MAGNETIC DEFECTS IN ANTIFERROMAGNETS

Neutron polarisation analysis scattering studies have been undertaken on a number of metallic antiferromagnetic alloys based on gamma-Mn. Re sults obtained for the Mn-Cu alloy system will be reviewed. The common feature in this study and other gamma-Mn alloys is a component transv erse to the antiferromagnetic direction in the defect centred on the a lloying element. The local canting of the moment appears to be due to the occurrence of unsatisfied antiferromagnetic interactions in the fa ce centred cubic type-I antiferromagnetic structure. A classical spin model of the defect structure will be presented. This local structure is derived by minimising the energy of the local spin configuration in the presence of a rigid long range antiferromagnetic order. The local configuration is then allowed to perturb the long range antiferromagn etic order through the wavevector dependent susceptibility estimated f rom the measured magnon dispersions in this material.