Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                

Electronic and magnetic properties of iron hydride under pressure: An experimental and computational study using x-ray absorption spectroscopy and x-ray magnetic circular dichroism at the Fe K edge

Nadejda Bouldi, Philippe Sainctavit, Amélie Juhin, Lucie Nataf, and François Baudelet
Phys. Rev. B 98, 064430 – Published 31 August 2018
PDFHTMLExport Citation
Abstract
Authors
Article Text
  • INTRODUCTION
  • METHODOLOGY
  • RESULTS AND DISCUSSION
  • CONCLUSION
  • ACKNOWLEDGMENTS
    • References

    Abstract

    The application of a 3.5 GPa pressure on Fe in a H2 environment leads to the formation of iron hydride FeH. Using a combination of high pressure x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at the Fe K edge, we have investigated the modification of electronic and magnetic properties induced (i) by the transition from bcc-Fe to dhcp (double hexagonal)-FeH under pressure and (ii) by the compression of FeH up to 28 GPa. XAS and XMCD spectra under pressure have been computed in bcc-Fe and dhcp-FeH within a monoelectronic framework. Our approach is based on a semirelativistic density-functional theory (DFT) calculation of the electron density in the presence of a core hole using plane waves and pseudopotentials. Our method has been successful to reproduce the experimental spectra and to interpret the magnetic and electronic structure of FeH. In addition, we have identified a transition around 28 GPa, which is a purely magnetic transition from a ferromagnetic state to a paramagnetic state.

    • Figure
    • Figure
    • Figure
    • Figure
    • Figure
    • Figure
    • Figure
    1 More
    • Received 28 June 2018

    DOI:https://doi.org/10.1103/PhysRevB.98.064430

    ©2018 American Physical Society

    Physics Subject Headings (PhySH)

    1. Physical Systems
    HydridesTransition metals
    1. Techniques
    Density functional theoryX-ray absorption near-edge spectroscopyX-ray magnetic circular dichroism
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Nadejda Bouldi1,2,*, Philippe Sainctavit1, Amélie Juhin1, Lucie Nataf2, and François Baudelet2

    • 1IMPMC, UMR7590, CNRS, Sorbonne université, IRD, MNHN, 4 place Jussieu, 75005 Paris, France
    • 2Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, 91192 Gif-sur-Yvette, France

    • *n.bouldi@thphys.uni-heidelberg.de, presently at the Institute for Theoretical Physics, Heidelberg University, Philosophenweg 19, 69120 Heidelberg, Germany.

    Article Text (Subscription Required)

    Click to Expand

    References (Subscription Required)

    Click to Expand
    Issue

    Vol. 98, Iss. 6 — 1 August 2018

    Reuse & Permissions
    Access Options
    Author publication services for translation and copyediting assistance advertisement

    Authorization Required

    Log In
    Other Options
    ×

    Images

    • Figure 1
      Figure 1

      Crystal structure of dhcp-FeH [25]. Iron atoms are shown in two different colors to emphasize the fact that they occupy nonequivalent sites. Letters A, B, and C are the usual notations for close-packed layers in compact structures. The atomic coordinates in the conventional unit cell (a, b, c) and the site symmetries are given in the table. If H atoms were positioned in the middle or the interlayer, zH=0.875. The experimental [25] value of zH is 0.882, while in the present study zH was determined to 0.880 from atomic relaxation. The arrows represent the direction of their displacement with respect to the middle of the interlayer.

      Reuse & Permissions
    • Figure 2
      Figure 2

      Left: Experimental XAS and XMCD spectra at the Fe K edge of a Fe foil under H2 atmosphere before (blue/dark gray solid), during (blue/gray dashed), and after (green/light gray solid) the pressure induced transition. Right: Calculated XAS and XMCD spectra at the Fe K edge in bcc-Fe (blue/dark gray solid) and dhcp-FeH (green/light gray solid). The dashed lines represent the average of the spectra for Fe and FeH. The experimental XMCD spectra were not corrected for the rate of circular polarization of the light Pc≈0.7.

      Reuse & Permissions
    • Figure 3
      Figure 3

      Calculated contributions of the two crystallographic sites to the XAS and XMCD spectra at the K edge of Fe in dhcp-FeH (sum of the three terms D-D, Q-Q, and D-SP with the absorbing atom in one site or the other). Inset: Detail of the three terms of the cross section in the XMCD of each site.

      Reuse & Permissions
    • Figure 4
      Figure 4

      Calculated contributions of both crystallographic sites to the XAS and XMCD spectra at the K edge of Fe in dhcp-Fe (solid lines) and dhcp-FeH (dashed lines) in the absence of core hole. In light gray, XAS and XMCD spectra in the absence of core hole in bcc-Fe.

      Reuse & Permissions
    • Figure 5
      Figure 5

      Left: Difference between the electron density calculated for dhcp-FeH and dhcp-Fe in the [110] plane which contains both types of Fe atoms and H atoms. Only a portion of the cell is represented. Right: Isosurface Δρ=−0.03 on the same portion of the cell. For this calculation, H atoms were positioned at the middle of the interlayer (zH=0.875).

      Reuse & Permissions
    • Figure 6
      Figure 6

      Experimental XAS and XMCD spectra for FeH for several values of increasing pressure (the experimental XMCD spectra were not corrected for the circular polarization rate of the light Pc≈0.7).

      Reuse & Permissions
    • Figure 7
      Figure 7

      Calculated total energy as a function of the volume of the dhcp-FeH cell. Red squares correspond to nonmagnetic (NM) calculations and black circles to spin-polarized calculations that converged into a ferromagnetic (FM) structure. Both curves are fitted with Murnaghan equation of state [36]. The fitted parameters are displayed in the table. The arrows indicate the pressure corresponding to the volume at their abscissa.

      Reuse & Permissions
    • Figure 8
      Figure 8

      Calculated XAS and XMCD spectra without core hole at the Fe K edge in FeH at several pressures. The calculation for 28 GPa is not spin polarized so that no XMCD can be computed.

      Reuse & Permissions
    ×

    Sign up to receive regular email alerts from Physical Review B

    Log In

    Cancel
    ×

    Search

    Article Lookup

    Paste a citation or DOI
    Enter a citation
    ×