Competing charge and magnetic order in the candidate centrosymmetric skyrmion host ${\mathrm{EuGa}}_{2}{\mathrm{Al}}_{2}$

Letter
Open Access

Competing charge and magnetic order in the candidate centrosymmetric skyrmion host ${EuGa}_{2} {Al}_{2}$

A. M. Vibhakar, D. D. Khalyavin, J. M. Moya, P. Manuel, F. Orlandi, S. Lei, E. Morosan, and A. Bombardi

Phys. Rev. B 108, L100404 – Published 22 September 2023

Abstract

$Eu {({Ga}_{1 - x} {Al}_{x})}_{4}$ are centrosymmetric systems that have recently been identified as candidates to stabilize topologically nontrivial magnetic phases, such as skyrmion lattices. In this Letter, we present a high-resolution resonant x-ray and neutron scattering study on ${EuGa}_{2} {Al}_{2}$ that provides new details of the complex coupling between the electronic ordering phenomena. Our results unambiguously demonstrate that the system orders to form a spin density wave with moments aligned perpendicular to the direction of the propagation vector below 19.5 K, and upon further cooling below 15 K, a cycloid with moments in the $a b$ plane, in contrast to what has been reported in the literature. We show that concomitant with the onset of the spin density wave is the suppression of the charge density wave order, indicative of a coupling between the localized $4 f$ electrons and itinerant electron density. Furthermore, we demonstrate that the charge density wave order breaks the fourfold symmetry present in the $I 4 / m m m$ crystal structure, thus declassifying these systems as square-net magnets.

Received 17 April 2023
Revised 20 July 2023
Accepted 6 September 2023

DOI:https://doi.org/10.1103/PhysRevB.108.L100404

Published 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 Society

Physics Subject Headings (PhySH)

Charge density waves Skyrmions Spin density waves Topological materials Topological phases of matter

Noncollinear magnets

Neutron diffraction Resonant elastic x-ray scattering X-ray resonant magnetic scattering

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

A. M. Vibhakar ^1,*, D. D. Khalyavin², J. M. Moya^3,4,5, P. Manuel², F. Orlandi ², S. Lei ^4,5, E. Morosan^3,4,5, and A. Bombardi ^1,6

¹Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, United Kingdom
²ISIS facility, Rutherford Appleton Laboratory-STFC, Chilton, Didcot OX11 0QX, United Kingdom
³Applied Physics Program, Smalley-Curl Institute, Rice University, Houston, Texas 77005, USA
⁴Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA
⁵Rice Center for Quantum Materials (RCQM), Rice University, Houston, Texas 77005, USA
⁶Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom

^*Corresponding author: anuradha.vibhakar@diamond.ac.uk

Article Text

Click to Expand

Supplemental Material

Click to Expand

References

Click to Expand

Issue

Vol. 108, Iss. 10 — 1 September 2023

Reuse & Permissions

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) Single unit cell of ${EuGa}_{2} {Al}_{2}$ in the $I 4 / m m m$ space group projected from (110) direction. (b) Cross section of $z = \frac{1}{4}$ and $z = \frac{3}{4}$ planes of the $I 4 / m m m {EuGa}_{2} {Al}_{2}$ unit cell projected in the $a b$ plane. $I 4 / m m m$ unit cell is shown by the solid black line, and the Eu, Ga, and Al ions are given by the gray, black, and white circles, respectively. The red arrows indicate the displacement of the Al ions that would give rise to a charge density wave structure of $F m m m$ symmetry. Reciprocal space maps of (c) the (1, $\bar{1}$ ,8) (d) (1,1,8) charge reflections between 300 K and 7 K projected in the $h k$ plane collected at two different positions on the sample. (e) RXS data collected on the (0,1, $5 + τ$ ) and ( $\bar{2}$ ,0, $8 + τ$ ) CDW reflections between 7 K and 55 K. Data were collected using incident $σ$ polarized light.
Reuse & Permissions
Figure 2
(a) Reciprocal space maps centered about the (1, $1 + β$ ,8) reflection in the $h k$ plane collected in the PM, AFM1, AFM2, and AFM3 phases. Temperature dependence of the normalized integrated intensity and the magnitude of the propagation vector of (b) ( $α$ ,0,8), (c) (0, $β$ ,8), and (d) (1,1, $8 + τ$ ) reflections. We note that $α_{1}$ and $β_{1}$ refer to the magnetic satellites found exclusively in the AFM1 phase, and $α_{3}$ and $β_{3}$ refer to the magnetic satellites found exclusively in the AFM3 phase. These data were collected using incident $σ$ polarized light.
Reuse & Permissions
Figure 3
Scattered intensity plotted as a function of azimuth collected in (a) $π σ^{'} + π π^{'}$ channels, (b) $σ π^{'}$ channel, and (c) the $CR σ + CR π$ and $CL σ + CL π$ channels for the (0, $β$ ,8) reflection at 17 K, in the AFM1 phase. Unfilled markers represent the normalized data. Lines represent the simulated azimuthal dependencies for the different magnetic structure solutions. Details of the simulations are presented in Sec. S4 of the SM.
Reuse & Permissions
Figure 4
(a) Representation of the experimentally determined AFM1 and AFM3 magnetic structures projected in the $a b$ plane for ( $0.5 \leq z \leq 1$ ). Gray arrows represent the moments on the Eu ions, and the Ga and Al ions are denoted by the dark gray and white circles, respectively. The $I 4 / m m m$ crystallographic unit cell is shown by the solid black line. Moments on Eu ions separated along $c$ are coupled ferromagnetically.
Reuse & Permissions
Figure 5
NPD data collected on WISH at ISIS on ${EuGa}_{2} {Al}_{2}$ at temperatures (a) 25 K, (b) 17 K, and (c) 1.5 K. Inset in (a) shows the RMXS data collected on (0, $β$ ,8) magnetic satellite with CR and CL incident light. Insets in (b) and (c) show the subtracted NPD data (25 K data was subtracted) giving only the magnetic reflections. The fit to the data was made with a SDW $m | | b$ at 17 K and a circular cycloid with moments in the $a b$ plane at 1.5 K. The data is given by the red circles, the fit of the data by the solid black line, and their difference as a blue line. The green tick marks are the nuclear and magnetic reflections from top to bottom of ${EuGa}_{2} {Al}_{2}$ , labeled (1), and the impurity phases, labeled (2) and (3).
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Competing charge and magnetic order in the candidate centrosymmetric skyrmion host ${EuGa}_{2} {Al}_{2}$

A. M. Vibhakar, D. D. Khalyavin, J. M. Moya, P. Manuel, F. Orlandi, S. Lei, E. Morosan, and A. Bombardi

Phys. Rev. B 108, L100404 – Published 22 September 2023

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text

Supplemental Material

References

Issue

Physical Review B

covering condensed matter and materials physics

Competing charge and magnetic order in the candidate centrosymmetric skyrmion host EuGa2Al2

A. M. Vibhakar, D. D. Khalyavin, J. M. Moya, P. Manuel, F. Orlandi, S. Lei, E. Morosan, and A. Bombardi

Phys. Rev. B 108, L100404 – Published 22 September 2023

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text

Supplemental Material

References

Issue

Authorization Required

Other Options

Download & Share

Images

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Reuse & Permissions

Log In

Search

Article Lookup

Paste a citation or DOI

Enter a citation

Competing charge and magnetic order in the candidate centrosymmetric skyrmion host ${EuGa}_{2} {Al}_{2}$