Magnetostructural transformation and large magnetocaloric effect in Mn0.9Cu0.1CoGe1-xSix alloys

The structural transition temperature 71 increases largely with the introduction of Si in Mn0.9Cu0.1CoGe1-xSix alloys due to the enhancement of degree of hexagonal distortion. Thus, the first-order magnetostructural transformation from ferromagnetic orthorhombic to paramagnetic hexagonal phase can be obtained in the range of 0.15 < x < 0.21. Large magnetocaloric effect (MCE) under low magnetic field change of 2 T is obtained due to the magnetostructural transformation, e.g., the maximum magnetic entropy change (-Delta S-M) value for x = 0.16 is 10.3 J/kg K at 297 K, which is comparable to or even larger than those of some typical room-temperature magnetocaloric materials. The nature of magnetostructural transition has been studied by different methods, and it is found that the Arrott plots fail to determine the order of phase transition. In contrast, the universal curve of ASm is proved to be a more effective criterion to distinguish the order of phase transition. Besides, a linear relationship between -Delta SMSm and Delta mu H-0 is found, and so the -Delta Sm values for higher field changes can be estimated by linear fitting. Consequently, large MCE induced by magnetostructural transformation suggests that Mn0.9Cu0.1CoGe1-xSix alloys could be promising candidates for room-temperature magnetocaloric materials.