Exploring the details of the martensitic phase transition and magnetocaloric effect of CoMnGe0.95Ga0.05 by synchrotron and magnetic measurements

► CoMnGe0.95Ga0.05 alloy shows a structural phase transformation from hexagonal to orthorhombic. ► In CoMnGe0.95Ga0.05, the giant magnetocaloric effect is observed around room temperature. ► The maximum magnetic entropy change is −5.2Jkg−1K−1 in magnetic field change of 1T. The structural, magnetic and magnetocaloric properties of CoMnGe0.95Ga0.05 have been investigated by using electron microscopy, calorimetric, synchrotron and magnetic measurements. The substitution of Ga for Ge leads to decreasing on the martensitic transition temperature from 650K to 315K. CoMnGe0.95Ga0.05 has hexagonal structure (space group P63/mmc) above the martensitic transition temperature and orthorhombic structure (space group Pnma) below this temperature. The magnetic field dependence of magnetization measurements are performed in the heating and cooling processes around the martensitic transition temperature to determine magnetocaloric effect. It is observed that the magnetic entropy change associated with the martensitic transition temperature can be as high as −5.2Jkg−1K−1 in field of 1T.