  Heavy metal (HM)/magnet bilayers host many magnetoresistances (MR) and spin
caloritronic effects. Here we show that the spin Peltier effect and
electron-phonon scattering produce much larger unidirectional MR of an HM on a
magnetic insulator than existing theories that neglect the interplay between MR
and spin caloritronic effects. By accounting for local nonequilibrium in both
the magnon chemical potential and temperature, our analytical model attributes
the observed frequency dependence of the spin Peltier MR and the spin Seebeck
effect to the reduction of the thermal penetration depth, which approaches the
1 micron scale magnon spin diffusion length at high frequencies.
