  A key challenge in antiferromagnetic spintronics is the control of spin
configuration on nanometer scales applicable to solid-state technologies.
Bismuth ferrite (BiFeO3) is a multiferroic material that exhibits both
ferroelectricity and canted antiferromagnetism at room temperature, making it a
unique candidate in the development of electric-field controllable magnetic
devices. The magnetic moments in BiFeO3 are arranged into a spin cycloid,
resulting in unique magnetic properties which are tied to the ferroelectric
order. Previous understanding of this coupling has relied on average, mesoscale
measurements to infer behavior. Using nitrogen vacancy-based diamond
magnetometry, we show that the spin cycloid can be deterministically controlled
with an electric field. The energy landscape of the cycloid is shaped by both
the ferroelectric degree of freedom and strain-induced anisotropy, restricting
the magnetization changes to specific ferroelectric switching events. This
study provides understanding of the antiferromagnetic texture in BiFeO3 and
paves new avenues for designing magnetic textures and spintronic devices.
