Effects of structure on exchange interactions in crystalline and amorphous alloys Gd xY 50−xAg 50

Abstract

Magnetic interactions and effects of dilution with nonmagnetic Y on the magnetic properties of crystalline and amorphous alloys Gd x Y 50− x Ag 50 (10 ≤ x ≤ 50) have been investigated by measurements of bulk magnetization and susceptibility and by Mössbauer spectroscopy with 155Gd. The crystalline alloys order antiferromagnetically for all Gd concentrations with a noncollinear arrangement of Gd moments induced by negative biquadratic exchange interactions. In amorphous alloys, ferromagnetic order is found for large Gd concentrations ( x ≥ 40). Below the critical concentration x cr, in the range 30< x cr<40, properties typical for magnetic cluster glasses are observed. Magnetic hyperfine fields B hf at 155Gd nuclei vary with x in opposite directions in amorphous and in crystalline alloys. In crystalline alloys, the variation is due to a positive transferred hyperfine field. In amorphous alloys, a reduction of | B hf| with decreasing Gd concentration is caused by a reduction of the frozen Gd moments in the cluster glass phase.