Evidence for ordered magnetic moments at oxygen sites in antiferromagnetic Sr${}_2$IrO${}_4$ and Sr${}_3$Ir${}_2$O${}_7$

Abstract

In this study, the magnetic ground state of iridium perovskites (Sr${}_{n+1}$Ir${}_n$O${}_{3n+1}$, where $n=1$, 2, and $\infty$) was considered using muon spin spectroscopy ($\mu$SR). When probed by muons in Sr${}_2$IrO${}_4$ and Sr${}_3$Ir${}_2$O${}_7$ ($n=1,2$), the internal field ($B_{\mathrm{loc}}$) showed clear sign of a magnetic order in two stages at transition temperatures $T_{\mathrm{N}}\simeq 230$ K and $T_{\mathrm{m}}\simeq 90$ K in Sr${}_2$IrO${}_4$ and $T_{\mathrm{N}}\simeq 280$ K and $T_{\mathrm{m}}\simeq 70$ K in Sr${}_3$Ir${}_2$O${}_7$, respectively. In contrast, no long-range magnetic order was observed in orthorhombic SrIrO${}_3$ ($n=\infty$). Based on the known magnetic structure in Sr${}_2$IrO${}_4$ and Sr${}_3$Ir${}_2$O${}_7$, we successfully identified muon sites in these compounds from the magnitude of $B_{\mathrm{loc}}$ in the first stage ($T_{\mathrm{m}}\le T\le T_{\mathrm{N}}$). Below $T_{\mathrm{m}}$, $B_{\mathrm{loc}}$ probed by a fraction of muons occupying sites near the apical oxygen of IrO${}_6$ octahedra exhibited a further increase but remained mostly unchanged for sites close to the in-plane oxygen. While such behavior cannot be explained by the alteration of the Ir spin structure, it is consistent with the selective appearance of ordered magnetic moments on the apical oxygen. The oxygen polarization was also in line with the reported magnetization anomalies in these compounds below $\sim T_{\mathrm{m}}$. A possible link between the oxygen polarization and ferroelectric (multiferroic) behavior in Sr${}_2$IrO${}_4$ was considered.

arXiv comment9 figures, 12 pages

References in corpus (13)

• Mott Insulators in the Strong Spin-Orbit Coupling Limit: From Heisenberg to a Quantum Compass and Kitaev Models
• Novel Jeff = 1/2 Mott State Induced by Relativistic Spin-Orbit Coupling in Sr2IrO4
• Bandwidth-Controlled Insulator-Metal Transition and Correlated Metallic State in 5$d$ Transition Metal Oxides Sr${}_{n+1}$Ir${}_n$O${}_{3n+1}$ ($n$=1, 2, and $\infty$)
• The magnetic and crystal structures of Sr2IrO4: A neutron diffraction study
• Dimensionality Driven Spin-Flop Transition in Layered Iridates
• Site-Dilution in quasi one-dimensional antiferromagnet Sr2(Cu1-xPdx)O3: reduction of Neel Temperature and spatial distribution of ordered moment sizes
• Weak antiferromagnetism of J_eff=1/2 band in bilayer iridate Sr3Ir2O7
• Tuning Jeff = 1/2 Insulating State via Electron Doping and Pressure in Double-Layered Iridate Sr3Ir2O7
• Measurement of the internal magnetic field in the correlated iridates Ca${}_4$IrO${}_6$, Ca${}_5$Ir${}_3$O${}_{12}$, Sr${}_3$Ir${}_2$O${}_7$ and Sr${}_2$IrO${}_4$
• Magnetic structural change of Sr2IrO4 upon Mn doping
• On the magnetic structure of Sr3Ir2O7: an x-ray resonant scattering study
• Oxygen Moment Formation and Canting in Li2CuO2
• Antiferromagnetically spin polarized oxygen observed in magneto-electric TbMn2O5

Cited by in corpus (10)

• Choreographed entangle dances: topological states of quantum matter
• The influence of electron-doping on the ground state of (Sr{1-x}La{x})2IrO4
• Crystal growth and intrinsic magnetic behavior of Sr${}_2$IrO${}_4$
• First-Principles Calculation of Spin and Orbital Contributions to Magnetically Ordered Moments in Sr${}_2$IrO${}_4$
• Thermoelectric behavior of Ruddlesden-Popper series iridates
• Magnetization density distribution of Sr${}_2$IrO${}_4$: Deviation from a local $j_{\text{eff}}=1/2$ picture
• Direct observation of oxygen polarization in Sr${}_2$IrO${}_4$ by O $K$-edge x-ray magnetic circular dichroism
• Electron doping in ${\text{Sr}}_3{\text{Ir}}_2{\text{O}}_7$: collapse of band gap and magnetic order
• Critical fluctuations in the spin-orbit Mott insulator Sr${}_3$Ir${}_2$O${}_7$
• Local electronic structure of dilute hydrogen in $\beta$-MnO${}_2$