  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.
