High frequency properties of soft metallic ferromagnetic micro- and nano-wires

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Our research consists principally of two closely related activities concerning fundamental properties of soft metallic ferromagnetic micro- and nano-wires at frequencies ranging from MHz to THz. Microwires are of considerable interest for a high frequency transport effect, called giant magnetoimpedance (GMI), which arises because the penetration of high frequency electromagnetic radiation depends upon the magnetic permeability. The behavior of real wires in this regime is very different from that predicted by the best curent models, which indicate that the effect should be even larger than what is observed. We are performing experiments and modeling the effect of material surface and bulk in both the linear and non-linear regimes, since the highest sensitivity is observed at the limit between the two. The study of high frequency properties of ferromagnetic nanowire arrays (FMNW) is developing rapidly, in part due to the possibility of their application to integrated part improved microwave devices. We have recently shown that each wire switches completely in a small field range, once it begins to reverse. Thus, below saturation the static configuration consists of two populations of wires, with up or down magnetizations. This leads to two ferromagnetic resonance (FMR) peaks, whose positions and amplitudes can be adjusted by the proper field history, and which can be maintained with zero bias. This is of great interest for microwave applications. We are particularly interested in the FMR behavior of these arrays above 50 GHz, and eventually, above 100 GHz, entering into the THz region. Of particular interest is the FMR linewidth and the origin of the damping mechanisms which determine it. At present, the intrinsic damping parameter appears to be quite small, suggesting that high frequency linewidths may not be too large.