Noise Studies of Disordered Condensed Matter

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Noise Studies of Disordered Condensed Matter
Colossal Magnetoresistive MaterialsM. B.
Weissman, UIUC, DMR-0240644
Colossal Magnetoresistive (CMR) materials have
inspired interest for their potential as sensors
of magnetic fields, most evident in a regime
where a magnetic electrically conducting phase
and an insulating phase coexist. Understanding
the nature of the phases and why they coexist is
important for optimizing the materials. We have
recently used an experiment on how the noise,
random conductance fluctuations, depend on
magnetic field history to show that a special
type of insulating phase, called
antiferromagnetic, plays a key role in an
unexpected way. The ferromagnetic metal sits in a
background of antiferromagnetism, not simple
non-magnetic material.
.
The noise power at zero field depends on whether
the last applied field greater than 100 G was
positive or negative, showing a fixed
symmetry-breaking magnetic background. The large
field scale required to change the background
shows it is antiferromagnetic.
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Noise Studies of Disordered Condensed MatterM.
B. Weissman, UIUC, DMR-0240644
Outreach The PI has prepared and edited hundreds
of answers for a question-and-answer Web site run
by the Physics Department http//van.hep.uiuc.edu/
van/qa/qaform.htm This site draws questions on
all sorts of science topics from students of all
ages from around the world. Heres the PIs
favorite http//van.hep.uiuc.edu/van/qa/section/
stuff_about_space/the_earth_and_the_moon/200208212
10810.htm. Heres another, with more serious
substance http//van.hep.uiuc.edu/van/qa/section/
states_of_matter_and_energy/boiling_evaporating_an
d_condensing/20030626151340.htm.
Education The work described in this nugget was
done by recent student Aki Palanisami (now a
post-doc in Japan) working with N. Mathurs group
from Cambridge University and with J. Ecksteins
group at Illinois. This grant currently supports
work by a graduate student (Lambert Chao), an
undergraduate (Kara Lamb) and a Visiting
Research Professor (Eugene Colla). Recent
graduates from this group have gone on to work
for several hard-drive developers, as well as for
other hardware developers, national labs, and
universities.