Ru-induced spin rotation in La1.2Sr1.8Mn1.9Ru0.1O7 bilayered manganite

We have studied the magnetic properties of Ru-doped La1.2Sr1.8Mn1.9Ru0.1O7 bilayered manganite using neutron diffraction (ND) technique. The ND measurements show that the compound exhibits ferromagnetic ordering with the spins direction parallel to the c-axis. This is in sharp contrast to the parent compound where the spins are oriented along the a-b plane. The large spin-orbit coupling constant of Ru+4 ion (λ=∼900cm-1) seems to play an important role on lifting of the orbital degeneracy of the eg state by which the eg electron prefers to occupy the d3z2-r2 orbital and therefore, the spins align along the c-axis.