1H NMR study of static and fluctuating internal Magnetic fields in Tb(C2H5SO4)3 · 9 H2O ising ferromagnet

The pulsed NMR method is applied to an analysis of a complicated structure of inhomogeneous internal fields in a ferromagnetic crystal. Proton magnetic resonance in the Ising ferromagnet TbES at a temperature range from 1.6 K down to 35 mK is studied at frequencies of 10–35 MHz. A complicated picture of static and fluctuating internal magnetic fields in the crystal is presented. Interatomic distances are shown to have an uncertainty of the order of 0.2% due to defects in the crystal lattice. The fluctuations of internal magnetic fields produced by thermal excitation and spin-spin relaxation of Tb³⁺ ions give rise to the effective nuclear magnetic relaxation: 1/T₁₍₂₎～exp (δ/kT), where δ is the energy splitting of the lowest Tb³⁺ quasi-doublet. The rate of these fluctuations in TbES at low temperatures is approximately equal to 2×10⁷ s^?1 being independent of temperature and magnetic field.