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SUMMARY:Structural and magnetic transitions in minerals and functional mat
 erials: the pervasive roles of strain and elasticity - Prof. Michael Carpe
 nter\, Department of Earth Sciences\, Cambridge
DTSTART:20210304T150000Z
DTEND:20210304T160000Z
UID:TALK154429@talks.cam.ac.uk
CONTACT:Daniel Field
DESCRIPTION:Lattice distortions\, formally described as "strain"\, accompa
 ny almost all types of phase transitions in crystalline materials\, either
  as the driving order parameter (acoustic mode instability) or by coupling
  with some other driving mechanism\, which may be structural (soft mode\, 
 atomic ordering\, hydrogen bonding\, …)\, ferroelectric (displacive\, or
 der/disorder\, relaxor\, …)\, magnetic (ferro/antiferromagnetic\, spin-g
 lass …)\, or electronic (charge order\, Jahn-Teller\, spin state\, super
 conducting\, metal-insulator\, …). The underlying physics is the same fo
 r minerals as for functional materials used in device applications: critic
 al fluctuations are suppressed\, coupling between multiple order parameter
 s occurs via common strains\, and microstructures such as twin walls\, vor
 tices and skyrmions interact with point defects or with each other. If the
 re are changes in strain\, it is inevitable that there will also be change
 s in elastic moduli and these provide clear insights into the dynamics and
  mechanisms of any phase transition of interest. Amongst minerals\, transi
 tions in quartz and stishovite give rise to large and characteristic patte
 rns of elastic softening which should be detectable in seismic data. Recen
 t focus\, however\, has been on materials which undergo more than one phas
 e transition. Amongst minerals with such multiple instabilities are feldsp
 ars (displacive transitions\, Al/Si ordering) and pyrrhotites (vacancy ord
 ering\, magnetic transitions). Landau theory provides a coherent and robus
 t description of how these materials will evolve with temperature\, while 
 Resonant Ultrasound Spectroscopy provides a convenient experimental method
  for following the variations of elastic moduli through the phase transiti
 ons. Current focus\, in particular\, is on the strength of magnetoelastic 
 coupling and examples provided by pyrrhotite\, hematite and ilmenite show 
 that this can be highly variable in minerals. As an example of a functiona
 l material\, the interacting structural\, magnetic and superconducting tra
 nsition in the pnictide Ba(Fe1-xCox)2As2 will be described. Future directi
 ons for work on functional materials relate to the use of twin walls for d
 evice applications on a nanoscale.\n\nReferences\n\nCarpenter\, M.A. and E
 .K.H.Salje (1998) Elastic anomalies in minerals due to structural phase tr
 ansitions. European Journal of Mineralogy 10\, 693–812.\n\nCarpenter\, M
 .A.\, R.J.Hemley and H.K.Mao (2000) High-pressure elasticity of stishovite
  and the P42/mnm - Pnnm phase transition. Journal of Geophysical Research 
 105\, 10807–10816.\n\nCarpenter\, M.A. (2006) Elastic properties of mine
 rals and the influence of phase transitions. American Mineralogist 91\, 22
 9–246.\n\nOravova\, L.\, Z.Zhang\, N.Church\, R.J.Harrison\, C.J.Howard\
 , M.A.Carpenter (2013) Elastic and anelastic relaxations accompanying magn
 etic ordering and spin-flop transitions in hematite\, Fe2O3. Journal of Ph
 ysics: Condensed Matter 25\, 116006.\n\nCarpenter\, M.A. (2015) Static and
  dynamic strain coupling behaviour of ferroic and multiferroic perovskites
  from Resonant Ultrasound Spectroscopy. Journal of Physics: Condensed Matt
 er 27\, 263201.\n\nSalje\, E.K.H\, M.A.Carpenter (2015) Domain glasses: tw
 in planes\, Bloch lines\, and Bloch points. Physica Status Solidi B 252\, 
 2639–2648.\n\nEvans\, D.M.\, J.A.Schiemer\, T.Wolf\, P.Adelmann\, A.E.B
 öhmer\, C.Meingast\, S.E.Dutton\, Y.-T.Hsu\, M.A.Carpenter (2019) Strain 
 relaxation behaviour of vortices in a multiferroic superconductor. Journal
  of Physics: Condensed Matter 31\, 135403.\n\nCarpenter\, M.A.\, D.L.Evans
 \, J.A.Schiemer\, T.Wolf\, P. Adelmann\, A.E.Böhmer\, C.Meingast\, S.E.Du
 tton\, P.Mukherjee\, C.J.Howard (2019) Ferroelasticity\, anelasticity and 
 magnetoelastic relaxation in Co-doped iron pnictide: Ba(Fe0.957Co0.043)2As
 2. Journal of Physics: Condensed Matter 31\, 155401.\n\nHaines\, C.R.S.\, 
 C.J.Howard\, R.J.Harrison\, M.A.Carpenter (2019) Group theoretical analysi
 s of structural instability\, vacancy ordering and magnetic transitions in
  the system troilite (FeS) – pyrrhotite (Fe1−xS). Acta Crystallographi
 ca B 75 1208–1224.\n\nHaines\, C.R.S.\, S.E.Dutton\, M.W.R.Volk\, M.A.Ca
 rpenter (2020) Magnetoelastic properties and behaviour of 4C pyrrhotite\, 
 Fe7S8\, through the Besnus transition. Journal of Physics: Condensed Matte
 r 32\, 405401.\n\nHaines\, C.R.S.\, G.I.Lampronti\, M.A.Carpenter (2020) M
 agnetoelastic coupling associated with vacancy ordering and ferrimagnetism
  in natural pyrrhotite\, Fe7S8. Journal of Physics: Condensed Matter 32 38
 5401.\n\nZhang\, Y.\, S.Fu\, B.Wang\, J.-F.Lin (2021) Elasticity of a pseu
 doproper ferroelastic transition from stishovite to post-stishovite at hig
 h pressure. Physical Review Letters 126\, 025701\n\n
LOCATION:Zoom Seminar
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