Magnetostriction of polycrystalline Co-Pd alloys

Magnetostriction of polycrystalline Co100−xPdx alloys was measured by the strain gauge method from 4 to 300 K. The saturation magnetostriction λs=(2/3)[(ΔL/L)s∥−(ΔL/L)s⊥], where (ΔL/L)s∥ and (ΔL/L)s⊥ are the saturated values (when HE≳5 kG) of ΔL/L in fields parallel and perpendicular to sample’s length (L). λs at 4 K is found to change sign from positive to negative value as x is increased from below x0=50 at. % Pd to above. This phenomenon can be understood from the split-band theory for Co-Pd alloy. However, since some experimental facts indicate that unquenched orbital moments may exist in the x≳50 at. % Pd alloys it is necessary to consider λs = λsband+ λsion, where λsband is due to the split-band theory and λsion is from the one-ion mechanism. Under this proposal, it is possible to explain why λs(4 K) is not antisymmetric with respect to x0. Finally, two different origins of temperature dependence of λs are discussed.