Ca0.5Ba0.5MnO3多铁性的第一性原理

Homologous multiferroicity in Ca0.5Ba0.5MnO3 from first-principle investigation

利用第一性原理电子结构计算方法,通过对CaMnO3,BaMnO3的软声子模式分析,构造出一种Ca0.5Ba0.5MnO3(CBMO)合金结构.此合金可同时具有源于Mn原子的铁电(ferroelectric,FE)性与铁磁(ferromagnetic,FM)性,其中G型反铁磁(antiferromagnetic,AFM)构型下的电极化强度为6.70μC/cm2,铁磁构型下的电极化强度为23.214μC/cm2.其产生的机制是半径较大的Ba原子可导致晶格发生应变,产生有效负压,减弱CaMnO3的反铁畸变(antiferrodistortive,AFD)模对铁电模的抑制,进而诱导铁电极化.此性质意味着这种材料在磁场的作用下,由G型反铁磁构型转变为铁磁构型时的电极化强度会发生显著变化.基于第一性原理电子结构计算给出的不同磁结构总能,进一步拟合出了海森堡模型的参数,并针对其哈密顿量展开了有限温度下的Monte-Carlo模拟,模拟出的奈尔温度为70 K.这些结果从理论层面提出了一种新型的、源于相同原子的,并可能提供有效磁电耦合的多铁材料,并且可以为今后类似系统的相关实验提供理论参考.

Using first-principle electronic structure calculations,a new alloy structure with Ca0.5Ba0.5MnO3(CBMO)stoichiometry is found,which possesses ferromagnetic(FM)and ferroelectric(FE)originating from Mn(6.70μC/cm^2 in the G-type antiferromagnetic(AFM)structure and 23.214μC/cm^2 in the FM structure).By applying a strong external magnetic field,FM properties can change dramatically,indicating a strong coupling between FM and FE properties.The large radius of Ba atom in CBMO suppresses the antiferrodistortive(AFD)mode,and enhances ferroelectricity associated with the FE mode.By comparing the whole different magnetic structures,parameters are further generated for the Heisenberg model and Monte-Carlo simulations are perpormed at finite temperatures.The simulated Néel temperature is 70 K.This study gives a candidate structure for multiferroics applications.In the meantime,it also provides theoretical references to further experimental studies in similar systems.