Structural and magnetic phase diagrams of MnFe0.6Ni0.4(Si,Ge) alloys and their giant magnetocaloric effect probed by heat capacity measurements

•Structural and magnetic phase diagrams of MnFe0.6Ni0.4Si1−xGex alloys (0 ≤ x ≤ 1) are reported.•Magneto-structural transition is found at 204 K for x = 0.5.•DSC experiments reveal a recalescence event at the first cooling.•In-field specific heat measurements are used to obtain the magnetocaloric effect.•A sizable magnetocaloric temperature change is found for x = 0.5.