Noncollinear Magnetism in Fe 3 O 4 Induced via Site‐Selective Rare‐Earth Substitution Boosting Its Saturation Magnetization

作者：Haining Li, Masaki Kobayashi, Sonju Kou, Md Shamim Sarker, E.M.K. Ikball Ahamed, Kohei Yamagami, Tetsuya Fukushima, Kaijie Ma, Shuting Ma, Takahito Takeda, Ryo Okano, M. Hussein N. Assadi, Hiroyasu Yamahara, Hiroshi Katayama‐Yoshida, Hitoshi Tabata, Munetoshi Seki · 发表于：Small · 年份：2025 · DOI：10.1002/smll.202411133 · 被引用次数：3 · 研究领域：Magnetic Properties and Synthesis of Ferrites、Multiferroics and related materials、Advanced Condensed Matter Physics

Abstract Substituting rare‐earth Eu ions with a large atomic number into 3 d transition metal oxides can precisely control their magnetic properties through significant spin‐orbit coupling, leading to noncollinear magnetism. Experimental investigations are combined with density functional theory to explore site‐selective Eu 3+ substitution as a strategy to enhance the magnetic properties of Fe 3 O 4 thin films. The substitution location of Eu 3+ , that is, octahedral versus tetrahedral, is confirmed by electrical resistivities and valence band photoemission measurements. Tetrahedrally Eu‐substituted Fe 3 O 4 exhibited an exceptionally enhanced saturation magnetization M S of up to 4.4 μ B /f.u. because of noncollinearity, whereas octahedrally Eu‐substituted Fe 3 O 4 showed significantly reduced M S . X‐ray absorption spectroscopy and X‐ray magnetic circular dichroism measurements clearly revealed that in the tetrahedrally Eu‐substituted Fe 3 O 4 , the Eu 3+ magnetic moment positively contributed to the orbital magnetic moment that exhibited strong magnetic anisotropy. The deviation of the observed M S from the lower value predicted by Néel's theory of collinear ferrimagnetism further supported the role of noncollinearity. These results provide empirical evidence for the spin configuration of tetrahedrally Eu‐substituted Fe 3 O 4 and a new perspective for designing practical ferrimagnetic 4 f compounds with exceptional M S .