Magnon confinement in epitaxial antiferromagnetic oxide heterostructures

Antiferromagnets provide a route to fast and non-destructive read out for spin-based information transfer. Here, we report magnon transport and its emergent anisotropic nature in BiFeO3 layers confined between ultrathin layers of the antiferromagnet LaFeO3. Due to the confined state, BiFeO3 serves as an efficient magnon transmission channel as well as a magnetoelectric knob by which to control the stack by means of an electric field. We discuss the mechanism of the anisotropic spin transport based on the interaction between the antiferromagnetic order and the electric field. This allows us to manipulate and amplify the spin transport in such a confined geometry. Furthermore, suppression of the spin cycloid in ultrathin BiFeO3 stabilizes a non-trivial antiferromagnetic state exhibiting symmetry-protected spin-split bands that provide for non-trivial sign inversion of the spin current; which is possibly a characteristic of an altermagnet. This work provides an understanding of the spin transport in complex antiferromagnetic heterostructures where ferroelectricity and altermagnetism coexist, paving the way for a new route to realize electric-field control of a novel state of magnetism.