Observation of Magnon Spin Transport in BiFeO₃ Thin Films

Magnon, a quanta of spin waves, can transport in magnetically ordered insulators without substantial heat dissipation. The recently demonstrated magnon-mediated spin torque through antiferromagnetic insulators is regarded as a highly efficient approach for electrical manipulation of magnetization. To control the magnon transport in antiferromagnets, a very large magnetic field is required, since antiferromagnets show immunity to external magnetic disturbance. The antiferromagnetic order can be electrically controlled in multiferroic materials via the magnetoelectric coupling between the antiferromagnetic and ferroelectric orders. Here, we report the experimental observation of magnon spin transport through multiferroic BiFeO3 thin films in SrRuO3/BiFeO3/NiFe tri-layers at room temperature. We find highly efficient magnon current transmission through BiFeO3 thin film with a thickness exceeding 80 nm by the spin pumping measurement. The magnon spin-torque efficiency in the tri-layers measured by the spin-torque ferromagnetic resonance is comparable with that in the SrRuO3/NiFe bilayer. This results suggest multiferroic BiFeO3 to be an excellent platform for investigating the antiferromagnetic magnon transport and developing magnonic devices.