摘要
采用传统的固相反应法制备了La_(0.5-x)Nd_xSr_(0.5)CoO_3(x=0,0.1,0.15)多晶样品,并通过磁化强度与温度的变化曲线(M-T曲线)和磁化强度与外场的变化曲线(M-H曲线)对其磁性进行了研究。研究结果表明,随着温度的降低三个样品的磁性都先后经历了顺磁、铁磁和反铁磁转变。掺杂量x的增加使得系统的居里外斯温度逐步上升(θ_(x=0)≈215 K;θ_(x=0.1)≈226 K;θ_(x=0.15)≈242 K),这表明Nd^(3+)掺杂使系统内部的铁磁耦合增强。通过对磁化率倒数与温度的变化曲线的拟合,发现三个样品都出现了向上背离居里外斯定律的现象,这种背离是由于系统内部反铁磁相互竞争所致。因此,三个样品均不具有类Griffiths相。另外,通过对高温部分的实验测量与理论计算发现,Co^(4+)的自旋态随着掺杂量x的增加逐渐由低自旋态向中间自旋态过渡。
The polycrystalline samples of doped perovskite cobalt oxides La0.5 - x NdxSr0.5 CoO3 （ x = 0, 0.1, 0.15 ） have been prepared by solid state reaction method. Magnetic properties of these samples were investigated by measuring the magnet- ization- temperature （M -T） and magnetization- field （M -H ） curves. Experimental resuhs show that paramagnetic （PM）, ferromagnetic （FM） and antiferromagnetic （AFM） transitions successively occur with decreasing temperatures in these samples. The Curie temperature gradually increase with doping concentration x（θ_（x=0）≈215 K;θ_（x=0.1）≈226 K;θ_（x=0.15）≈242 K）, which suggests that doped Nd3＋ ions enhance ferromagnetic couplings in such systems. The temperature dependence curves of the inverse susceptibility （X- l _ T） deviate upward from the Curie -Weiss Law, which implies the susceptibility de- creases to be smaller than the pure paramagnetic value and Griffiths -like phase is therefore not observed these systems. We argue that the absence of Griffiths - like phase is probably due to the presence of antiferromagnetic interactions. In addition, from experimental measurements and theoretical calculations in high temperature region, it is revealed that the Co4＋ ions trans- form from a low- spin （LS） to intermediate- spin （IS） state upon increasing doping concentration x.
出处
《稀土》
EI
CAS
CSCD
北大核心
2015年第6期39-44,共6页
Chinese Rare Earths
基金
国家自然科学基金项目(11164019)
内蒙古自然科学基金项目(2011MS0101)
内蒙古高校科研重点项目基金(NJZZ11166
NJ10163
NJZY12202)
