Mesoscopic noise probe of an inhomogeneous colossal magnetoresistance phase
Merithew, Robert David
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https://hdl.handle.net/2142/31256
Description
Title
Mesoscopic noise probe of an inhomogeneous colossal magnetoresistance phase
Author(s)
Merithew, Robert David
Issue Date
2000
Doctoral Committee Chair(s)
Weissman, Michael B.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
epitaxial single-crystal films
Language
en
Abstract
Epitaxial single-crystal films of La2; 3Ca1; 3Mn03 exhibit large discrete equilibrium
resistance fluctuations in the region of phase space where colossal magnetoresistance
effects are strongest. The fluctuators' dependence on magnetic field indicates that
the resistance steps represent small regions of material fluctuating between a paramagnetic
insulating phase and a ferromagnetic conducting phase. The dependences of
Boltzmann factors on field and temperature give the magnetic moment and entropy
differences between the states, providing quantitative thermodynamic information
about the locally homogeneous CMR phase transition in an otherwise inhomogeneous
sample. The size of the discrete resistance fluctuations reveals a very inhomogeneous
current density. The temperature dependence of some fluctuators provides evidence
for thermodynamic effects which stabilize the mixed phase. A separate experiment
on the spin glass CuMnAu investigates the effect of strong local anisotropy on spin
glass dynamics. The result demonstrates that altering the symmetry of a spin glass
Hamiltonian on the scale of the two-spin interaction has a strong qualitative effect
on the low-energy frozen spin glass state space.
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