The pervasive influence of strain coupling and dynamic strain relaxation associated with ferroic, multiferroic and superconducting phase transitions.

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• Prof. Michael Carpenter, University of Cambridge, Dept. of Earth Sciences
• Wednesday 01 March 2017, 11:15-12:15
• Mott Seminar Room (531), Cavendish Laboratory, Department of Physics.

If you have a question about this talk, please contact Helen Verrechia.

It is well understood that strain has a fundamental and pervasive influence on almost all types of phase transitions, 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, order/disorder, relaxor, …), magnetic (ferro/antiferromagnetic, spin-glass …), or electronic (charge order, Jahn-Teller, spin state, superconducting, metal-insulator, …). The most overt implications are, firstly, suppression of critical fluctuations (reduced Ginsburg interval), secondly, coupling between multiple order parameters in multiferroics via common strains, and, thirdly, interaction with defects of microstructures such as twin walls, vortices and skyrmions. The most sensitive method of detecting both static and dynamic strain coupling effects is via their influence on the elastic constants. In the last few years Resonant Ultrasound Spectroscopy has proved to be an effective method for measuring elastic and anelastic properties of samples with dimensions of between _{1 and} 5 mm, as a function of temperature or as simultaneous functions of temperature and magnetic 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 enough with strain to break the cubic lattice geometry but which still provides subtle evidence of magnetoelastic coupling. The Co-doped pnictide, Ba(Fe0.957Co0.043)As2, provides an example of an unconventional superconductor with competing ferroelastic, antiferromagnetic and superconducting transitions 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-superconducting transition in high fields.

Carpenter, M.A. (2015) Static and dynamic strain coupling behaviour of ferroic and multiferroic perovskites from Resonant Ultrasound Spectroscopy. Journal of Physics: Condensed Matter 27, 263201 Schiemer, J.A., L.J.Spalek, S.S.Saxena, C.Panagopoulos, T.Katsufuji, A.Bussmann-Holder, J.Köhler, M.A.Carpenter (2016) Magnetic field and in situ stress dependence of elastic behavior in EuTiO3 from resonant ultrasound spectroscopy. Physical Review B 93 , 054108. Evans, D.M., J.A.Schiemer, M.Schmidt, H.Wilhelm, M.A.Carpenter (2017) Strain relaxation behaviour of magnetoelectric Cu2OSeO3. Physical Review B (in press)

This talk is part of the Quantum Matter Seminar series.

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