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

Abstract

We investigate ferromagnetic and insulating thin films of the B-site ordered double perovskite Nd₂NiMnO₆ (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 bulk-like TC of 200K at a thickness of 30 unit cells. We explore the thickness dependence of the NNMO/SrTiO₃(001) system and find ferromagnetism down to ultralow thicknesses of only 3 unit cells (∼1.2nm). Below 10 unit cells, the magnetic properties deteriorate due to an interfacial charge transfer caused by the polar discontinuity at the NNMO/SrTiO₃ 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.