Magnetocaloric effect and its implementation in critical behavior study of Mn₄FeGe_3-xSi_x intermetallic compounds

Abstract

Magnetocaloric effect in Mn₄FeGe_3-xSi_x compounds has been studied by dc magnetization measurements. For the parent compound Mn₄FeGe₃, the paramagnetic to ferromagnetic transition temperature T_C is above room temperature (320 K), which initially remains constant for small Si substitution at the Ge site and then decreases marginally with an increase in Si concentration. A large change in magnetic entropy at the T_C, under a magnetic field variation of 50 kOe, with typical values of 5.9, 6.5, 5.9, and 4.4 J kg⁻¹ K⁻¹ for x = 0, 0.2, 0.6, and 1 samples, respectively, along with a broad operating temperature range and a negligible hysteresis make Mn₄FeGe_3-xSi_x series a promising candidate for magnetic refrigerant material around room temperature. Mn₄FeGe_3-xSi_x series is found to undergo a second-order magnetic phase transition. The field dependence of the magnetic entropy change has been brought out and implemented to deduce the critical exponents. The critical behavior study shows that the magnetic interactions for x = 0 and 0.2 samples have two different behaviors below and above T_C. Below T_C, it follows the mean field theory with long-range magnetic interaction and above T_C it follows the Heisenberg three-dimensional model with short-range or local magnetic interaction. The magnetic exchange interactions for the x = 0.6 and 1 samples follow the mean-field theory.