High resolution diffraction and small angle scattering neutron investigations of LaCo<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>O<Subscript>3+</Subscript> <Subscript>δ</Subscript>: effect of oxygen content

We have investigated LaCo<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>O<Subscript>3+</ Subscript> <Subscript>δ</Subscript> compounds with different oxygen content by means of magnetization, high resolution and small-angle neutron diffraction measurements. Oxygen content decrease down to stoichiometric composition leads to an essential increase of T<Subscript>C</Subscript> and magnetic moment while Co/Mn ionic ordering degree is kept almost constant. It is assumed that upon oxygen reduction Co<Superscript>3+</Superscript> ions change their valence state down to 2+ one that leads to dominating of Co<Superscript>2+</Superscript>-Mn<Superscript>4+</Superscript> ferromagnetic interactions as well as T<Subscript>C</Subscript> increase. Magnetic properties can be explained in terms of coexistence of long-range ferromagnetic order and short-range clusters with antiferromagnetic interactions prevailing. Size distribution of the mentioned short-range magnetic inhomogeneities is rather mild within the samples but it is strongly temperature dependent. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2007