论文标题
尖晶石Femn $ _ {2} $ o $ _ {4} $中的多面体变形和异常磁性顺序
Polyhedral distortions and unusual magnetic order in spinel FeMn$_{2}$O$_{4}$
论文作者
论文摘要
尖晶石化合物AB $ _ {2} $ x $ _ {4} $由四面体（AX $ _ {4} $）和八面体（BX $ _ {6} $）组成，前者形成了钻石lattice和后者的GEOMERTIAL PYROCHLORE CYROCHLORE LATTICE LATTICE LATTICE。探索引人入胜的特性及其与结构特征的相关性对于理解这些材料至关重要。据报道，femn $ _ {2} $ o $ _ {4} $展示了一个结构过渡和两个连续的磁过渡。在这里，我们通过采用高分辨率中子粉末衍射，报告了多面体畸变及其与结构的相关性及其相关性和两个磁性转换。虽然即使在高温立方阶段也发现了巨大的三角变形，但与$ c $ axis沿$ t_ {s} \ the+$ 750 k的一阶四方结构过渡沿$ t_ {s} \ $ 750 k发生在$ 750 k上，由jahn-teller protime bybital protimd $ cy+cy^$ c.强烈的磁弹性耦合以$ t_ {n1} \约400 $ k的形式推出，这表现为Nèeltypecolul-type colul-type colunear ferrimagnetic顺序，在四面体和八面体畸形中是一种异常，并且是$ c $ $ c $ $ a $ a nomales and nomoal and nomoal sanemoal and $ a $ a a。在$ t_ {n2} \大约65 $ k的冷却以下时，它将演变为非共聚的铁磁性顺序，其倾斜为半b site $ mn^{3+} $/$ fe^{3+} $ spins in Pyrochlore lattice spins spins spins spins of pyrochlore lattice spins of pyrochlore lattice spins of Spinels中的独特磁性订单。这种非共线级会诱导八面体中O-B-O键角的修改，而不会影响四面体/八面体的键长。我们的研究表明，FEMN $ _ {2} $ o $ _ {4} $是一个揭示有趣的磁性秩序并研究其与多面体畸变和晶格的相关性的绝妙平台。
Spinel compounds AB$_{2}$X$_{4}$ consist of both tetrahedral (AX$_{4}$) and octahedral (BX$_{6}$) environments with the former forming a diamond lattice and the latter a geometrically frustrated pyrochlore lattice. Exploring the fascinating properties and their correlations with structural features is critical in understanding these materials. FeMn$_{2}$O$_{4}$ has been reported to exhibit one structural transition and two successive magnetic transitions. Here, we report the polyhedral distortions and their correlations to the structural and two magnetic transitions in FeMn$_{2}$O$_{4}$ by employing the high-resolution neutron powder diffraction. While a large trigonal distortion is found even in the high-temperature cubic phase, the first-order cubic-tetragonal structural transition associated with the elongation of both tetrahedra and octahedra along the $c$ axis occurs at $T_{S} \approx$ 750 K, driven by the Jahn-Teller effect of the orbital active B-site Mn$^{3+}$ cation. A strong magnetoelastic coupling is unveiled at $T_{N1}\approx 400$ K as manifested by the appearance of Nèel-type collinear ferrimagnetic order, an anomaly in both tetrahedral and octahedral distortions, as well as an anomalous decrease of the lattice constant $c$ and a weak anomaly of $a$. Upon cooling below $T_{N2}\approx65$ K, it evolves to a noncollinear ferrimagnetic order with a canting of half B-site $Mn^{3+}$/$Fe^{3+}$ spins in the pyrochlore lattice, which is a unique magnetic order among spinels. Such a noncollinear order induces modifications of the O-B-O bond angles in the octahedra without affecting much the bond lengths of the tetrahedra/octahedra. Our study indicates that FeMn$_{2}$O$_{4}$ is a wonderful platform to unveil interesting magnetic order and to investigate their correlations to polyhedral distortions and lattice.
