AN INVESTIGATION OF THE ATOMIC AND MAGNETIC-STRUCTURE OF MECHANICALLYALLOYED CU2MNAL USING NEUTRON-DIFFRACTION AND THE RIETVELD METHOD

The Heusler alloy Cu2MnAl was prepared by mechanical alloying and subs equent heat treatment at 973 K for 1 h. At saturation, the resulting m aterial had an atomic magnetic moment of 2.34 mu(B)/Mn atom. Neutron d iffraction experiments were carried out at room temperature, both with and without an applied magnetic field of 12 kOe. The Rietveld method was used to fit calculated curves to both sets of data. Nuclear and ma gnetic contributions were modelled simultaneously, using a large Debye -Waller thermal parameter to model the Mn2+ magnetic form factor. The results showed that the material was ferromagnetic. Cu atoms occupied approximately 10% of the Mn sites. Particle and magnetic domain sizes were determined from the results of the Rietveld analysis. These were respectively similar to 164 and similar to 29 nm. The nuclear contribu tion to the diffraction pattern was separated from the magnetic, by su btraction of the two sets of data. This was studied using the Rietveld method and the resulting structure was similar to that obtained when nuclear and magnetic components were modelled simultaneously.