Microwave magnetic dynamics in highly conducting magnetic nanostructures

Abstract

We performed low-noise broadband microstrip ferromagnetic resonance (FMR) measurements of the resonant modes of an array of metallic ferromagnetic nanostripes. In addition to a strong signal of the fundamental mode, we observed up to five weak-amplitude peaks in the field-resolved FMR traces, depending on the frequency. These higher-order absorption peaks have been theoretically identified as due to resonant excitation of odd and even standing spin waves across the direction of confinement in array plane (i.e., across the stripe width). The theory we developed suggests that the odd modes become excited in the spatially uniform microwave field of the FMR setup due to the large conductivity of metals. This promotes excitation of large-amplitude eddy currents in the sample by the incident microwave magnetic field and ultimately results in excitation of these modes. Following this theory, we found that the eddy current contribution is present only for patterned materials and when the microwave magnetic field is incident on one surface of sample surface, as it is in the case of a microstrip FMR. V C 2014 AIP Publishing LLC.

Microwave magnetic dynamics in ferromagnetic metallic nanostructures lacking inversion symmetry

“…This is clearly seen from Fig. 2(a2) -2(c2), where we employed the theory from [49] to produce the traces.…”

“…This procedure is the same as previously employed in [44,49]. The important peculiarity of the present geometry is the presence of two different ferromagnetic materials, potentially in exchange contact through the interface between them.…”

“…Our samples are made of highly conducting metals. Therefore, in the conditions of the stripline FMR one may expect strong non-uniformity of the microwave magnetic field over the stripe cross-section [46,49] due to the microwave shielding effect. This effect arises because the single-side incidence of the microwave magnetic field on the sample surface breaks symmetry of the microwave field geometry.…”

“…We employ an original numerical code which is a further development of the quasi-analytical approach from [44] and [49]. It is based on solution of the linearized Landau-Lifshitz-Gilbert (LLG) equation in the magnetostatic approximation.…”

“…The perfect shielding effect due to high conductivity of metals breaks the inversion symmetry. This leads to strong excitation of anti-symmetric standing spin wave modes across the confinement directions, which are the thickness [48] and the width [49] of nanoelements. The shielding is due to excitation of microwave eddy currents in the conductive materials.…”