Ferromagnetism in the unusual low-valence layered material LaSrNiRuO4

Abstract

Using density functional calculations and spin-lattice Monte Carlo simulation, we study a quite strong ferromagnetism (FM) in the layered material LaSrNiRuO4 with an unusual low-valence Ni+/Ru2+ state. Our results show that the Ru2+ ion remains in the S = 1 state and does not undergo a spin state transition around room temperature. A strong intralayer FM coupling and a relatively weak interlayer FM one are demonstrated by density functional calculations, and using these exchange parameters, our Monte Carlo simulations well reproduce the measured Curie temperature of about 200 K. All these results are in line with analyses of the crystal field level diagrams and the spin-orbital states of the square planar Ni+ (S = 1/2) and Ru2+ (S = 1) ions.