Switchable, Anisotropic Magnon Propagation Through the Spin Cycloid in Multiferroic BiFeO₃

Magneto-electric spin orbit (MESO) devices have been proposed as an alternative to CMOS devices for computational logic and memory, providing a possible solution to greatly reduce the energy consumption of conventional computers. This is expected to be done by electric field control of the magnetic order parameter of a ferromagnet through the magnetoelectric coupling of a BiFeO₃ (BFO) multiferroic attached to a ferromagnet. Here, we demonstrate a simplified version of a MESO device where we remove the ferromagnet entirely, and directly manipulate and measure the antiferromagnetic order of the BFO with electric fields and magnon detection, respectively. Using only the antiferromagnetic BFO in the MESO device is an attractive proposal for such a spintronic memory element due to its robustness against external fields, its lack of stray fields, and its fast switching dynamics. Furthermore, the insulating nature of BFO greatly reduces Ohmic losses in the transfer of spin information via magnons, creating a pathway for realizing ultra-low power spintronics. First, we present a bi-stable state switching of the AFM order, controlled by electric fields and measured using the inverse spin Hall effect in a platinum detector wire. Second, we demonstrate anisotropic magnon propagation in BFO, where the direction of magnon transport relative to the propagation of the spin cycloid in BFO – made visible by novel nitrogen vacancy center imaging techniques – is paramount to the retention of magnon spin information. With a better understanding of the controllable magnons in BiFeO₃, we aim to demonstrate novel AFM memory devices for energy efficient spintronic applications.