Synthesis, structure, and magnetic properties of novel B-site ordered double perovskites, SrLaMReO6 (M = Mg, Mn, Co and Ni)

Abstract

Four new double perovskites, SrLaMReO₆ (M = Mg, Mn, Co, Ni) in which Re⁵⁺ (5d²) is present, were prepared via conventional solid state reactions and characterized by X-ray and neutron powder diffraction, XANES, SQUID magnetometry, and muon spin relaxation (μSR). Synchrotron X-ray and neutron diffraction experiments confirmed that all compounds crystallize in the monoclinic P2₁/n structure type, which consists of alternately corner-shared octahedra of MO₆ and ReO₆. Rietveld refinement results indicated anti-site mixing of less than 7% on the M/Re sites. Bond valence sum calculations (BVS) suggest all M and Re ions are 2+ and 5+, respectively, and for the Mn-containing phase this is also supported by XANES measurements. All of the materials are paramagnetic at room-temperature and their Curie–Weiss temperatures are positive (except for Mg) indicating net ferromagnetic interactions. No evidence for long-range magnetic order is evident in the dc magnetic susceptibility and μSR measurements for SrLaMgReO₆ to 2 K. The Mn-phase shows long-range order at T_C = 190 K and neutron diffraction revealed a ferromagnetic structure with a refined net moment of ∼3.7μ_B. Both Co- and Ni-containing phases exhibit spin glass behavior at T_G = 23 and 30 K, respectively, which is supported by neutron diffraction and a.c. susceptibility data. The structure and physical properties of these four new rhenium based ordered double perovskites are compared to the closely related “pillared perovskites”, La₅Re₃MO₁₆, the isoelectronic Os⁶⁺ (5d²) double perovskite Sr₂CoOsO₆, and the Re⁶⁺ (5d¹) double perovskites, Sr₂MReO₆, (M = Mg, Ca, Mn, Co, Ni).