Modulated magnetic properties of hard/soft exchange-coupled SmFe/NiFe multilayers

Very well-defined induced in-plane uniaxial anisotropy, not obtainable in single layer SmFe films, has been observed in Sm₄₀Fe₆₀/Ni₈₀Fe₂₀ multilayers. The easy axis coercivity monotonically decreases as the thickness of NiFe (SmFe) layers increases (decreases). These experimental results are well described theoretically by an extended domain wall unpinning model. The easy axis coercivity and the hard axis saturation field can be reduced by appropriate annealing procedures. Moreover, for multilayers with well-defined uniaxial anisotropy, a linear relationship between the easy axis coercivity and the hard axis saturation field is found, no matter whether the change in coercivity and saturation field is caused by a change in thickness or by annealing. Finally, the evolution in structure caused by annealing is studied by X-ray diffraction and correlated with changes in the coercivity and saturation field. The ability to tailor the magnetic behavior of such systems is critical to optimizing the performance of multilayered giant magnetostrictive films.