Title page for ETD etd-08092012-104008


Type of Document Dissertation
Author Kim, Yong-Jae
Author's Email Address ykim07@vt.edu, krone95kim@gmail.com
URN etd-08092012-104008
Title Electrical injection and detection of spin polarization in InSb / ferromagnet nanostructures
Degree PhD
Department Physics
Advisory Committee
Advisor Name Title
Heremans, Jean J. Committee Chair
Heflin, James R. Committee Member
Park, Kyungwha Committee Member
Soghomonian, Victoria Committee Member
Keywords
  • semiconductor
  • spin
  • ferromagnetism
  • spintronics
  • InSb
Date of Defense 2012-07-30
Availability unrestricted
Abstract
We present studies of the electical detection of spin injection and

transport in InSb/CoFe heterostructures. As a narrow gap

semiconductor, InSb has a high mobility and strong spin-orbit

interaction. Using ferromagnetic CoFe, lateral InSb/CoFe devices are

fabricated by semiconductor processing techniques. The saturation

magnetizations of various CoFe electrodes with different widths are

calculated from Hall measurements in which the fringing fields of

the CoFe electrodes are detected. A magnetic model provides

reasonable estimation of the saturation magnetization for micrometer

scale geometries. The interface magnetoresistance measurements of

InSb/CoFe thin film layered structures present a unique peak at low

field, having a symmetric behavior in magnetic field with a critical

field Hc and a strong temperature dependence. We attribute our

signal to a ferromagnetic phase in the InSb induced by spin

injection. In a non-local lateral spin valve measurement, we

observed the following. Firstly, Hc of the lateral spin valve

signals is identical to Hc of interface magnetoresistance

signals. Secondly, the non-local lateral spin valve signals are

strongly dependent on temperature, which is also a unique

characteristic magnetoresistance. Thirdly, the signals are tunable

in response to an applied injector bias. Lastly, the signals are

dependent on the exact interfaces. Based on these observations, the

detected signals may be considered as spin current signals. The Hall

and magnetoresistance signals are measured locally and non-locally

in InSb/CoFe Hall devices. The non-local magnetoresistance signals

exhibit asymmetric behavior in applied magnetic field which are

considered as signatures of spin phenomena. The non-local Hall

signals present switching behavior with the CoFe magnetization

switching at the coercive field. The non-local Hall signals in a

perpendicular field show Hc, similarly seen in non-local

lateral spin valves. Inverse spin Hall effect measurements with

tilted magnetic fields show an in-plane magnetic field dependence in

non-local type Hall signal and a perpendicular magnetic field

dependence in the local Hall measurement. We have found that the

signal can have its origin in a spin current from our observation of

Hc and hysteresis in the magnetization traces. As yet, the spin

current transport mechanism is unknown.

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