Crystal field excitations in the ferromagnetic Kondo lattice: YbNiSn

We report our results of inelastic neutron scattering, thermoelectric power and magnetoresistance studies on the ferromagnetic Kondo lattice compound YbNiSn with T_c = 5.6 K. Inelastic neutron scattering studies on YbNiSn show two well-defined crystal field excitations at 12.2 and 18.1 meV and a quasi-elastic excitation centered at zero energy. A calculation of crystal field potential on the basis of a superposition model has been given. The thermoelectric power exhibits a broad minimum at 100 K, a maximum at 17 K, and a sharp peak at 7.5 K, followed by a sign change from negative to positive below 5 K. This behaviour of thermoelectric power could be explained on the basis of crystal field and Kondo interactions. At 1.5 K, magnetoresistance is positive in low field limits and shows a crossover to a negative sign at 3.7 T field. The negative magnetoresistance becomes as large as -66% just above T_c. The present studies show that the crystal fields, Kondo and interactions between 4f spins are important for the low-temperature properties of YbNiSn.