Tutic Ibrica, Herran Juliana, Staten Bradley, Gray Paul, Paudel Tula R, Sokolov Andrei, Tsymbal Evgeny Y, Lukashev Pavel V
Department of Physics, University of Northern Iowa, Cedar Falls, IA 50614, USA.
J Phys Condens Matter. 2017 Feb 22;29(7):075801. doi: 10.1088/1361-648X/aa50e0. Epub 2016 Dec 29.
A high degree of spin polarization in electron transport is one of the most sought-after properties of a material which can be used in spintronics-an emerging technology utilizing a spin degree of freedom in electronic devices. An ideal candidate to exhibit highly spin-polarized current would be a room temperature half-metal, a material which behaves as an insulator for one spin channel and as a conductor for the other spin channel. In this paper, we explore a semi-Heusler compound, IrMnSb, which has been reported to exhibit pressure induced half-metallic transition. We confirm that the bulk IrMnSb is a spin-polarized metal, with dominant contribution to electronic states at the Fermi energy from majority-spin electrons. Application of a uniform pressure shifts the Fermi level into the minority-spin energy gap, thus demonstrating pressure induced half-metallic transition. This behavior is explained by the reduction of the exchange splitting of the spin bands consistent with the Stoner model for itinerant magnetism. We find that the half-metallic transition is suppressed when instead of uniform pressure the bulk IrMnSb is exposed to biaxial strain. This suppression of half-metallicity is driven by the epitaxial strain induced tetragonal distortion, which lifts the degeneracy of the Mn 3d t and e orbitals and reduces the minority-spin band gap under compressive strain, thus preventing half-metallic transition. Our calculations also indicate that in thin film geometry, surface states emerge in the minority-spin band gap, which has detrimental for practical applications impact on the spin polarization of IrMnSb.
电子输运中的高度自旋极化是一种材料最受追捧的特性之一，这种材料可用于自旋电子学——一种在电子器件中利用自旋自由度的新兴技术。表现出高自旋极化电流的理想候选材料是室温半金属，即一种在一个自旋通道中表现为绝缘体而在另一个自旋通道中表现为导体的材料。在本文中，我们研究了一种半赫斯勒化合物IrMnSb，据报道它表现出压力诱导的半金属转变。我们证实块状IrMnSb是一种自旋极化金属，费米能级处的电子态主要由多数自旋电子贡献。施加均匀压力会使费米能级移入少数自旋能隙，从而证明了压力诱导的半金属转变。这种行为可以用与巡游磁性的斯托纳模型一致的自旋带交换分裂的减小来解释。我们发现，当块状IrMnSb受到双轴应变而不是均匀压力时，半金属转变受到抑制。这种半金属性的抑制是由外延应变诱导的四方畸变驱动的，它消除了Mn 3d t和e轨道的简并性，并在压缩应变下减小了少数自旋带隙，从而阻止了半金属转变。我们的计算还表明，在薄膜几何结构中，少数自旋带隙中会出现表面态，这对IrMnSb的自旋极化的实际应用有不利影响。
