Er2Fe14B single crystal as magnetic refrigerant at the spin reorientation transition

In this paper we study the specific heat under magnetic field c(p)(H-a, T) and the magnetic field induced isothermal entropy change Delta s(H-a, T) of Er2Fe14B by direct calorimetry and magnetic measurements. We find that the spin reorientation temperature is T-SR = 322.8 +/- 0.1 K and the entropy change is Delta s = 0.735 +/- 0.005 J kg(-1) K-1. The measured data are interpreted by a model of the magnetization process taking into account a temperature-dependent uniaxial anisotropy constant K-1(T), the magnetic field energy, and the effect of the demagnetizing field. The model is able to describe the essential features of the measured Delta s(H-a, T) in terms of reversible rotation of the magnetization induced by the magnetic field. From the model we find that the entropy change has a magnetic field independent saturation value.Delta s(K)(T) = 735 - 5.5 x 10(-3) (T - T-SR) and that the magnetic field amplitude increases the temperature range over which the effect is observed as Delta T = beta mu H-0 with beta = 54 K T-1. (C) 2011 American Institute of Physics. [doi:10.1063/1.3567925]