Spinel CoFe2O4: a room temperature magnetic semiconductor with optical transparency†

Finding a suitable ferromagnetic transparent semiconducting material is of utmost importance for the development of advanced devices with unique functionalities. Herein, the electronic, magnetic, and optical attributes of bulk and (111) surfaces of cobalt ferrite (CFO) are comprehensively explored through rigorous first-principles calculations. Bulk CFO and (111) thin films of thickness 1-unit cell (1UC) and 2-unit cell (2UC) with Fe terminations have ferrimagnetic semiconducting behavior with band gaps of 1.82 eV (bulk), 0.64 eV (1UC) and 0.54 eV (2UC). Bulk CFO displays an in-plane magnetic anisotropy energy of −35 μeV per atom, whereas both 1UC and 2UC structures with Fe terminations exhibit −60 and −91 μeV per atom. Bulk CFO has a Curie temperature (T_C) of 843 K, and the critical temperature is suppressed in thin films. Nonetheless, we still find a Cuire temperature higher than room temperature. For instance, the calculated Curie temperature is 471 K and 582 K for 1UC and 2UC films with Fe terminations. Besides, the 1UC and 2UC thin films of CFO show optical transparency in the visible range with a transmittance of around ∼94 to 96%. These findings suggest the potential of the CFO bulk and surfaces for application in spintronic and optoelectronic devices at elevated temperatures.