Résonances antiferromagnétiques de CoCl2.6H2O; polarisation, influence de la fréquence et de la température

The experimental study of the coupling between the magnetizations and the high-frequency field h allows us to observe four resonances R₁, R₂, R₃, R₄ (at increasing resonance fields) with various polarizations. At hyperfrequencies, R₁ and R₄ are elliptically polarized in a plane normal to the cristallographic plane bc; the intersection of these two planes depends of the orientation of the d.c. field H. The polarization of the lines R₂ and R₃ is linear along c. This direction is independent of the orientation of H, within the experimental errors. At radio frequencies, the elliptical polarization of RR₁ and RR₄ is reduced to linear polarization in bc along the major axis of the ellipse. The resonances R₂ and R₃ remain polarized along c. The behaviour of these four resonances is studied as a function of the temperature and the frequency. At 1.91 K and at radio frequencies, the line shape depends strongly of the frequency.