Liao Ching-Te, Wang Yu-Chun, Tien Yu-Cheng, Huang Ssu-Yen, Qu Danru
Department of Physics, <a href="https://ror.org/05bqach95">National Taiwan University</a>, Taipei 10617, Taiwan.
Center of Atomic Initiatives for New Materials, <a href="https://ror.org/05bqach95">National Taiwan University</a>, Taipei 10617, Taiwan.
Phys Rev Lett. 2024 Aug 2;133(5):056701. doi: 10.1103/PhysRevLett.133.056701.
Recently, a significant amount of attention has been attracted toward a third classification of magnetism, altermagnetism, due to the unique physical properties of altermagnetic materials, which are compensated collinear antiferromagnets that host time-reversal symmetry-breaking phenomena like a ferromagnet. In an altermagnetic material, through the nonrelativistic altermagnetic spin-splitting effect (ASSE), a transverse spin current is generated upon charge current injection. However, it is very challenging to experimentally establish the ASSE since it is inevitably mixed with the spin Hall effect due to the relativistic spin-orbit coupling of the material. Additionally, the dependence on the hard-to-probe and hard-to-control Néel vectors makes it even more difficult to observe and establish the ASSE. In this Letter, we utilize the thermal spin injection from the ferrimagnetic insulator yttrium iron garnet and detect an inverse altermagnetic spin-splitting effect (IASSE) in the high-quality epitaxial altermagnetic RuO_{2} thin films. We observe an opposite sign for the spin-to-charge conversion through the IASSE compared to the inverse spin Hall effect (ISHE). The efficiency of the IASSE is approximately 70% of the ISHE in RuO_{2}. Moreover, we demonstrate that the ASSE or IASSE effect is observable only when the Néel vectors are well aligned. By modifying the Néel vector domains via RuO_{2} crystallinity, we study the ASSE or IASSE unequivocally and quantitatively. Our Letter provides significant insight into the spin-splitting effect in altermagnetic materials.
最近，由于交变磁性材料独特的物理性质，一种新的磁性分类——交变磁性，引起了人们的广泛关注。交变磁性材料是一种补偿共线反铁磁体，具有类似于铁磁体的时间反演对称性破缺现象。在交变磁性材料中，通过非相对论性交变磁自旋分裂效应（ASSE），注入电荷电流时会产生横向自旋电流。然而，由于材料的相对论性自旋轨道耦合，ASSE不可避免地与自旋霍尔效应混合，因此通过实验确定ASSE极具挑战性。此外，对难以探测和控制的奈尔矢量的依赖使得观察和确定ASSE变得更加困难。在本信函中，我们利用来自亚铁磁绝缘体钇铁石榴石的热自旋注入，在高质量外延交变磁性RuO₂薄膜中检测到了反向交变磁自旋分裂效应（IASSE）。与逆自旋霍尔效应（ISHE）相比，我们观察到通过IASSE的自旋到电荷转换具有相反的符号。在RuO₂中，IASSE的效率约为ISHE的70%。此外，我们证明只有当奈尔矢量良好对齐时，ASSE或IASSE效应才是可观测的。通过改变RuO₂的结晶度来修改奈尔矢量域，我们明确且定量地研究了ASSE或IASSE。我们的信函为交变磁性材料中的自旋分裂效应提供了重要的见解。
