Magnetism and hyperfine interactions in the hexagonal polymorph of delafossite CuFeO2

Abstract

The magnetic susceptibility of and hyperfine interactions in the hexagonal 2H polymorph of delafossite CuFeO2 were investigated by SQUID magnetometry and Mössbauer spectroscopy, respectively, at low temperatures. The hydrothermally synthesized 2H-CuFeO2 sample contained a 10 vol-% α-Fe2O3 impurity detected by X-ray diffraction, whose contribution to the susceptibility and hyperfine interactions were easily distinguishable from the major 2H-CuFeO2 one. Morphology and indirect optical band gap investigated by scanning electron microscopy and diffuse reflectance measurements showed well expected results for a hydrothermally synthesized delafossite sample. The magnetic susceptibility of 2H-CuFeO2 revealed a first antiferromagnetic like transitions at 16 K and a second transition at 13.5 K or 10 K depending on measurement protocol, which points towards modified exchange interactions as compared to the 3R polymorph. Complementary Mössbauer measurements revealed complicated spectral shapes at low temperatures indicating rather complex magnetic structures and magnetic relaxations above 20 K.