Magnetic and theoretical studies of NiFe layers coupled through a nonmagnetic interlayer

Polycrystalline double-permalloy (Ni₈₀Fe₂₀) films separated by a copper interfilm were investigated by FMR (ferromagnetic resonance), vibrating sample magnetometry, and Lorentz microscopy. The samples are deposited from e-gun sources onto both glass and NaCl substrates in an ultrahigh vacuum. A long-range exchange coupling between the Permalloy films is indicated by the dependence of the resonant field position of the spin wave modes on the thickness of the copper interfilm. Spin wave resonance experiments have shown the onset of exchange coupling to occur at an interfilm thickness of ≈30 Å and that the coupling is sufficiently strong for the degeneracy of the in-phase and out-of-phase coupled modes to be lifted when the interfilm thickness is ⩽20 Å. The results are discussed in terms of a theoretical model based on a transfer matrix method. The model predicts that, at the onset of coupling, the spin wave modes become unpinned at the interfaces with the interfilm. This effect has been observed experimentally. Coercivity measurements and domain-wall structure observations are consistent with the exchange coupling range obtained from the spin wave resonance data