University of Minnesota
School of Physics & Astronomy

Condensed Matter Seminar

Thursday, October 29th 2009
1:25 pm:
Condensed Matter Seminar in 210 Physics
Speaker: Chris Leighton, Chemical Engineering and Materials Science, University of Minnesota
Subject: Nanoscopic Magnetic Phase Separation in the Doped Perovskite Cobaltites

Complex oxides such as perovskites have emerged as one of the most important platforms for the discovery of new phenomena in condensed matter physics. Colossal magnetoresistance in the maganites, and high temperature superconductivity in the cuprates are classic examples. The extraordinarily diverse physical phenomena displayed by these materials is due in large part to the strong competition between the various active degrees of freedom, which leads to a subtle energy balance between the multitude of available ground states. It is perhaps unsurprising that under these conditions, particularly in randomly doped systems, nanoscopic electronic inhomogeneity is ubiquitous. “Magneto-electronic phase separation”, where multiple electronic and magnetic phases coexist spatially, even in the absence of chemical segregation, has been observed in a wide range of materials and is widely believed to be due to electronically-driven phase separation. In this talk I will elaborate on the features of the doped perovskite cobaltites (e.g. La1-xSrxCoO3) which make them model systems for the study of this nanoscopic phase separation. We have used single crystals of these materials to study the phenomenology, consequences, and origins, of the magnetically phase-separated state, mostly by neutron scattering, transport, and heat capacity. Our primary conclusions are that (i) the spontaneous magnetic nanostructuring has many interesting consequences including the existence of “GMR-type” effects in a bulk solid, and (ii) the magnetic phase separation is driven purely by the local doping fluctuations that are inevitable at these nanoscopic length scales. In essence the nanoscale inhomogeneity is doping fluctuation-driven rather than electronically-driven, challenging, at least in these materials, the commonly accepted electronic phase separation scenario

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