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Physics & Astronomy Colloquium – 3/28/2018
March 28, 2018 @ 3:30 pm - 5:00 pm
Speaker: Christianne Beekman (Florida State University)
Title: Structural Tuning of Orbital and Spin Order in Frustrated Antiferromagnets
Abstract: Magnetic oxides comprised of a frustrated magnetic network of 3d transition metals, in which orbital, spin and structural degrees of freedom are strongly coupled, have been an active playground for researchers due to the promise of finding routes to new behaviors, such as charge-order, spin glass behavior and new types of multiferroics [1-3]. Spinel vanadates, poster materials for orbital physics in frustrated antiferromagnets, have been intensely studied to gain a better understanding on how orbital order can help relieve spin degeneracy. For example, FeV2O4 and MnV2O4 compounds show multiple structural phase transitions as a function of temperature eventually leading to non-collinear and orbital ordered ground states  that exhibit ferroelectricity and signs of appreciable magnetoelectric coupling . CoV2O4, the focus of this talk, is the most interesting of the vanadates because of its proximity to a localized-itinerant crossover regime. Experimentally, CoV2O4 defies predictions by showing orbital degeneracy seemingly lasting to very low temperatures. Only recently a weak spin canting and a first order structural transition associated with an orbital glass transition has been identified at T = 90 K at the edge of detectability [5,6]. The proximity to itinerancy has been indicated as the cause for the difficulties in observing these transitions reproducibly. In contrast to the weak effects seen in cubic bulk samples, I will present recent results on our orthorhombic CoV2O4 thin films that demonstrate unmistakable signatures of spin canting and structural effects that indicate long-ranged orbital order . Apparently, the slight change in the unit cell has driven the system deeper into the insulating state showing that structural tuning in thin films is a viable knob for ground state manipulation in frustrated systems.
Speaker Biography: Dr. Beekman holds the position of Assistant Professor at Florida State University. She was a postdoctoral researcher at the University of Toronto and Oak Ridge National Laboratory after she received her PhD. at Leiden University, Netherlands.
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