30 November 2019 | New Scientist | 43O
NE April night in 1820, the Danish
experimentalist Hans Christian
Øersted made a remarkable
discovery. By bringing an electrical wire near
a compass lying on his workbench, he found
its needle could be made to shiver and dance.
Whether a lucky accident or an inspired bit
of experimentation, that moment cemented
Øersted’s reputation. What he had discovered
was that electricity and magnetism, long
thought to be entirely distinct phenomena,
were in fact inextricably linked.
Two hundred years later, this connection
powers our world. Moving magnets give rise
to electric fields, driving the motors in electric
cars and generators in hydroelectric dams.
Flowing electric currents in turn give rise to
magnetic fields, such as those used in MRI
scanners and particle accelerators like the Large
Hadron Collider at CERN. But this symbiosis
has its limits. Until recently, it was thought
to be impossible to produce a single material
that could possess a permanent magnetic
field and electric field at the same time.
Then, one day in 1998, a researcher at
Yale University named Nicola Spaldin asked
a deceptively simple question. Why?
“It was a question that really no one was
asking, or had thought to ask before,” says
Spaldin. That moment marked a turning point
in her career and launched a revolution in
materials science, a decades-long pursuit
of elusive wonder stuff with both properties.
Today, the first examples of these so-called
multiferroics could change technology for
good. There might be no end to their power:
from making better solar cells and boosting
computational power to helping search for
the universe’s missing matter (see “Heroic
multiferroics”, right and following pages).
Spaldin, now at the Swiss Federal Institute
of Technology in Zurich, was ideally suited
to hunt such substances. “My passion is really
electrons,” she says. “I love thinking about
them.” That boded well because understanding
electrons is key to understanding why
multiferroics are so valuable.
Virtually all the matter that we can see is
made up of atoms. These, in turn, consist of
electrons spinning around a nucleus formed
of protons and neutrons. Despite their tiny
size, electrons play a vital role in determining
a material’s electric and magnetic properties.
Let’s take magnetism first. All electrons have
a quantum property called spin that can be
thought of as an arrow that points in one of
two directions. Most of the time, these arrows
are oriented randomly, with no one direction
dominating. In some materials, however, the
arrows get in formation when they are exposed
to an external magnetic field. If all the arrows
are aligned the same way, the material starts
generating a magnetic field of its own.“ It was a question
that really no
one was asking,
or had thought
to ask before”
>CANCER DETECTION
AND BRAIN MAPPINGFrom the signal-sending of
neurons to the ion channels
of cells, your body is positively
tingling with electrical activity.
“If you have access to electricity
at the molecular level, then
you can actually control cells,
treat diseases and even control
biological processes,” says
Sakhrat Khizroev, a physicist
and inventor at the University
of Miami in Florida looking for
medical applications for a new
class of wonder materials called
multiferroics (see main story).
The potential is vast.
Multiferroics might reduce the
need for invasive techniques
by being made into nanobots
designed to swim through blood
vessels and deliver life-saving
drugs. They would be guided by
magnetic fields outside the body
and able to interact with tissues
through their electric properties.
For his part, Khizroev
has developed multiferroic
nanoparticles to spot signs
of cancer. The idea is that
once inside the body, the
multiferroics flag cancerous
cells in a way that can be detected
through nuclear magnetic
resonance imaging. Studies
suggest they can outperform
traditional, cobalt-based
nanoparticles.
Ultimately, he has other
targets in mind, including
the brain. “The brain is more
energy-efficient than any
computer working today,”
he says. His vision is to use
multiferroic particles to map
the organ’s network of neurons,
and then develop a computer
based on that map.Heroic
multiferroics
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