11B NMR study of GdB4

We have performed 11B nuclear magnetic resonance (NMR) measurements on the single crystals of GdB4 to investigate local electronic structure and 4f spin dynamics. 11B NMR spectrum, Knight shift, spin-lattice and spin-spin relaxation rates, 1/T1 and 1/T2, were measured down to 4K at 8T. 11B NMR shift and linewidth are huge and strongly temperature-dependent due to the 4f moments. In addition, both are proportional to magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the 4f spins of Gd. Below TN, the single broad resonance peak of 11B NMR splits into several peaks reflecting the local magnetic fields due to antiferromagnetic spin arrangements. The spin-lattice relaxation rate, independent of temperature above TN, decreases significantly below TN confirming huge suppression of spin fluctuation