(February 17, 2016) The
research group of Professor Hideo Ohno and Associate Professor Shunsuke Fukami
of Tohoku University has studied the control of magnetization using a current
applied to heterostructures comprising an antiferromagnet. They found that the
current gives rise to a flow of electron spin in the antiferromagnet, which
induces magnetization switching in a neighboring ferromagnet.
The obtained results shed light on a new physics of
antiferromagnet and also open various pathways toward ultralow-power integrated
circuits and other novel applications such as neuromorphic computing.
Spintronics devices that can store information via the
magnetization direction under no power supply, are expected to realize
ultralow-power integrated circuits. A key issue for the application is
how to achieve a fast and reliable magnetization switching with low power
consumption.
fig. 1: Schematics
of the antiferromagnet-ferromagnet bilayer system studied in this work.
The current applied
to the bilayer gives rise to a flow of electron spin in the perpendicular
direction to the
film plane. The magnetization of ferromagnet in the vicinity of interface
is biased in the
film plane direction due to an interaction with the antiferromagnet,
which allows for
the field-free switching.
Recently, a switching scheme utilizing the flow of electron
spin, the so-called spin current, originating from the spin-orbit interaction,
has attracted a great deal of attention as a new method to achieve fast and
reliable control of magnetization. This scheme has been observed in
heterostructures typically consisting of ferromagnet and nonmagnetic heavy
metal layer and is called the spin-orbit torque induced magnetization
switching.
fig. 2: The Hall
resistance versus applied current measured at zero magnetic fields.
The Hall
resistance represents the perpendicular component of magnetization.
The reversed
component of magnetization depends on the magnitude of applied current.
The research group investigated the spin-orbit torque
induced switching in an antiferromagnet-ferromagnet bilayer system. Until now,
the motion of electron spin in antiferromagnetic materials has not yet been
studied well. They fabricated switching devices from a stack with an
antiferromagnetic PtMn and a ferromagnetic Co/Ni multilayer, and electrically
evaluated the switching properties at room temperature. They found that the
current flowing in the antiferromagnet generates a spin-orbit torque large
enough to induce the magnetization switching in the neighboring ferromagnet.