Dynamic ferromagnetic resonance (FMR, X-band 9.8 GHz) and static first-order reversal curve (FORC) techniques are combined to study the intrinsic exchange-bias distribution via measurements of in-plane angular variation in (FeNi/IrMn) n multilayers. The angular dependence of the exchange bias field was qualitatively and quantitatively investigated using both methods, which are sensitive to different couplings between the ferromagnetic layers. We have used the analysis of the angular dependence of first-order reversal curve (AFORC) data, extracted from FORC curves measured from up to in steps. In addition, its counterpart angular dependence of FMR (AFMR) measurements were carried out and correlated with the AFORC results. The AFORC proved to be useful for simultaneously studying the magnetization reversal processes and magnetic interactions between the layers of the (FeNi/IrMn) n . These interactions are related to the structure and interfaces in the (FeNi/IrMn), and the results obtained by AFMR and AFORC are contrasted with a modified theoretical model for domain-wall formation.
22 December 2012 in Journal of Superconductivity and Novel Magnetism
The magnetic properties of radially oriented Co, Ni, and CoNi alloy nanowires synthesized by pulsed electrodeposition into porous alumina structures are measured and compared with those of similar nanowires grown in a planar geometry. The alloy composition affects the anisotropy axis direction, which is determined by the balance between the magnetocrystalline and shape anisotropies, lying transverse to the nanowires for Co samples and along the nanowire axis for Ni. Monte Carlo simulations were performed to model the magnetic hysteresis of the radially oriented and planar geometry nanowires using an approach based on the conical distribution of anisotropies. The model provides an excellent fit compared with experimental hysteresis loops.
The dependence of the asymmetric magnetoimpedance (MI) response on the directions of both the magnetic field and the exchange bias is studied for an multilayer system. The antiferromagnetic (AFM) layers create an exchange bias that shifts both the hysteresis loop and the MI response of ; the strength of this coupling depends on the thicknesses of both the ferromagnetic layer and the AFM layer. Tuning the exchange-bias angle and the applied-magnetic-field direction provides a practical method to control the symmetry and the magnitude of the MI response. The observed asymmetric response can be attributed to the coexistence of two anisotropies, the induced exchange-bias anisotropy and the magnetocrystalline anisotropy. Both are distinct components of the exchange-coupled Stoner-Wohlfarth energy density that forms a basis for simulations within the conventional Landau-Lifshitz-Gilbert framework. The model reproduces the main features of the experimental results, providing a deeper understanding of the effect of the anisotropy components on the MI characteristic curve and ratio. The results can be used for the development of an asymmetric MI exchange-biased thin-film element in an autobiased linear-magnetic-field sensor.