Near-Room Temperature Magnetocaloric Effect and Critical Exponent Analysis in Mn_4.8Cu_0.2Ge₃ Compound

Mn₅Ge₃ compound is a well-established rare-earth-free magnetocaloric material with a near-room temperature magnetocaloric effect. Chemical modification could increase its relative cooling power and to achieve that we have substituted copper and synthesized Mn_4.8Cu_0.2Ge₃ polycrystalline compound through arc-melting process. Mn_4.8Cu_0.2Ge₃ is an itinerant ferromagnet with a second-order magnetic transition in the vicinity of room temperature. In comparison with the pure Mn₅Ge₃ compound, the temperature span of the magnetocaloric effect has widened, which is a favorable requirement in practical devices. The magnetization critical exponents were estimated through the modified Arrott plot and Kouvel-Fischer methods. An unconventional critical behavior was noticed in this compound, in which the critical exponents \(\beta\) $\beta$ and \(\gamma\) $\gamma$ fall close to the standard 3D-XY and 3D-Ising models, respectively. On the other hand, the pure Mn₅Ge₃ single crystal shows 3D-Ising critical behavior, and the deviation from the standard universality class in Mn_4.8Cu_0.2Ge₃ could be attributed to the modification in Mn–Mn distance induced by the copper. On analyzing the magnetic properties of Mn_5-xCu_xGe₃ (x = 0.1, 0.2, and 0.3) series, we speculate that x = 0.2 compound breaks the series monotonicity due to the unique influence of Cu substitution on Mn–Mn interactions.