Microstructure and some thermomagnetic properties of amorphous and partially crystallized Fe–(Pt)–Zr–Nb–Cu–B alloys

Abstract Microstructure and magnetic entropy changes in amorphous and partially crystallized Fe 86− x Pt x Zr 7 Nb 1 Cu 1 B 5 ( x =0 or 5) alloys are studied. The transmission Mossbauer spectrum for the as-quenched Fe 86 Zr 7 Nb 1 Cu 1 B 5 alloy is typical of weak amorphous ferromagnets with the average hyperfine field of (4.78±0.02) T. The replacing of 5% of Fe atoms by Pt increases the average hyperfine field up to (13.12±0.02) T. High resolution electron microscopy and transmission Mossbauer spectroscopy do not reveal the existence of medium range ordering regions. In the as-quenched state of both alloys the maximum magnetic entropy change occurs near the Curie points and is equal to 0.51 J kg −1  K −1 and 0.85 J kg −1  K −1 for Fe 86 Zr 7 Nb 1 Cu 1 B 5 and Fe 81 Pt 5 Zr 7 Nb 1 Cu 1 B 5 , respectively. The maximum magnetic entropy change decreases after partial crystallization of the alloys. Both alloys in the as-quenched state above their Curie points behave like Curie–Weiss paramagnets with the paramagnetic Curie temperature equals to Θ 1 =(330±1) K for Fe 86 Zr 7 Nb 1 Cu 1 B 5 alloy and Θ 2 =(370±1) K for Fe 81 Pt 5 Zr 7 Nb 1 Cu 1 B 5 alloy.