Anisotropy of magnetization and specific heat of TmTi₂Al₂₀ single crystal

The magnetization M, magnetic susceptibility M=H, and specific heat C of TmTi₂Al₂₀ single crystal have been measured in an external magnetic field along the crystalline principal directions, [001], [101], and [111], at temperatures down to 0.5 K. Antiferromagnetic transition was observed at 0.62 K in both M(T)=H and C(T) curves. The metamagnetic transitions were detected at the critical field H_c ranging from 0.12 to 0.16 T depending on the field direction. M(H) curves at 0.5 K showed a large magnetic anisotropy, revealing that the hard and easy axes of magnetization were along the [001] and [111] directions below approximately 4 T, respectively, but above the critical field, the easy axis changed to the [101] direction. The observed C(T) peaks appeared remarkably sharp below H_c, being almost independent of the field direction. The peak heights and positions in the C(T) curves were substantially decreased by a small external field. The C(T) curves above H_c, in contrast, showed anisotropic behaviors depending on the field direction. These anisotropies observed in M(T)=H, M(H), and C(T) were analyzed by taking into account the crystalline-field effect, Zeeman effect, and magnetic exchange interactions.