Higo Tomoya, Man Huiyuan, Gopman Daniel B, Wu Liang, Koretsune Takashi, van 't Erve Olaf M J, Kabanov Yury P, Rees Dylan, Li Yufan, Suzuki Michi-To, Patankar Shreyas, Ikhlas Muhammad, Chien C L, Arita Ryotaro, Shull Robert D, Orenstein Joseph, Nakatsuji Satoru
Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan.
Nat Photonics. 2018 Feb;12(2):73-78. doi: 10.1038/s41566-017-0086-z. Epub 2018 Jan 26.
When a polarized light beam is incident upon the surface of a magnetic material, the reflected light undergoes a polarization rotation. This magneto-optical Kerr effect (MOKE) has been intensively studied in a variety of ferro- and ferrimagnetic materials because it provides a powerful probe for electronic and magnetic properties as well as for various applications including magneto-optical recording. Recently, there has been a surge of interest in antiferromagnets (AFMs) as prospective spintronic materials for high-density and ultrafast memory devices, owing to their vanishingly small stray field and orders of magnitude faster spin dynamics compared to their ferromagnetic counterparts. In fact, the MOKE has proven useful for the study and application of the antiferromagnetic (AF) state. Although limited to insulators, certain types of AFMs are known to exhibit a large MOKE, as they are weak ferromagnets due to canting of the otherwise collinear spin structure. Here we report the first observation of a large MOKE signal in an AF metal at room temperature. In particular, we find that despite a vanishingly small magnetization of ~0.002 µ/Mn, the non-collinear AF metal MnSn exhibits a large zero-field MOKE with a polar Kerr rotation angle of 20 milli-degrees, comparable to ferromagnetic metals. Our first-principles calculations have clarified that ferroic ordering of magnetic octupoles in the non-collinear Néel state may cause a large MOKE even in its fully compensated AF state without spin magnetization. This large MOKE further allows imaging of the magnetic octupole domains and their reversal induced by magnetic field. The observation of a large MOKE in an AF metal should open new avenues for the study of domain dynamics as well as spintronics using AFMs.
当一束偏振光束入射到磁性材料表面时，反射光会发生偏振旋转。这种磁光克尔效应（MOKE）已在各种铁磁和亚铁磁材料中得到深入研究，因为它为电子和磁性特性以及包括磁光记录在内的各种应用提供了强大的探测手段。最近，反铁磁体（AFM）作为用于高密度和超快存储器件的潜在自旋电子材料引起了人们极大的兴趣，这是由于它们的杂散场极小，并且与铁磁体相比，自旋动力学要快几个数量级。事实上，MOKE已被证明对反铁磁（AF）态的研究和应用很有用。尽管仅限于绝缘体，但已知某些类型的AFM会表现出较大的MOKE，因为它们由于原本共线的自旋结构发生倾斜而成为弱铁磁体。在此，我们报告首次在室温下的AF金属中观察到较大的MOKE信号。特别是，我们发现尽管~0.002 µ/Mn的磁化强度极小，但非共线AF金属MnSn仍表现出较大的零场MOKE，其极克尔旋转角为20毫度，与铁磁金属相当。我们的第一性原理计算表明，在非共线奈尔态中磁八极子的铁电有序即使在其无自旋磁化的完全补偿AF态下也可能导致较大的MOKE。这种较大的MOKE进一步使得能够对磁八极子畴及其由磁场引起的反转进行成像。在AF金属中观察到较大的MOKE应为使用AFM研究畴动力学以及自旋电子学开辟新的途径。
