~(11)B Nuclear Magnetic Resonance Study of Spin Structure and Dynamics in Gadolinium Tetraboride

摘要

~(11)B nuclear magnetic resonance (NMR) measurements were performed on single crystals of GdB_(4) to investigate local electronic structure and 4f spin dynamics. The ~(11)B NMR spectrum, Knight shift, spin-lattice and spin-spin relaxation rates, 1/T_(1) and 1/T_(2), were measured down to 4 K at 8 T. The ~(11)B NMR shift and linewidth are huge and strongly temperature-dependent due to the 4f moments. In addition, both are proportional to the magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the 4f spins of Gd. Below T_(N), the single broad resonance peak of ~(11)B NMR splits into several peaks reflecting the local magnetic fields due to antiferromagnetic spin arrangements. The longitudinal and the transverse relaxation rates, 1/T_(1) and 1/T_(2), which are independent of temperature above T_(N), both decrease tremendously below T_(N) confirming the suppression of spin fluctuations.