Magnetocaloric effect and critical behavior near the paramagnetic to ferrimagnetic phase transition temperature inTbCo2−xFex

Abstract

Magnetocaloric effect (MCE) in TbCo 2-x Fe x has been studied by dc magnetization measurements.On substituting Fe in TbCo 2 , 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 TbCo 2 to 95 K for TbCo 1.9 Fe 0.1 . The maximum magnetic entropy change (-ΔS M ) for TbCo 1.9 Fe 0.1 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 TbCo 2 belongs to the 3D 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 ΔS M , indicating that TbCo 2 and TbCo 1.9 Fe 0.1 belong to two different universality classes.PACS number(s): 75.30.Sg, 61.05.fm, 75.40.Cx * Electronic mail: smyusuf@barc.gov.in FAX: +91 22 25505151

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