Probing thermal magnon current via nitrogen-vacancy centers in diamond.

Currently, thermally excited magnons are being intensively investigated owing to their potential in computing devices and thermoelectric conversion technologies. We report the detection of thermal magnon current propagating in a magnetic insulator yttrium iron garnet under a temperature gradient, using electron spins associated with nitrogen-vacancy (NV) centers in diamond. By exploiting the interplay between coherent and incoherent magnons, thermal magnon current is observed via NV spins hosted in a beam-shaped bulk diamond and a nanodiamond coupled with coherent magnon in the form of modified Rabi oscillation frequencies as well as spin relaxation rates. The local probing of thermal magnon current serves as a basis for creating a new device platform hybridizing spin caloritronics and spin qubits.