Electronic structure, magnetic properties and order-disorder phenomena in Co2Mn1-xFexAl

The substitutional series of Heusler compounds Co2Mn1-xFexAl was investigated by experimental and theoretical methods. In the experiments a B2 type structure was found for the complete series by means of powder x-ray diffraction. The magnetic moment increases with the Fe content from about 4 mu(B) in Co2MnAl to above 5 mu(B) in Co2FeAl. All samples exhibit a soft magnetic character. The Curie temperature is above 700K and governed by structural changes. The magneto-structural properties, as determined by Mossbauer spectroscopy, show that a statistical distribution of the hyperfine fields appears rather than a single value. The observed isomer shifts point to a transfer of charge between Mn and Fe atoms depending on the Fe content. The experimental findings are well supported by ab initio calculations of the electronic and magnetic structure for disordered systems.