Magnetization and magnetic anisotropy of R₂Co₁₄B and Nd₂(Fe_1−xCo_x)₁₄B measured on single crystals

Magnetization and anisotropy field of R2Co14B with R being La, Nd, and Gd and of Nd2(Fe1−xCox)14B have been measured on single-crystal specimens. The cobalt sublattice has a planar anisotropy: K1=−1.30 MJ/m3 at 4.2 K for La2Co14B with the [110] direction being the room-temperature easy direction of magnetization. The rare-earth ions in R2Co14B experience a smaller exchange field than in R2Fe14B, which results in a rapid reduction of the rare-earth sublattice magnetization and anisotropy with increasing temperature. Because of the planar anisotropy of cobalt and the weaker R-Co interactions than R-Fe, the anisotropy field of Nd2(Fe1−xCox)14B turns out to be almost independent of the cobalt concentration in a temperature range between 300 and 500 K.