11B Nuclear Magnetic Resonance Study of Spin Structures in Terbium Tetraboride

Abstract

11B nuclear magnetic resonance (NMR) measurements were performed on the single crystals of TbB4 to investigate local electronic structure and 4f spin dynamics. 11B NMR spectrum, Knight shift, spin-lattice and spin-spin relaxation rates were measured down to 4 K at 8 T. 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 Tb. 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 longitudinal and the transverse relaxation rates, 1/T1 and 1/T2, independent of temperature above TN, decreases tremendously confirming huge suppression of spin fluctuation below TN. Key words : TbB4, 11B NMR, antiferromagnetism, rare-earth tetraborides