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SUMMARY:The pervasive influence of strain coupling and dynamic strain rela
 xation associated with ferroic\, multiferroic and superconducting phase tr
 ansitions. - Prof. Michael Carpenter\, University of Cambridge\, Dept. of 
 Earth Sciences
DTSTART:20170301T111500Z
DTEND:20170301T121500Z
UID:TALK70524@talks.cam.ac.uk
CONTACT:Helen Verrechia
DESCRIPTION:It is well understood that strain has a fundamental and pervas
 ive influence on almost all types of phase transitions\, either as the dri
 ving order parameter (acoustic mode instability) or by coupling with some 
 other driving mechanism\, which may be structural (soft mode\, atomic orde
 ring\, hydrogen bonding\, …)\, ferroelectric (displacive\, order/disorde
 r\, relaxor\, …)\, magnetic (ferro/antiferromagnetic\, spin-glass …)\,
  or electronic (charge order\, Jahn-Teller\, spin state\, superconducting\
 , metal-insulator\, …). The most overt implications are\, firstly\, supp
 ression of critical fluctuations (reduced Ginsburg interval)\, secondly\, 
 coupling between multiple order parameters in multiferroics via common str
 ains\, and\, thirdly\, interaction with defects of microstructures such as
  twin walls\, vortices and skyrmions. The most sensitive method of detecti
 ng both static and dynamic strain coupling effects is via their influence 
 on the elastic constants. In the last few years Resonant Ultrasound Spectr
 oscopy has proved to be an effective method for measuring elastic and anel
 astic properties of samples with dimensions of between ~1 and ~5 mm\, as a
  function of temperature or as simultaneous functions of temperature and m
 agnetic field. Examples of ferroelastic materials which also have magnetic
  transitions are provided by KMnF3 and EuTiO3. Cu2OSeO3\, is an example of
  a material in which a helimagnetic structure does not couple strongly eno
 ugh with strain to break the cubic lattice geometry but which still provid
 es subtle evidence of magnetoelastic coupling. The Co-doped pnictide\, Ba(
 Fe0.957Co0.043)As2\, provides an example of an unconventional superconduct
 or with competing ferroelastic\, antiferromagnetic and superconducting tra
 nsitions which all have an influence on the macroscopic strain and\, hence
 \, on the elastic properties. In particular\, the presence of vortices in 
 the superconducting phase can cause elastic stiffening by 10’s of % and 
 is responsible for significant anelastic losses at the normal-superconduct
 ing transition in high fields.\n\nCarpenter\, M.A. (2015) Static and dynam
 ic strain coupling behaviour of ferroic and multiferroic perovskites from 
 Resonant Ultrasound Spectroscopy. Journal of Physics: Condensed Matter 27\
 , 263201\nSchiemer\, J.A.\, L.J.Spalek\, S.S.Saxena\, C.Panagopoulos\, T.K
 atsufuji\, A.Bussmann-Holder\, J.Köhler\, M.A.Carpenter (2016) Magnetic f
 ield and in situ stress dependence of elastic behavior in EuTiO3 from reso
 nant ultrasound spectroscopy. Physical Review B 93\, 054108.\nEvans\, D.M.
 \, J.A.Schiemer\, M.Schmidt\, H.Wilhelm\, M.A.Carpenter (2017) Strain rela
 xation behaviour of magnetoelectric Cu2OSeO3. Physical Review B (in press)
 \n
LOCATION:Mott Seminar Room (531)\, Cavendish Laboratory\, Department of Ph
 ysics
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