Süperlattice
structure of lithium osmate and lithium niobate
New design sandwiches a polar metallic oxide between an
insulating material
(August 21, 2015) From
the spinning disc of a computer’s hard drive to the varying current in a
transformer, many technological devices work by merging electricity and
magnetism. But the search to find a single material that combines both electric
polarizations and magnetizations remains challenging.
This elusive class of materials is called multiferroics,
which combine two or more primary ferroic properties. Northwestern
Engineering’s James Rondinelli and his research team are interested in
combining ferromagnetism and ferroelectricity, which rarely coexist in one
material at room temperature.
“Researchers have spent the past decade or more trying to
find materials that exhibit these properties,” said Rondinelli, assistant
professor of materials science and engineering at the McCormick School of
Engineering. “If such materials can be found, they are both interesting from a
fundamental perspective and yet even more attractive for technological
applications.”
In order for ferroelectricity to exist, the material must be
insulating. For this reason, nearly every approach to date has focused on
searching for multiferroics in insulating magnetic oxides. Rondinelli’s team
started with a different approach. They instead used quantum mechanical
calculations to study a metallic oxide, lithium osmate, with a structural disposition
to ferroelectricity and sandwiched it between an insulating material, lithium
niobate.
While lithium osmate is a non-magnetic and non-insulating
metal, lithium niobate is insulating and ferroelectric but also non-magnetic.
By alternating the two materials, Rondinelli created a superlattice that — at
the quantum scale — became insulating, ferromagnetic, and ferroelectric at room
temperature.