Magnetism of Ir5+ -based double perovskites: Unraveling its nature and the influence of structure

Abstract

A combination of x-ray-diffraction, x-ray absorption, x-ray magnetic circular dichroism, macroscopic magnetization, and muon-spin relaxation measurements is used to investigate the interplay between structure (both crystallography and microstructure) and magnetism in Sr 2 YIrO 6 as a function of both chemical (Ca-doping) and physical (hydrostatic) pressure. X-ray absorption spectroscopy clearly shows that the physical pressure is more effective in modifying the structure. On the other hand, the dichroic measurements evidence a constant magnetic signal with physical pressure and strong differences with Ca-doping. Muon-spin relaxation reveals the presence of magnetic order, even when this is hidden in the magnetization data. From the combined analysis, the magnetic results are explained in terms of the presence of Ir 6+ or Ir 4+ ions in magnetic clusters, most likely located at and triggered by antisite disorder. The measurements under high physical pressure indicate that the magnetic state is independent of the crystallographic details such as Ir-O distances and Ir-O-Y angles.

Spin-glass transition in the spin–orbit-entangled Jeff = 0 Mott insulating double-perovskite ruthenate

“…A similar enhancement of magnetization has been reported in highly solid-solution double perovskite iridates Sr 2- x Ca x YIrO 6 21 . An X-ray magnetic circular dichroism (XMCD) measurement demonstrates an emergent partial charge disproportionation (PCD) of Ir 5+ → 0.5Ir 4+ + 0.5Ir 6+ due to a site-randomness 21 .…”

“…A similar enhancement of magnetization has been reported in highly solid-solution double perovskite iridates Sr 2- x Ca x YIrO 6 21 . An X-ray magnetic circular dichroism (XMCD) measurement demonstrates an emergent partial charge disproportionation (PCD) of Ir 5+ → 0.5Ir 4+ + 0.5Ir 6+ due to a site-randomness 21 . In light of this result, similar Ru 3+ /Ru 5+ magnetic defects possibly occurs in SrLaInRuO 6 and SrLaGaRuO 6 due to a similar intrinsic A-site randomness.…”

“…Both M/H data for SrLa M RuO 6 are in the rough agreement above 250 K, but below 250 K, are greatly enhanced compared to the χ calc curve. In Ir 5+ double perovskites, in which a similar J eff = 0 ground state is expected, the M/H data of Sr 2 YIrO 6 shows almost temperature-independent behavior 21 . On the other hand, a similar enhancement in low-temperature M/H data is observed in the solid solution system Sr 2- x Ca x YIrO 6 21 .…”

“…In Ir 5+ double perovskites, in which a similar J eff = 0 ground state is expected, the M/H data of Sr 2 YIrO 6 shows almost temperature-independent behavior 21 . On the other hand, a similar enhancement in low-temperature M/H data is observed in the solid solution system Sr 2- x Ca x YIrO 6 21 . Therefore, this increase in magnetization may affect randomness, of which a mechanism will be discussed later.…”

“…This situation is because the energy scale of Δ is too large; the 5 d 4 (Ir 5+ and Os 4+ ) compounds should be typically nonmagnetic. Indeed, the weak magnetic anomalies observed in some Ir 5+ double perovskites are better explained by the Ir 4+ and Ir 6+ magnetic defects rather than SOEC 14 – 21 . Therefore, a SOEC seems to be much less feasible for 5 d compounds.…”