click to enlarge Researchers have discovered that magnetic and dielectric properties can be largely controlled by substituting other atoms for the nonmagnetic atoms in a magnetic material.

A
research group headed by Dr. Noriki Terada, a Senior Researcher of the
Neutron Scattering Group of the Quantum Beam Unit in the National
Institute for Materials Science (NIMS) and Dr. Yoshihiro Tsujimoto, a
ICYS-MANA Researcher of the NIMS International Center for Materials
Nanoarchitectonics (MANA), in joint work with the Rutherford Appleton
Laboratory and the University of Oxford, both in the U.K., discovered
that magnetic and dielectric properties can be largely controlled by
substituting other atoms for the nonmagnetic atoms in a magnetic
material.

The
magnetic dielectrics called multiferroics have attracted attention
recently. Multiferroics are expected to be applied to a new type of
memory devices in which dielectric polarization is controlled by a
magnetic field and magnetization is controlled by an electric field,
unlike the conventional technology, in which magnetization is controlled
by a magnetic field and dielectric polarization is controlled by an
electric field. In recent years, researchers around the world have
searched for multiferroic materials which display gigantic ferroelectric
polarization at room temperature. However, material development based
on new ideas was needed, as multiferroic materials which function at
room temperature are rare.

Using
the ultra-high pressure synthesis device at NIMS, the group led by Dr.
Terada succeeded in synthesizing a high quality AgFeO₂ specimen in which
Ag ions are completely substituted for the nonmagnetic Cu ions in the
delafossite oxide CuFeO₂, and clarified the fact that the new material
displays ferroelectric polarization in an environment without a magnetic
field. The research group also carried out high resolution neutron
diffraction experiments on AgFeO₂ jointly with a group at the Rutherford
Appleton Laboratory in the U.K. As a result, the crystal structure and
spin structure of the material were revealed for the first time, and the
mechanism of ferroelectric polarization was elucidated.

This
research result is the first example in which multiferroic properties
were successfully obtained by substituting other nonmagnetic ions for
the nonmagnetic ions in a delafossite oxide, which gives a new concept
to explorations of room-temperature multiferroic. This achievement is
expected to make an important contribution to the development of
next-generation large capacity memories and the development of new
energy conversion materials.

This
research was carried out with financial support from the “Young
Researchers Overseas Visits Program for Vitalizing Brain Circulation”
and the “Postdoctoral Fellowship for Research Abroad” program of the
Japan Society for the Promotion of Science (JSPS). This result is
scheduled to be published in the bulletin of the American Physical
Society, Physical Review Letters.

Source: NIMS