MAGNETIC-STRUCTURE, PHASE-TRANSITIONS AND FEATURES OF ELECTROMAGNETIC-WAVE PROPAGATION IN LA2CUO4

The frequency-field diagram and the components or the tensor or the hi gh-frequency magnetic susceptibility are obtained for antiferromagneti c structures realized in La2CuO4 in the longitudinal magnetic field. T he coefficient of the electromagnetic wave propagation through the sam ple is calculated, and the changes in the propagation spectrum due to the switch-over of the magnetic phases are analysed thoroughly. The po lariton effects are shown to vary for different magnetic structures, a nd each of the possible scenarios of the phase switch-over is characte rized by its specific changes in the propagation spectrum. The charact er of the changes is indicative of approaching the phase transition po ints. Thus, the spectrum of the electromagnetic wave propagation is he lpful in restoring the phase diagram, finding the AFMR frequencies in different phases and restoring on their bases the constants or the spi n Hamiltonian of La2CuO4.