Manganite oxide lattices (purple) doped with lanthanum (magenta) and strontium (green) have potential for use in spintronic memory devices, but their usual disorderly arrangement (left) makes it difficult to explore their properties. The ANL/NIST team’s use of a novel orderly lattice (right) allowed them to measure some of the material’s fundamental characteristics. Image: Argonne National Laboratory |
An advanced material that could help bring about
next-generation “spintronic” computers has revealed one of its
fundamental secrets to a team of scientists from Argonne National Laboratory (ANL)
and NIST.
The material, constructed of two different compounds, might
one day allow computers to use the magnetic spin of electrons, in addition to
their charge, for computation. A host of innovations could result, including
fast memory devices that use considerably less power than conventional systems
and still retain data when the power is off. The team’s effort not only
demonstrates that the custom-made material’s properties can be engineered
precisely, but in creating a virtually perfect sample of the material, the team
also has revealed a fundamental characteristic of devices that can be made from
it.
Team members from ANL began by doing something that had
never been done before—engineering a highly ordered version of a magnetic oxide
compound that naturally has two randomly distributed elements: lanthanum and
strontium. Stronger magnetic properties are found in those places in the
lattice where extra lanthanum atoms are added. Precise placement of the
strontium and lanthanum within the lattice can enable understanding of what is
needed to harness the interaction of the magnetic forces among the layers for
memory storage applications, but such control has been elusive up to this
point.
“These oxides are physically messy to work with, and
until very recently, it was not possible to control the local atomic structure
so precisely,” says Brian Kirby, a physicist at the NIST Center
for Neutron Research (NCNR). “Doing so gives us access to important
fundamental properties, which are critical to understand if you really want to
make optimal use of a material.”
The team members from ANL have mastered a technique for
laying down the oxides one atomic layer at a time, allowing them to construct
an exceptionally organized lattice in which each layer contains only strontium
or lanthanum, so that the interface between the two components could be
studied. The NIST team members then used the NCNR’s polarized neutron
reflectometer to analyze how the magnetic properties within this oxide lattice
changed as a consequence of the near-perfect placement of atoms.
They found that the influence of electrons near the
additional lanthanum layers was spread out across three magnetic layers in
either direction, but fell off sharply further away than that. Tiffany Santos,
lead scientist on the study from ANL, says that the measurement will be
important for the emerging field of oxide spintronics, as it reveals a
fundamental size unit for electronic and magnetic effects in memory devices
made from the material.
“For electrons to share spin information—something
required in a memory system—they will need to be physically close enough to
influence each other,” Kirby says. “By ordering this material in such
a precise way, we were able to see just how big that range of influence is.”
