Materials chemistry

Magnetic and ferroelectric materials

Connect magnetic order and ferroelectric polarization to crystal symmetry, domains, coupling, and functional devices.

1 Lower secondary 2 Upper secondary 3 Undergraduate 4 Advanced 5 Research

IntuitionTwo kinds of order

A magnet can retain a preferred direction of its microscopic moments; a ferroelectric can retain a preferred direction of electric dipoles. Both form domains. In multiferroics, magnetic and electric orders coexist and may influence one another, opening routes to control one property with the other.

Visualize oppositely oriented ferroic domains and how an applied field can move domain walls or switch order.

SchoolOrder parameters and domains

Definition: Ferroelectricity

Definition: Magnetoelectric coupling

Ferromagnetic order aligns moments, while antiferromagnetic order alternates them so the net moment may cancel. Ferroelectric domains differ in polarization direction; domain walls separate them and can dominate switching and loss.

P_i=\frac{1}{V}\sum_s q_s r_{s,i},\qquad M_i=\frac{1}{V}\sum_s m_{s,i}

Example

Solution

P = p/V = 2.0 × 10⁻²⁸ / 5.0 × 10⁻²⁸ = 0.40 C m⁻².

UndergraduateSymmetry and coupling

Spontaneous polarization requires a polar structure and switchability distinguishes a ferroelectric from a merely polar dielectric. Magnetic order requires exchange interactions and competes with thermal disorder. Symmetry constrains allowed couplings: a linear magnetoelectric response is forbidden in many, but not all, magnetic point groups.

Order	Order parameter	Typical field
Ferroelectric	Polarization P	Electric field E
Magnetic	Magnetization M / staggered order	Magnetic field H

AdvancedMicroscopic mechanisms

In perovskite ferroelectrics, off-centering of cations and lattice distortions can create a dipole; in magnetic oxides, superexchange through oxygen often sets spin order. Spin–orbit interaction and noncollinear textures can couple polarization to magnetic order, but strong coupling does not guarantee room-temperature operation or easy switching.

ResearchResearch frontier

References

Multiferroic and magnetoelectric materials · W. Eerenstein, N. D. Mathur, J. F. Scott, 2006
The evolution of multiferroics · M. Fiebig, T. Lottermoser, D. Meier, M. Trassin, 2016
Electric-field control of local ferromagnetism using a magnetoelectric multiferroic · Y.-H. Chu, L. W. Martin, M. B. Holcomb, M. Gajek, S.-J. Han, Q. He, N. Balke, C.-H. Yang, D. Lee, W. Hu, Q. Zhan, P.-L. Yang, A. Fraile-Rodríguez, A. Scholl, S. X. Wang, R. Ramesh, 2008