Specific heat and thermal conductivity of ferromagnetic magnons in Yttrium Iron Garnet

Abstract

The specific heat and thermal conductivity of the insulating ferrimagnet Y${}_3$Fe${}_5$O${}_{12}$ (Yttrium Iron Garnet, YIG) single crystal were measured down to 50 mK. The ferromagnetic magnon specific heat $C$${}_m$ shows a characteristic $T^{1.5}$ dependence down to 0.77 K. Below 0.77 K, a downward deviation is observed, which is attributed to the magnetic dipole-dipole interaction with typical magnitude of 10${}^{-4}$ eV. The ferromagnetic magnon thermal conductivity ${\kappa }_m$ does not show the characteristic $T^2$ dependence below 0.8 K. To fit the ${\kappa }_m$ data, both magnetic defect scattering effect and dipole-dipole interaction are taken into account. These results complete our understanding of the thermodynamic and thermal transport properties of the low-lying ferromagnetic magnons.

5 pages, 5 figures