Coupled Electronic and Magnetic Phase Transition in the Infinite-Layer Phase LaSrNiRuO₄

Abstract

Topochemical reduction of the ordered double perovskite LaSrNiRuO6 with CaH2 yields LaSrNiRuO4, an extended oxide phase containing infinite sheets of apex-linked, square-planar Ni(1+)O4 and Ru(2+)O4 units ordered in a checkerboard arrangement. At room temperature the localized Ni(1+) (d(9), S = (1)/2) and Ru(2+) (d(6), S = 1) centers behave paramagnetically. However, on cooling below 250 K the system undergoes a cooperative phase transition in which the nickel spins align ferromagnetically, while the ruthenium cations appear to undergo a change in spin configuration to a diamagnetic spin state. Features of the low-temperature crystal structure suggest a symmetry lowering Jahn-Teller distortion could be responsible for the observed diamagnetism of the ruthenium centers.

Ferromagnetism in the unusual low-valence layered material LaSrNiRuO 4

“…As a result, a special spin-orbital state associated with the unusual charge state could offer a remarkable property. In line with this expectation there appears a layered ferromagnetic (FM) insulator LaSrNiRuO 4 , which has an unusual low-valence Ni + /Ru 2+ state and a quite high Curie temperature of about 200 K [15].LaSrNiRuO 4 has a square planar NiO 2 -RuO 2 layer where the Ni and Ru atoms are checkerboard ordered, see fig. 1.…”

“…• at 300 K [15]. As seen below, two sets of results differ insignificantly and arrive at the same conclusions, and, therefore, our discussion will focus on the results based on the structural data measured at 5 K. Moreover, using the magnetic exchange parameters estimated from those density functional calculations, we also carried out Monte Carlo simulations for the NiRu magnetic sublattices, and the simulation details and results will be seen below.…”

“…1. This layered structure is due to a topochemical reduction and simultaneously a remarkably low valence Ni + -Ru 2+ state emerges [15]. Topochemical synthesis routes provide many opportunities to prepare novel extended oxide phases containing arrays of transition metal cations [15].…”

“…This layered structure is due to a topochemical reduction and simultaneously a remarkably low valence Ni + -Ru 2+ state emerges [15]. Topochemical synthesis routes provide many opportunities to prepare novel extended oxide phases containing arrays of transition metal cations [15]. Here, layered LaSrNiRuO 4 is striking due to the ordered Ni-Ru arrangement in the infinite sheets, the unusual low-valence Ni + -Ru 2+ state, and the quite high (a) E-mail: wuh@fudan.edu.cn T C .…”

“…2(c)) state, depending on a subtle competition between the Hund exchange and crystal field splitting. It was suggested that a spin state transition of the Ru 2+ ion from S = 1 to S = 0 is associated with the paramagnetic-ferromagnetic transition observed in LaSrNiRuO 4 at about 200 K [15].…”