(August 11, 2015) Colossal
magnetoresistance is a property with practical applications in a wide array of
electronic tools including magnetic sensors and magnetic RAM. New research from
a team including Carnegie’s Maria Baldini, Ho-Kwang “Dave” Mao, Takaki
Muramatsu, and Viktor Struzhkin successfully used high-pressure conditions to
induce colossal magnetoresistance for the first time in a pure sample of a
compound called lanthanum manganite, LaMnO3. It is published by Proceedings of
the National Academy of Sciences.
Metals are compounds that are capable of conducting the flow
of electrons that makes up an electric current. Non-metals cannot conduct such
a current. Magnetoresistance is the capacity of compounds to be changed from
electrically resistant to electrically conductive depending on the presence of
an external magnetic field. The ability to switch on and off from metal to
non-metal is what makes the phenomenon so useful for electronic and spintronic
devices.
Manganite compounds, such as the LaMnO3 studied by the
research team, are particularly promising when it comes to colossal
magnetoresistance, because the change from insulator to metal is several orders
of magnitude stronger than in other types of compounds. But controlling and
understanding it has remained largely elusive. It has been induced before in
chemically doped manganite samples, but not in a pure one until this study.
The transition from insulator to metal in LaMnO3 takes place
when the room temperature compound is placed under about 316,000 times normal
atmospheric pressure (32 gigapascals). What the team was able to demonstrate by
examining LaMnO3 across a range of temperatures and pressures, is that under
pressure LaMnO3 separates into two distinct phases, one metallic and one
non-metallic. The chemical structure of the non-metallic phase is distorted,
and the metallic phase is not.