Anisotropic exchange-coupled nanocomposites provide us a salient candidate for the new generation of permanent magnets owing to their huge predicted maximum energy product. However, previous research basically focused on thin films or bulk materials and the impact of easy-axis alignment on the exchange coupling behavior is not clear. Herein, strongly coupled FePt/Co core/shell nanoparticles with single-phase-like hysteresis loops were synthesized by the seed mediated method. Then, these nanoparticles were successfully aligned by the external magnetic field and fixed in an acrylic binder, so that FePt/Co core/shell nanoparticle-based anisotropic nanocomposites were obtained. The nanocomposites exhibited high degree of orientation as indicated by the increased remanence ratio from 0.62 for isotropic nanoparticles to 0.78 for anisotropic nanocomposites. However, a visible kink in the demagnetization curve was observed around the zero field, implying the exchange spring behavior. This result suggests that the aligned FePt cores impose a stronger overall dipolar field in Co shells and finally, force the Co shells to reverse at a low field before the switch of FePt cores. Our research extends the preparation methods of anisotropic hard/soft-phase nanocomposites and might be helpful for the design of high-performance anisotropic exchange-coupled nanocomposites.

中文翻译：

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基于FePt / Co核/壳纳米粒子的各向异性纳米复合材料及其交换弹簧行为†

各向异性交换耦合纳米复合材料因其巨大的预测最大能量积而为我们提供了新一代永磁体的显着候选。然而，先前的研究基本上集中在薄膜或块状材料上，并且易轴对准对交换耦合行为的影响尚不清楚。在本文中，通过种子介导的方法合成了具有单相样磁滞回线的强耦合FePt / Co核/壳纳米粒子。然后，这些纳米颗粒通过外部磁场成功取向并固定在丙烯酸粘合剂中，从而获得基于FePt / Co核/壳纳米颗粒的各向异性纳米复合材料。纳米复合材料表现出高度的取向性，如各向同性纳米粒子的剩磁比率从0.62增加到0所示。各向异性纳米复合材料为78。但是，在零磁场附近观察到了退磁曲线中的可见扭结，这表明交换弹簧的行为。该结果表明，排列的FePt核在Co壳中施加了更强的整体偶极场，并且最终迫使Fe壳在切换FePt核之前在低场处反转。我们的研究扩展了各向异性硬/软相纳米复合材料的制备方法，可能对高性能各向异性交换耦合纳米复合材料的设计有所帮助。在切换FePt磁芯之前，迫使Co壳在低磁场下反转。我们的研究扩展了各向异性硬/软相纳米复合材料的制备方法，可能对高性能各向异性交换耦合纳米复合材料的设计有所帮助。在切换FePt磁芯之前，迫使Co壳在低磁场下反转。我们的研究扩展了各向异性硬/软相纳米复合材料的制备方法，可能对高性能各向异性交换耦合纳米复合材料的设计有所帮助。