Rotating magnetocaloric effect in TmB4 – A comparison between estimations based on heat capacity and magnetization measurements

We present a comparison of the rotating magnetocaloric effect (R-MCE) carried out on TmB₄, a strongly anisotropic magnetic system, which is based on the determination of the entropy S and entropy change ΔS. Both quantities are determined using independent measurements of the heat capacity and the magnetization as a function of temperature and magnetic field. The comparison of these two approaches shows that estimates of the R-MCE, in particular the estimate of the temperature difference ΔT that occurs during sample rotation in magnetic field H, based on magnetization measurements (which usually present a simpler and faster way to obtain the necessary data) provide similar results to those obtained from detailed temperature dependencies of heat capacity. However, to take the advantage of magnetisation measurements it is necessary to make an approximation concerning heat capacity data. There one has to be careful and use the right approximation for the ΔT estimate. In case of materials with a complex temperature dependence of the heat capacity common approach can lead to significant errors. Our results here suggest for the entropy calculation from magnetic data sets the following procedure: first determine the zero-field (H = 0) contribution to S from heat capacity data, then add to this the magnetic entropy change contribution determined from magnetization measurements.