The effect of substitutional elements on the strain-induced ferromagnetism in B2-structured Fe–Al single crystals

Strain-induced ferromagnetism in B2-structured Fe–Al arises mostly from anti-phase boundary (APB) tubes where groups of moment-bearing Fe atoms with at least three like nearest-neighbors are large enough to be magnetically coupled and behave ferromagnetically. Following our previous work on binary Fe–Al, strain-induced ferromagnetism in ternary single crystals of Fe–40 at.%Al–3 at.%Cu and Fe–40 at.%Al–3 at.%Cr was studied. When deformed to similar rolling strains along the same orientation, the saturation magnetization, MS, was found to be greatest for Fe–40 at.%Al, followed by Fe–40 at.%Al–3 at.%Cu, Fe–40 at.%Al–3 at.%Cr and Fe–43 at.%Al. This behavior can be explained by the site preferences of the Cu and Cr atoms on the Fe and Al sublattices, which both change the probability of a Fe atom having like nearest-neighbors in the APB tubes and affect the energy of the anti-phase boundaries. Calculations of MS at 0 K of rolled Fe–40 at.%Al–3 at.%Cu and Fe–40 at.%Al–3 at.%Cr specimens, based on APB tube densities and considerations of the APB tube size and geometry, were found to be in reasonable agreement with experimentally determined values. APB tubes were observed by transmission electron microscopy in Fe–40 at.%Al, Fe–40 at.%Al–3 at.%Cu and Fe–40 at.%Al–3 at.%Cr.