To facilitate the recent developments of computer-aided microwave device designs and to improve polycrystalline materials, the knowledge of ferrite loss parameters (ΔH, ΔHeff, ΔHk) is required over a large range of frequencies and temperatures. As a first step, a fully automatic resonance linewidth spectrometer has been designed and set up. The ferromagnetic resonance linewidth ΔH is measured versus frequency (0.5–18 GHz), temperature (100–600 K), and power level (≤10 mW). With numeric and automatic instrumentation, our technique using a nonresonant coupling circuit has sufficient sensitivity to measure linewidths from 2 Oe up to 250 Oe with an accuracy of ±5%. The technique is based on the fact that a superimposed dc field modulation allows the differentiated uniform precession (UPR) mode peak to be extracted with a lock-in amplifier. Results on narrow linewidth garnets (Y-Ca-V-In) agree reasonably well with the predicted anisotropy and porosity contributions model. A peculiar, very low power nonlinear effect, which has been observed at levels of the order of 100 mW/cm3 as the UPR passes through the top of the magnon manifold, is discussed.
The knowledge of microwave intrinsic losses of ferrimagnetic single crystals is often obscured by the scattering process induced by surface defects. The existing data and the corresponding model dealing with this effect are far from sufficient to understand the phenomenon; in the millimetric range, the importance of the surface imperfection linewidth ΔHs is a major difficulty for obtaining the single-crystal intrinsic linewidth ΔHi from ΔH measurements. We have investigated on a pure YIG single crystal the full dependence of the surface effect as a function of the surface pit size, the frequency, and the temperature. An automatic linewidth spectrometer is used, which allows measurements in the frequency range 1–18 GHz and the temperature range −100 to 270 °C. The dc magnetic field is aligned with the 111] easy axis of the crystal. Three main conclusions are obtained: (1) For a constant sample diameter, the variation of the surface contribution ΔHs is found to be a nonlinear function of the pit size. (2) Whatever the surface roughness, ΔHs is a minimum when passing the top of the spin-wave manifold. This is similar to the behavior of the volume porosity line-broadening contribution observed in polycrystalline materials. (3) For a constant reduced internal field Ω (Ω=Hi/4πMs), the temperature dependence of ΔHs follows the temperature dependence of the saturation magnetization.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.