Crystallization to Fine TbFe2 Grains and Magnetic Properties in Rapidly Quenched Fe-Tb-B Alloys

The magnetic properties of Fe-Tb-B alloys with fine TbFe2 grains crystallized from an amorphous state were investigated. Amorphous samples with boron contents in excess of 5 mol%, situated on the line connecting Fe2Tb and FeB in a composition diagram, were prepared by rapid quenching. An amorphous Fe65Tb30B5 alloy began to crystallize into a single TbFe2 phase at 803K, and a microstructure with a grain size of about 10 nm was obtained by heating at this crystallization temperature for one hour. The fine TbFe2 phase acted to lower the coercive force. Substitution of 5 mol% Mo in Fe65Tb30B5 led to the smaller grain size and also to a lower coercive force. On the other hand, the magnetostriction of Fe-Tb-B alloys under an applied field of 1.28 MA/m was increased by replacing Fe with 5 mol% Ti or 5mol% Cr.