INTERPRETATION OF THE TEMPERATURE-DEPENDENCE OF MN2-FIELD ESR-SPECTRAIN THE FIRST INCOMMENSURATELY MODULATED PHASE OF BETAINE CALCIUM-CHLORIDE DIHYDRATE( HIGH)

By a combination of X-band and e-band ESR investigations it was possib le to distinguish between effects of first and second order in the cri tical behavior, which are influenced in different ways by the dynamics of the order-parameter fluctuations. The theoretical analysis is base d on a Fourier expansion of the ESR fine-structure elements in terms o f the harmonics of the incommensurate modulation. Second-order perturb ation theory for the evaluation of the ESR spectra was applied. The sp litting between thr edge singularities should show a temperature depen dence given by the superposition of two different critical contributio ns: Delta B-ES=a(T-i-T)(<(beta)over bar>)+b(T-i-T)(2 beta). The second contribution depends on the strength of the external magnetic held. T his could be clearly revealed in the comparison between Q- and X-band measurements. The influence of the Mn content c(Mn) or of the gamma-ir radiation dose c(gamma) on the splitting of the edge singularities was analyzed. [S0163-1829(98)03929-0].