Double magnetic transitions, complex field-induced phases, and large magnetocaloric effect in the frustrated garnet compound Mn3Cr2Ge3O12

A detailed study of the magnetic and magnetocaloric properties of the garnet compound Mn₃Cr₂Ge₃O₁₂ is carried out using x-ray diffraction, magnetization, heat capacity, and neutron diffraction measurements as well as ab initio band-structure calculations. This compound manifests two successive magnetic transitions at TN14.50.16em0exK and TN22.70.16em0exK. Neutron powder diffraction experiments reveal that these two transitions correspond to the collinear and noncollinear antiferromagnetic ordering of the nonfrustrated Cr³⁺ and frustrated Mn²⁺ sublattices, respectively. The interactions within each of the Cr and Mn sublattices are antiferromagnetic, while the intersublattice interactions are ferromagnetic. The H-T phase diagram is quite complex and displays multiple phases under magnetic field, which can be attributed to the frustrated nature of the spin lattice. Mn₃Cr₂Ge₃O₁₂ shows a large magnetocaloric effect with a maximum value of isothermal entropy change ΔSₘ-23 J/kg K and adiabatic temperature change ΔTad90.16em0exK for a field change of 7 T. Further, a large value of the relative cooling power (RCP360 J/kg) demonstrates the promise of using this compound in magnetic refrigeration.