Ferromagnetic resonance and magnetization studies in exchange-coupled NiFe/Cu/NiFe structures

Abstract

We report on the dependence of the ferromagnetic resonance and magnetization on the NiFe thickness, t, of NiFe/Cu(9 Å) magnetic monolayers and symmetrical NiFe/Cu(9 Å)/NiFe/Cu(9 Å) exchange-coupled magnetic bilayer structures, deposited onto Si(1 0 0) substrate. The out-of-plane resonance field variations showed the presence of both the acoustic and optic precession modes in most of the bilayer structures. These variations and the magnetization curves were fitted using a phenomenological model, which indicated different effective magnetizations for the first and second NiFe layers as well as dependence of the magnetization and the coupling on t. Up to t = 43 Å , the bilayers are discontinuous and direct interaction between the adjacent NiFe layers occurs. For higher t, they could be considered continuous and the exchange coupling changes from ferromagnetic to antiferromagnetic at 64 Å < t < 128 Å . Coexistence of ferromagnetic and antiferromagnetic coupling was detected for the bilayer with t = 1280 Å , for which a biquadratic interlayer exchange coupling was also considered in the fittings, indicating the presence of pinholes. The results show that the techniques used are very sensitive for the evaluation of the continuity of the layers, the exchange coupling, and the possible presence of pinholes in such structures.