The magneto-structural transition in Mn1-xFexCoGe

Large refrigeration capacities, between 212(30) J kg-1 and 261(40) J kg-1 for a magnetic field change from 0 T to 5 T, were obtained in Mn1-xFexCoGe (x = 0.01, 0.02, 0.03 and 0.04) compounds. A partial magnetic phase diagram has been derived on the basis of magnetic transition and martensitic transformation temperatures determined from differential scanning calorimetry (200 K to 450 K), variable temperature x-ray diffraction (20 K to 310 K) and magnetisation measurements (5 K to 340 K; 0.01 T). Mn1-xFexCoGe compounds with compositions in the range x = 0.01 to 0.03 exhibit magneto-structural transitions. Neutron diffraction experiments were carried out on the Mn0.98Fe0.02CoGe sample over the temperature range of 5 K to 450 K. The diffraction patterns were analysed based on irreducible representation theory which confirms a ferromagnetic structure in the sample with an atomic magnetic moment of 3.7(1)μB at 5 K on the Mn sublattice, oriented along the orthorhombic c axis. More significantly, a magneto-structural transition around TM ∼ 297(1) K with a full width at half maximum of 29 K is demonstrated directly via neutron diffraction. Larger magnetic entropy changes are obtained for the Mn1-xFexCoGe (x = 0.01, 0.02 and 0.03) samples than for Mn0.96Fe0.04CoGe which has separate structural and magnetic transitions. In addition, it is noted that standard Arrott plots do not provide unambiguous insight to the nature of the magneto-structural transition in the Mn1-xFexCoGe compounds.