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

Abstract

The structural and magnetic phase diagrams of MnFe0.6Ni0.4Si1−xGex alloys (0 ≤ x ≤ 1) are explored using powder X-ray diffraction, magnetic and calorimetric measurements. At room temperature, the crystal structure evolves from the orthorhombic TiNiSi-type to the hexagonal Ni2In-type with the increase in Ge. A magneto-structural coupling leading to a first-order ferromagnetic transition is found at 204 K for x ~ 0.5. Differential scanning calorimetry reveals a recalescence-like event at the first cooling across the structural transition. In-field specific heat measurements are used to quantify the giant magnetocaloric effect and show that the latent heat of the magneto-structural transition is less than in closely related MnMX alloys, which leads to sizable transition sensitivity to the magnetic field and finite adiabatic temperature change.