Altermagnetism in epitaxial NiCo₂O₄ thin films via higher-order magnetic anisotropy

Abstract NiCo 2 O 4 is a ferrimagnetic oxide with an inverse spinel structure that has garnered significant research interest due to its unique properties, including relatively high electrical conductivity, mixed-valence cations, and a Néel temperature exceeding room temperature. Furthermore, epitaxial NiCo 2 O 4 thin films provide an exciting platform for tuning material properties and uncovering novel phenomena that are not observed in bulk single crystals. In this review, we highlight recent advancements in epitaxial NiCo 2 O 4 thin films, focusing on: (i) the tunability of anti-site defects through controlled fabrication conditions, (ii) the emergence of easy-cone magnetic anisotropy (ECMA) induced by these anti-site defects, (iii) the realization of a nontrivial spin structure characterized by magnetic toroidal quadrupole order, driven by the ECMA, (iv) novel magneto-transport phenomena arising from this nontrivial spin structure, and (v) the correlation between this nontrivial spin structure and the concept of altermagnetism.