Abstract
We use high-resolution resonant inelastic x-ray scattering (RIXS) to study a thin film of NdNiO3, a compound whose unusual spin- and bond-ordered electronic ground state has been of long-standing interest. Below the magnetic ordering temperature, we observe well-defined collective magnon excitations along different high-symmetry directions in momentum space. The magnetic spectra depend strongly on the incident photon energy, which we attribute to RIXS coupling to different local electronic configurations of the expanded and compressed NiO6 octahedra in the bond-ordered state. Both the noncollinear magnetic ground state and the observed site-dependent magnon excitations are well described by a model that assumes strong competition between the antiferromagnetic superexchange and ferromagnetic double-exchange interactions. Our study provides direct insight into the magnetic dynamics and exchange interactions of the rare-earth nickelates and demonstrates that RIXS can serve as a site-selective probe of magnetism in these and other materials.Received 3 August 2017Revised 20 June 2018DOI:https://doi.org/10.1103/PhysRevX.8.031014Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAntiferromagnetismExchange interactionMagnonsSpin wavesPhysical SystemsComplex materialsStrongly correlated systemsTechniquesExact diagonalizationHeisenberg modelResonant inelastic x-ray scatteringX-ray absorption spectroscopyCondensed Matter, Materials & Applied Physics
Highlights
The spin ordering and dynamics in transition metal oxides are of long-standing interest from both fundamental and practical points of view [1,2]
Our study provides direct insight into the magnetic dynamics and exchange interactions of the rare-earth nickelates and demonstrates that RIXS can serve as a site-selective probe of magnetism in these and other materials
The RIXS experiment was performed at the ID32 beam line of the European Synchrotron Radiation Facility using the new ERIXS spectrometer [41]
Summary
The spin ordering and dynamics in transition metal oxides are of long-standing interest from both fundamental and practical points of view [1,2]. We have witnessed a surging effort in realizing a new generation of spintronic devices that may outperform the conventional electronic ones using magnetic oxides [3,4,5]. Many of these proposals are based on artificial heterostructures [6], or materials including multiple magnetic elements such as the double perovskites [7]. The NiAðBÞ sites with more ionic (covalent) Ni─O bonds host spins of different sizes with SA > SB [36] At low temperatures, they condense into a four-sublattice noncollinear antiferromagnetic (AF) state with an ordering vector Q 1⁄4 ð1=4; 1=4; 1=4Þ (in pseudocubic notation). After decades of research on the electronic phase behavior of RNiO3, these experiments can determine the magnetic exchange interactions and yield unprecedented insight into the mechanism driving the formation of the unusual noncollinear magnetic structure in this system
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