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

Microstructure and magnetic entropy changes in amorphous and partially crystallized Fe86−xPtxZr7Nb1Cu1B5 (x=0 or 5) alloys are studied. The transmission Mössbauer spectrum for the as-quenched Fe86Zr7Nb1Cu1B5 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 Mössbauer 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 Fe86Zr7Nb1Cu1B5 and Fe81Pt5Zr7Nb1Cu1B5, 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 Θ1=(330±1) K for Fe86Zr7Nb1Cu1B5 alloy and Θ2=(370±1) K for Fe81Pt5Zr7Nb1Cu1B5 alloy.