热压处理对Nd0.7Sr0.3MnO3陶瓷磁电输运影响

在温度1273 K、压强9 GPa条件下对固相烧结Nd_0.7Sr_0.3MnO₃陶瓷样品进行热压处理. 结果发现, 处理后样品的晶体结构和空间群没有改变, 但晶胞参数和结构参数, 特别是样品的显微结构发生了很大变化. 这些变化对样品的磁电输运产生显著影响: 在磁性上, 热压样品的低温饱和磁矩减小并出现磁矩排列弥散特点; 在电输运方面, 当负载电流小于1.5 mA时, 与烧结样品一样, 热压样品不产生电致电阻 (ER) 效应, 并在金属-绝缘体转变点出现最大磁电阻 (MR). 但在低温下, 热压样品仍有较大MR值. 当负载电流超过1.5 mA时, 热压样品原R-T曲线中的电阻峰替变为一电阻平台, 且随负载电流增大, 平台逐渐宽化, 阻值减小, 出现ER行为. 有趣的是, 在外磁场作用下, 电阻平台随外场增大逐渐变窄、消失并又演变为一电阻峰. 这些奇特的输运行为除与热压处理导致样品晶粒绝缘化有关外, 可能还与热压导致粒间相的形成有关.

Effect of thermal-pressure treatment on magnetoelectric transport in Nd0.7Sr0.3MnO3 ceramics

The Nd_0.7Sr_0.3MnO₃ compounds are treated at a thermal pressure（HTP） of temperature 1273 K and pressure 9 GPa.The results show that the crystal structure and space group of samples keep unchanged while the lattice and structural parameters,especially the microscopic structure change remarkably,which produces significant influence on magnetoelectric transport of the Nd_0.7Sr_0.3MO₃ ceramic.For electrical transport of the HTP sample,no electroresistance（ER） effect occurs when loaded current is less than 1.5 mA, however,an ER effect around 200%takes place when the loaded current goes up to more than 1.5 mA.Interestingly,the peak atρ-T curve disappears by replacing a platform,which can return to a peak if a magnetic field is applied again.The formation of intergranular phase and insulating behaviour of sample under thermal pressure condition are suggested to be responsible for the unique transport properties.