The temperature dependence of the ferromagnetic and paramagnetic resonance spectra in thin yttrium‐iron‐garnet films

摘要

The ferromagnetic resonance (FMR) spectra of an yttrium‐iron‐garnet (YIG) film were studied from room temperature to 120 K aboveTC(TC= 553 K). The spectra were measured for a magnetic field parallel to the film as well as perpendicular to it. In the ferromagnetic phase the FMR lines represent the magnetostatic modes whose field positions and spacing are determined by the magnetization of the sample. When anisotropy terms are added to the theoretical expressions for magnetostatic waves of Damon and van de Vaart J. Appl. Phys.36, 3453 (1965) for the perpendicular orientation and of Damon and Eshbach J. Phys. Chem. Solids19, 308 (1961) for the parallel one, a good agreement is obtained between the experimental results and theory. Magnetization values extracted from the FMR spectra are also in good agreement with the published magnetization data for YIG, obtained by a vibrating sample magnetometer. At temperatures higher than 413 K the normalized cubic anisotropyK1/Mis found to be practically temperature independent, in contrast with previous studies on YIG spheres which conclude thatK1/M→ 0 when approachingTC. In the paramagnetic phase we observe an anisotropy in the resonance fields due to the sample shape and the induced magnetization. The linewidths Dgr;Hhave also been measured and the product Dgr;H− Dgr;H(TC) ×Tis found to be practically linearly dependent onT−TCin a wide range of temperatures. Dgr;H(TC) is the linewidth atTC. This result is in good agreement with recent experimental studies of paramagnetic YIG linewidths and in fair agreement with Huber’s zero‐field theory of paramagnetic linewidths nearTCof non‐Heisenberg ferromagnets, where the ‘‘critical speeding‐up’’ effect is absent J. Phys. Chem. Solids36, 723 (1975).