Using light irradiation to manipulate magnetization over a prolonged period of time offers a wealth of opportunities for spin‐based electronics and photonics. To date, persistent photomagnetism has been frequently reported in spin systems composed of molecular magnets; yet this phenomenon is rarely observed in nanoparticle‐based systems comprised of transition metal oxides. Here, detailed studies of persistent photomagnetism in superparamagnetic iron oxide (Fe₃O₄) nanoparticles at temperatures below their blocking temperature are presented and it is demonstrated that the magnetization change does not occur through steady‐state spin transitions or photothermal heating. Instead, it is found that exciton–spin exchange‐coupling plays a critical role in modulating the magnetization by lowering the anisotropic energy barrier of Fe₃O₄ nanoparticles to facilitate their optically driven conversion from ferrimagnetic to superparamagnetic. Collectively, these insights establish a comprehensive understanding of the underlying photophysical processes that regulate photomagnetism in nanoparticle‐based magnetic systems composed of transition metal oxides.

中文翻译：

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超顺磁性氧化铁纳米粒子中的持久光磁

长时间使用光辐射来控制磁化强度为自旋电子和光子学提供了很多机会。迄今为止，在由分子磁体组成的自旋系统中经常报告有持久的光磁现象。然而，这种现象在由过渡金属氧化物组成的基于纳米颗粒的系统中很少观察到。在这里，对超顺磁性氧化铁（Fe ₃ O ₄）展示了低于其阻断温度的纳米粒子，并证明了通过稳态自旋跃迁或光热加热不会发生磁化变化。相反，发现激子-自旋交换耦合通过降低Fe ₃ O ₄纳米粒子的各向异性能垒，促进其从亚铁磁性到超顺磁性的光驱动转换，在调节磁化强度方面起着关键作用。总而言之，这些见解建立了对调节过渡金属氧化物组成的基于纳米粒子的磁系统中的光磁性的基本光物理过程的全面理解。