Mechanical attrition and magnetic properties of CsCl-structure Co-Ga

Structural changes in stoichiometric CoGa during mechanical attrition in a high-energy ball mill were monitored by measurements of magnetic properties and lattice parameter. The high-field magnetization increases, whereas the lattice parameter decreases as a function of milling time. For long milling times, values of both parameters saturate. The results are interpreted by the generation of atomic triple-defect disorder, also characteristic of this compound in equilibrium at high temperatures: antisite Co atoms in combination with vacancies on the Co sublattice in a 1:2 ratio. By comparison to the magnetic properties of ${\mathrm{Co}}_{\mathit{x}}$ ${\mathrm{Ga}}_{100\mathrm{-}\mathit{x}}$ compounds with excess Co, the fractions of antisite Co atoms and vacancies are derived. On the basis of these values, the decrease of the lattice parameter can be calculated and compared to the actual measurement. The good agreement proves that, by the apparently crude technique of mechanical attrition, well-defined nonequilbrium states in intermetallic compounds can be generated.