A 57Fe Mössbauer 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 57Fe Mössbauer spectroscopy measurements on (Mn 0.96Fe 0.04)CoGe and Mn(Co 0.96Fe 0.04)Ge samples doped with 0.5 wt % 57Fe. 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 0.96Fe 0.04)Ge. Analysis of the 20 K Mössbauer 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 0.96Fe 0.04)CoGe and Mn(Co 0.96Fe 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 Bhf−Mn= 16.4(4) T and Bhf−Co= 21.1(4) T.