论文标题
熵工程和可调磁性尖型尖晶石高熵氧化物
Entropy engineering and tunable magnetic order in the spinel high entropy oxide
论文作者
论文摘要
尖晶石氧化物是探索高熵氧化物中构型熵,位点选择性和磁性之间的相互作用的理想场所。在这项工作中,我们表征了尖晶石(CR,Mn,Fe,Co,Ni)的磁性特性$ _ 3 $ o $ _4 $,并研究其磁性的演变,这是非磁性胆汁替代的函数。在此处研究的一系列组合物中,从0%到40%GA,磁化率和粉末中子衍射测量结果表明,尖晶石HEO中的铁磁阶稳定。但是,我们还发现,铁磁序具有高度调节,订购温度,饱和度和散型矩,磁硬度都随着GA浓度的函数而显着变化。通过X射线吸收和磁性圆形二色性,我们能够将这种磁性可调性与尖晶石结构中各种阳离子和四面体和四面体部位之间的强度选择性相关联。特别是,我们发现,尽管Ni和Cr在很大程度上不受GA替代的影响,但MN,CO和FE的占领都被显着重新分布。 GA替换还需要总体降低过渡金属价,这完全由MN容纳。最后,我们表明,尽管位点选择性对构型熵具有总体抑制作用,但在一定范围的组成部分中,GA替换会导致构型熵的显着增加,并可能赋予额外的稳定。可以将尖晶石氧化物从低渗透到高渗透方案无缝调整,使其成为熵工程的理想平台。
Spinel oxides are an ideal setting to explore the interplay between configurational entropy, site selectivity, and magnetism in high entropy oxides. In this work we characterize the magnetic properties of the spinel (Cr,Mn,Fe,Co,Ni)$_3$O$_4$ and study the evolution of its magnetism as a function of non-magnetic gallium substitution. Across the range of compositions studied here, from 0% to 40% Ga, magnetic susceptibility and powder neutron diffraction measurements show that ferrimagnetic order is robust in the spinel HEO. However, we also find that the ferrimagnetic order is highly tunable, with the ordering temperature, saturated and sublattice moments, and magnetic hardness all varying significantly as a function of Ga concentration. Through x-ray absorption and magnetic circular dichroism, we are able to correlate this magnetic tunability with strong site selectivity between the various cations and the tetrahedral and octahedral sites in the spinel structure. In particular, we find that while Ni and Cr are largely unaffected by the substitution with Ga, the occupancies of Mn, Co, and Fe are each significantly redistributed. Ga substitution also requires an overall reduction in the transition metal valence, and this is entirely accommodated by Mn. Finally, we show that while site selectivity has an overall suppressing effect on the configurational entropy, over a certain range of compositions, Ga substitution yields a striking increase in the configurational entropy and may confer additional stabilization. Spinel oxides can be tuned seamlessly from the low-entropy to the high-entropy regime, making this an ideal platform for entropy engineering.