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SUMMARY:IEEE Magnetics Society Distinguished Lecturer 2010: A New Paradigm
  for Exchange Bias in Polycrystalline Films - Professor Kevin O'Grady\, De
 partment of Physics\, The University of York\, Heslington\, York
DTSTART:20100729T133000Z
DTEND:20100729T143000Z
UID:TALK25088@talks.cam.ac.uk
CONTACT:Adrian Ionescu
DESCRIPTION:The phenomenon of exchange bias has remained something of a my
 stery since it was discovered in core-shell particles in 1956 [1]. Over th
 e subsequent years many different models have been proposed to explain thi
 s effect\, most of which agree with some experimental data that can be fou
 nd in the literature. No single theory\, however\, has been able to explai
 n the data consistently for different systems. \nIn this lecture the reaso
 n for our inability to explain exchange bias will be reviewed\, and a new 
 paradigm to explain the phenomenon in sputtered polycrystalline films will
  be presented. This new paradigm is based on an original granular model de
 scribed by Falcomer and Charap [2]. Its premise is that very careful therm
 al and magnetic cycling is required to ensure that the order in the antife
 rromagnetic grains is controlled. Without such careful control\, reproduci
 ble data cannot be obtained.\nThese time-consuming and complex measurement
  procedures\, to which we refer as the York protocol\, have been developed
  over the last 9 years. Using the York protocol and an extension of the fo
 rmer granular model\, effects such as the film thickness dependence and gr
 ain size dependence of exchange bias can be fully explained with an excell
 ent fit between theory and experiment [3]. The York protocol also allows f
 or the measurement of the anisotropy constant of antiferromagnetic grains 
 [4]. This model provides an understanding of the behavior of the individua
 l antiferromagnetic grains in detail. Since the behavior of the "bulk" of 
 the antiferromagnetic grains is now known\, preliminary data describing th
 e behavior of the interface spins can now be distinguished from the behavi
 or of the bulk. Possible mechanisms for the behavior of the interfaces the
 mselves will also be presented.\n\n[1] W.H. Meiklejohn and C.P. Bean\, Phy
 s. Rev. 102\, 1413 (1956)\; IEEE Trans. Magn. 37\, 3866 (2001).\n[2] E. Fu
 lcomer and S.H. Charap\, J. Appl. Phys. 43\, 4190 (1972).\n[3] G. Vallejo-
 Fernandez\, L.E. Fernandez-Outon and K. O’Grady\, J. Phys. D: Appl. Phys
 . 41\, 112001 (2008).\n[4] G. Vallejo-Fernandez\, L.E. Fernandez-Outon and
  K. O’Grady\, Appl. Phys. Lett. 91\, 212503 (2007). \n\nCurriculum Vitae
 \n\nProf. K O'Grady received the Ph.D. in physics from The University of W
 ales in Bangor. He was a junior professor at Loughborough University of Te
 chnology and subsequently in the School of Electronic Engineering at Bango
 r\, where he achieved a full professorship. In 2000 Prof. O’Grady reloca
 ted to the Physics Department at the University of York.\n Prof. O'Grady's
  work concentrates on magnetization reversal in a wide range of materials\
 , but particularly those finding application in the information storage in
 dustry such as magnetic hard disk drives. In his early career Prof. O'Grad
 y investigated fundamental fine particle magnetism by utilizing colloidal 
 dispersions (ferrofluids) as the medium for study. His current research in
 terests are in the field of materials for hard disks\, and also in exchang
 e bias materials where an antiferromagnet is grown in contact with a ferro
 magnet and is used to pin one layer in a giant magnetoresistance stack in 
 disk drive read sensors.\nProf. O'Grady has published over 250 refereed wo
 rks on the subject of magnetization reversal. He is a former president of 
 the IEEE Magnetics Society and an editor of The Journal of Physics D: Appl
 ied Physics. He has been associated with the Intermag Conference as Progra
 m Committee co-chair in 1996\, 2002 and 2008\, and will serve as the gener
 al chair of the 2010 Joint MMM-Intermag Conference. He is the founding dir
 ector of the York Materials Research Institute.
LOCATION:Mott Seminar Room\, Cavendish Laboratory
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