  A coupling of the first-order paramagnetic-to-induced-ferromagnetic
martensitic and the second-order antiferromagnetic-to-ferromagnetic
metamagnetic transitions was found in MnNi0.8Fe0.2Ge alloy. Based on the
coupling, a magneto-volume effect driven by the martensitic transition and a
table-like magnetocaloric effect generated by the successive magnetic phase
transitions arise collectively. By using the magneto-volume effect, the
internal pressure stress in the volume-expansion martensitic transition was
determined at 350 MPa. The magnetocaloric effect, with a wide working
temperature range of 26 K around room temperature, shows a small hysteresis
loss (5 J/kg) and a large net refrigerant capacity (157 J/kg).
