Abstract
We use resonant soft X-ray diffraction to track the photo-induced dynamics of the antiferromagnetic structure in a NdNiO$_{3}$ thin film. Femtosecond laser pulses with a photon energy of 0.61 eV, resonant with electron transfer between long-bond and short-bond nickel sites, are used to excite the material and drive an ultrafast insulator-metal transition. Polarization sensitive soft X-ray diffraction, resonant to the nickel L$_{3}$-edge, then probes the evolution of the underlying magnetic spiral as a function of time delay with 80 picosecond time resolution. By modelling the azimuthal dependence of the scattered intensity for different linear X-ray polarizations, we benchmark the changes of the local magnetic moments and the spin alignment. The measured changes are consistent with a reduction of the long-bond site magnetic moments and an alignment of the spins towards a more collinear structure at early time delays.
Highlights
Rare-earth nickelates exhibit sharp metal-insulator transitions and unusual noncollinear antiferromagnetic (AFM) spin ordering at low temperatures [1], which may become interesting for device applications [2]
We have shown that the azimuthal angle dependence of time-resolved, linearly polarized resonant xray-diffraction measurements can be used to determine the spin ordering dynamics coupled to light-induced phase transformations
The excitation of a NdNiO3 thin film by 0.61-eV fs laser pulses was found to result in an abrupt reduction in (b) the scattered intensity of a magnetic superlattice reflection
Summary
Rare-earth nickelates exhibit sharp metal-insulator transitions and unusual noncollinear antiferromagnetic (AFM) spin ordering at low temperatures [1], which may become interesting for device applications [2]. Optical pulses have been shown to dynamically induce transitions between insulating and metallic phases in NdNiO3 thin films, using either light resonant with optical-phonon vibrations in the underlying substrate [21,22,23,24] or by exciting electrons into the conduction band of the nickelate film directly [25,26,27,28] In some of these studies, time-resolved resonant soft x-ray diffraction was used to probe the evolution of the magnetic order parameter across these transformations by measuring transient changes in the intensity of a superlattice reflection for a fixed incident x-ray polarization. We combine time and polarization resolved resonant soft x-ray diffraction to provide insight into the dynamical changes of the AFM structure across the light-induced phase transformation, as well as during its recovery back to the equilibrium state
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