Magnetocaloric effect, thermal conductivity, and magnetostriction of epoxy-bonded La(Fe_0.88Si_0.12)₁₃ hydrides

Magnetic materials with large magnetocaloric effect are significantly important for magnetic refrigeration. La(Fe_0.88Si_0.12)₁₃ compounds are one of the promising magnetocaloric materials that have a first order magnetic phase transition. Transition temperature of hydrogenated La(Fe_0.88Si_0.12)₁₃ increased up to room temperature region while keeping metamagnetic transition properties. From view point of practical usage, bonded composite are very attractive and their properties are important. We made epoxy bonded La(Fe_0.88Si_0.12)₁₃ hydrides. Magnetocaloric effect was studied by measuring specific heat, magnetization, and temperature change in adiabatic demagnetization. The composite had about 20% smaller entropy change from the hydrogenated La(Fe_0.88Si_0.12)₁₃ powder in 2 T. Thermal conductivity of the composite was several times smaller than La(Fe,Si)₁₃. The small thermal conductivity was explained due to the small thermal conductivity of epoxy. Thermal conductivity was observed to be insensitive to magnetic field in 2 T. Thermal expansion and magnetostriction of the composite material were measured. The composite expanded about 0.25% when it entered into ferromagnetic phase. Magnetostriction of the composite in ferromagnetic phase was about 0.2% in 5 T and much larger than that in paramagnetic phase. The composite didn't break after about 100 times magnetic field changes in adiabatic demagnetization experiment even though it has magnetostriction.