Magnetic anisotropy of NaxCoO2 single crystals

Abstract

We report the magnetic properties of single crystals of NaxCoO2 (x=0.42, 0.82, and 0.87). The magnetic susceptibility measurements revealed considerable anisotropy along H∥ab and H∥c for the as-grown single crystals. It was found that an antiferromagnetic transition with a Neel temperature TN=21K occurred for the x=0.82 sample, and there was a paramagnetic phase for the x=0.87 sample over a wide temperature range from 2to300K, but the sample with x=0.42 shows a monotonic increase of χ with increasing temperature above ∼100K. In addition, the x=0.82 sample has the largest derived anisotropic g-factor ratio (gab∕gc∼1.30), whereas the sample with x=0.42 is nearly isotropic (gab∕gc∼0.96).