Low Temperature NMR Study of Quasi-One-Dimensional Planar Ferromagnets in a Magnetic Field

Abstract

NMR in quasi-one-dimensional Ni²⁺ salts, CsNiF₃ and TMNC is studied in an external field up to 35 kG in liq. He temperature range. The easy-plane-type (planar) anisotropy of these salts is confirmed from the measurements of the nuclear relaxation time as well as NMR shift. When H is applied in the easy plane, the spin fluctuations are strongly suppressed by a relatively low field, as evidenced by a saturated behavior of the hyperfine field and also by a rapid decrease of the transverse relaxation rate T₂⁻¹ varing as H^−3⁄2. In a high field of this configuration the spin dynamics can be well described by spin-wave excitations characteristic to the planar ferromagnets. In contrast, for H⊥easy-plane, the systems behave paramagnetically and still show one-dimensional fluctuations, giving rise to a divergent behavior of T₂⁻¹ with decreasing temperature as T⁻¹.