The artificial intelligence boom has a power problem. The data centers that
train and run AI models are consuming electricity at a rate that is
straining grids and drawing comparisons to the energy appetite of entire
countries. A meaningful part of that consumption comes down to a basic fact
about how computers work: moving and storing information using electrical
charge generates heat, and heat is wasted energy. One path toward more
efficient computing runs through a different approach entirely, using
electron spin rather than charge to carry and store information. The
obstacle is that no single material has been able to bridge the electric and
magnetic worlds reliably, at room temperature, in a way that could be
practically built upon.
A study
just published
in Proceedings of the National Academy of Sciences reports that a
new phase of a well-known material may have broken that pattern. Jonathan E.
Spanier, Hess Family Endowed Chair Professor and department head in
mechanical engineering and mechanics and affiliated faculty in physics at
Drexel University, was part of the international research team, which
included Lane W. Martin, Robert A. Welch Professor of Materials Science and
Nanoengineering at Rice University, and Ilya Grinberg, associate professor
of chemistry at Bar-Ilan University. Together with colleagues at MIT, the
University of Pennsylvania, Northeastern University, the U.S. Naval Research
Laboratory, the University of California at Berkeley, and Lawrence Berkeley
National Laboratory, the team set out to unravel the findings.
The material is a solid solution of bismuth ferrite and barium titanate.
When combined in a specific ratio and grown as an ultrathin film under
precisely controlled conditions, it takes on a crystal structure that
researchers had not previously observed in bismuth ferrite-based systems.
In that new structure, the film simultaneously exhibits strong, spontaneous,
remanent, and re-orientable electrical polarization and magnetization at
room temperature, and those two properties are tightly coupled. That
coupling is the key for potential applications: it means an applied electric
(magnetic) field can be used to change the magnetic (electric) dipolar
state, without the energy losses that come from engineering magneto-electric
interactions across the boundaries between different materials.
“This material and its intriguing new mechanism brings the possibility of
using a magnetic field to control electronic charge, and a voltage to
manipulate electron spin, and realized through the exquisite quality films
attained by Professor Martin and postdoctoral scientist Dr. Taeyeon Kim,”
Spanier said.
“The original goals of this research were very different,” Spanier recalled.
“Our initial team conceived and launched an investigation of the
high-frequency dynamics of how domain walls, or boundaries between different
regions of dipolar ordering, fluctuate in a material containing magnetic
ions, based on our earlier work. As is typically the case, we started by
making the bulk ceramic material needed for the thin-film growth and
characterization.”
But as different research groups brought their measurements and theory
together, something unexpected came into focus.
“This work unfolded somewhat serendipitously,” Spanier said, “which is one
of the things I find enthralling about doing science.”
The Drexel team’s contribution to characterizing the new material included
inelastic light scattering spectroscopy, which uses laser light to probe the
collective dynamics of excitations in a material, including spins. Those
measurements helped the collaboration track how the internal magnetic
ordering shifts as the film’s composition changes, providing evidence that
something fundamentally different was happening in the new structural phase.
First-principles calculations by collaborators at Bar-Ilan University and
the University of Pennsylvania identified a proposed mechanism: the
unusually large magnetic response appears to arise from a specific
intermediate-range ordering of, paradoxically, the nonmagnetic titanium
atoms within the crystal, substituted for the magnetic iron, producing an
imbalance between opposing magnetic spins that generates a net moment far
larger than the parent material.
What makes breakthroughs such as these possible is long-term investment in
multi-institution research. “Funding for students and postdoctoral scholars
in science and engineering research is crucial,” he said. “Our team is
grateful to the Army Research Office and its program managers Dr. James
Harvey and Dr. Joe Qiu for their support, along with Dr. Brendan M. Hanrahan
of the Army Research Laboratory.”
That support has already opened a new chapter. The work is the foundation
for a new five-year, $1 million grant from the Office of Naval Research, on
which Spanier serves as principal investigator with Martin as a key
collaborator. That project, titled “Energy-Efficient Single-Phase
Multiferroic Magnetoelectric Thin Films,” extends the research into new
families of materials and will work to deepen understanding of why and how
the coupling between electrical and magnetic order arises, and how strong it
can be made.
For Spanier, the arc from an unexpected experimental result to the research
team’s publication in one of science’s most prestigious journals and a new
grant reflect something important about how basic research works at its
best. The ceramic his lab synthesized set something larger in motion, and
following where that led produced results that none of the collaborators had
mapped out at the start. The need now is to better understand the coupling
between dielectric polarization and magnetism and what future applications
it may enable.