Magnetic resonance in molybdenum spinel-like compounds

Measurements of the magnetic resonance linewidth ΔH of molybdenum spinels are reported for both paramagnetic and ferromagnetic phases, with particular attention to the region near critical temperature. The magnetic resonance spectra have been measured in the temperature range from 10 K to 300 K with a standard X-band ESR spectrometer. It was shown that the characteristic temperature changes of ΔH could be due to the influence of fast relaxing ions. For «pure» molybdenum spinels it can be qualitatively described in the frame of existing theories. The substitution of these spinels by nonmagnetic atoms (C, Si, Ge) significantly influences its critical behaviour, and the origin of this effect is not yet clear Mesures de RPE entre 10 et 300 K. Etude particuliere des largeurs de raie ΔH autour de la transition para-ferromagnetique. Les variations thermiques de ΔH s'expliquent par la presence d'ions a relaxation rapide. Pour les spinelles purs, elle s'explique qualitativement dans le cadre des theories actuelles. La substitution de ces spinelles par des ions non magnetiques (C, Si, Ge) modifie le comportement critique