Abstract
Following the XMCD measurements that have shown that the magnetisation in Co doped ZnO and In2O3 does not originate from the polarised partly filled d shell of the substituted Co ions there has been much interest to determine the origin of the ferromagnetic signals that are certainly present at room temperature. There are two obvious candidates, polarised defects and inclusions of metallic cobalt. These two mechanisms have quite different magnetic circular dichroism (MCD) spectra, in the visible range, and hence MCD is a very powerful method to identify the contribution of each to the total magnetisation.
This talk will describe results on two different samples, one made by sputtering in Cambridge and the other by PLD in KACST Saudi Arabia. The Cambridge sample [1] is a clear case of an electronic origin. The states are a polarised band with energy near the top of the band gap. The KACST sample is dominated by metallic Co, however when it is grown including a small percentage of tin the metallic cobalt disappears and the electronic contribution to the MCD is enhanced because of the concomitant rise in the carrier density [2].
[1] A M Hakimi Phys Rev 84, 085201 (2011)
[2] M S Alshammari et al (to be presented at ICM 2012) and Thesis University of Sheffield 2012
Brief CV
Gillian Gehring
University education:
1959-62 University of Manchester B.Sc. Class I (with honours in Physics)
1963-5 University of Oxford D. Phil (supervised by W Marshall)
Employment:
1965-7 Leverhulme Research Fellow St Hugh's College University of Oxford
1967-8 NATO Research Fellow University of California Berkeley with C Kittel
1968-89 Lecturer and Tutor in Physics St Hugh's College in the University of Oxford.
1989-06 Professor of Solid State Physics University of Sheffield
1996-99 Head of Physics Department University of Sheffield
2006- Emeritus Professor University of Sheffield
Honours:
1992 Honorary DSc, University of Salford
2004 Honorary Fellow of St Hugh’s College Oxford
2005 O.B.E ‘For Services to Physics and to Equal Opportunities’
2006 -8 Leverhulme Emeritus Fellowship
2009 Mott Medal and Prize awarded by the Institute of Physics
2009 Honorary Fellow of the Institute of Physics
2010 Honorary Member of the European Physical Society
2011 Honorary DSc, University of Sheffield – to be conferred in 2012
2012-14 Leverhulme Emeritus Fellowship
Research Areas: Theoretical and experimental studies on condensed matter physics, mostly in magnetism. Currently magnetic oxides particularly magnetic oxide semiconductors.
Selected publications:
1. Co-operative Jahn-Teller effects GA Gehring and KA Gehring Rep Prog Phys 38 (1975) 1-85
2. The density-matrix renormalization-group for a quantum spin chain at nonzero temperature RJ Bursill, T Xiang and GA Gehring J Phys Cond Matt 8 (1996) 583
3. Ferromagnetism above Room Temperature in Bulk and Transparent Thin films of Mn doped ZnO Parmanand Sharma, Amita Gupta, K.V. Rao, Frank J. Owens, Renu Sharma, Rajeev Ahuja, J. M. Osorio Guillen, Börje Johansson and GA Gehring Nature Mater 2 (2003) 673-77.
4. Room-temperature magneto-optics of ferromagnetic transition-metal-doped ZnO thin films JR Neal, AJ Behan, RM Ibrahim, H J Blythe, M Ziese, AM Fox and GA Gehring Phys Rev Lett 96 (2006) 197208
5. Two magnetic regimes in doped ZnO corresponding to a dilute magnetic semiconductor and a dilute magnetic insulator, AJ Behan, J R NealA Mokhtari, HJ Blythe,D Score, XH Xu, JR Neal, AM Fox and GA Gehring, Phys Rev Lett 100 (2008) 047206
6. Complex Multicolor Tilings and Critical Phenomena in Tetraphilic Liquid Crystals. XB Zeng, R Kieffer, B Glettner, C Nurnberger, F Liu, K Pelz, M Prehm, U Baumeister, H Hahn, H Lang, GA Gehring, CHM Weber, JK Hobbs, C Tschierske, and G Ungar, Science 331 (2011) 1302-1306
