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

In the field of spin caloritronics, knowledge of the magnon temperature is crucial. We investigate the temperature sensing capabilities of Brillouin light scattering (BLS), a technique which is commonly used in studying magnons. The magnon BLS spectra are characterized by three parameters: peak frequency, linewidth, and integrated intensity, each of which can be used for temperature sensing. The BLS spectra of magnons in both an insulator (yttrium iron garnet or YIG) and a metal (permalloy $\mathrm{N}{\mathrm{i}}_{80}\mathrm{F}{\mathrm{e}}_{20}$ or Py) are measured at different temperatures as the sample is uniformly heated. Unexpectedly, we find the temperature dependence of the BLS integrated intensity is opposite between YIG and Py. The mechanisms contributing to the temperature dependence of the three BLS spectra parameters are discussed and the temperature precision of each parameter is determined.

Figure 1

BLS spectra of (a) YIG and (b) Py with increasing stage temperature. Black circles are the raw data points and the red curves are Lorentzian fits.

Figure 2

BLS frequency and full width half maximum (FWHM) linewidth for (a) and (b) YIG and (c) and (d) Py. The frequency shifts in (a) and (c) decrease with increased stage temperature, following the magnetization dependence included in the respective magnon dispersion relations. The linewidths in (b) and (d) increase with increasing temperature as predicted by considering magnon scattering processes.

Figure 3

The BLS intensity for (a) YIG decreases with increasing temperature and for (c) Py increases with increasing temperature. The normalized Bose-Einstein distribution and normalized, magnetization corrected BLS intensity for (b) YIG and (d) Py. The Bose-Einstein distribution is found from the respective magnon frequencies and normalized by the value at 300 K. The corrected BLS intensity is found by dividing BLS intensity by the magnetization, which is calculated from the frequency shift and magnon dispersion relations. The corrected intensity is then normalized by the value at 300 K.