Low‐field non‐resonant microwave absorption in glass‐coated Co‐rich microwires

Abstract

A study of low‐field non‐resonant microwave absorption (LFA) at 9.8 GHz, on as‐cast amorphous Co‐rich CoFeBSi microwires under different measuring geometries is presented. Results confirm that LFA is associated with the magnetization processes from the unmagnetized state (HDC = 0) to the saturated condition, in many aspects similar to Giant Magnetoimpedance (GMI), and clearly different from ferromagnetic resonance (FMR). LFA signal showed large variations in its maximum–minimum separation as a function of the measuring geometry, which is interpreted in terms of the total anisotropy in the process. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Microwave Absorption in Nanostructured Spinel Ferrites

“…In most cases, LFMA exhibits a critical behavior at the total anisotropy field in the form of a maximum and a minimum, leading to a characteristic signal as shown in Fig. 21 [59]. In bulk Ni-Zn ferrite, a correlation exists between the magnetocrystalline anisotropy and the halfpeak-to-peak, measurement of LFMA.…”

On the state‐of‐the‐art in magnetic microwires and expected trends for scientific and technological studies

“…From this standpoint, contactless resonance methods such as a cavity perturbation technique provide accurate data but could be performed at certain constant frequencies whilst applying a dc or low frequency magnetic field 43–45. The frequency scan of the impedance can be deduced from S‐parameter measurements in a coaxial line placing the wire as a central conductor 46–48.…”

“…Even if the wire sample is measured using an ideally short and lossless circuit, the sample itself, together with the ground plane of the microstrip line, constitutes another transmission line, whose electrical effects are difficult to account for. The microwave methods of measuring MI have been developed by different groups and most comprehensive investigations have been reported by Raul Valenzuela's group in Mexico 45, 46.…”

“…At relatively low fields, the impedance change is associated with the magnetization process leading to magnetic saturation of the sample in the axial direction. This effect is also known as low‐field (nonresonance) microwave absorption 43, 45, 47. At such frequencies, a large change in ac permeability that could be expected near a ferromagnetic resonance frequency would require much stronger external applied fields, in the range of more than 10 kA/m and frequencies higher than 5 GHz.…”

Magnetic microwires in microwave applications

“…This low magnetic field effect is responsible for giant MI effect in magnetic wires (Panina and Mohri, 1994;Mohri et al, 1995;Knobel and Pirota, 2002;Phan and Peng, 2008;Zhukova et al, 2002) and is also known as low magnetic field absorption (Lofland et al, 1999(Lofland et al, , 2002Valenzuela et al, 2009). Therefore, the theoretical analysis suggests that strong tuning of the effective permeability m ef will be realised if the external stimuli (magnetic field or stress) cause the change in the direction of the wire magnetic moment.…”