Magnetocaloric effect and critical behavior near the paramagnetic to ferrimagnetic phase transition temperature in TbCo2-xFex

Magnetocaloric effect (MCE) in TbCo2-xFex has been studied by dc magnetization measurements. On substituting Fe in TbCo2, not only the magnetic transition temperature is tuned to room temperature but also the operating temperature range for MCE is increased from 50 K for TbCo2 to 95 K for TbCo1.9Fe0.1. The maximum magnetic entropy change (-Delta S-M) for TbCo1.9Fe0.1 is found to be 3.7 J kg(-1) K-1 for a 5 T field change, making it a promising candidate for magnetic refrigeration near room temperature. The temperature-dependent neutron-diffraction study shows a structural phase transition (from cubic to rhombohedral phase with lowering of temperature) which is associated with the magnetic phase transition and these transitions broaden on Fe substitution. To investigate the nature of the paramagnetic to ferrimagnetic phase transition, we performed a critical exponent study. From the derived values of critical exponents, we conclude that TbCo2 belongs to the three-dimensional Heisenberg class with short-range interaction, while on Fe substitution it tends towards mean field with long-range interaction. The derived values of critical exponents represent the phenomenological universal curve for the field dependence of Delta S-M, indicating that TbCo2 and TbCo1.9Fe0.1 belong to two different universality classes.