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Title: Ultrafast Control of Magnetism in Ferromagnetic Semiconductors via Photoexcited Transient Carriers

Abstract

The field of spintronics offers perspectives for seamless integration of coupled and inter-tunable electrical and magnetic properties in a single device. For integration of the spin degree of freedom with current electronic technology, new semiconductors are needed that show electrically-tunable magnetic properties at room temperature and above. Dilute magnetic semiconductors derived from III-V compounds, like GaMnAs and InMnAs, show coupled and tunable magnetic, transport, and optical properties, due to the fact that their ferromagnetism is hole-mediated. These unconventional materials are ideal systems for manipulating the magnetic order by changing the carrier polarization, population density, and energy band distribution of the complementary subsystem of holes. This is the main theme we cover in this thesis. In particular, we develop a unique setup by use of ultraviolet pump, near-infrared probe femtosecond laser pulses, that allows for magneto-optical Kerr effect (MOKE) spectroscopy experiments. We photo-excite transient carriers in our samples, and measure the induced transient magnetization dynamics. One set of experiments performed allowed us to observe for the first time enhancement of the ferromagnetic order in GaMnAs, on an ultrafast time scale of hundreds of picoseconds. The corresponding transient increase of Curie temperature (Tc, the temperature above which a ferromagnetic material loses itsmore » permanent magnetism) of about 1 K for our experimental conditions is a very promising result for potential spintronics applications, especially since it is seconded by observation of an ultrafast ferromagnetic to paramagnetic phase transition above Tc. In a different set of experiments, we "write" the magnetization in a particular orientation in the sample plane. Using an ultrafast scheme, we alter the distribution of holes in the system and detect signatures of the particular memory state in the subsequent magnetization dynamics, with unprecedented hundreds of femtosecond detection speed. The femtosecond cooperative magnetic phenomena presented here further our understanding of Mn-hole correlations in III-V dilute magnetic semiconductors, and may well represent universal principles of a large class of carrier-mediated ferromagnetic materials. Thus they offer perspectives for future terahertz (1012 Hz) speed"spintronic" functional devices.« less

Authors:
 [1]
  1. Univ. of California, Berkeley, CA (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
945360
Report Number(s):
LBNL-1323E
TRN: US200903%%109
DOE Contract Number:  
AC02-05CH11231
Resource Type:
Thesis/Dissertation
Resource Relation:
Related Information: Designation of Academic Dissertation: Doctoral; Academic Degree: Ph.D.; Name of Academic Institution: University of California, Berkeley; Location of Academic Institution: Berkeley
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; 77 NANOSCIENCE AND NANOTECHNOLOGY; CURIE POINT; DETECTION; FERROMAGNETIC MATERIALS; FERROMAGNETISM; FUNCTIONALS; KERR EFFECT; LASERS; MAGNETIC PROPERTIES; MAGNETIC SEMICONDUCTORS; MAGNETISM; MAGNETIZATION; OPTICAL PROPERTIES; POLARIZATION; POPULATION DENSITY; PROBES; SPECTROSCOPY; SPIN; TRANSIENTS; VELOCITY; ultrafast; ferromagnetic semiconductors; phase transition; ferromagnetism enhancement; magnetic memory detection; spintronics

Citation Formats

Cotoros, Ingrid A. Ultrafast Control of Magnetism in Ferromagnetic Semiconductors via Photoexcited Transient Carriers. United States: N. p., 2008. Web. doi:10.2172/945360.
Cotoros, Ingrid A. Ultrafast Control of Magnetism in Ferromagnetic Semiconductors via Photoexcited Transient Carriers. United States. doi:10.2172/945360.
Cotoros, Ingrid A. Mon . "Ultrafast Control of Magnetism in Ferromagnetic Semiconductors via Photoexcited Transient Carriers". United States. doi:10.2172/945360. https://www.osti.gov/servlets/purl/945360.
@article{osti_945360,
title = {Ultrafast Control of Magnetism in Ferromagnetic Semiconductors via Photoexcited Transient Carriers},
author = {Cotoros, Ingrid A.},
abstractNote = {The field of spintronics offers perspectives for seamless integration of coupled and inter-tunable electrical and magnetic properties in a single device. For integration of the spin degree of freedom with current electronic technology, new semiconductors are needed that show electrically-tunable magnetic properties at room temperature and above. Dilute magnetic semiconductors derived from III-V compounds, like GaMnAs and InMnAs, show coupled and tunable magnetic, transport, and optical properties, due to the fact that their ferromagnetism is hole-mediated. These unconventional materials are ideal systems for manipulating the magnetic order by changing the carrier polarization, population density, and energy band distribution of the complementary subsystem of holes. This is the main theme we cover in this thesis. In particular, we develop a unique setup by use of ultraviolet pump, near-infrared probe femtosecond laser pulses, that allows for magneto-optical Kerr effect (MOKE) spectroscopy experiments. We photo-excite transient carriers in our samples, and measure the induced transient magnetization dynamics. One set of experiments performed allowed us to observe for the first time enhancement of the ferromagnetic order in GaMnAs, on an ultrafast time scale of hundreds of picoseconds. The corresponding transient increase of Curie temperature (Tc, the temperature above which a ferromagnetic material loses its permanent magnetism) of about 1 K for our experimental conditions is a very promising result for potential spintronics applications, especially since it is seconded by observation of an ultrafast ferromagnetic to paramagnetic phase transition above Tc. In a different set of experiments, we "write" the magnetization in a particular orientation in the sample plane. Using an ultrafast scheme, we alter the distribution of holes in the system and detect signatures of the particular memory state in the subsequent magnetization dynamics, with unprecedented hundreds of femtosecond detection speed. The femtosecond cooperative magnetic phenomena presented here further our understanding of Mn-hole correlations in III-V dilute magnetic semiconductors, and may well represent universal principles of a large class of carrier-mediated ferromagnetic materials. Thus they offer perspectives for future terahertz (1012 Hz) speed"spintronic" functional devices.},
doi = {10.2172/945360},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2008},
month = {12}
}

Thesis/Dissertation:
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