Moessbauer spectroscopy of Co2Mn1-xFexAl

Heusler compounds have been recognized as suitable materials for magneto-electronics. The Co2 based compounds are of special interest for applications as they exhibit a wide range of magnetic properties and Curie temperatures up to 1100 K. In this work solid solutions of Co2Mn1-xFexAl with x=0, 0.1,..,1 were prepared by arc melting and annealed for 7 days at 800 C. The structure was characterized by XRD and a single B2 phase was found over the entire range of compositions. The magnetic properties were measured with a SQUID magnetometer revealing that the moments are higher than expected for half-metallic ferromagnetism. The local environment and hyperfine magnetic fields of the iron atoms were studied by 57Fe Moessbauer spectroscopy in transmission geometry at room temperature for Co2Mn1-xFexAl samples with x=0.2..1. The obtained spectra are explained by hyperfine magnetic field distributions implying 7 contributions with different values and line widths in agreement with the local structure in the cubic lattice. A shift of the relative intensities of the seven hyperfine magnetic fields is explained by the appearance of an additional ordered portion with L21 structure for samples with Fe concentrations of x>0.7 not being detected by XRD