Effects of carbon substitution on magnetic properties and magnetocaloric effects in Mn65-xGa17C18+x compounds

Abstract

We present an investigation involving the tuning of the magnetic, magnetocaloric, and room-temperature structural properties of Mn_65-xGa₁₇C_18+x (0 ≤ x ≤ 4) compounds prepared using a high-energy ball milling (HEBM) technique. This study indicates that the crystal structure of all the compounds can be described as an anti-perovskite cubic structure with the Pm-3m space group and the crystal cell volume decreases with increasing carbon concentration. The system shows a first-order structural phase transition at a temperature T = T_M between two cubic phases having different magnetic structures. The phases are characterized by antiferromagnetic (AFM) and ferromagnetic (FM) -like behavior at low (T < T_M) and high (T_M ˃ T) temperature regions, respectively. A suppression of the AFM phase was observed with increasing C concentration. The temperature-induced first-order transitions (FOTs) were found to possess a small thermal hysteresis in the magnetization (∼ 2–3 K) in an applied magnetic field of H = 50 kOe. Magnetic entropy changes estimated from isothermal magnetization curves indicate that the largest value of the magnetic entropy change of |ΔS_M| = 2.1 J kg^-1 K⁻¹ for x = 4 with ΔH = 50 kOe, with a relative cooling power (RCP) of ∼ 190 J kg⁻¹.Thus high-energy ball milling (HEBM), a scalable technique, has been demonstrated as a viable method to synthesize magnetocaloric materials with substantial RCP values.