Enhanced Spin‐Reorientation Transition and Polarization in DyFeO$_3$ Thin Films

Epitaxial strain in antiferromagnetic orthoferrite thin films is predicted to significantly enhance magnetic and polar properties with a shift of the polar response from below 4 K to room temperature and above by strengthening the rare earth-Fe interaction. In DyFeO$_3$, the Fe-spins undergo a spin reorientation transition between 40–50 K, and a magnetic field-induced ferroelectric phase transition is triggered by Dy ordering and displacement below 4 K. Here we report an increase in the spin reorientation temperature by more than 20 K in compressively strained DyFeO$_3$ films. The expected sharp spin transition is several 10 K wide, incomplete and largely suppressed, with the magnetic point group remaining at Γ4 at all temperatures. The strain-induced Dy ordering above 4 K reduces the magnetic symmetry and introduces room-temperature polar order with the electrical polarization vector oriented along [100] and polarization values of more than 3 µC/cm$^2$.