L'interaction magntique dans les structures de K2NiF4

aucun ordre magnétique n’a été trouvé par diffraction neutronique du moins jusqu’aux températures de l’hydrogène liquide. Des résultats préliminaires de Cs2MnCl4 sont présentés. Abstract. 2014 In the tetragonal layer structure K2NiF4, strong magnetic interactions between atoms belonging to the same plane are present, while the interaction between two layers is much weaker. Neutron diffraction work revealed an antiferromagnetic interaction in the planes, the direction of the moments being that of the c-axis. The compounds La0,5Sr1,5MnO4 and La2NiO4 have the same crystal structure. At low tempe- ratures their magnetic susceptibility also deviates from the Curie-Weiss behaviour. Nevertheless no magnetic long range order has been found with neutron diffraction, at least at temperatures down to that of liquid hydrogen. Preliminary results on Cs2MnCl4 are presented.