Tuning phase transitions and optimization of the magnetocaloric effect in Ho(Co1-xMnx)2 alloys

In magnetic refrigerants, tuning the materials to the first-order/second-order borderline is expected to equip the material with the advantages of the first- and second-order transitions. In this work, we performed a systematic study on the nature of the phase transition, the magnetic entropy change, and the hysteresis loss in the Mn-doped Ho(Co1-xMnx)(2 )alloys. We found that at x = 0.02, the material was close to the borderline of the first-order/second-order transition and exhibited a large magnetocaloric effect along with a small hysteresis loss. At x>0.02, the phase transition in the sample became a second-order type, and the magnetocaloric effect was greatly reduced. These results indicate that tuning the nature of phase transition in the RCo2-based magnetic material is an effective strategy of optimizing its magnetocaloric performance.