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

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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.