Abstract
Manganese (Mn)-based strong magnets have long been a challenge because their 3d half-filled nature, owing to the close proximity of Mn atoms, results in antiferromagnetic ordering. Among various Mn magnetic materials, L10-MnAl (τ-phase) has received much attention since it shows ferromagnetism at a high Curie temperature despite the very short Mn–Mn distance. However, because of the difficult synthesis of the stoichiometric and perfectly ordered τ-phase, its intrinsic magnetic properties and mechanism are unclear. Here, we show the first observation of antiferromagnetism, having sixfold magnetic superstructure along the c-axis, in stoichiometric and chemically ordered τ-phase. Moreover, we found that super-exchange interaction between Mn atoms via p-electrons of Al atoms causes antiferromagnetism in τ-phase. The ferromagnetism in the conventional Mn-rich τ-phase results from the suppression of the super-exchange interaction due to the substitution the excess Mn atoms for the Al atoms. The current study of Mn-based magnetic materials mainly focuses on the lattice constant engineering based on the simple Beth-Slater picture of direct exchange. These findings present effective ways to obtain high magnetization without antiferromagnetic ordering.
Highlights
Manganese (Mn)-based strong magnets have long been a challenge because their 3d half-filled nature, owing to the close proximity of Mn atoms, results in antiferromagnetic ordering
We conclude that the mechanism of antiferromagnetism in τ-phase is the super-exchange interaction between Mn atoms via p-electrons of Al atoms
We conclude that the mechanism of antiferromagnetism in τ-phase is the super-exchange interaction between Mn atoms via p-electrons of Al atoms, and the stable magnetic structure was not strongly affected by the Mn–Mn distance but by Mn occupancy of the Al site
Summary
In the range of high temperature range, the magnetization increases as elevating temperature and has a broad peak This behaviour indicates antiferromagnetic to paramagnetic transition. The dotted line, which is a single straight line fit to the data above 600 K, shows the data obeys the Curie–Weiss law and the Neel temperature T N was estimated to be about 570 K These results indicate the mechanism of metamagnetism involved antiferromagnetic to ferromagnetic transition. These peaks were indexed as rational “l” miller indexes of 1/6, where the unit cell is regarded as a BCT structure.
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