| Summary: | CsCoCl₃ has been of considerable interest for some time because it is an excellent realisation of a one-dimensional Ising-like antiferromagnet. Moving domain walls or 'solitons' have been observed in the one-dimensionally ordered Co²⁺chains from ∼ 75 K down to 9 K. At 9 K full three-dimensional order is formed. However, experiments on Mg doped CsCoCl₃ indicate that the Mg suppresses this transition so that it may be possible for solitons to be present below 9 K.
In this work Mössbauer spectra of CsCo₁₋x₋y⁵⁷FexMgyCl₃ (where x ∼ 1%, and y = 0.07, 0.3, 0.7, 2.6 %) in powdered form have been taken for a range of temperatures from 250 K down to 1.2 K. The spectra of these compounds taken below 21 K could be analysed in the same way as the spectra of CsCo₀.₉₉Fe₀₀₁ Cl where the fits to the spectra are consistent with the magnetic phases of pure CsCoCl₃. No evidence to indicate the presence of solitons below 9 K in Mg doped CsCoCl₃ could be found in the Mössbauer spectra; possible reasons for this are discussed. The soliton relaxation rates determined above 9 K are found to be between one and two orders of magnitude below the theoretical prediction and it is suggested that the non-interacting soliton gas model is not appropriate for CsCoCl3. It was found that the addition of the Mg lowers the temperature of the transition to the partially disordered phase, TN1, from 21.1 ± 0.3 K (no Mg) to 19.6 ± 0.3 K (2.6 at. % Mg). The soliton relaxation rates determined for CsCoCl₃ doped with 2.6 at. % Mg were found to be approximately a factor of two higher than the rates determined for the other compounds. Small differences in some of the Fe²⁺ electronic parameters were also observed for this compound.
The quadrupole splitting values obtained from the spectra taken above 21 K have been used to fit crystal field and spin-orbit parameters to the electronic Hamiltonian describing the Fe²⁺ion in CsCoCl₃. The addition of the Mg does not affect the values of the quadrupole splitting and the parameters obtained for the Fe²⁺Hamiltonian are the same as those published by Ward et al (1987 A). An orbit-lattice interaction calculation was performed to try to account for discrepancies in the quadrupole splitting values predicted for the low temperature spectra, however, the calculation does not improve the model predictions
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