Abstract
AbstractMultiferroics are materials that evince both ferroelectric and magnetic order parameters. These order parameters when coupled can lead to both exciting new physics as well as new device applications. Potential device applications include memory, magnetic field sensors, small antennas and so on. Since Kimura’s discovery of multiferroicity in TbMnO3, there has been a renaissance in the study of these materials. Great progress has been made in both materials discovery and in the theoretical understanding of these materials. In type-II systems the magnetic order breaks the inversion symmetry of the material, driving a secondary ferroelectric phase transition in which the ferroelectric polarisation is exquisitely coupled to the magnetic structure and thus to magnetic field. In type-I systems, the magnetic and ferroelectric orders are established on different sublattices of the material and typically are weakly coupled, but electric field can still drive changes in the magnetisation. Besides single-phase multiferroics, there has been exciting progress in composite heterostructures of multiferroics. Here, we review neutron measurements of prototypical examples of these different approaches to achieving multiferrocity.
Highlights
Neutron scattering plays an important role in determining the ferroelectric properties of multiferroics in terms of the detailed crystal structure, but the central role is in elucidating the magnetic structures and spin dynamics, and in understanding the origin of how, and how strongly, the magnetic and ferroelectric order parameters are coupled
We emphasise the role of magnetic scattering here and reference the standard techniques for crystal structure refinements and exploring the lattice dynamics, which are similar in concept to magnetic Bragg scattering and measuring the spin dynamics, respectively
Neutron scattering will continue to play a critical role in determining the magnetic structures of these materials and the strength of their exchange interactions, and how they couple to the electric polarisation
Summary
Neutron scattering plays an important role in determining the ferroelectric properties of multiferroics in terms of the detailed crystal structure, but the central role is in elucidating the magnetic structures and spin dynamics, and in understanding the origin of how, and how strongly, the magnetic and ferroelectric order parameters are coupled. (Widely available numerical codes permit rigorous analysis including the non-kinematical behaviour of the reflectivity for all Q.) ρ(z) consists of nuclear and magnetic SLDs such that ρ±(z) = ρn(z) ± CM (z), where C = 2.9109 × 10− 9 Å − 2(kA/m) − 1, and M(z) is the magnetisation (kA/m) depth profile.[8,9] Unlike change across an interface, PNR can distinguish magnetism at magnetometry, which measures magnetic moment, reflection of interfaces and other nanoscale structures from contamination within a substrate or on the sample.[6] Extensive reviews of PNR can polarised neutron beams depends on a variation of moment density across a planar interface. The specular away from the applied field, polarisation analysis of the specularly reflectivity, R, is determined by the neutron scattering length reflected beam provides information about the projection of the density (SLD) depth profile, ρ(z), averaged over the lateral net magnetisation vector onto the sample plane. A Hamiltonian that captures the basic physics of the problem can be written as
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