Epitaxial growth of antiferromagnetic α-Fe₂O₃ thin films with Morin transition

Hematite (α-Fe₂O₃) is a promising material for antiferromagnetic spintronics due to its unique properties, including the Morin transition, a phase change from easy-plane to easy-axis near 260 K, and the Dzyaloshinskii-Moriya (DM) interaction along the c-axis. While hematite thin films are essential for practical applications, their Morin transition temperatures vary widely, ranging from near zero to room temperature. Furthermore, the variation of DM interaction strength in these films remains unclear. Here, we epitaxially grow high-quality α-Fe₂O₃ films on Al₂O₃ (0001) substrates using pulsed laser deposition (PLD), with real-time monitoring by reflection high-energy electron diffraction (RHEED). High-resolution X-ray diffraction (HRXRD) is employed to assess strain in films of varying thicknesses. The Morin transition is further investigated using spin Hall magnetoresistance (SMR) in α-Fe₂O₃/Pt heterostructures. Temperature-dependent SMR measurements reveal the Morin temperature (T_M) of thin films exceeding a critical thickness, correlating to strain. Additionally, anisotropic suppression of T_M by magnetic fields parallel and perpendicular to the DM vector allows us to determine the DM interaction strength in the thin films. These findings provide valuable insights into the role of the DM interaction in antiferromagnetic spin configurations and offer a promising approach for studying these materials in thin films and nanodevices.