.33MnO3中用Dy对La进行了部分替代.结果表明, 随替代量增加, 材料的居里温度和相变温度单调下降, 磁电阻比急剧增大.这些变化可以用稀土离子平均直径的减小和自旋团簇模型来解释.掺Dy使材料中形成大量无序自旋团簇, 外加磁场使自旋团簇取向一致, 从而增加了电子在团簇之间跳跃时的迁移率, 产生了磁场所致的庞磁电阻效应.     

Gd掺杂对La0.67 Sr0.33 CoO3、La0.67 Sr0.33 MnO3体系磁行为的影响

M~T curves and M~H curves of the systems La0.67Sr0.33CoO3, La0.67Sr0.33MnO3 (x=0.00, 0.05, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.67) were studied by experiments. Experimental results show that the magnetic structure of La0.67-xGdxSr0.33CoO3 system exhibits the cluster glass state with doping Gd increasing. The M~T curves of samples x>0.10 exhibit a peculiar phenomenon that M value rises sharply at low temperature range. The magnetic structure of La0.67-xGdxSr0.33MnO3 system changes from the long rang ferromagnetic order to the cluster glass state, and anti ferromagnetic state. The M~T curves of samples x≥0.50 decline sharply at low temperature range. The different phenomena shown by the two systems come from different coupling function between Gd and Co, Mn and from spin state transition of Co.     

States of Atoms and Interatomic Interactions in Complex Perovskite-like Oxides: XIV.1 Possibilities for Interatomic Interactions in Barium-containing Cuprates

The interatomic distances in dilute lanthanum-barium cuprates were examined to determine parameters of the local surrounding of copper atoms and interatomic exchange angles. In such cuprates, there are two possible directions of exchange interactions at an angle less than 180°.     

(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.     

States of Atoms and Interatomic Interactions in Complex Perovskite-like Oxides: XVI.1 Spin State of Nickel(III) Atoms in YyLa1 - yCaNixAl1 - xO4 Solid Solutions by EPR and Magnetic Susceptibility Data

The EPR spectra of Y_yLa_{1 - y}CaNi_xAl_{1 - x}O₄ solid solutions were studied. The simulated EPR spectra of low-spin Ni(III) atoms and the calculated specific integral intensity agree with magnetic susceptibility data, implying selective filling of octahedral sites by Ni(III) atoms and to non-monotone variation of the fraction of low-spin monomers on lanthanum substitution for yttrium.     

La0.67-xErxSr0.33MnO3 (0.00≤x≤0.20)体系的磁电特性和低温电阻率反常

实验研究了La0.67-xErxSr0.33MnO3(x=0．00，0．10，0．20)体系的M-T曲线、ρ-T曲线和MR-T曲线。结果发现：随掺杂量增加，体系的磁结构从长程铁磁有序向自旋团簇玻璃态过渡，极低温区出现M-T曲线上翘；体系的电阻率随掺杂量的增加而增加，并出现低温极小值现象。体系磁电性质的变化来源于掺杂引起的额外磁性耦合，以及晶格畸变和局域磁矩引起的类似于磁性杂质对电子自旋散射造成的近藤效应(Kondo Effect)。     

La0.67Ca0.33Mn1-xAlxO3体系的结构和输运特性研究

研究了Al离子的Mn位替代对巨磁阻材料La0.67Ca0.33MnO3体系的结构和输运特性的影响。结果表明,随Al3 替代量的增加,在整个替代范围内,晶胞体积表现出单调减小的规律。体系的电阻率急剧增加,绝缘体 金属转变温度TIM向低温方向移动,且与Al3 替代量存在线性关联。对少量Al3 替代量,在T>TIM的高温区域体系的输运特性满足热激活模型,在T相似文献   

La0.67Ba0.33MnO3中Bi掺杂产生的低场磁电阻增强效应

将Bi2O3掺杂到溶胶-凝胶法制备的La0.67Ba0.33MnO3(LBMO)微粉中, 结果发现随着Bi的掺杂, 材料的磁化强度和居里温度基本不变, 但电阻率发生明显变化, 在0～10% (摩尔分数)的掺杂范围内, 电阻率先急速上升后缓慢降低. 掺Bi可以使低温下的低场磁电阻得到显著增强, 但并不改变与双交换作用有关的本征磁电阻; 掺Bi也使室温下的磁电阻得到明显增强.     

微观结构对溶胶-凝胶法合成的La0.67Sr0.33MnO3电磁性能影响

采用溶胶-凝胶法制备了不同烧结温度的钙钛矿类锰氧化物La0.67Sr0.33MnO3样品。实验结果表明,在1573 K以上烧结的样品,晶粒出现异常长大,晶界效应明显。随着烧结温度的提高,磁化强度逐渐增大,但样品的居里温度基本不变。此外,在1173和1573 K温度下烧结的样品,均出现了低于居里温度的金属-半导体导电行为转变。在合适的烧结条件下,可以观察到隧道磁电阻(TMR)和超大磁电阻(CMR)2种磁电阻效应。实验表明,自旋电子的输运,不仅与样品平均粒径的大小和密度有关,而且与晶界的微观结构有密切关系。     

Magnetocapacitance and impedance spectroscopy of Ba0.7Sr0.3TiO3/La0.67Sr0.33MnO3 and Ba0.8Sr0.2TiO3/La0.67Sr0.33MnO3 thin film heterostructures

The paper discuses synthesis of Ba_0.7Sr_0.3TiO₃/La_0.67Sr_0.33MnO₃ and Ba_0.8Sr_0.2TiO₃/La_0.67Sr_0.33MnO₃ thin film heterostructures by sol–gel (citrate gel route) method. The XRD spectra are determined for confirmation of crystalline phases of Ba_0.7Sr_0.3TiO₃, Ba_0.8Sr_0.2TiO₃ and La_0.67Sr_0.33MnO₃ thin films. The observed variation of Cp, tan δ, magnetocapacitance (Mc), real part of dielectric constant ε′, imaginary part of dielectric constant ε″as a function of frequency, magnetoresistance R(H) and magnetoimpedance Z(H) are presented in the paper. Further the observed impedance spectra as a function of frequency f is also presented in the paper. The observed variation of Mc is qualitatively correlated with the stress induced effect and magnetoresistasnce effect occurring simultaneously.     

静电纺丝法制备La0.67Ba0.33MnO3微纳米纤维及其红外发射率研究

采用静电纺丝法结合溶胶-凝胶技术制备了钙钛矿型La_0.67Ba_0.33MnO₃微纳米纤维, 并利用差示扫描量热-热失重分析(DSC-TGA)、 X射线衍射(XRD)、 傅里叶变换红外光谱(FTIR)和扫描电子显微镜(SEM)等技术对产物进行了表征, 利用IR-2红外发射率测试仪测试了La_0.67Ba_0.33MnO₃在280~370 K范围内的红外发射率. 结果表明, La_0.67Ba_0.33MnO₃在600 ℃时已形成钙钛矿结构. 随着煅烧温度的升高, La_0.67Ba_0.33MnO₃的形貌由纤维状向三维网络状转变, 并最终失去纤维形态. 在280~370 K范围内, La_0.67Ba_0.33MnO₃微纳米纤维的红外发射率随温度升高而升高, 由0.564增加至0.689. 利用钙钛矿材料双交换理论解释了这一现象, 并进一步探讨了其在红外发射率可变材料中的应用前景.     

Letter: Lanthanum-calcium-manganate (La0.67Ca0.33MnO3) nanoparticle assisted affinity probes for MALDI MS analysis of proteins

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) has been used extensively for the analysis of -intact proteins and for proteomics. Proteins or proteomics analyses with low molecular mass range have some limitations because of background interference from the salt or surfactant ions. Lanthanum-calcium- manganate La(0.67)Ca(0.33)MnO(3) nanoparticles (LCMONPs) have been used as the matrix-assisting material after surface modification to reduce the salt or surfactant interference. The detectable mass range was tested in the range of 800-16,000 Da. The surface-modified LCMONPs have affinity with protein molecules through ionic or electrostatic interaction at pH 4.0. The nanoparticles mixed with proteins give a spectrum with a large signal-to-noise ratio for the analytes, and effectively eliminate the noise from interfering salt or surfactant ions. The results indicate that surface-modified La(0.67)Ca(0.33)MnO(3) nanoparticles can be used with MALDI matrix for proteins to eliminate the excessive noise of selective surfactants or salt ions from the MALDI spectrum.     

State of Atoms and Interatomic Interactions in Complex Perovskite-Like Oxides: XVIII. Magnetic Dilution in the LaCrO<Subscript>3</Subscript>-LaGaO<Subscript>3</Subscript> System

Magnetic susceptibility of dilute solid solutions of lanthanum chromate in lanthanum gallate was studied. The calculated antiferromagnetic exchange parameter and distribution of chromium atoms over the diamagnetic matrix gave evidence for enhanced chromium aggregation and weakened magnetic exchange in lanthanum gallate compared to lanthanum aluminate.     

Cation Distribution and Interatomic Interactions in Oxides with Heterovalent Isomorphism: VI. Solid Solutions Nd2Sr1 - xCaxAl2O7

The range of existence of Nd₂Sr_{1 - x} Ca _x Al₂O₇ solid solutions (x 0.5) was established. The distribution of neodymium, strontium, and calcium cations over two structural sites was studied by full-profile X-ray analysis. Unlike La₂Sr_{1 - x} Ca _x Al₂O₇ solid solutions, Ca^{2 +} cations fill not only nine-vertex AO₉ polyhedra, but also oxygen cubic octahedra AO_{1 2}. Introduction of calcium results in disordered distribution of Nd^{3 +} cations, destabilization of the layered structure, and decomposition of the solid solutions.     

Cation Distribution and Interatomic Interactions in Oxides with Heterovalent Isomorphism: V. Complex Aluminates LnCaAl3O7

A short-range ordering of lanthanide and calcium atoms was found in isomorphous La^{3 +} and Ca^{2 +} cations in stoichiometric oxides LnCaAl₃O₇ (Ln = La, Nd, Sm, Gd, Ho, Er). It takes place almost exclusively within the first cation coordination sphere. The cations form electrostatically linked mixed cation pairs Ln^{3 +}-Ca^{2 +} in the nearest neighboring points of a common structural site. No spatial ordering of the pairs themselves is observed.     

Magnetic transport behavior of nanocrystalline Nd0.67A0.33MnO3 (A = Ca,Sr, Pb and Ba)

Nanocrystalline A-doped manganites, with compositional formula, Nd_0.67A_0.33MnO₃ (A = Ca, Sr, Pb and Ba) were prepared by Polyvinly Alcohol (PVA) gel route. After characterizing the samples by X-ray diffraction studies and by measuring electrical, magnetic transition temperatures, a systematic investigation of magnetization and magnetoresistance measurements both as a function of magnetic field and temperature was undertaken. The variation of electrical and magnetic transition temperatures is explained on the basis of size variance parameter. It has been concluded from the M–H plots that NCMO, NPMO and NBMO samples are exhibiting narrow hystersis loops indicating soft ferromagnetic nature, while the NSMO is found to exhibit double hystersis loop indicating the presence of metamagnetic transition. It is also observed that among the four samples, Nd_0.67Ca_0.33MnO₃ is found to exhibit the highest magnetoresistance (MR) of 91% over a broad temperature region.     

Cation Distribution and Interatomic Interactions in Oxides with Heterovalent Isomorphism: VII. CrNbO4 and LiFeO2 Oxides

A high degree of local ordering of isomorphous cations, determined by a great difference in their effective charges, was found in stoichiometric CrNbO₄ and LiFeO₂ oxides. The character of the ordering (one-dimensional in CrNbO₄, supposedly approaching the AlWO₄ type, and two-dimensional in LiFeO₂ with a symmetry decreased to tetragonal and approaching the CuAu type) depends on the anisotropy of cation distribution in the cation coordination spheres. Microdomains with an almost complete ordering inside one block of the crystallite mosaic may develop in LiFeO₂.