MAGNETIZATION, COERCIVITY, AND REMANENCE IN AMORPHOUS TERBIUM-IRON METALLOID ALLOYS

Crystalline terbium-iron compounds generate large magnetostrictive str ains but for practical application require relatively large fields to overcome magnetocrystalline anisotropy. Their amorphous counterparts a re magnetically softer and yet potentially useful magnetostrictive str ains are still exhibited due to the presence of the Tb ions. As part o f our investigation into the origins and magnitudes of the magnetostri ction in amorphous rare earth-iron alloys, their magnetic properties h ave been subjected to close examination. Melt-spun ribbons of TbFe2 co ntaining between 3 and 14 at. % boron were prepared and shown to be am orphous (>6 at. % B). The field and temperature dependences of magneti zation have been measured in the region 4.5 K < T < 300 K with fields up to 5 T using a superconducting quantum interference device magnetom eter. The temperature dependences of coercivity and remanence have bee n determined. Zero field and field cooled magnetization curves indicat e a spin freezing temperature similar to 240 K. Analyzing the demagnet ization curves in terms of the random anisotropy model proposed by Har ris, Plischke, and Zuckermann (HPZ) [R. Harris, M. Plischke, and M. J. Zuckermann, Phys. Rev. Lett. 31, 160 (1974)] shows that the anisotrop y and exchange energy in (TbFe2)(1-x)B-x are of comparable magnitudes. Coupled with the sharp decrease of the anisotropy with increasing tem perature this leads to an interesting thermal behavior of the remanenc e with a local minimum at similar to 140 K. Different concentrations o f boron seem to have no significant effect on the magnetic properties. Boron acts purely as a ''glass former'' necessary for producing amorp hous TbFe2 by rapid cooling. (C) 1997 American Institute of Physics.