Crystal Orientation of Anisotropic Fe-Pt Permanent Magnet

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The head investigator in this project and his collaborates succeeded in fabricating c-axis oriented Fe-Pt based alloy thin films with the energy product exceeding 35 MG-Oe, which is the highest value as thin film magnets. Thus, apparent improvement of magnetic properties in bulk Fe-Pt alloys is expected by controlling their crystal orientation. In this project, we laid a research plan of investigating crystal orientation dependence of magnetic properties in Fe-Pt single crystals. This plan aims at adapting to shape multiplicity of permanent magnets and at optimizing magnetic properties of this alloy. Single crystal preparation of Fe-Pt alloy has been reported to be difficult, due to the formation of twin microstructures to release stress of order-disorder transformation. First, we prepared Fe-37at%Pt single crystals and investigated orientation dependence of magnetic properties in the sample aged at 640℃. In the case of the sample aged for 45 hours, showing the maximum coercivity, apparent difference of coercivity could not be observed between the directions of magnetization easy axis [001] and hard axis [100]. However, we could confirm a difference of coercivity by a factor of 2 in the over-aged sample (for 280 hours). On addition to the 37 at%Pt composition, fabrication of Fe- 39.5 at%Pt- 0.75 at%Nb single crystal was attempted by precise casting method using a molding material with low heat conductivity, resulted in a single crystal grain with the size of 2mm length. Solution growth of Fe-Pt single crystal was also attempted using Fe-Pt-B pseudo binary alloys as solvent.