Analyses of TmAl2 and ErAl2 composite for use as an active magnetic regenerator close to liquid helium temperature

We report the thermodynamic properties of selected intermetallic RAl2 (R = Er, Tm) compounds calculated by using a model Hamiltonian, including the Zeeman-exchange interactions and the crystalline electrical field, which are responsible for the magnetic anisotropy. The relationship between the behavior of the temperature-dependent magnetization, calculated in different crystallographic directions for several magnetic fields, and the influence of spin reorientation on the magnetocaloric effect, is discussed. In order to validate the obtained theoretical results, experimental data are compared to calculated data. Also, an optimum molar fraction of the ErAl2 and TmAl2 composite was determined theoretically, showing a high potential for use in a regenerative thermal cycle, especially close to the liquid helium temperature range.