SPIN–LATTICE RELAXATION TIME OF Fe3+ ION

The spin–lattice relaxation time T1 of Fe3+ ions in iron–rubidium alum [RbAl(SO4)2∙12H2O], in rutile [TiO2], and in potassium cobalticyanide [K3CO(CN)6] has been measured in the temperature range 1.6 °K to 4.2 °K at a frequency of 9400 Mc by the pulse saturation technique. For Fe3+ in rubidium alum, it is found that for crystals having a nominal concentration of 1% and lower the variation of relaxation time with temperature is of the form [Formula: see text]; for higher concentrations the variation is of the form [Formula: see text]. Cross-relaxation effects are noticed for higher concentrations at all settings of crystal orientations. For Fe3+ in rutile on the average, the relaxation time is approximately inversely proportional to temperature, thus indicating the presence of a direct process. There is no significant change in the relaxation time, when the angle of the applied magnetic field with the crystal axis is varied. For Fe3+in K3Co(CN)6, above 2.8 °K, it is found that the relaxation time is proportional to T−8; this is consistent with a two-phonon interaction process (Raman). It is not believed that at the lowest temperature used in this experiment relaxation is taking place through a single-phonon process (direct).