Understanding intrinsic exchange bias in nominally single‐component ferromagnetic or ferrimagnetic materials is crucial for simplifying related device architectures. However, the mechanisms behind this phenomenon and its tunability remain elusive, which hinders the efforts to achieve unidirectional magnetization for widespread applications. Inspired by the high tunability of ferrimagnetic inverse spinel NiCo2O4, the origin of intrinsic exchange bias in NiCo2O4 (111) films deposited on Al2O3 (0001) substrates are investigated. The comprehensive characterizations, including electron diffraction, X‐ray reflectometry and spectroscopy, and polarized neutron reflectometry, reveal that intrinsic exchange bias in NiCo2O4 (111)/Al2O3 (0001) arises from a reconstructed antiferromagnetic rock‐salt NixCo1‐xO layer at the interface between the film and the substrate due to a significant structural mismatch. Remarkably, by engineering the interfacial structure under optimal growth conditions, it can achieve exchange bias larger than coercivity, leading to unidirectional magnetization. Such giant intrinsic exchange bias can be utilized for realistic device applications. This work establishes a new material platform based on NiCo2O4, an emergent spintronics material, to study tunable interfacial magnetic and spintronic properties.

中文翻译：

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外延 NiCo2O4 薄膜中巨大本征交换偏压的微观结构基础


了解标称单组分铁磁或亚铁磁材料中的本征交换偏压对于简化相关器件架构至关重要。然而，这种现象背后的机制及其可调性仍然难以捉摸，这阻碍了实现单向磁化以实现广泛应用的努力。受亚铁磁性反向尖晶石 NiCo2O4 的高可调性的启发，研究了沉积在 Al2O3 （0001） 衬底上的 NiCo2O4 （111） 薄膜中本征交换偏压的来源。包括电子衍射、X 射线反射和光谱学以及偏振中子反射法在内的综合表征表明，NiCo2O4 （111）/Al2O3 （0001） 中的本征交换偏压是由于显着的结构错配而在薄膜和衬底之间的界面处重建的反铁磁岩盐 NixCo1-xO 层引起的。值得注意的是，通过在最佳生长条件下设计界面结构，它可以实现大于矫顽力的交换偏压，从而导致单向磁化。这种巨大的本征交换偏置可用于实际的器件应用。这项工作建立了一个基于新兴自旋电子学材料 NiCo2O4 的新材料平台，以研究可调界面磁和自旋电子学的性质。