A 57Fe Mossbauer study of magnetocaloric Fe doped MnCoGe

MnCoGe-based compounds are of interest with respect to the magnetocaloric effect due to a martensitic phase transition from the low-temperature orthorhombic phase to the high-temperature hexagonal phase. A key feature is that the transition temperature can be readily tuned to obtain a magneto-structural transition. Fe is an effective substitute for Mn or Co to stabilize the hexagonal phase at low temperature. Here we present initial Fe-57 Mossbauer spectroscopy measurements on (Mn Fe-0.96 (0.04))CoGe and Mn(Co Fe-0.96 (0.04))Ge samples doped with 0.5 wt % Fe-57. The martensitic transition temperatures were determined to be 239 K and 304 K with transition full widths at half maximum of 44 K and 39 K respectively as determined from x-ray diffraction experiments over the temperature range 10-310 K. The magnetic properties were studied over the temperature range 5-300 K and a magneto-structural transition found in Mn(Co Fe-0.96 (0.04))Ge. Analysis of the 20 K Mossbauer spectra reveals that the Fe atoms are distributed on both the Mn and Co sites and tend to prefer to occupy the Co site in both the (Mn Fe-0.96 (0.04))CoGe and Mn(Co Fe-0.96 (0.04))Ge samples. The hyperfine fields determined for Fe atoms on the Mn and Co sites at 20 K in the ferromagnetic orthorhombic phases are B (hf-Mn)= 16.4(4) T and B (hf-Co)= 21.1(4) T.