Exchange Anisotropy in Epitaxial and Polycrystalline NiO/NiFe Bilayers

(001) oriented NiO/NiFe bilayers were grown on single crystal MgO (001) substrates by ion beam sputtering in order to determine the effect that the crystalline orientation of the NiO antiferromagnetic layer has on the magnetization curve of the NiFe ferromagnetic layer. Simple models predict no exchange anisotropy for the (001)-oriented surface, which in its bulk termination is magnetically compensated. Nonetheless exchange anisotropy is present in the epitaxial films, although it is approximately half as large as in polycrystalline films that were grown simultaneously. Experiments show that differences in exchange field and coercivity between polycrystalline and epitaxial NiFe/NiO bilayers couples arise due to variations in induced surface anisotropy and not from differences in the degree of compensation of the terminating NiO plane. Implications of these observations for models of induced exchange anisotropy in NiO/NiFe bilayer couples will be discussed.Comment: 23 pages in RevTex format, submitted to Phys Rev B

Large nonlinear magnetoimpedance in amorphous Co80.89Fe4.38Si8.69B1.52Nb4.52 fibers

Fourier analysis of the nonlinear response of the impedance signal of amorphous Co80.89Fe4.38Si8.69B1.52Nb4.52 fibers is presented. The harmonic components of the voltage signal present a strong asymmetry. A strong variation (around 1400%) of the second-harmonic signal (V-2 (f)) as a function of the applied magnetic field is observed. Nonlinear effects and the asymmetric behavior in harmonics can be associated with the anisotropies induced during the fabrication process. These results can lead to improvement of the performance of future magnetoimpedance sensors. (C) 2003 American Institute of Physics.8319910

The effect of helical magnetoelastic anisotropy on magnetoimpedance and its second harmonic component in amorphous wires

The frequency dependence of the magnetoimpedance of an amorphous magnetic wire displays a behavior that appears to be ferromagnetic resonance, at a frequency of about 900 kHz. A helical anisotropy is induced in this wire by applying a torsional strain. The second harmonic component of the magnetoimpedance signal is also investigated. The reinforcement of this component by the helical magnetoelastic anisotropy is analyzed in terms of the asymmetry in coercivity of the circumferential hysteresis loops of the wire. (C) 2003 Elsevier B.V. All rights reserved.2714170039039