Gippius, A. A.6; Baenitz, M.7; Okhotnikov, K. S.6; Johnsen, Simon8; Iversen, Bo Brummerstedt8; Shevelkov, A. V.6
1 Department of Chemistry, Science and Technology, Aarhus University2 Department of Chemistry - Centre for Materials Crystallography (CMC), Department of Chemistry, Science and Technology, Aarhus University3 Interdisciplinary Nanoscience Center, Science and Technology, Aarhus University4 Department of Chemistry - Centre for Energy Materials (CEM), Department of Chemistry, Science and Technology, Aarhus University5 Interdisciplinary Nanoscience Center - INANO-Kemi, Langelandsgade, Interdisciplinary Nanoscience Center, Science and Technology, Aarhus University6 Moscow State University7 Max Planck Inst Chem Phys Solids, Max Planck Society8 Department of Chemistry, Science and Technology, Aarhus University
We report on a comparative study of the narrow-band semimetals FeSb2 and its structural homologue RuSb2 by means of Sb-121,Sb-123 nuclear quadrupole (NQR) and nuclear magnetic resonance (NMR) spectroscopy. From NQR for both compounds two temperature regimes could be identified by use of (123)(1/T (1)) measurements. Above 40 K a conventional activated behavior (with Delta/k (B) a parts per thousand... 400 K for FeSb2) dominates in (123)(1/T (1)), whereas below 40 K in both systems an unconventional (123)(1/T (1)) behavior with a smooth maximum at around 10 K is observed. To analyze this behavior, we propose the presence of T-dependent in-gap states forming a narrow energy level of localized spins with S = A1/2 near the bottom of the conduction band. These states might have originated from an inherent Sb-deficiency in both compounds. This model enables us to fit the (123)(1/T (1)) data in the entire investigated temperature range (2-200 K) for FeSb2. Ab initio band structure calculations reveal more than a factor of two larger Delta value for RuSb2 as compared with FeSb2. This results in dissimilar behavior of (123)(1/T (1)) in FeSb2 and RuSb2 above 40 K evidencing the inefficiency of thermal activation of electrons over the large energy gap at T a parts per thousand currency sign 300 K in RuSb2 and dominating of quadrupole relaxation channel in RuSb2 in this temperature range caused by phonon relaxation involving two-phonon (Raman) scattering. In addition, extra wide range field-sweep NMR measurements are performed at various temperatures on FeSb2 and RuSb2. The complex broad spectra could be modeled and from the shift of the Sb-121 central transition the 3d component of the shift K (3d) (T) could be extracted.
Applied Magnetic Resonance, 2014, Vol 45, Issue 11, p. 1237-1252