Brillouin light scattering spectra as local temperature sensors for thermal magnons and acoustic phonons

Abstract

We demonstrate the use of the micro-Brillouin light scattering (micro-BLS) technique as a local temperature sensor for magnons in a Permalloy (Py) thin film and phonons in the glass substrate.When the Py film is uniformly heated, we observe a systematic shift in the frequencies of two thermally excited perpendicular standing spin wave modes. Fitting the temperature dependent magnon spectra allows us to achieve a temperature resolution better than 2.5 K. In addition, we demonstrate that the micro-BLS spectra can be used to measure the local temperature of magnons and the relative temperature shift of phonons across a thermal gradient. Such local temperature sensors are useful for investigating spin caloritronic and thermal transport phenomena in general.

Optical detection of transverse spin-Seebeck effect in permalloy film using Sagnac interferometer microscopy

“…This is accompanied by a flow of balancing spin current that diffuses towards (away from) the hot (cold) end of FM/NM (say Pt) interface, which, if electrical detection is used results in a linear asymmetrical spatial dependence of the ISHE signal in the Pt overlayer [4]. If the Sagnac MOKE only senses the magnetization distribution in the NiFe film (represented by the T (x) profile), then according to the 'phonon-magnon drag' model the measured T (x) slope should be similar or slightly smaller than that of the phonon temperature profile T (x), similar to that inferred using the BLS method [22,23]. However this is opposite to what we observed in Figs.…”

“…In principle, optical spectroscopy such as micro-Brillouin light scattering (BLS) offers an elegant non-contact measurement method for investigating the spatial difference between the thermally activated magnon and phonon populations in a magnetic system [22,23], which is considered to be the underlying mechanism accounting for the SSE (dubbed 'phonon-magnon drag' effect) [24][25][26][27][28]. However, the present BLS resolution for sensing magnon/phonon temperature difference that results from a limited thermal gradient in the FM still cannot provide direct evidence in support of this model [22,23].…”

Temperature-dependent Brillouin light scattering spectra of magnons in yttrium iron garnet and permalloy

“…The BLS spectra are generally characterized by three parameters: frequency, linewidth, and integrated intensity (further referred to simply as intensity). Previous BLS experiments have solely used the frequency shift to determine the temperature of magnons 11,19 . In a different study, it was shown that frequency shift, linewidth, and intensity of BLS spectra of acoustic phonons in silicon all provide temperature sensing capabilities, though each probes different ranges of the acoustic phonon spectrum 16 .…”

“…The Curie temperatures of these materials are 560 K for YIG, and 550K to 870K for Py depending on the crystal structure 20,21 . BLS spectra are collected using a µBLS system, briefly described as follows 12,19,22 . A single frequency, linearly polarized 532 nm laser beam, normally incident on the sample, is focused using an objective lens (NA 0.70) to a spot size of approximately 1 µm in diameter.…”

Temperature dependence of Brillouin light scattering spectra of acoustic phonons in silicon

“…32,33 Recently, Brillouin light scattering (BLS) techniques have been used as a local temperature sensor for magnons in metallic and insulating ferromagnetic materials and for low-frequency phonons in glass. 34,35 However, the application of this thermometry method for acoustic phonons in semiconductors remains to be investigated.…”