Anomalous hyperfine field and orbital moment of cobalt in RCo 2; R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm
59Co spin echo NMR spectra in the magnetically ordered phase of the MgCu 2 type RCo 2 compounds (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm) have been observed. For the RCo 2 with the easy direction of magnetication parallel to the <011> or <111> direction, the 59Co hyperfine fields at two magnetically inequivalent Co sites are found to be antiparallel, revealing a large anisotropy in the 59Co hyperfine field. The results are discussed in terms of a large and anisotropic orbital moment of Co. The transferred hyperfine field due to rare earth spins is estimated from well resolved satellite lines observed in Tb 1- xY xCo 2. The nuclear quadrupole splitting in the magnetically ordered phase is found to be always larger than that in the paramagnetic phase.