UNIVERSITY of CALIFORNIA Santa Barbara Magnetism in Transition-Metal-Substituted Semiconducting Oxides A Dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Materials by Aditi S. Risbud Committee in charge: Professor Ram Seshadri, Chair Professor Anthony K. Cheetham Professor Nicola A. Spaldin Professor Juergen Eckert September 2005 The dissertation of Aditi S. Risbud is approved. Professor Anthony K. Cheetham Professor Nicola A. Spaldin Professor Juergen Eckert Professor Ram Seshadri, Committee Chair August 2005 Magnetism in Transition-Metal-Substituted Semiconducting Oxides Copyright c 2005 by Aditi S. Risbud iii for my parents iv Acknowledgements Often as a chapter in one’s life comes to a close, an appreciation for what is about to be lost begins to surface. It is a credit to Santa Barbara that from the moment of my arrival, I was aware of how fortunate I would be to complete my Ph.D. work in such a beautiful environment. This work would not have been possible without the help of my advisor, Ram Seshadri, who I thank for being a wonderful advisor these past few years. Ram’s enthusiasm and re- lentless curiosity about science has been an inspiration, and I appreciate all his guidance over my time here. I must also (grudgingly) admit that I am now a Linux user, and happy about it. My thesis research has been a collaborative effort, and I must thank all those that have made my dissertation work complete. Nicola Spaldin’s sup- port throughout my thesis has been invaluable; on top of that, she is proba- bly the coolest professor I know. Thanks for the careful reading of my thesis. Gavin Lawes’ straightforward and innovative description of the magnetic be- v havior of my materials systems lent valuable insight into my research. Lauren Snedeker was a fantastic intern, cheerily plugging away in the lab and helping my thesis work along. Mentoring is a highly rewarding part of science and I was happy to work with Lauren, Margaret MacRae and Rey Honrada dur- ing my time here. Many thanks to my committee members Tony Cheetham, Juergen Eckert, and David Clarke for their input and suggestions. I must also thank Z.Q. Chen, S. Stemmer, J.P. Attfield, J. Ensling, C. Felser, M.M. Elcombe, and A.P. Ramirez for their contributions. Before I began my Ph.D. work, there were a number of individuals who helped in the development of my science abilities. My undergraduate advisor at UC Davis, Alexandra Navrotsky, has an amazing devotion to science, and I thank her for inspiring me to pursue my doctoral degree. I also thank Kate Helean for her mentoring and friendship. My next research stint at Caltech was guided by Harry Atwater. Harry’s ability to communicate science effec- tively resounded with me and sparked the motivation for my current career goal. I also thank Regina Ragan for being a great mentor and role model dur- ing my time at Caltech. Upon my arrival at UCSB, the Lange group allowed me to make a seamless transition to the Materials department, and I thank Fred Lange, Geoff & Denice Fair, Mark & Nicole Snyder, Biao and Zhou, Ryan Bock, Scott Fillery, Haksung Moon, and Lars Loeffler for their support and vi friendship. Dave Andeen is probably the best officemate I have ever had, and I will miss our conversations about Barry Switzer, the Raiders, Kings, and stay- ing cool, Lakers-style. The Seshadri group has seen a few members come and go in its relative youth, and I thank our post-docs K. Ramesha and Ombretta Masala for their help with magnetic measurements and electron microscopy. Eric Toberer and I have spent far too much time together being officemates and the only graduate students in the Seshadri group, most memorably at MRS Boston, home of the world’s best public transportation Kit Kat. As for MRS San Francisco- I’m sorry about those contact lenses. I will miss our fashion and color scheme discussions. Someday we’ll compile that list of quotes and pass it on to future group members. The best part of graduate school has been all the great people I have spent time with, both on and off the court. Jenny Andrew has been a source of endless friendship, replete with silly accents, Bollywood dance sequences, kothimbeer-laden meals, and lame materials science jokes. Tu kasli whooshaar ahes! Thanks for sitting through all my practice talks (and the real ones too). Michael Pontin helped me see the conspiracies of the world, and even though he projects ’bitter old man,’ he is one of the kindest, most thoughtful people I know. David Follman has been a great housemate and friend. He is a talented writer and a tolerant individual, especially during basketball season. Adam vii Pyzyna was a fun housemate and friend, and I will miss watching Chappelle and discussing the latest hip-hop scoop. Emily Parker has been a great friend, workout buddy (only a good friend would be willing to come to Sean’s brutal spin class and save seats) and sounding board for all my ridiculous drama. Remember: You are a Genius. Seth Boeshore has been a fine source of South Park quotes and car bomb synergy. Over many a coffee, he has continually surprised me with his intellect (beyond just science) and sharp personal ob- servations. Weak. Thanks also to Garrett Cole for discussions on excitons, book hoarding, and general science enthusiasm. Katie Schaefer has been a great friend, shopping buddy (a convert, in fact) and listener, letting me whine about my day over a coffee (just not iced) or lunch. Justin Abramson is prob- ably the worst officemate but most interesting friend I’ve had- I will miss our discussions from science to life philosophies. You’ve certainly taught me a thing or two about myself, and I appreciate that. Also, thanks for all your help with SC. Larken Euliss was our favorite non-Materials person- thanks for in- troducing me to GVAC, bumble & bumble, and ‘thinking in chapters.’ Good luck at UT Arlington! I must also thank the Materials girls: Felicia Pitek, Lisa Kinder, Meghan Kerner, Molly Gentleman and Lori Callaghan for a great time, whether it was dancing downtown or in Vegas. There are a few people who let me ignore them for months and then are viii willing to talk to me when we finally see each other. I call them long-distance friends. Stephanie Moore introduced me to Travis, dressing red, and Jude Law. She’s a great friend and an Australian, but I don’t hold that against her. Nils-Eric Snekkevik has been a great friend, e-mailing from all over the world and allowing me to vent about grad school, career paths, and singing along to Coldplay. Julie Casperson (now Brewer) has been a wonderful support through Caltech and grad school, managing to give me advice about school, shoes, and boys in a single afternoon. Thanks for including me in your wed- ding. Jason Holt has been a good friend over the years as well, in the homes of the Lakers, Warriors, and Kings. At least we can make fun of the Clippers together. I also thank Chelsea McClain, Malini Jain, Sean Chen, Sonia Dass, and Jay Young for their friendships over the years. I must now thank the people without whom I wouldn’t have made it where I am today. My cousin Sarita and I have grown up together, whether it was in one house or across continents. She has been there through every event (ex- cept when her phone dies) of my life, from our crazy family reunions to con- ventions and college experiences (unfortunately G Street cannot compete with 6th Street) with her own brand of sarcasm. She is the closest thing I have to a sister, and I hope that never changes. Thanks also to Seema, Raja, Vikram, and Himaunshu for being sibling stand-ins and playing basketball (or football, it’s ix hard to tell sometimes) in that crazy Oklahoma heat. Go Sooners! Finally, I thank my mom and dad, Smita and Subhash Risbud, for being my true best friends in this world. Dad has kept up with every science project or goal I have every pursued, often sending me articles or newspaper clippings to read, proofreading my work, patiently listening no matter what the situation, sci- ence or otherwise. Mom is tireless, and has always been willing to go have fun at any time of day or night, chat about friends and family, and told me what I needed to hear (even if I didn’t want to hear it). She is definitely the genetic source of my sense of humor. I especially appreciate all the trips you guys have made to SLO, driving the entire day so that we could spend an afternoon together, bringing me Co-op cookies. I am a very lucky girl. As it comes to a close, I am happy to say that this chapter of my life has been one of the most rewarding and enjoyable, and I wouldn’t trade it for a thing. x Curriculum Vitæ Aditi S. Risbud Education 1996-2000 B.S. in Materials Science and Engineering University of California, Davis Davis, CA 2001-2005 Ph.D. Materials University of California, Santa Barbara Santa Barbara, CA Publications A. S. Risbud, R. Seshadri, J. P. Ensling, and C. Felser. Dilute Ferrimagnetic Semiconductors in Fe-substituted Spinel ZnGa2O4. Journal of Physics: Condensed Matter, 17, 1003 (2005). G. Lawes, A. S. Risbud, A. P. Ramirez, and R. Seshadri. Absence of ferromagnetism in Co and Mn substituted polycrystalline ZnO.