Min Lujin, Barber John P, Wang Yu, Gayathri Ayyagari Sai Venkata, Niculescu Gabriela E, Krysko Evan, Bejger Gerald R, Miao Leixin, Lee Seng Huat, Zhang Qiang, Alem Nasim, Rost Christina M, Mao Zhiqiang
Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, United States.
Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States.
J Am Chem Soc. 2024 Sep 4;146(35):24320-24329. doi: 10.1021/jacs.4c04765. Epub 2024 Aug 20.
How disorder affects magnetic ordering is always an intriguing question, and it becomes even more interesting in the recently rising high entropy oxides due to the extremely high disorder density. However, due to the lack of high-quality single crystal samples, the strong compositional disorder effect on magnetic transition has not been deeply investigated. In this work, we have successfully synthesized high-quality single crystalline high entropy spinel ferrites (MgMnFeCoNi)FeO. Our findings from high-temperature magnetization and neutron diffraction experiments showed ferrimagnetic transitions at 748, 694, and 674 K for values of 1, 1.5, and 1.8, respectively. Notably, the magnetic transition almost showed no broadening for values of 1 and 1.5, compared to FeO. Extended X-ray absorption fine structure measurements provided insights into the elemental distribution among the octahedral and tetrahedral sites. The random distribution of elements across these sites reduced the formation of local clusters and short-range orders, enhancing sample homogeneity and preserving the sharpness of the magnetic transition, despite bond length variation. Our study not only marks the first successful synthesis of an HEO bulk single crystal exhibiting long-range magnetic order but also sheds light on the interaction between high configurational entropy and magnetic orderings. This opens new avenues for future research and applications of magnetic high entropy oxides.
无序如何影响磁有序一直是一个引人入胜的问题，在最近兴起的高熵氧化物中，由于极高的无序密度，这个问题变得更加有趣。然而，由于缺乏高质量的单晶样品，强成分无序对磁转变的影响尚未得到深入研究。在这项工作中，我们成功合成了高质量的单晶高熵尖晶石铁氧体（MgMnFeCoNi）FeO。我们从高温磁化和中子衍射实验中得到的结果表明，对于值为1、1.5和1.8的样品，亚铁磁转变分别发生在748 K、694 K和674 K。值得注意的是，与FeO相比，对于值为1和1.5的样品，磁转变几乎没有展宽。扩展X射线吸收精细结构测量提供了关于八面体和四面体位置之间元素分布的见解。尽管键长发生变化，但元素在这些位置上的随机分布减少了局部团簇和短程有序的形成，提高了样品的均匀性并保持了磁转变的尖锐性。我们的研究不仅标志着首次成功合成了具有长程磁有序的高熵氧化物块状单晶，还揭示了高组态熵与磁有序之间的相互作用。这为磁性高熵氧化物的未来研究和应用开辟了新途径。
