半掺杂铋基锰氧化物的磁相变和输运性质

Magnetic Transition and Transport Properties of Half-Doped Bi-Based Manganites

为了探测电荷有序锰氧化物中自旋动力学、短程磁相互作用及微观磁相的形成,文中通过磁化强度、电子自旋共振和电阻研究了半掺杂铋基锰氧化物Bi0.5Ca0.5MnO3的磁相变和输运性质.研究结果表明:高温顺磁区域存在铁磁自旋团簇,及"瓶颈"自旋-晶格相互作用;在电荷有序态,伴随着轨道有序的增强,反铁磁相互作用逐渐增强并占优势,反铁磁相变温度发生在奈耳温度(TN=125K).由于铁磁有序和反铁磁有序的竞争,在自旋冻结温度(Tf=35K)附近发生自旋玻璃转变.电阻表现为半导体导电行为,并在电荷有序相变温度出现电阻突变.电阻数据符合Mott可变程跃迁模型,在TN出现斜率的变化,这与自旋相关的输运机制有关.Bi0.5Ca0.5MnO3中的反铁磁和电荷有序相变伴随着铁磁和反铁磁电荷有序相的激烈竞争.

In order to investigate the spin dynamics,short-range magnetic interactions and micromagnetic phase formation in charge-ordered （CO）manganites,magnetic transition and transport properties of Bi0.5 Ca0.5 MnO3 are studied systematically by magnetization,electron spin resonance （ESR） and resistivity.Magnetic properties suggest that ferromagnetic （FM）spin correlations exist in the paramagnetic （PM）state,and there is a “Bottleneck”spin-lattice interaction.In the CO state,the orbital ordering builds up gradually,and the strength of antiferromagnetic （AFM）spin correlations increases gradually and is dominant,resulting in the AFM transition at Neel temperature（T N = 125 K.A spin-glasslike behavior appears at frozen temperature （T f =35 K）due to the competition between AFM and FM ordering.Resistivity shows semiconducting behaviour with a sharp increase at CO temperature.The resistivity data are fitted by Mott＇s the variable-range hoping （VRH）model,and there is a change in slope at TN due to the spin-dependent transport mechanism.Both CO and AFM transitions in Bi0.5 Ca0.5 MnO3 are accompanied by the intense competition between FM and AFM-CO phases.