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

我们的研究主要包括两个密切相关的活动，涉及从兆赫到太赫兹频率范围内的软金属铁磁微线和纳米线的基本特性。由于高频电磁辐射的穿透取决于磁导率，因此微线对高频传输效应（称为巨磁阻抗（GMI））具有相当大的兴趣。在这种情况下，真实电线的行为与目前最好的电流模型所预测的非常不同，这表明这种影响应该比观察到的还要大。我们正在进行实验并模拟材料表面和体积在线性和非线性两种情况下的影响，因为在两者之间的极限处观察到最高的灵敏度。铁磁纳米线阵列（FMNW）高频特性的研究正在迅速发展，部分原因是它有可能应用于集成部分改进的微波器件。我们最近已经证明，一旦每根导线开始反转，它就会在一个小的磁场范围内完全切换。因此，在饱和状态下，静态结构由两组具有向上或向下磁化的导线组成。这导致两个铁磁共振（FMR）峰，其位置和振幅可以通过适当的场历史来调整，并且可以在零偏置下保持。这对微波应用具有重要意义。我们对这些阵列在50 GHz以上的FMR行为特别感兴趣，最终，在100 GHz以上，进入太赫兹区域。特别令人感兴趣的是FMR线宽和决定它的阻尼机构的起源。目前，本征阻尼参数似乎很小，这表明高频线宽可能不会太大。

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. Finally, I continue to investigate the multi-excitation entropy (MEE) effects which appear in kinetics when energy barriers are far larger than the energies of excitations, for example when barriers are on the order of 1 eV, whereas phonon energies are tens of meV. Examples are found in many fields of science and engineering.