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

Abstract

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