Mapping of Spin-Wave Transport in Thulium Iron Garnet Thin Films Using Diamond Quantum Microscopy

Spin waves, collective dynamic magnetic excitations, offer crucial insights into magnetic material properties. Rare-earth iron garnets offer an ideal spin-wave (SW) platform with long propagation length, short wavelength, gigahertz frequency, and applicability to magnon spintronic platforms. Of particular interest, thulium iron garnet (TmIG) has attracted a huge interest recently due to its successful growth down to a few nanometers, observed topological Hall effect and spin orbit torque-induced switching effects. However, there is no direct spatial measurement of its SW properties. This work uses diamond nitrogen vacancy (NV) magnetometry in combination with SW electrical transmission spectroscopy to study SW transport properties in TmIG thin films. NV magnetometry allows probing spin waves at the sub-micrometer scale, seen by the amplification of the local microwave magnetic field due to the coupling of NV spin qubits with the stray magnetic field produced by the microwave-excited spin waves. By monitoring the NV spin resonances, the SW properties in TmIG thin films are measured as function of the applied magnetic field, including their amplitude, decay length (~ 50 um), and wavelength (0.8 - 2 um). These results pave the way for studying spin qubit-magnon interactions in rare-earth magnetic insulators, relevant to quantum magnonics applications.