Disorder Induced Negative Magnetization in LaSrCoRuO6

This paper reports effect of thermally induced disorder on the magnetic properties of LaSrCoRuO6 double perovskite. While the ordered sample is antiferromagnetic, the disordered sample exhibits negative values of magnetization measured in low applied fields. Isothermal magnetization on this sample shows hysteresis due to presence of ferromagnetic interactions. Based on neutron diffraction and X-ray Absorption Fine Structure (XAFS) studies, these results have been interpreted to be due disorder in site occupancy of Co and Ru leading to octahedral distortions and formation of Ru-O-Ru ferromagnetic linkages. Below 150K these ferromagnetic Ru spins polarize the Co spins in a direction opposite to that of the applied field resulting in observed negative magnetization.