Ca缺位的Ca_(3-x)Mn_2O_(7-d)的结构、磁性研究  

Influence of Ca Voids on Structural and Magnetic Properties of Ca_(3-x)Mn_2O_(7-d)

作　　者：武强[1] 常虹[1] 庞艳波[1] 高玉[1] 云月厚[1] 

机构地区：[1]内蒙古大学物理科学与技术学院,呼和浩特010021

出　　处：《内蒙古大学学报（自然科学版）》2016年第2期165-172,共8页Journal of Inner Mongolia University：Natural Science Edition

基　　金：国家自然科学基金项目(项目编号11264024);内蒙古自然科学基金(项目编号:2015MS0102;2015MS0524)

摘　　要：采用固相反应法合成了具有Ca缺陷的钙钛矿氧化物Ca_(3-x)Mn_2O_(7-d)(x=0.04,0.08,0.12).其空间点群由原来的正方晶系的I4/mmm转变为斜方晶系的Cmcm,而且其倾斜程度随x增大而变大.随着x增大,晶格体积逐渐减小,但是沿着平面轴向(co和bo)膨胀.样品的XPS图谱分析表明Mn离子处于Mn^(3+)/Mn4+的混合价态,Ca-O键在固定区间内震动.Ca缺陷导致Ca_(2.96)Mn_2O_(7-d)样品在低于350K时出现了明显的铁磁性.Ca_(2.92)Mn_2O_(7-d)样品在345K出现了一个很小的停顿.电子的离域和本地化可以用来解释上面的磁性反常现象.样品具有低维磁性行为,x=0.04、0.08和0.12时的交换积分J0的估算值分别为25.4K、22.6K和19.7K.发现在x=0.04,0.08和0.12样品的转变温度(115K)存在一个倾斜的反铁磁性转变,而且这一温度随x增大而减小的程度是非常轻微的.线性变化的Ca_(2.88)Mn_2O_(7-d)样品的H/M-T曲线与居里-外斯近似匹配.计算出的Curie-Weiss温度θCW为164K,有效磁矩μeff为2.36μB.Ca3-xMn2O7-d with the Ca deficiency of x=0.04,0.08,0.12 are synthesized with the solid state reaction.The structure is refined with the orthorhombic space group Cmcm instead of the tetragonal I4/mmm.The orthorhombic distortion increases with x.The deficiency of the Ca ions decreases the overall lattice volume,but expands along the axes（coand bo）in the plane.The XPS spectrum shows that the Mn ions in the Ca deficient compounds are at the mix-valent Mn^3＋/Mn^4＋state,and the Ca-O bonds are variable in a certain range.The Ca deficiency induces a conspicuous ferromagnetic component in Ca3-xMn2O7-d below 350 K.In Ca3-xMn2O7-d a small step is observed at345 K.The electronic delocalization and localization are applied to the above magnetic phenomenon in the Ca deficient compounds.The compounds have low dimensional magnetic behavior,and the estimated exchange integral J0 is 25.4,22.6and 19.7Kfor x=0.04,0.08 and 0.12,respectively.It has a canted antiferromagnetic transition with the transition temperature at about 115 Kin the compounds with x=0.04,0.08 and 0.12 and the temperature decreases slightly with the increasing amount of the Ca voids.The linear variation of H/M versus Tof Ca3-xMn2O7-d is fitted with the Curie-Weiss approximation,and the estimated Curie-Weiss temperatureθCWis 164 Kand the effective magnetic momentμeffis 2.36μB.

关 键 词：RUDDLESDEN-POPPER 掺杂 磁性 

分 类 号：O482.5[理学—固体物理]