WEAK FERROMAGNETISM AND MAGNETIC-INTERACTIONS IN LA2NIO4

Experimental evidence of weak ferromagnetic behaviour in the low-temperature tetragonal phase of stoichiometric La2NiO4 is given from both isothermal magnetization and magnetic susceptibility studies. A clear anomaly is observed in the magnetic susceptibility around the first-order structural phase transition at T(cl) congruent-to 80 K. The symmetric and antisymmetric exchange interactions in La2NiO4 are evaluated within the scope of the mean-field approximation and compared to those reported in La2CuO4. In spite of the strong similarities in the overall magnetic behaviour of La2NiO4 and La2CuO4 oxides, severe quantitative differences exist in the magnetic interactions, which lead to a strong reduction in the two-dimensional character in La2NiO4. It is suggested that this different magnetic behaviour may be related to the absence of superconducting behaviour in the Ni oxides.