Physical Properties of Magnetic as-Grown and Oxygen Annealed SnO2:Co Thin Films

132 Pages·2015·4.62 MB·English

by  Gratiela Moncia Stoian

Florida State University Libraries
Electronic Theses, Treatises and Dissertations The Graduate School
2013
Physical Properties of Magnetic As-Grown
and Oxygen Annealed SnO#: Co Thin Films
Gra#iela M. Stoian
Follow this and additional works at the FSU Digital Library. For more information, please contact [email protected]
FLORIDA STATE UNIVERSITY

COLLEGE OF ARTS AND SCIENCES

PHYSICAL PROPERTIES OF MAGNETIC AS-GROWN AND OXYGEN ANNEALED

SnO :Co THIN FILMS
2

By

GRAŢIEδA ε. STOIAN

A Dissertation submitted to the
Department of Physics
in partial fulfillment of the
requirements for the degree of
Doctor of Philosophy

Degree Awarded:
Fall Semester, 2013
i
1
Gratiela-Monica Stoian defended this dissertation on November 18th, 2013.
The members of the supervisory committee were:

Stephan von Molnár
Professor Directing Dissertation

Albert Stiegman
University Representative

Volker Crede
Committee Member

Vladimir Dobrosavljevic
Committee Member

Peng Xiong
Committee Member

The Graduate School has verified and approved the above-named committee members, and
certifies that the dissertation has been approved in accordance with university requirements.
ii
To my husband, parents, brother and grandparents

iii
ACKNOWLEDGMENTS
I would like to acknowledge a few people that have been invaluable in guiding me
throughout the time I spent at Florida State University, as a graduate student in the former
MARTECH and the current CMMP group. Much of the work presented in this thesis would have
never been completely materialized without the support, advice and encouragements I got from
the people both in my professional, as well as in my personal life.
The first and foremost, I would like to acknowledge my doctoral advisor and mentor,
Prof. Stephan von Molnár. Having him as my thesis coordinator turned out to be a truly life
changing experience. Working under his guidance gave me the opportunity to learn, grow as a
future scientist and become a very responsible person. His vast expertise in Spintronics, the ease
with which he explains complex physics concepts and the extraordinary ability to focus only on
essential aspects of the research have been the key to succeed in this project. Throughout my
graduate school years, his leadership, patience, continuing support and encouragement and the
fair evaluation of my work has motivated me to move forward in achieving my goals. And for
this, I will be forever grateful to Prof. von Molnár. The next person I would like to thank is my
co-advisor, Prof. Patricia A. Stampe, for her constant guidance and unconditioned help. She is a
fine, knowledgeable scientist and most importantly, a person with a superb character. Her
charming personality made the work with Pat truly enjoyable. The project we have collaborated
on would have not been completed without her help. She has been my supervisor but also a
friend.
I would also want to thank Prof. Robin J. Kennedy for the invaluable help with the
project. The samples grown by Robin (the PLD guru) were the essence of this thesis. Working in
the FAMU lab was quite delighting when Robin was around. I will definitely miss the advice he
gave me while working on this project and his jovial attitude.
I would like to thank Prof. Peng Xiong, who is also a member of my advisory committee,
for willing to give me advice whenever I needed guidance with my experimental work. His
excellent recommendations and suggestions, as well as the fundamental physics questions he had
always asked during group meetings have helped me advance with my research. I would like to
thank Prof. Vladimir Dobrosavljevic, my committee member and also my professor for one of
classes I took in grad school, who was always available for discussions regarding my research
iv
and very helpful with his students. I would also like to thank Dr. Volker Crede and Prof. Albert
E. Stiegman for their cooperation and guidance related to this research.
I am grateful to Prof. David van Winkle who has been always willing to find financial
support for me as a research assistant. Moreover, his presence at our group meeting talks has
been a good call to consider other aspects of my research. I would also want to thank Dr. Steve
Lenhart for exposing me to other research topics, such as biomaterials.
The next person I would like to recognize is Dr. Eric Lochner for not only training me on
most of the equipment (SQUID, XRD, AFM, XPS, PPMS, SEM) but also for discussing
fundamental physics concepts related to material investigation, and assisting me whenever
difficulties with the operation of instruments occurred. He is a knowledgeable scientist and
always willing to help. Jim Valentine is one of the people who have helped me a great deal,
especially during my first years as graduate student, when we had to upgrade the sputtering
system, when I had to design electronic devices or when things often broke in the lab. He taught
me many things related to electronics and I will always be grateful for his help and for the nice
discussions we always had.
Special thanks to Bob Smith, not only for helping me with the He transfer and making
sure we had enough He in the dewars, but also for being a wonderful person, sometimes greeting
me with coffee and cookies in the lab, and always helpful regardless if I needed his help during
the working hours or weekends. He has always been the person I relied on when my car broke or
I needed tools to repair something.
I wish to thank Dr. Yan Xin for her kind cooperation in performing TEM characterization
for these studies. She instructed me how to prepare specimens for TEM analysis, how to interpret
the data, and her vast expertise in microscopy helped us understand more about the materials we
studied.
I would also like to thank Dr. Irinel Chiorescu, under whose guidance I worked during
my first summer semester at FSU.
I would like to thank other people from our wonderful staff: Kurt Koetz for helping me
with the Janis and the sputtering system, Ian Winger for his ability to find the best solutions for
designing special parts for our equipment, Joe Ryan for repairing, upgrading the office and lab
computers, installing new software and helping me many times to print my posters for
v
conferences. I thank Roger Beck, Kathy Bailey and Nellie Speirs for the administrative aspects
of being a graduate student.
I want to acknowledge my former colleagues in the group: Dr. Khaled Aledealat, Dr.
Kurtice Chen, Dr. Jeff Gardner, Dr. Jennifer Misuraca, Dr. Yi Cheng, Dr. Ashwani Kumar, Dr.
Erhong Hu, Dr. Xiaohang Zhang and my current collegues: Liuqi Yu, Joon-Il Kim, Jorge
Barreda, Tim Keiper, Konstantinos Kountouriotis, Longqian Hu, Troy Lowry, Ling Wei and
Plengchart Prommapan for the support and the friendly environment in the office and lab. Their
presence exposed me to new ideas and techniques and they were there to help when it was
needed. I would like to thank the senior grad students: Khaled and Kansheng for training me on
the sputtering machine and photolithography and Jen for helping me with the Oxford cryostat.
Last, but not least, I am incredibly grateful to my loving family, who has encouraged me
over the years and gave me strength to finish this degree. Without their constant support I would
have not graduated. I thank my husband, George Trifu, with whom I shared all the joys and
pitfalls over the past 6 years. I am grateful to my brother, Razvan- Ionut Stoian, for talking me
out of quitting numerous times this program. I thank the greatest supporters I could ever have,
my parents and grandparents, for their love and for making the impossible sometimes to provide
the best familial, social and scholar environment for my personal and professional development.

The work presented in this thesis was supported by NSF Grant No. DMR-0605734

vi
TABLE OF CONTENTS
List of Tables ................................................................................................................................. ix
List of Figures ..................................................................................................................................x
Abstract ...................................................................................................................................... xviii
1. INTRODUCTION ...................................................................................................................1
1.1 Background ....................................................................................................................1
1.2 Spintronics .....................................................................................................................4
1.3 Physical Motivation and Thesis Outline ........................................................................6

2. DILUTE MAGNETIC SEMICONDUCTING OXIDES ......................................................10
2.1 Introduction ..................................................................................................................10
2.2 Magnetic Interactions in DMSOs ................................................................................11
2.2.1 The Double Exchange Interaction ......................................................................14
2.2.2 The Bound Magnetic Polaron Model ..................................................................16
2.2.3 The RKKY Model...............................................................................................17
2.2.4 Other: Grain Boundaries, Spin Glasses, Magnetic Clusters ...............................18
2.3 Fabrication of DMSOs .................................................................................................22
2.3.1 Introduction .........................................................................................................22
2.3.2 Growth Methods of DMSOs ...............................................................................23
2.3.2.1 Thin films .............................................................................................24
2.3.2.2 Nanoparticles .......................................................................................29
2.3.3 Influence of Dopant Concentration .....................................................................31
2.3.4 Effect of Oxygen During Growth and Post Deposition Thermal Treatment ......32
2.4 Summary ......................................................................................................................33

3. EXPERIMENTAL TECHNIQUES ......................................................................................34
3.1 Thin Film Fabrication ..................................................................................................34
3.1.1 RF Sputtering ...................................................................................................35
3.1.1.1 RF Co-sputtering ..................................................................................38
3.1.1.2 RF Sputtering from a doped target.......................................................41
3.1.2 Pulsed Laser Deposition (PLD) .......................................................................41
3.2 Characterization Techniques ........................................................................................43
3.2.1 X-ray Diffraction (XRD) .................................................................................44
3.2.2 X-ray Photoelectron Spectroscopy (XPS) .......................................................48
vii
3.2.3 Magnetic Characterization ...............................................................................50
3.2.4 Electrical Transport ..........................................................................................54

4. SnO :Co FILMS GROWN BY PULSED LASER DEPOSITION .......................................59
2
4.1 Introduction ..................................................................................................................59
4.2 Initial Structural Characterization ................................................................................59
4.3 Results and Discussion ................................................................................................63
4.3.1 Effect of Deposition Parameters on Films’ Physical Properties ......................63
4.3.1.1 Evidence of crystallinity - related magnetism and conduction ............66
4.3.2 Effect of Oxygen Annealing on Magnetization ...............................................73
4.3.3 Magnetic Characterization ...............................................................................74
4.3.3.1 Magnetism of as grown PLD films ......................................................75
4.3.3.2 Oxygen annealed PLD films ................................................................81
4.3.4 Transport Measurements ..................................................................................83
4.4 Conclusions ..................................................................................................................86

5. SnO :Co FILMS GROWN BY RF SPUTTERING ..............................................................88
2
5.1 Introduction ..................................................................................................................88
5.2 SnO :Co Films Grown by Co-sputtering .....................................................................89
2
5.2.1 Initial Structural Characterization ....................................................................89
5.2.2 Evidence of Co2+ Ions Presence in Sputtered Films ........................................91
5.3 SnO :Co Films Grown by Sputtering From a Doped Target .......................................96
2
5.3.1 Initial Characterization.....................................................................................96
5.3.2 Oxygen Annealing Studies ..............................................................................97
5.4 Summary ....................................................................................................................102

6. CONCLUSIONS .................................................................................................................103

REFERENCES ............................................................................................................................105

BIOGRAPHICAL SKETCH .......................................................................................................112

viii
LIST OF TABLES
Table 2.1 List of thin films deposited by RF sputtering (PM, FM, AHE, MR stand for:
paramagnetism, ferromagnetism, Anomalous Hall Effect, magnetoresistance, respectively)….. 25
Table 2.2 List of films grown by the PLD method ........................................................................28
Table 4.1 Values of d spacing and FWHM for SnO undoped thin films grown in vacuum and
(101) 2
in 0.1 mTorr and for SnO films doped with 5 at. % Co deposited in the same conditions. Perfect
2
silicon single crystals measured with the same optics have FWHM on the order of 0.15° ...........61
Table 4.2 Growth conditions for Samples 1, 2 and oxygen annealing treatment of Samples 3, 4,
studied in the following subchapter .............................................................................................74
Table 4.3 Calculated paramagnetic and ferromagnetic fractions for the as grown (Sample 2), 5
min. annealed (Sample 3), 30 min. annealed (Sample 4) samples. ...............................................82
Table 5.1 Interplanar distances determined from the diffraction patterns in Figure 5.3 ...............93

ix