论文标题
无稀土铁磁MN4N低于20 nm薄膜作为高温旋转材料
Rare-earth-free ferrimagnetic Mn4N sub-20 nm thin films as high-temperature spintronic material
论文作者
论文摘要
预测，具有低饱和磁化强度（例如GDCO和MN4N）的垂直（平面外）磁各向异性（PMA）的铁磁合金薄膜预计将有利于托管用于室温的小型Neel Skyrmions。由于界面dzyaloshinskii-moriya相互作用（DMI）的指数衰减以及可用于驱动天际运动运动的旋转轨道弯曲的有限范围，因此，铁磁层的厚度必须小，优选低于20 nm。虽然有一些示例，例如20 nm，稀土转移金属（RE-TM），由溅射沉积制造的铁磁性薄膜，迄今为止，仅据报道，具有PMA的无稀土低于20 nm MN4N薄膜，仅通过分子束相互疗法来实现，这不适合大量产生。在这里，我们报告了通过反应性溅射在MGO底物上以400-450°C的PMA在400-450°C底物温度下的PMA的成功热生长。通过通过高温真空退火过程降低MGO底物的表面粗糙度来实现MN4N膜。最佳膜显示出低饱和度磁化（MS = 43 EMU/CC），低磁各向异性能量（0.7 MERG/CC），以及在室温下1接近1的饱和磁化率（MR/MS）的对饱和磁化率（MR/MS）。初步的ABINITIO密度功能理论（DFT）计算已证实MGO上生长的MN4N的铁磁基态。与RE-TM薄膜相比，MN4N薄膜的较高热稳定性，为将来研究实用的基于Skyrmion的旋转材料提供了一个平台。
Ferrimagnetic alloy thin films that exhibit perpendicular (out-of-plane) magnetic anisotropy (PMA) with low saturation magnetization, such as GdCo and Mn4N, were predicted to be favorable for hosting small Neel skyrmions for room temperature applications. Due to the exponential decay of interfacial Dzyaloshinskii-Moriya interaction (DMI) and the limited range of spin-orbit-torques, which can be used to drive skyrmion motion, the thickness of the ferrimagnetic layer has to be small, preferably under 20 nm. While there are examples of sub-20 nm, rare earth-transition metal (RE-TM), ferrimagnetic thin films fabricated by sputter deposition, to date rare-earth-free sub-20 nm Mn4N films with PMA have only been reported to be achieved by molecular beam epitaxy, which is not suitable for massive production. Here we report the successful thermal growth of sub-20 nm Mn4N films with PMA at 400-450 °C substrate temperatures on MgO substrates by reactive sputtering. The Mn4N films were achieved by reducing the surface roughness of MgO substrate through a high-temperature vacuum annealing process. The optimal films showed low saturation magnetization (Ms = 43 emu/cc), low magnetic anisotropy energy (0.7 Merg/cc), and a remanent magnetization to saturation magnetization ratio (Mr/Ms) near 1 at room temperature. Preliminary ab-initio density functional theory (DFT) calculations have confirmed the ferrimagnetic ground state of Mn4N grown on MgO. The magnetic properties, along with the high thermal stability of Mn4N thin films in comparison with RE-TM thin films, provide the platform for future studies of practical skyrmion-based spintronic materials.
