Magneto-transport properties of giant magnetoresistive systems
Shi, Jing
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https://hdl.handle.net/2142/20132
Description
Title
Magneto-transport properties of giant magnetoresistive systems
Author(s)
Shi, Jing
Issue Date
1994
Doctoral Committee Chair(s)
Salamon, Myron B.
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Language
eng
Abstract
To understand the cause of the giant magnetoresistance effect, we have systematically investigated magnetothermopower, magneto-thermal conductivity and magnetoresistivity in both ferromagnetic/non-magnetic multilayers and granular solids which exhibit the giant magnetoresistance effect.
A large magnetic field-dependent diffusion thermopower, S(H, T), was found to accompany the giant magnetoresistance in these systems. The thermopower is closely correlated with the resistance at all temperatures examined as the magnetic field varies, indicating that the same underlying mechanism is responsible for both the giant magnetothermopower and magnetoresistance effects. We have concluded that the spin-split density-of-states (DOS) of the ferromagnetic d-bands provides the needed asymmetry in both spin conduction channels, and therefore is the fundamental cause of these effects.
The Wiedemann-Franz law was found to be well obeyed by the field dependent electrical and thermal conductivities in granular systems. The Lorentz number is a weak function of temperature. Both facts demonstrate that the scattering causing the GMR effect is primarily elastic in granular solids. However, the Lorentz number is magnetic field-dependent in multilayer systems, indicating that the spin-flip scattering into the spin-split d-bands is important.
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