NMR Study of 59Co and 11B in RECo4B4 (RE=Gd, Tb, Dy, Ho, Er and Tm)

Abstract

Pulsed NMR studies of 59 Co and 11 B have been performed in a series of antiferromagnetic RECo 4 B 4 compounds (RE=Gd, Tb, Ho, Er, Tm) in both paramagnetic and magnetically ordered states. In the paramagnetic state, NMR signals of both 59 Co and 11 B were observed only in GdCo 4 B 4 in the temperature range of 77–300 K. From the isotropic Knight shift measurement, we obtained the conduction electron spin polarization at both Co and B sites generated by the d - f exchange interaction on the rare earth site. The electron spin polarization estimated in RECo 4 B 4 is about twice as large as that in RERh 4 B 4 system. In the antiferromagnetic state, zero-field resonances of 59 Co and 11 B were observed for GdCo 4 B 4 , TbCo 4 B 4 and DyCo 4 B 4 at 1.3 K. From the hyperfine fields and NMR spectra, the spin structure is shown to be the same type as in the antiferromagnetic superconductor Ho(Rh 0.3 Ir 0.7 ) 4 B 4 .