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The dependence of the ac-magnetic susceptibility of La0.85Sr0.15CoO3 on the annealing temperature used during synthesis is addressed. Such dependence has been previously attributed to compositional inhomogeneities. Nevertheless, the presence of distinct phases with different chemical compositions is excluded after explorations by several techniques. Instead it is proposed that an electronic phase separation takes place in the material, whose state is changed after charge-carrier redistributions due to the thermal history of the samples, analogously to parent manganese-based perovskites.

The magnetic response of CeFe2 single crystals was studied by direct-current magnetization and linear and nonlinear alternating-current susceptibility measurements. Several anomalies have been observed below the Curie temperature (TC=228 K). A kink near 30 K in the real component of the linear susceptibility, χ1′(T), is accompanied by a frequency dependent peak in both the linear imaginary part, χ1″(T), and the third-harmonic nonlinear susceptibility, |(3/4)χ3H02|. It is suggested that these features are related to the development of antiferromagnetic spin fluctuations of growing spatial extension, indicating an electronic instability below 80 K.

Measurements of the real (χ') part of the ac magnetic susceptibility have been performed on two polycrystalline Gd2CuO4 samples sintered at different temperatures, 850°C and 1080°C in the temperature range 10