Craig Fennie, assistant professor of applied and engineering physics, and research associate Nicole Benedek usedtheoretical calculationsto understand exactly why and how a particular crystalline ceramic, a layered perovskite, is multiferroic. Multiferroic materials are simultaneously ferroelectric (electrically polarized) and ferromagnetic (they exhibit a permanent magnetic field). Their results were published online March 7 inPhysical Review Letters, appearing later in print, and are also the subject of a"Viewpoint"in the journalPhysicsand a"News and Views"column in the journalNature Materials.
A lot of materials respond to electric fields; others to magnetic fields -- but a small subset of materials called multiferroics respond to both. This discovery decades ago caused excitement due to the potential implications for, for example, magnetic storage devices that barely require power.
The Cornell researchers'density functional theorycalculations revealed that octahedron rotations -- lattice distortions ubiquitous in complexcrystalline materialssuch as perovskite -- simultaneously induce and thereby couple ferroelectricity, magnetoelectricity and ferromagnetism.
This prediction is remarkable because octahedral rotations usually cannot produce a polarization. It also lends new insight into the problem of how to introduce multiferroic order into different materials and the possibility of discovering the best materials to make low-power electronics at room temperature.
Their study demonstrates the possibility of robust, controllable coupling of magnetization and ferroelectric polarization, as well as suggesting electric field switching of the magnetization.
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