Structural and chemical order impact magnetic properties of solids, which are governed by spin- orbit coupling and exchange interaction. The ordered L10 phase of FePt is a key material to heat-assisted magnetic recording; to enable high storage density, a solid understanding is needed of structural and chemical disorder at small length scales, as well as associated modifications of the electronic band structure. Here, we investigate the effect of boron and copper additions (<6 mol.%Cu) on structural and magnetic properties of L10 FePt granular media. Two copper- driven mechanisms, although competing, can lead to improvements in both structural and magnetic properties. In particular, the Cu substitution on the Fe-site leads to a degradation of magnetic properties due to the delocalized electron orbitals originating from a larger Cu d-orbital occupancy. At the same time, Cu substitution leads to an enhanced crystallographic order and consequently magneto-crystalline anisotropy, which offsets the former effect to a large extent. Our study is based on magnetometry, x-ray absorption spectroscopy, ab-initio calculations and a phenomenological theory of disordered FePt granular media. We do not observe a sizable modification to Fe moments and electronic configuration; Cu reveals two different resonances associated with the presence and absence of Cu-B bonds that vary with total Cu concentration.

中文翻译：

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FePt-BN-SiO2热辅助磁记录介质中Cu添加量的影响

结构和化学顺序影响固体的磁性，这些磁性由自旋轨道耦合和交换相互作用控制。FePt的有序L10相是热辅助磁记录的关键材料；为了实现高存储密度，需要对小长度尺度的结构和化学无序以及电子能带结构的相关修改有深入的了解。在这里，我们研究了添加硼和铜（<6 mol.%Cu）对 L10 FePt 颗粒介质的结构和磁性的影响。两种铜驱动机制虽然相互竞争，但可以改善结构和磁性。特别是，Fe 位点上的 Cu 取代会导致磁性能下降，因为离域电子轨道源自较大的 Cu d 轨道占有率。同时，Cu取代导致晶序增强，从而导致磁晶各向异性，这在很大程度上抵消了前者的影响。我们的研究基于磁力测量、X 射线吸收光谱、从头算计算和无序 FePt 颗粒介质的现象学理论。我们没有观察到 Fe 矩和电子配置有相当大的变化；Cu 揭示了两种与 Cu-B 键的存在和不存在相关的不同共振，这些共振随总 Cu 浓度的变化而变化。很大程度上抵消了前者的影响。我们的研究基于磁力测量、X 射线吸收光谱、从头算计算和无序 FePt 颗粒介质的现象学理论。我们没有观察到 Fe 矩和电子配置有相当大的变化；Cu 揭示了两种与 Cu-B 键的存在和不存在相关的不同共振，这些共振随总 Cu 浓度的变化而变化。很大程度上抵消了前者的影响。我们的研究基于磁力测量、X 射线吸收光谱、从头算计算和无序 FePt 颗粒介质的现象学理论。我们没有观察到 Fe 矩和电子配置有相当大的变化；Cu 揭示了两种与 Cu-B 键的存在和不存在相关的不同共振，这些共振随总 Cu 浓度的变化而变化。