Ferromagnetic resonance study of the exchange bias field in NiFe∕FeMn∕NiFe trilayers

Abstract

The ferromagnetic resonance (FMR) technique is used to study the exchange bias field in asymmetrical NiFe∕FeMn∕NiFe trilayers produced by dc magnetron sputtering under different working pressures. The FMR spectra give evidence of two resonance modes attributed to the two asymmetrical noninteracting NiFe layers. The study of the in-plane angular dependence of the absorption field allows the measurement of the exchange bias field at both bottom ferromagnetic (FM)∕antiferromagnetic (AFM) and top AFM∕FM interfaces.

Bottom and top AF/FM interfaces of NiFe/FeMn/NiFe trilayers

“…Thus, the most probably explanation is the reason (ii), i.e., the atomic diffusion has a strong contribution to the s values of the NiFe/FeMn interfaces. The evidence of atomic diffusion at the NiFe/FeMn interfaces was also found by ferromagnetic resonance results [19] (not shown here) which confirmed that the upper AF/FM interface are less homogeneous than the lower one probably due to an atomic diffusion at the AF/FM interfaces (stronger in the upper interface).…”

“…However, when one layer is deposited subsequently on the other, it favors the diffusion of Ni and Mn atoms at the interface, since the associated heat of mixing is more negative (DH mix = À8 kJ/ mol) [37]. The evidence that an increasement in the argon working pressure enhances the atomic diffusion at the interface is also corroborated by ferromagnetic resonance measurements [19] and Mössbauer spectroscopy results (not shown here). The increase of the argon working pressure could also induce other structural effects like changes in grain size, that can contribute to the enhancement of the s values of the NiFe/FeMn interfaces, i.e., if the growth of the NiFe and FeMn layers are not columnar, changes in grain size could also produce modifications in the interfacial roughness.…”

“…The plasmas' ignition was done by DC process to deposit the Ni 81 Fe 19 and Fe 50 Mn 50 targets and by RF to deposit the W 90 Ti 10 target. The series were prepared to yield information about the roughness properties of each layer surface of the Si/ WTi (7 nm)/NiFe (30 nm)//FeMn (13 nm)/NiFe (10 nm)/WTi (7 nm) multilayer.…”

“…In previous works [19,20], some of us have shown the dependence of the H ex with the roughness of the lower and upper interfaces (including the atomic grading at the interface) for the NiFe/FeMn/NiFe trilayers prepared at different working pressures. We have also carried out a layer-by-layer investigation on the roughness properties of the interfaces of the Si/WTi/ NiFe/FeMn/WTi multilayer [21], where it was studied how successive layer depositions may change the roughness properties of the subsequent interfaces, and consequently the magnetism of the NiFe/FeMn exchanged-biased system deposited onto the Si/WTi substrate.…”

Instrumentation for Ferromagnetic Resonance Spectrometer

“…Since materials used for spintronics are either ferromagnetic or spin correlated, and FMR is not only employed to study their magneto static behaviors, for instances, anisotropies [1,2], exchange coupling [3,4,5,6], but also the spin dynamics; such as the damping constant [7,8,9], g factor [8,9], spin relaxation [9], etc. In this chapter a brief description about the key components and techniques of FMR will be given.…”