Optically controlled large-coercivity room-temperature thin-film magnets

Abstract

Photo-controlled room-temperature hard magnets could open new horizons for high-density information storage. For this, the material should be fabricated as device-integrable (conformal, stretchable, transparent, etc.) thin films and preferably from readily available and innocuous chemical constituents. Here we report a viable material candidate to address all these criteria. The material basis is the ferrimagnetic ε-Fe₂O₃ polymorph of trivalent iron oxide with an exceptionally high room-temperature magnetic coercivity. To bring the photo-controllability, azobenzene moieties with trans–cis isomerization tendency are embedded into this matrix as regular monomolecular layers. The strongly emerging atomic/molecular layer deposition (ALD/MLD) technique offers us a scientifically elegant yet industrially feasible tool to fabricate these superlattice thin films with nanoscale precision. We demonstrate reversible changes in both coercivity and magnetization values with alternating irradiations of the films with UV and visible light. Interestingly, the azobenzene layers not only add this switching functionality but also enhance the overall magnetic performance of the ε-Fe₂O₃ matrix.