Magnetocaloric effect in amorphous and partially crystallized Fe₄₀Ni₃₈Mo₄B₁₈ alloys

A study of magnetocaloric effect in amorphous and partially crystallized Fe₄₀Ni₃₈Mo₄B₁₈ alloys is reported. Amorphous Fe₄₀Ni₃₈Mo₄B₁₈, near its magnetic ordering temperature (600K) showed a magnetic entropy change ΔS_M of 1.1 J/KgK and a relative cooling power of 36J/Kg in a field change of 10 kOe. Amorphous samples were partially crystallized by annealing at 700 K at different time intervals. Partially crystallized samples showed two distinct magnetic ordering temperature, one corresponding to the precipitated FeNi nanocrystals and the other one corresponding to the boron rich amorphous matrix. Magnetic ordering temperature of the residual amorphous matrix got shifted to the lower temperatures on increasing the annealing duration. Partially crystallised samples showed a magnetic entropy change of about 0.27J/kgK near the magnetic ordering temperature of the amorphous matrix (540K) in a field change of 10 kOe. The decrease in ΔS_M on partial crystallisation is attributed to the biphasic magnetic nature of the sample.