Antiferromagnetic iron-based magnetoelectric compounds

DOI: 10.1103/PhysRevB.107.144432

Authors: S. W. Lovesey (ISIS Facility; Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review B , VOL 107

State: Published (Approved)
Published: April 2023

Abstract: The Landau free energy of a compound that benefits from a linear coupling of an electric field and a magnetic field includes a product of the two fields, one polar and time even and one axial and time odd. Evidently, the coefficient of the product of fields is unchanged by a simultaneous change in the directions of space and time, a symmetry operation labeled anti-inversion. Invariance with respect to anti-inversion is the defining symmetry of the linear magnetoelectric (ME) effect included in 58 of 122 magnetic crystal classes, 19 of which prohibit higher-order (nonlinear) contributions to the free energy. In ME compounds, expectation values of some atomic magnetic tensors are invariant with respect to anti-inversion. An invariance shared by the Dirac monopole (an element of charge allowed in Maxwell's equations that has not been observed) and a Zel'dovich anapole, is also known as a Dirac dipole. From the science of materials perspective, it has been established that Dirac multipoles contribute to the diffraction of x rays and neutrons. We identify Dirac monopoles in bulk magnetic properties of iron tellurate ( Fe 2 Te O 6 ) and a spin ladder ( Sr Fe 2 S 2 O ). They are visible in the diffraction of light using an iron electric dipole–magnetic dipole absorption event. Both cited compounds present a simple antiferromagnetic configuration of axial dipoles, and their different magnetic crystal classes allow a linear ME effect. However, the Kerr effect is symmetry allowed in the spin ladder and forbidden in iron tellurate. Anapoles are forbidden in iron tellurate and allowed in the spin ladder compound, a difference evident in diffraction patterns fully informed by symmetry. More generally, we identify a raft of Dirac multipoles, and axial multipoles beyond dipoles, visible in future experiments using standard techniques with beams of neutrons or x rays tuned in energy to an iron atomic resonance. ME invariance imposes a phase relationship between nuclear (charge) and magnetic contributions to neutron (x-ray) diffraction amplitudes. In consequence, intensities of Bragg spots in an x-ray pattern do not change when helicity in the primary beam is reversed. A like effect occurs in the magnetic diffraction of polarized neutrons.

Journal Keywords: Magnetoelectric effect; Physical Systems; Magnetic monopoles; Neutron diffraction; X-ray resonant magnetic scattering

Diamond Keywords: Antiferromagnetism

Subject Areas: Materials, Physics


Technical Areas: Theoretical Physics

Added On: 03/05/2023 11:42

Documents:
PhysRevB.107.144432.pdf

Discipline Tags:

Quantum Materials Physics Magnetism Materials Science Theoretical Physics

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