Magnetic excitations of the hybrid multiferroic $({\mathrm{ND}}_{4}{)}_{2}{\mathrm{FeCl}}_{5}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{D}}_{2}\mathrm{O}$

Magnetic excitations of the hybrid multiferroic $({ND}_{4})_{2} {FeCl}_{5} \cdot D_{2} O$

Xiaojian Bai, Randy S. Fishman, Gabriele Sala, Daniel M. Pajerowski, V. Ovidiu Garlea, Tao Hong, Minseong Lee, Jaime A. Fernandez-Baca, Huibo Cao, and Wei Tian

Phys. Rev. B 103, 224411 – Published 9 June 2021

Abstract

We report a comprehensive inelastic neutron scattering study of the hybrid molecule-based multiferroic compound $({ND}_{4})_{2} {FeCl}_{5} \cdot D_{2} O$ in the zero-field incommensurate cycloidal phase and the high-field quasicollinear phase. The spontaneous electric polarization changes its direction concurrently with the field-induced magnetic transition, from mostly aligned with the crystallographic $a$ axis to the $c$ axis. To account for such a change in polarization direction, the underlying multiferroic mechanism was proposed to switch from the spin-current model induced via the inverse Dzyaloshinskii-Moriya interaction to the $p − d$ hybridization model. We perform a detailed analysis of the inelastic neutron data of $({ND}_{4})_{2} {FeCl}_{5} \cdot D_{2} O$ using linear spin-wave theory to quantify magnetic interaction strengths and investigate the possible impact of different multiferroic mechanisms on the magnetic couplings. Our result reveals that the spin dynamics of both multiferroic phases can be well described by a Heisenberg Hamiltonian with easy-plane anisotropy. We do not find notable differences between the optimal model parameters of the two phases. The hierarchy of exchange couplings and the balance among frustrated interactions remain the same between two phases, suggesting that magnetic interactions in $({ND}_{4})_{2} {FeCl}_{5} \cdot D_{2} O$ are much more robust than the electric polarization in response to delicate reorganizations of the electronic degrees of freedom in an applied magnetic field.

Received 19 August 2020
Revised 27 April 2021
Accepted 24 May 2021

DOI:https://doi.org/10.1103/PhysRevB.103.224411

Physics Subject Headings (PhySH)

Electric polarization Magneto-dielectric effect Molecular magnetism Spin dynamics

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Xiaojian Bai ^1,*, Randy S. Fishman², Gabriele Sala ¹, Daniel M. Pajerowski ¹, V. Ovidiu Garlea¹, Tao Hong¹, Minseong Lee ³, Jaime A. Fernandez-Baca¹, Huibo Cao ¹, and Wei Tian ^1,†

¹Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
²Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
³National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

^*baix@ornl.gov
^†wt6@ornl.gov

Article Text (Subscription Required)

Click to Expand

Supplemental Material (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 103, Iss. 22 — 1 June 2021

Reuse & Permissions

Access Options

Article Available via CHORUS

Download Accepted Manuscript

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Low-temperature crystal and magnetic structures determined by neutron diffraction study using deuterated $({ND}_{4})_{2} {FeCl}_{5} \cdot D_{2} O$ . (a) Partial crystal structure and magnetic exchange pathways of $({ND}_{4})_{2} {FeCl}_{5} \cdot D_{2} O$ below the structural transition at $T_{S} \approx 79$ K. The transition is associated with an orientational ordering of [ ${ND}_{4}]^{-}$ tetrahedra. Two symmetry-inequivalent groups of [ ${ND}_{4}]^{-}$ are rendered in gray and blue. Three dominant exchange interactions $(J_{1}, J_{2}, J_{4})$ are plotted as solid lines, and two subleading ones $(J_{3}, J_{5})$ are plotted as dashed lines. Antiferromagnetic $J_{2}$ and $J_{4}$ bonds form a buckled frustrated triangular-lattice plane (orange). The octahedrally coordinated local environment of the ${Fe}^{3 +}$ atom produces a weak easy-plane magnetic anisotropy, which coincides with the $a c$ plane and is illustrated by orange disks on one of the four ${Fe}^{3 +}$ sublattices. (b) The low-temperature magnetic structures of $({ND}_{4})_{2} {FeCl}_{5} \cdot D_{2} O$ in zero field [cycloidal, $k = (0, 0, 0.23)$ ] and high fields [quasicollinear, $k = (0, 0, 0)$ ], projected onto the $a c$ plane. The transverse cycloids of spins are stabilized by competing $J_{2}$ (orange) and $J_{4}$ (green) exchanges on the buckled triangular-lattice plane. The open and solid arrows represent spins on two parallel cycloids. Magnetic moments on sublattices 1 and 3 in the same unit cells (solid grey lines are unit cell edges) are strictly antiparallel, so the moments on sublattices 2 and 4 across neighboring unit cells are favored by the dominant antiferromagnetic $J_{1}$ (blue) couplings. The subleading interaction $J_{5}$ is omitted for clarity. A spin-flop transition leads to the canted antiferromagnetic structure when an external field ( $\approx 5$ T) is applied along $a$ at $T = 2$ K. The electric polarization switches from mostly parallel to $a$ to parallel to $c$ after the transition.
Reuse & Permissions
Figure 2
Polarized neutron scattering data of $({ND}_{4})_{2} {FeCl}_{5} \cdot D_{2} O$ measured at $T = 2$ K with incident neutron energy $E_{i} = 3.8$ meV on the HYSPEC instrument. (a) Energy-momentum slices in the spin-flip (SF) and non-spin-flip (NSF) channels with neutrons polarized along the momentum transfer ( $P_{x} ∥ c$ ) and perpendicular to the scattering plane ( $P_{z} ∥ a$ ). (b) Constant- $Q$ cuts at the incommensurate ordering wave vector. (c) Schematic plot of the scattering geometry in the polarized neutron experiment, showing the cycloidal plane (pink disk), polarization of incoming neutrons (black arrows), and scattering wave vector (yellow arrow).
Reuse & Permissions
Figure 3
Magnetic excitations of $({ND}_{4})_{2} {FeCl}_{5} \cdot D_{2} O$ measured at $T = 2$ K in $B = 0$ and 6 T applied field with incident neutron energy $E_{i} = 3.32$ meV on the CNCS instrument and a comparison with the respective best fits using linear spin-wave theory. (a) Representative energy-momentum slices in the $(0, k, l)$ plane of the zero-field data and its best-fitted model. An integration over $| Δ l | \leq 0.05$ r.l.u. ( $| Δ k | \leq 0.05$ r.l.u.) is performed for constant- $k$ (- $l$ ) cuts. (b) Momentum dependence of excitation spectra of the zero-field data and the model integrated over $\pm 0.05$ meV at selected energies. (c) and (d) Similar plots for the $B = 6$ T data and the best-fitted model. Note that the discrepancy between the data and modeling for the $l = 0.5$ r.l.u. data at 6 T can be attributed to background oversubtraction, as illustrated in Fig. S3. An integration over $| h | \leq 0.05$ r.l.u. is applied throughout all panels. The fitted linear background functions are not plotted for clarity.
Reuse & Permissions
Figure 4
A $χ_{red}^{2}$ map in the parameter space of $J_{1}$ and $J_{2}$ with all the other parameters fixed at optimal values. The star indicates the optimal fit. The numbers on the white contours label percentage increases from the minimal value of $χ_{red}^{2}$ .
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Magnetic excitations of the hybrid multiferroic $({ND}_{4})_{2} {FeCl}_{5} \cdot D_{2} O$

Xiaojian Bai, Randy S. Fishman, Gabriele Sala, Daniel M. Pajerowski, V. Ovidiu Garlea, Tao Hong, Minseong Lee, Jaime A. Fernandez-Baca, Huibo Cao, and Wei Tian

Phys. Rev. B 103, 224411 – Published 9 June 2021

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text (Subscription Required)

Supplemental Material (Subscription Required)

References (Subscription Required)

Issue

Access Options

Physical Review B

covering condensed matter and materials physics

Magnetic excitations of the hybrid multiferroic (ND4)2FeCl5·D2O

Xiaojian Bai, Randy S. Fishman, Gabriele Sala, Daniel M. Pajerowski, V. Ovidiu Garlea, Tao Hong, Minseong Lee, Jaime A. Fernandez-Baca, Huibo Cao, and Wei Tian

Phys. Rev. B 103, 224411 – Published 9 June 2021

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text (Subscription Required)

Supplemental Material (Subscription Required)

References (Subscription Required)

Issue

Access Options

Authorization Required

Other Options

Download & Share

Images

Figure 1

Figure 2

Figure 3

Figure 4

Log In

Search

Article Lookup

Paste a citation or DOI

Enter a citation

Magnetic excitations of the hybrid multiferroic $({ND}_{4})_{2} {FeCl}_{5} \cdot D_{2} O$