Low-Temperature Line-Width Maximum in Yttrium Iron Garnet

Abstract

Measurements of the ferromagnetic resonance line-width maximum in single-crystal yttrium iron garnet (YIG) were previously reported by Dillon. 1 His data show that the line width increases with decreasing temperature, reaches a maximum below liquid nitrogen temperature, and decreases again to approximately the roomtemperature value at liquid helium temperatures. We have been investigating the nature of this line-width maximum at low temperatures to determine if the effect is intrinsic to ferromagnetic resonance and to determine its origin. The line widths reported in this paper are determined from the absolute absorption of the sample and the saturation magnetization vs T curve measured on single-crystal YIG. The large effects on the line width AH at room temperature due to inhomogeneous broadening by scattering from pits on the surface of a YIG sphere were evaluated previously. 2 Consequently, we measured AH vs T for a series of three spheres prepared using polishing papers having mean grit sizes of 15, 5, and 0.3 microns, respectively. These measurements were made at 9300 Mc/sec. Figure 1 shows that the ratios of maximum line widths to room temperature line widths are 2.5, 4, and 13, respectively, the larger ratios occurring for the better polished spheres. It is also clearly shown that the contribution to the line width due to surface preparation is essentially additive over the temperature range. We conclude therefore that the low-temperature line-width maximum is an intrinsic property of the material and not of the surface. Further, if perfect polishing were attained the line-width maximum would still be approximately 6 oersteds in this sample.Earlier investigations on the same samples 3 have shown a small but repeatable frequency dependence of line width at room temperature. The line width AH (full width between half maximum values) is 0.44 oersted at 3000 Mc/sec and 0.52 oersted at 9300 Mc/sec along the [111] axis. Taking these measurements over the temperature range, there are three essential features. See Fig. 2. The line width maximum at 3000 Mc/sec is reduced by 40 % in magnitude and is shifted from 40°K to 30°K. Also it is seen that the room-temperature frequency dependence of 300 FIG. 1. AH vs_ T for single-crystal spheres of YIG 0.014 to 0.017 inch in diameter. H^c oriented along the [111] axis. The labels on the curves indicate the mean grit size of the final polishing paper used to prepare the spheres. The lowest curve is Fig. 3 repeated here for comparison. 300 FIG. 2. AH vs T measured at 9300 and 3000 Mc/sec. Hfc oriented along the [111] axis. 32

Interfacial Origin of the Magnetisation Suppression of Thin Film Yttrium Iron Garnet

“…It may be that the Gd appears as impurities that could be seen, for example, in low temperature increases in the FMR linewidth 27,28 as was recently evoked as an explanation for low temperature damping 29 . In phenomena that rely on the magnon propagation length 30 , and where the YIG films are thin, then we expect the Gd-layer, which will be paramagnetic at room temperature and will gradually align antiparallel as the sample is cooled, will have to be considered.…”

Topological Frequency Conversion in Strongly Driven Quantum Systems

“…On the other hand, from Eq. (22), the pumping power depends linearly on the spin size; thus, by taking a large magnetic particle with low magnetic anisotropy (e.g., a Yttrium iron garnet sphere [50]), or NMR or electron spin resonance systems [51], one can dramatically increase the pumping power to macroscopic levels.…”

Increased low-temperature damping in yttrium iron garnet thin films

“…Researchers in the 1960's produced a rich body of literature which shows that the linewidth in bulk YIG samples can increase dramatically at low temperatures when impurity relaxation is active. 1,[22][23][24][25][26]35 The frequency and temperature dependence of ∆H in our samples can be explained well using a model of slowly-relaxing impurities. 1,26,36 The contribution to the linewidth from this mechanism is expected to have the form…”