Spin-lattice relaxation studies of selected hexaboride compounds

We report the results of B-11 spin-lattice relaxation studies of SrB6, EuB6 and LaB6 at low temperatures. The temperature and field dependencies of the spin-lattice relaxation rate T-1(-1) follow the expectation for a simple metal only for the case of LaB6. Although the charge carrier concentration in EuB6 is at least two orders of magnitude smaller than in LaB6, its relaxation rate at 20 K is about five orders of magnitude larger, and is attributed to fluctuations of the Eu moments. In spite of an again much smaller charge carrier density, T-1(-1) of SrB6 at 20 K is close to that of LaB6. A cross-over or phase transition phenomenon below 0.5 K previously indicated by specific heat and resistivity data, is also reflected in T-1(-1)(T) of SrB6. (C) 2000 Elsevier Science B.V. All rights reserved.