Fe位Al掺杂对Sr_2FeMoO_6磁结构和磁输运性质的影响

Influence of doping Al at Fe site on the magnetic structure and magnetotransport properties of Sr_2FeMoO_6

研究了Sr_2Fe_(1-x)Al_xMoO_6(0≤x≤0·30)系列多晶样品的磁学和输运性质.室温X射线衍射谱图的精修结果显示Al^(3+)掺杂没有改变样品的晶格结构,但提高了Sr_2FeMoO_6晶格的阳离子有序度.5K时样品的磁化曲线说明平均单位分子饱和磁矩随着Al含量的增加而下降,但平均单位Fe离子磁矩却逐渐提高.磁化曲线的拟合结果显示样品内反铁磁相互作用对饱和磁矩的贡献随着Al含量的增加而下降,说明一定量的Fe离子被Al替代后,抑制了样品内Fe—O—Fe反相边界的形成,从而提高了Sr_2FeMoO_6晶格的阳离子有序度和平均单位Fe离子磁矩.对饱和磁矩的分析表明非磁性Al^(3+)离子掺杂会形成无磁相互作用的Mo—O—Al—O—Mo区,可以将原来较大的Mo—O—Fe亚铁磁区分割成许多小的区域,并且使这些亚铁磁区间的磁耦合作用变弱,从而提高了低场磁电阻效应.阳离子有序度的提高使来源于自旋相关电子在反相边界处散射的高场磁电阻明显降低,导致了样品的磁电阻在x=0·15时达到了最大值.

Double perovskite Sr2FeMoO6 with Al doping at Fe site up to 30% were prepared by traditional solid-state reaction. The degree of the cation ordering of Sr2 FeMoO6 increases with Al doping obviously as shown by the refinement of room-temperature X- ray diffraction. The saturated magnetic moment per formula unit of these compounds decreases gradually with increasing Al concentration, but the magnetic moment per Fe ion increases markedly, which is consistent with the improvement of cation ordering. Basing on the analysis of magnetic structure with A1 doping, doping of Al will lead to the formation of non-magnetic coupled Mo-O-Al-O-Mo chains, which can divide the large Mo-O-Fe ferrimagnetic region into smaller patches and enhance the low field magnetoresistance. The formation of Fe-O-Fe antiphase boundaries are suppressed by the doping Al due to the improvement of the cation ordering, and the high field magnetoresistance that roots in spin-dependent scattering at the antiphase boundaries is reduced. Therefore, the total magnetoresistance reaches a maximum value at x = 0.15.