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.