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First-order valence transition: Neutron diffraction, inelastic neutron scattering, and x-ray absorption investigations on the double perovskite Ba2PrRu0.9Ir0.1O6

DOI: 10.1103/PhysRevB.99.184440 DOI Help

Authors: J. Sannigrahi (ISIS Facility) , D. T. Adroja (ISIS Facility; University of Johannesburg) , C. Ritter (Institut Laue Langevin) , W. Kockelmann (ISIS Facility) , A. D. Hillier (ISIS Facility) , K. S. Knight (ISIS Facility) , A. T. Boothroyd (University of Oxford) , M. Wakeshima (Hokkaido University School of Science) , Y. Hinatsu (Hokkaido University School of Science) , J. F. W. Mosselmans (Diamond Light Source) , S. Ramos (Diamond Light Source; University of Kent)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review B , VOL 99

State: Published (Approved)
Published: May 2019
Diamond Proposal Number(s): 63810

Abstract: Bulk studies have revealed a first-order valence phase transition in Ba 2 PrRu 1 − x Ir x O 6 ( 0.10 ≤ x ≤ 0.25 ), which is absent in the parent compounds with x = 0 ( Pr 3 + ) and x = 1 ( Pr 4 + ), which exhibit antiferromagnetic order with transition temperatures T N = 120 and 72 K, respectively. In the present study, we have used magnetization, heat capacity, neutron diffraction, inelastic neutron scattering, and x-ray absorption measurements to investigate the nature of the Pr ion in x = 0.1 . The magnetic susceptibility and heat capacity of x = 0.1 show a clear sign of the first-order valence phase transition below 175 K, where the Pr valence changes from 3+ to 4+. Neutron diffraction analysis reveals that x = 0.1 crystallizes in a monoclinic structure with space group P 2 1 / n at 300 K, but below 175 K two phases coexist, the monoclinic having the Pr ion in a 3+ valence state and a cubic one ( F m ¯ 3 m ) having the Pr ion in a 4+ valence state. Clear evidence of an antiferromagnetic ordering of the Pr and Ru moments is found in the monoclinic phase of the x = 0.1 compound below 110 K in the neutron diffraction measurements. Meanwhile, the cubic phase remains paramagnetic down to 2 K, a temperature below which heat capacity and susceptibility measurements reveal a ferromagnetic ordering. High energy inelastic neutron scattering data reveal well-defined high-energy magnetic excitations near 264 meV at temperatures below the valence transition. Low energy INS data show a broad magnetic excitation centered at 50 meV above the valence transition, but four well-defined magnetic excitations at 7 K. The high energy excitations are assigned to the Pr 4 + ions in the cubic phase and the low energy excitations to the Pr 3 + ions in the monoclinic phase. Further direct evidence of the Pr valence transition has been obtained from the x-ray absorption spectroscopy. The results on the x = 0.1 compound are compared with those for x = 0 and 1.

Journal Keywords: Magnetism; Heavy-fermion systems; Inelastic neutron scattering

Diamond Keywords: Ferromagnetism; Antiferromagnetism

Subject Areas: Materials, Physics

Instruments: B18-Core EXAFS

Added On: 15/08/2019 14:30

Discipline Tags:

Materials Science Quantum Materials Physics Hard condensed matter - structures Magnetism

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Extended X-ray Absorption Fine Structure (EXAFS)