Speaker
David Sherrington
(Rudolf Peierls Centre for Theoretical Physics, University of Oxford, UK)
Description
In 1979 John Hertz introduced the concept of the Stoner
Glass to describe spin glass ordering in itinerant
transition metal magnetic alloys.
Two decades earlier an interesting behaviour (of distinctly
frequency-dependent but sharpish peaks in the dynamical
permittivity) was observed in some ceramic ionic alloys, now
known as relaxor ferroelectrics. They have received a great
deal of attention and practical application, but, even over
half a century later, their microscopic their underlying
physics has remained ill-understood and controversial. In
this talk I shall argue that they are actually displacive
analogues of John’s Stoner glass, the peaking corresponding
to the onset of the quasi-Stoner spin glass phase.
Displacive relaxor ferroelectrics have also been shown to
exhibit polar nano-regions persisting for measurable times
at temperatures higher than those of the permittivity peaks.
I shall argue that this behaviour and both the pseudo-Stoner
glass and pseudo-Stoner ferro-order can be understood in
terms of a mapping to the problem of Anderson localization,
analogous to (but extended beyond) one I devised in 1973 to
understand the same experimental systems as inspired John,
based on a similar disordered Hubbard model to that he used
(but with a complementary methodology). Recent experimental
measurements corroborate the argument for PNRs.
These observations extrapolate to several further
suggestions and questions for both relaxors and itinerant
spin glasses and the light of new knowledge could stream
again through the window that John opened half a lifetime ago.
Reference
1. J.A.Hertz: The Stoner Glass; PRB 19, 4796 (1979)
2. D.Sherrington and K.Mihill: Effects of Clustering on the
Magnetic Properties of Transition Metal Alloys: J.Physique
Colloque 35, C4-199 (1974)
3. D.Sherrington: BZT: A Soft Pseudospin Glass; PRL 111,
227601 (2013)
4. D.Sherrington: Pb(Mg1/3Nb2/3)O3: A minimal induced-moment
soft pseudospin glass perspective; PRB 89, 064105 (2014)
5. M.E.Manley et al.: Phonon localization drives polar
nanoregions in a relaxor ferroelectric; Nature Comm. 5:3683
DOI:10.1038/ncomms4683 (online April 2014)
