Anisotropic spin-density distribution and magnetic anisotropy of strained La1\u2212xSrxMnO3 thin films: angle-dependent x-ray magnetic circular dichroism

Goro Shibata,Shoya Sakamoto,Mitsuho Furuse,Hideyuki Fujihira,Hiroshi Kumigashira,Kazunori Watanabe,Tomoyuki Harano ,S Fuchino ,Takashi Kadono ,Jun-Ichi Fujihira,K Yoshimatsu ,Kousei Ishigami ,Akira Uchida,S Fujihira ,Yosuke Nonaka,Miho Kitamura,Makoto Okano,T Koide ,Makoto Minohara,Y Takahashi ,A Tanaka ,Keisuke Ikeda,Zhendong Chi,A Fujimori

doi:10.1038/s41535-018-0077-4

Abstract

Magnetic anisotropies of ferromagnetic thin films are induced by epitaxial strain from the substrate via strain-induced anisotropy in the orbital magnetic moment and that in the spatial distribution of spin-polarized electrons. However, the preferential orbital occupation in ferromagnetic metallic La1−xSrxMnO3 (LSMO) thin films studied by x-ray linear dichroism (XLD) has always been found out-of-plane for both tensile and compressive epitaxial strain and hence irrespective of the magnetic anisotropy. In order to resolve this mystery, we directly probed the preferential orbital occupation of spin-polarized electrons in LSMO thin films under strain by angle-dependent x-ray magnetic circular dichroism (XMCD). Anisotropy of the spin-density distribution was found to be in-plane for the tensile strain and out-of-plane for the compressive strain, consistent with the observed magnetic anisotropy. The ubiquitous out-of-plane preferential orbital occupation seen by XLD is attributed to the occupation of both spin-up and spin-down out-of-plane orbitals in the surface magnetic dead layer.

Highlights

Magnetic anisotropy is one of the most important properties of ferromagnets and its external control has been a major challenge both from the fundamental and applied science points of view.[1]From the application point of view, enhancement of the magnetic anisotropy is necessary to realize magnets with high coercive fields, which can be utilized as high-density energy-storage magnets
The magnetic anisotropy of the LSMO thin films depends on the epitaxial strain: the magnetic easy axes are inplane when grown on the STO substrate and out-of-plane when grown on the LAO substrate.[4,5]
We report on the angle-dependent x-ray magnetic circular dichroism (XMCD) and TXMCD experiments on ferromagnetic LSMO (x = 0.3) thin films grown on STO and LAO substrates, and investigate the effect of epitaxial strain on the orbital states of spin-polarized electrons

Summary

INTRODUCTION

Magnetic anisotropy is one of the most important properties of ferromagnets and its external control has been a major challenge both from the fundamental and applied science points of view.[1]. Previous x-ray linear dichroism (XLD) experiments have shown that the d3z2Àr2 orbital is preferentially occupied for both STO and LAO substrates.[6–8]. This apparent discrepancy with theory has been ascribed to the different orbital occupation between the surface and the bulk, that is, the spatial symmetry breaking at the surface leads to the preferential occupation of the d3z2Àr2 orbital.[6–8]. We report on the angle-dependent XMCD and TXMCD experiments on ferromagnetic LSMO (x = 0.3) thin films grown on STO and LAO substrates, and investigate the effect of epitaxial strain on the orbital states of spin-polarized electrons. The origin of the difference between the spindensity and charge-density distributions is attributed to the preferential occupation of both the spin-up and spin-down d3z2Àr2 orbitals at the surface, which suggests the formation of magnetic dead layers at the surface

RESULTS

DISCUSSION

METHODS