${\mathrm{BiMnTeO}}_{6}$: A multiaxis Ising antiferromagnet

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${BiMnTeO}_{6}$ : A multiaxis Ising antiferromagnet

N. Matsubara, S. Petit, C. Martin, F. Fauth, E. Suard, S. Rols, and F. Damay

Phys. Rev. B 100, 220406(R) – Published 12 December 2019

Abstract

The crystal and magnetic properties of honeycomb ${BiMnTeO}_{6}$ have been studied between 1.5 and 300 K using synchrotron x-rays and neutron-scattering experiments. Commensurate magnetic ordering is observed below $T_{N} = 10 K$ , and corresponds to a noncollinear spin arrangement, with spins tilted away from the anisotropy easy-axis set by the Jahn-Teller distortion of the ${MnO}_{6}$ octahedra. Inelastic-scattering experiments show two main nearly localized magnetic excitations, which can be well described by an exchange Hamiltonian involving weak Mn-Mn magnetic interactions and a crystal-field Hamiltonian characterizing the strong easy-axis anisotropy associated with the $d_{z 2}$ orbital ordering of ${Mn}^{3 +}$ . The crystal-field levels can be accurately calculated, taking into account a transverse molecular field imposed by the magnetic ordering of the neighboring atoms below $T_{N}$ . This makes ${BiMnTeO}_{6}$ an interesting example of a multiaxis Ising system in a self-imposed transverse magnetic field.

Received 27 July 2019
Revised 9 November 2019

DOI:https://doi.org/10.1103/PhysRevB.100.220406

Physics Subject Headings (PhySH)

Jahn-Teller effect Spin dynamics

Noncollinear magnets

Inelastic neutron scattering

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

N. Matsubara ^1,2, S. Petit², C. Martin¹, F. Fauth ³, E. Suard⁴, S. Rols⁴, and F. Damay ^2,*

¹CRISMAT, 6 Bvd. Maréchal Juin, 14050 Caen Cedex, France
²Laboratoire Léon Brillouin, CEA-CNRS UMR12, Université Paris-Saclay, 91191 Gif sur Yvette Cedex, France
³CELLS ALBA Synchrotron, E-08290 Barcelona, Spain
⁴Institut Laue-Langevin, 71 Avenue des Martyrs, 38042 Grenoble Cedex 9, France

^*Corresponding author: francoise.damay@cea.fr

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Vol. 100, Iss. 22 — 1 December 2019

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Figure 1
${BiMnTeO}_{6}$ structure viewed along $a$ (a) and in the $a b$ plane (b), showing corrugated planes separated by Bi cations, the Mn/Te order, and the $d_{z 2}$ orbitals orientation (longest axis of the ${MnO}_{6}$ octahedra, shown as thick purple lines). Bi (Mn/Te/O) atoms are symbolized as yellow (purple/gray/red) spheres. Magnetic exchange paths $J_{C}, J_{a f}, J_{f}$ , and $J_{a}$ are also shown (see text).
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Figure 2
(a) Temperature evolution of the NPD data (G4.1) between 1.5 and 12 K. (b) Corresponding temperature evolution of the Mn ordered magnetic moment (from Rietveld refinement results). The red line is a guide to the eye. (c) Rietveld refinement of the NPD pattern at 1.5 K $(R_{Bragg mag} = 7.5 %$ and global $χ^{2} = 3.6)$ (Experimental data: red open circles; calculated profile: black line; allowed Bragg reflections: vertical green marks; purple marks indicate magnetic Bragg reflections. The difference between the experimental and calculated profiles is displayed as a blue line.) (d) Magnetic structure of ${BiMnTeO}_{6} ({Mn}^{3 +}$ spins are shown as green arrows, longest Mn-O bonds as thick gray shapes). First-neighbor Mn-Mn distances in the triangular lattices are indicated.
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Figure 3
TOF INS data (IN4) of ${BiMnTeO}_{6}$ at 5 K (a) and 20 K (b) (incident wavelength 3.2 Å). No additional excitation, whether of magnetic or lattice origin, are seen up to 15 meV. (c) Constant $Q = 0.8 Å^{- 1}$ cut (4F2) at 3.6 K, showing the two modes at 1.8 and 3.1 meV. The dotted red line is calculated using Hamiltonian (1) with parameters $B_{20} = - 0.17 meV, (J_{a} + J_{C}) = 0.14 meV, (J_{a f} + | J_{f} |) = 0.08 meV$ . (d) Temperature evolution (up to 50 K) of constant $Q = 0.8 Å^{- 1}$ cuts.
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Figure 4
(a) Calculated variation with $(J_{a f} + | J_{f} |)$ of the neutron cross section of ${Mn}^{3 +}$ crystal-field transitions $[(J_{a} + J_{C}) = 0.14 meV, B_{20} = - 0.17 meV]$ . (b) Corresponding variation with $(J_{a f} + | J_{f} |)$ of the angle between the anisotropy axis (axis of longest elongation of the ${MnO}_{6}$ octahedron, set parallel to $h z)$ and the internal magnetic field $H_{loc}$ . In (a) and (b) the green dotted line corresponds to the set of parameters giving the best agreement with the experimental data. (c) Schematic drawing of $H_{loc}$ and of its projection $h x$ and $h y$ (transverse components) and $h z$ (longitudinal component). If $h x = h y = 0$ , and $h z \neq 0$ , the molecular field is purely longitudinal. (d) Calculations of the powder average INS excitation spectrum of ${BiMnTeO}_{6}$ (at 0 K), based on Hamiltonian (1), with parameters $B_{20} = - 0.17 meV, (J_{a} + J_{C}) = 0.14 meV, (J_{a f} + | J_{f} |) = 0.08 meV$ [calculations include the Mn magnetic form factor for direct comparison with Fig. 3].
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Physical Review B

covering condensed matter and materials physics

${BiMnTeO}_{6}$ : A multiaxis Ising antiferromagnet

N. Matsubara, S. Petit, C. Martin, F. Fauth, E. Suard, S. Rols, and F. Damay

Phys. Rev. B 100, 220406(R) – Published 12 December 2019

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Physical Review B

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BiMnTeO6: A multiaxis Ising antiferromagnet

N. Matsubara, S. Petit, C. Martin, F. Fauth, E. Suard, S. Rols, and F. Damay

Phys. Rev. B 100, 220406(R) – Published 12 December 2019

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${BiMnTeO}_{6}$ : A multiaxis Ising antiferromagnet