Magnetic properties and Mn mixed valence in and

Electron paramagnetic resonance (EPR) and static magnetic susceptibility data have been collected on a set of powder samples of and , Mn analogues of one-layer BSCCO superconductors. EPR spectra, analysed in a crystal field approach, indicate that typically 40 - 50% of ions are substituted by species in the lead-free compound and that strong deviations of the average Mn oxidation state can be introduced by reduced thermal cycles during the preparation procedure, as supported by XPS analysis. Susceptibility data, compared with the EPR response, suggest that Mn mixed valence may be a crucial factor, together with structural modulations or local anisotropy, in determining the variety of magnetic behaviours (mainly antiferromagnetic and metamagnetic) observed in these compounds.