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Type of Document Dissertation Author Chakarvorty, Raja Author's Email Address rchakarv@nd.edu, raja8sp@gmail.com URN etd-04162009-231650 Title Investigation of the Role of Compensation and Origin of Ferromagnetism in Ga1−xMnxAs Using Magnetic Circular Dichroism Studies Degree Doctor of Philosophy Department Physics Advisory Committee
Advisor Name Title Prof. M. Dobrowolska Committee Chair Prof. B. Bunker Committee Member Prof. B. Janko Committee Member Prof. C. Tanner Committee Member Keywords
- GaMnAs
- III-Mn-V
- magnetic circular dichroism
- semiconductor
- ferromagnetic
- compensation
Date of Defense 2009-04-03 Availability unrestricted Abstract III-Mn-V dilute magnetic semiconductors have emerged as promising candidatematerials for future spintronic devices that could use the spin property of the carriers
(in addition to their electrical charge) to manipulate information. During the past
decade the most extensively studied semiconductor in this family is GaMnAs.
It is widely accepted that the long-range ferromagnetic ordering of Mn moments in
this material is induced by holes contributed by the Mn ions. These acceptors can
either be neutral or in the form of compensated negatively charged centers. The
precise role which these two centers play in determining the magnetic properties
of GaMnAs is still not fully understood. Moreover, the role of Mn acceptors in
determining the Zeeman splitting of band edges of GaMnAs needs to be investigated
in depth. Magnetic circular dichroism (MCD) is a powerful tool for investigating
magneto-optical properties in thin magnetic layers, and in this study we apply this
method to address the problem of Mn acceptor compensation in GaMnAs and its
implication in determining the Zeeman splitting of band edges of GaMnAs, with the
aim of shedding additional light on the co-relation of hole concentration and Curie
temperature of these samples with Zeeman splitting of band edges.
The focus of this thesis is the analysis of magnetic circular dichroism data taken
on thin GaMnAs films with low Mn concentration. Our measurements revealed that
exchange-induced spin splitting of the band edges occurs only in samples that show
ferromagnetic order, and is not observed in paramagnetic samples. These results
lead to the conclusion that Mn ions in the A0 configuration (d5 + hole) provide
the only mechanism for exchange interaction between Mn spins and band carriers.
We also show that there is a linear relation between the observed exchange-induced
splitting of the band edges and the Curie temperature, pointing to a common origin
of the band edge splitting and ferromagnetism in GaMnAs.
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