Understanding the relationship between the structure, properties, processing
and performance of a material is the goal of materials science. The schematic shows this inter-relationship
for the material Ca3Mn2O7, a multiferroic layered perovskite oxide in which the magnetism is electric-field controllable.
See Hybrid improper ferroelectricity: A
mechanism for controllable polarization-magnetization coupling N. A. Benedek and C. J. Fennie, Phys. Rev. Lett. 106 107204 (2011).
Structure: Ferroelectricity in Ca3Mn2O7 arises from a combination of two different octahedral rotation distortions with different symmetries. These modes act like a ‘field’ and are responsible for switching on the polarization.
Properties: Because the primary order parameter is not the polarization, Ca3Mn2O7 is an improper ferroelectric. The polarization only becomes non-zero when the octahedral rotation modes switch on.
Processing: Many layered oxides are grown with atomic-layer control as thin-films, using techniques such as molecular beam epitaxy, as shown in this stylized graphic.
Performance: Since the ferroelectric distortion in Ca3Mn2O7 induces the magnetization (through spin-canting), the magnetization direction could in principle be switched with an electric field. This could lead to new types of low-power electronic and memory devices.
The Benedek Group
Bridging materials science, solid-state chemistry and condensed matter physics
Research in the Benedek Group cuts across the disciplines of materials science, solid-state chemistry and condensed matter physics. We use first-principles theoretical techniques, in combination with symmetry principles, to try to understand why materials have the structures that they have, how the structure of a material gives rise to its properties and how structure-property relationships can be exploited to create new functional materials with enhanced properties, with a particular emphasis on complex oxides and their interfaces. The ‘materials-by-design’ paradigm has been used with spectacular success to create new functional oxides with novel electronic and magnetic properties (see Publications).
Where is this research going?
Our group is taking this approach in several new directions: for example, establishing design rules for improved ionic transport in oxide energy materials and relating the structure, chemistry and physical properties of non-perovskite oxide interfaces to their bulk constituents.