Ferromagnetic resonance study of sputtered NiFe/V/NiFe heterostructures

Abstract

a b s t r a c tThe Ni 81 Fe 19 /V/Ni 81 Fe 19 heterostructures has been produced by magnetron sputtering and analyzed by ferromagnetic resonance. Two systems were investigated: the non symmetrical NiFe(50 Å)/V(t)/NiFe (30 Å) trilayers and the symmetrical NiFe(80 Å)/V(t)/NiFe(80 Å) trilayers, with variable ultrathin V thickness t. Ferromagnetic exchange coupling was evidenced for t below 10 Å by the excitation of the optic mode, in the case of the non symmetrical samples, and by the observation of a single resonance mode for the symmetrical trilayers. For larger V thickness, all samples exhibited two modes, which were attributed to the resonance of the individual NiFe layers with different effective magnetizations. The analysis with the equilibrium and resonance conditions provided the exchange coupling constants and effective magnetizations.

Modulation of interfacial magnetic relaxation timeframes by partially uncoupled exchange bias

“…the directions of the applied field, magnetization, uniaxial anisotropy field, and the anisotropy axis in the pinned AFM grains are parallel to each other (φ H = 0 • , φ M = 0 • , φ FM = 0 • and φ AFM = 0 • on figure 1(c)). In this approximation, ω/γ = 3372 Oe, 4πM eff = 9800 Oe [46,47] is effective magnetization, 4πM eff = 4πM S − H S , where H S is surface anisotropy field, and M S = 780 emu cm −3 is saturation magnetization for NiFe. The ω/γ and 4πM eff values were fixed, the H B was determined from the amplitude of the angular variation of FMR resonant field, and anisotropy fields H U and H RA were varied subsequently in a few iterations till the approximation converges.…”