Fabrication of Hard magnetic Amorphous Films Prepared by Laser Ablation Method and their properties

采用激光烧蚀法制备了厚度达50 μ m的Nd-Fe基薄膜。薄膜表面由光滑层和异常生长的液滴颗粒组成。液滴颗粒是nd基薄膜的特征，在fe基薄膜表面没有观察到。x射线衍射图显示出宽晕和尖峰，表明非晶相和α - nd晶体共存。去除液滴颗粒后，尖峰消失。厚度为25 mm的钕基薄膜的饱和磁化强度和矫顽力分别为0.11 T和13.5 kA/m。其矫顽力高于熔融纺丝制得的带状试样。这些薄膜表现出软磁性，最大矫顽力为2 kA/m。另一方面，在退火状态下制备的Nd-Fe二元薄膜和富Nd-Fe- b三元薄膜（由非晶相和结晶相组成）均表现出硬磁性，而其他Nd-Fe基薄膜则表现为非晶单相。在873 K下制备的富nd - fe - b薄膜矫顽力增加，在1.256 MAIm的外加磁场下磁化不饱和。这种现象与电弧熔化法制备的钮扣形试样不同，钮扣形试样的矫顽力为300 kA/m，退火后矫顽力增大。由于快速淬火，薄膜表现出软磁性，这限制了试样的结构松弛。阐明了激光烧蚀法制备的薄膜在非晶单一状态下不表现出硬磁性，而在非晶和纳米晶混合状态下则表现出硬磁性。

Nd-Fe base thin films with a thickness of up to 50 mum were prepared by laser ablation method. The surface of the thin films consists of a smooth layer and droplet particles abnormally grown. The droplet particles were characteristics of the Nd-based thin films and were not observed on the surface of the Fe-based thin films. The X-ray diffraction patterns exhibits broad halo with sharp peaks, indicating the coexisting of amorphous phase and alpha-Nd crystals. The sharp peaks disappeared when the droplet particles were removed. The saturation magnetization and coercive force of the Nd-based thin film with a thickness of 25 mum are 0.11 T and 13.5 kA/m, respectively. The coercive force is higher than that of the ribbon specimens prepared by melt-spinning. These thin films shows soft magnetism with a maximum coercive force of 2 kA/m. On the other hand, thin films prepared under an annealed state exhibit hard magnetism for both Nd-Fe binary and Nd-rich Nd-Fe-B ternary thin films which consisting of amorphous and crystalline phase while the other Nd-Fe base thin films exhibit amorphous single phase. Nd-richNd-Fe-B thin film prepared at 873 K increases in coercive force, and the magnetization does not saturate in an applied field of 1.256 MAIm. This phenomenon differs from that for button shaped specimens prepared by arc melting method : The coercive force of the button shpaped specimen is 300 kA/m and increase in coercive force when they were annealed. The thin films show soft magnetism due to rapid quenching which restrict structural relaxation in the specimens. It is clarified that thin films prepared by laser ablation method do not exhibit hard magnetism in an amorphous single state while hard magnetism was observed with a mixture of amorphous and nanocrystalline phase.