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

Abstract

Pulsed NMR studies of ⁵⁹Co and ¹¹B have been performed in a series of antiferromagnetic RECo₄B₄ compounds (RE=Gd, Tb, Ho, Er, Tm) in both paramagnetic and magnetically ordered states. In the paramagnetic state, NMR signals of both ⁵⁹Co and ¹¹B were observed only in GdCo₄B₄ 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 RECo₄B₄ is about twice as large as that in RERh₄B₄ system. In the antiferromagnetic state, zero-field resonances of ⁵⁹Co and ¹¹B were observed for GdCo₄B₄, TbCo₄B₄ and DyCo₄B₄ 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_0.3Ir_0.7)₄B₄.