钙钛矿锰氧化物La_(2/3)Sr_(1/3)Fe_xMn_(1-x)O_3的结构与磁性研究

本文利用溶胶-凝胶法制备了名义成分为La_(2/3)Sr_(1/3)Fe_xMn_(1-x)O_3(x=0.0,0.1,0.2,0.3,0.5)的系列样品,样品先后经过773,873,1073 K热处理,热处理时采用缓慢升温方式,X射线衍射分析表明,该系列样品均为单相钙钛矿结构,空间群为R3c,利用X'Pert HighScore Plus软件计算了样品的晶粒尺寸、晶格常数、晶胞体积及键长、键角,利用物理性能测量系统测量了样品的磁性,发现样品在10K的磁矩随掺杂量的增加而减小,但存在两个明显不同的变化区域:从x=0到x=0.2时,平均每个分子的磁矩从2.72μB迅速下降到0.33μB,居里温度从327 K下降到95 K,下降了232 K;而从x=0.2到x=0.5时,平均每个分子的磁矩从0.33μB缓慢下降到0.05μB,居里温度从95K下降到46K,只下降了49K,我们认为Fe与Mn离子磁矩反平行是样品磁矩随Fe掺杂量增加而下降的原因之一。

Structure and magnetic properties of perovskite manganites La2/3Sr1/3FexMn1-xO 3

Perovskite manganites with nominal composition La_2/3Sr_1/3Fe_xMn_1-xO₃ (x=0, 0.1, 0.2, 0.3, 0.5) are prepared by the sol-gel method. The samples are treated three times at 773 K, 873 K and 1073 K, separately, in which processes the temperature is slowly increased. The X-ray diffraction patterns indicate that the samples have a single phase and perovskite structure each. The dimensions of the crystalline particles, lattice constants, cell volumes of the samples are calculated using the X’Pert HighScore Plus software. The magnetic properties are measured using a Quantum Design Physical Property Measurement System. The magnetic moments of the samples at 10 K decrease with the increase of Fe doping level x. The decreasing process can be divided to two ranges: one is from x=0 to x=0.2, in which range the average magnetic moment per formula decreases rapidly from 2.72 μ_B to 0.33 μ_B, while the Curie temperature decreases rapidly from 327 K to 95 K, i.e., it is reduced by 232 K; the other is from x=0.2 to x=0.5, in which range, however, the average magnetic moment per formula decreases slowly from 0.33 μ_B to 0.05 μ_B, while the Curie temperature decreases slowly from 95 K to 46 K, i.e., it is reduced only by 49 K. The experimental result that the magnetic moments of the samples decrease with the increase of Fe doping level may be explained as the fact that the magnetic moment direction of the Fe cations is opposite to those of Mn cations.
Keywords：perovskite manganitenonmetallic ferromagnetic materialssol-gel processingmagnetic pro-perties