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SUMMARY:THERMAL ORDERING AND DEFECTS IN ARTIFICIAL MAGNETIC SQUARE ICE-Dr.
  Jason Morgan TFM - Speaker to be confirmed
DTSTART:20130214T143000Z
DTEND:20130214T160000Z
UID:TALK43583@talks.cam.ac.uk
CONTACT:Kimberly Cole
DESCRIPTION:THERMAL ORDERING AND DEFECTS IN ARTIFICIAL MAGNETIC SQUARE ICE
 \n\nArtificial spin ices (ASIs) are 2D arrays of single domain nanomagnets
 \, designed for the user-defined exploration of the physics of competing i
 nteractions and collective ordering [1-3]. A periodic lattice with strong 
 local anisotropies captures the essence of geometrically frustrated materi
 als such as pyrochlore spin ice and water ice [4]\, with Ising-like nanoba
 r magnets converging at interlinked vertices. Furthermore\, they are reali
 sations of well known models in statistical mechanics. Crucially\, the gov
 erning dipolar interactions can be tailored via nanopatterning and real-sp
 ace observation of magnetic order is allowed via microscopy.\n\nUntil rece
 ntly\, attention has largely focussed on the response of athermal systems 
 to applied fields. For example\, ac demagnetisation yields "icy" short-ran
 ge correlated states however fails to access the true square ice ground st
 ate (GS) [1]. Furthermore\, the generation and manipulation of magnetic "m
 onopole" charge defects\, analogous to ionic conduction defects in water i
 ce [5]\, has also become a topic of intense interest.\n\nIn this presentat
 ion I will discuss my previous work conducted at the University of Leeds\,
  which reports the first experimental observations and subsequent studies 
 of true thermal ordering in ASIs [2\,3\,6]. This is achieved via an one-sh
 ot early-fabrication-stage anneal process\, which can allow for extensive 
 GS ordering to be frozen into such systems. This picture is supported by t
 he identification of a thermal distribution of magnetic excitations\, with
 in which evidence for charge-charge interactions can be identified. I will
  show how the strength of magnetic ordering can be controlled by the compe
 ting effects of dipolar coupling strength and quenched disorder\, and para
 meterised using an effective temperature formalism.\n\nTo close\, future d
 irections for this fascinating\nfield will be discussed.\n\nReferences\n\n
 [1]  R. F. Wang et al.\, Nature 439\, 303 (2006)\; X. Ke et al.\, PRL 101\
 , 037205 (2008)\n\n[2] J. P. Morgan\, A. Stein\, S. Langridge & C.H. Marro
 ws\, Nature Physics 7\, 75 (2011)\n\n[3] Z. Budrikis\, K. Livesey\, J. P. 
 Morgan\, J. Akerman\, A. Stein\, S. Langridge\, C. H. Marrows & R. L. Stam
 ps\, New Journal of Physics 14\, 035014 (2012)\n\n[4]  M. J. Harris et al.
 \, Phys. Rev. Lett. 79(13)\, 2554 (1997)\n\n[5]  C. Castelnovo et al.\, Na
 ture 451\,42 (2008)\n\n[6] J. P. Morgan\, J. Akerman\, C. Phatak\, A. Stei
 n\, S. Langridge & C. H. Marrows\, Phys. Rev. B 87\, 024405\, (2013)\n	\nC
 lick here to Reply\, Reply to all\, or Forward\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory
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