Paramagnetic Nd sublattice and thickness-dependent ferromagnetism in Nd2NiMnO6 double perovskite thin films

We investigate ferromagnetic and insulating thin films of the $B$-site ordered double perovskite ${\mathrm{Nd}}_{2}{\mathrm{NiMnO}}_{6}$ (NNMO) grown by radio frequency off-axis magnetron sputtering. The films grow epitaxially strained on a selection of substrates and display a strain-independent and bulklike ${T}_{\text{C}}$ of $200\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at a thickness of 30 unit cells. We explore the thickness dependence of the NNMO/${\mathrm{SrTiO}}_{3}$(001) system and find ferromagnetism down to ultralow thicknesses of only 3 unit cells $(\ensuremath{\sim}1.2\phantom{\rule{4pt}{0ex}}\mathrm{nm})$. Below 10 unit cells, the magnetic properties deteriorate due to an interfacial charge transfer caused by the polar discontinuity at the NNMO/${\mathrm{SrTiO}}_{3}$ interface. A detailed x-ray magnetic circular dichroism study allows us to separate the magnetic components into a robust ferromagnetic Ni/Mn sublattice and a paramagnetic Nd sublattice.