Electromagnetic Phenomena In Cecu6, 3He-4He Solutions And Csnif3 At Low Temperatures

Abstract

This dissertation collates research on electromagnetic phenomena in three magnetic systems: the heavy fermion compound CeCu6 , dilute solutions of 3 He in superfluid 4 He and the quasi one-dimensional ferromagnet CsNiF3 . Evidence for magnetic order in CeCu6 at low temperatures is presented. The temperature dependence of the spin-lattice relaxation time T1 , measured using nuclear quadrupole resonance, and the AC magnetic susceptibility suggest some type of magnetic order in the low milli-Kelvin temperature regime. We report the first application of acoustic saturation nuclear quadrupole resonance (ASNQR) at temperatures in the low/sub milli-Kelvin regime. Application of pulsed ultrasound at a given NQR frequency clearly results in significant saturation of the NQR line at the same frequency while the remaining NQR transitions remain unaffected. Spin dynamics of 3 He-4 He solutions in the degenerate and non-degenerate regimes are discussed. Measurements of the longitudinal diffusion coefficient D , observation of multiple spin echoes, and the observation of a new long time-scale excitation are reported. Computer simulations of the full non-linear spin dynamics reveal the importance of domain walls and similar magnetic objects in the time evolution of the long time-scale phenomena. Results of a novel electron spin resonance transmission experiment on the quasi one-dimensional ferromagnet CsNiF3 are reported. The results are shown to be consistent with the scattering of the uniformly precessing magnetization mode by massively higher energy solitons into degenerate magnons in an energy conserving but momentum non-conserving process.