Microstructure and Magnetic Entropy Change in Amorphous <inline-formula> <tex-math notation="TeX">${\rm Fe}_{76}{\rm Mo}_{10}{\rm Cu}_{1}{\rm B}_{13}$ </tex-math></inline-formula> Alloy

Abstract

Microstructure and some thermomagnetic properties of the amorphous ${\rm Fe}_{{76}}{\rm Mo}_{{10}}{\rm Cu}_{{1}}{\rm B}_{{13}}$ alloy in the as-quenched state and after annealing at 623 and 673 K are studied. High-resolution electron microscopy, apart from the amorphous phase, reveals the existence of medium range ordered (MRO) regions 1–2 nm in size. Transmission Mossbauer spectroscopy confirms that these regions are $\alpha$ -Fe MRO ones and grow during annealing. The Curie point of the alloy is 277, 272, and 284 K in the as-quenched state and after mentioned above heat treatments, respectively. The maximum of the magnetic entropy change is rather modest and equal to $0.88~{\rm J}\cdot{\rm kg}^{{-1}}\cdot{\rm K}^{{-1}}$ in the as-quenched state and reaches the value of $1.12~{\rm J}\cdot{\rm kg}^{{-1}}\cdot{\rm K}^{{-1}}$ after annealing at 673 K. Magnetic entropy change depends not only on the temperature, but on the maximum of the magnetizing flux density, ${{B_{m}}=\mu_{0}{H_{m}}}$ (according to ${{\Delta}}{S_{M}}={C(T)}\cdot{B_{m}^{{n}}}$ ) as well. The exponent ${n}$ is close to 1 below the Curie point and does not reach 2 in high and equal to 2 in low magnetizing flux density range above the Curie point like in Curie–Weiss paramagnets. Such behavior is ascribed to the presence of MRO regions beside the amorphous phase and the material can be treated as biphasic.