A study of the incommmensurate phase of rubidium zinc halide by ESR

The ESR absorption spectrum of Mn2+ ions at Zn positions has been studied in the incommensurate phase of Rb₂ZnCl₄. It is known that Rb₂ZnCl₄ crystals exhibit an incommensurate phase between temperatures T_I = 303 K and T_L = 192 K.; The usefulness of ESR for study of incommensurate systems is based on the fact that the magnetic absorption spectrum varies in a way, which reflects the space variation of the incommensurate modulation. In the commensurate systems the number of absorption resonance lines in the spectrum equals the number of physically nonequivalent nuclei, or paramagnetic sites per unit cell. Since transnational lattice periodicity is lost in the incommensurate systems, the resulting spectrum consists of infinite number of nonequivalent paramagnetic sites that contribute to the resonance spectrum.; The distribution of lines strongly depends on the space dependence of the phase of the modulation. Any change in the local magnetic properties of the sites will result in some change in the spectrum. Therefore, EPR (magnetic resonance in general) is one of the most sensitive techniques to study the local nature of incommensurate modulation.; The form and the temperature dependence of ESR spectra are in good agreement with the predictions of the phase soliton theory. The parameters h₁ and h₂ determining the magnetic resonance field show, as expected, a power law as a function of the temperature. The superposition model was used to estimate the modulation amplitude of the incommensurate phase, and the principal axis of the zero-field splitting matrix D . Assuming one-dimensional modulation, the effect of the position of the Mn2+ ions on the D parameter were calculated. By modifying the x coordinate of the Mn2+ ion we have calculated the position dependency of the D parameter. The D parameter is very sensitive to the position of the Mn2+ ions. A small change in the position produces significant effect on the value of the D parameter.