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Viewing upcoming talks containing the keyword: 19
Speaker: Paul Attfield (Edinburgh)
Magnetic oxides revisited - new insights into manganites and magnetite J. Paul Attfield Centre for Science at Extreme Conditions and School of Chemistry, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, UK . email@example.com
Manganes e and iron based oxides a re important magne tic materials and continue to inspire new chemistry and electronic properties research . ‘Manganites’ are traditionally AMnO 3 perovskites such as La 0.7 Sr 0.3 MnO 3 with high Curie temperatures that show large magnetor esistances. High pressure has recently been used to synthesise new ‘A -site manganites’ with Mn 2+ cations at the A -sites. MnVO 3 perovskite has a helical spin order . Mn 2FeReO 6 has a high Curie temperature of 520 K and similar ferrimagnetic and spin -pola rised conducting properties to the much -studied magnetoresistive double perovskite Sr 2FeMoO 6, but also shows a novel switch from negative to large positive magnetoresistances at low temperatures driven by Mn 2+ spin ordering.  In contrast, Mn 2MnReO 6 (Mn 3ReO 6) shows successive antiferromagnetic ordering transitions for Re and Mn spins at 99 and 109 K respectively.  Investigation of possible rare earth (R) analogues has led to discovery of a new ‘double double perovskite’ type MnRMnSbO 6 (R = La, Pr, Nd, Sm) with simultaneous 1:1 cation order at both A and B sites [4 ].
Magnetite (Fe 3O4) is the original magnetic material and undergoes the complex Verwey structural distortion below 125 K. Determination of the full superstructure showed that charge order ing occurs , with a pronounced orbital ordering of Fe 2+ states, but an unexpected localization of electrons in linear, three -Fe ‘trimeron’ units was also discovered [5 ,6]. Trimerons are examples of orbital molecules, weakly bonded clusters of transition metal ions within an orbitally ordered solid . Recent studies of the orbital molecule orders in synthetic and natural magnetites [8,9], and related materials will be presented.
Our work on the magnetite structure has led to the development of a general new ellipsoidal method for analysing distorted polyhedra that will also be presented .
1. M. Markkula, A.M. Arevalo -Lopez, A. Kusmartseva, J.A. Rodgers, C. Ritter, H. Wu and J.P. Attfield. Phys. Rev. B 84, 094450 ( 2011). 2. Arévalo -López A.M., McNally G.M., Att field J.P. Angew. Chem. 54, 12074 (2015). 3. A. M. Arévalo -López, F. Stegemann, J. P Attfield. Chem . Comm . 2016, 52 , 5558. 4. E. Sola na -Madruga, Á. M. Arévalo -López, A. J. Dos Santos -García, E. Urones - Garrote, D. Ávila -Brande, R. Sáez -Puche, J. P. Attfield. Angew. Chem. 55, 9340 (2016). 5. Senn, M.S., Wright, J.P. & Attfield J.P. (2012), Nature 481, 173 -176. 6. Senn, M.S., Loa, I., Wright, J .P. & Attfield J.P. (2012). Phys. Rev. B 85, 125119. 7. J. P . Attfiel d (2015). Applied Physics Letters Materials 3, 041510. 8. Senn, M.S., Wright, J.P. , Cumby, J. & Attfield J.P. (2015 ). Phys. Rev. B 92 , 024104 . 9. G. Perversi , J Cumby , E. Pachoud , J. P. Wright, J. P. Attfield (2016). Chem. Comm. 52, 4864 -4867. 10. J. Cumby and J.P. Attfield. Nature Comm. (2017). Download PDF
On: February 1, 2017 From: 15h30 To: 16h30View talk
Cond Mat Seminars
Speaker: Behnam Tonekaboni Faghihnasiri (University of Queensland)
Heat engines are the heart of the thermodynamics. Different quantum heat engines have been proposed and built since 1980â€™s (For examples looking at [1, 2]). All of these engines use time-dependent, periodic Hamiltonian. Alternatively, we are interested in an autonomous quantum heat engine. Our proposed engine is a single-electron shuttle oscillating between two leads. This system was studied in  where it behaves as a mesoscopic electric motor driven by an external electrical bias. In contrast, our heat engine is a single-electron shuttle between two Fermi seas with the same chemical potentials but a temperature difference. Electrons can move from the high-temperature lead (source) to the low-temperature (drain) via the shuttle. The shuttle feels a force, when it carries an electron, due to the Johnson noise of the finite temperature lead. Since the average of the Johnson noise is zero; we need a rectifier to direct the force toward the drain. The rectification can be achieved by letting the shuttle oscillate in a half-harmonic potential.
Moreover, we propose a quantum ratchet battery which can be charged by absorbing the phonons from the engine. Then we define the power output of the engine as the rate of the absorption by the battery.
 Â R. Kosloff, The Journal of chemical physics 80, 1625 (1984).Â
 Â J. RoÃŸnagel, S. T. Dawkins, K. N. Tolazzi, O. Abah, E. Lutz, F. Schmidt-Kaler, and K. Singer, Science 352, 325 (2016).Â
 Â D. W. Utami, H.-S. Goan, C. Holmes, and G. Milburn, Physical Review B 74, 014303 (2006).
On: March 23, 2017 From: 12h00 To: 13h00View talk
Physics and Astronomy Colloquia
Speaker: Dr Silvia Vignolini (University of Cambridge)
Natureâ€™s most vivid colours rely on the ability to produce complex and hierarchical photonic structures with lattice constants on the order of the wavelength of visible radiation .Â A recurring strategy design that is found both in the animal and plant kingdoms for producing such effects is the helicoidal multilayers [2,3]. In such structures, a series of individual nano-fibers (made of natural polymers as cellulose and chitin) are arranged parallel to each other in stacked planes. When distance between such planes is comparable to the wavelength of light, a strong polarised, colour selective response can be obtained . These helicoidal multilayers are generally structured on the micro-scale and macroscopic scale giving rise to complex hierarchical structures.
Biomimetic with cellulose-based architectures enables us to fabricate novel photonic structures using low cost materials in ambient conditions [5-7]. Importantly, it also allows us to understand the biological processes at work during the growth of these structures in plants. In this talk the route for the fabrication of complex bio-mimetic cellulose-based photonic structures will be presented and the optical properties of artificial structures will be analyzed and compared with the natural ones. Kinoshita, S. et al. (2008). Physics of structural colors. Rep. Prog. Phys. 71(7), 076401.
 Vignolini, S. et al. (2012). Pointillist structural color in Pollia fruit PNAS 109, 15712-15716.
 Wilts, B. D, et al. (2014). Natural Helicoidal Structures: Morphology, Self-assembly and Optical Properties. Materials Today: Proceedings, 1, 177â€“185.
 de Vries, H. (1951). Rotatory power and other optical properties of certain liquid crystals. Acta Cryst., 4(3), 219â€“226.
 Dumanli, A. G., et al. (2014). Controlled, Bio-inspired Self-Assembly of Cellulose-Based Chiral Reflectors. Adv. Opt Mat., 2(7), 646â€“650.
 Parker R. et al. (2016). Hierarchical Self-Assembly of Cellulose Nanocrystals in a Confined Geometry ACS Nano, 2016, 10 (9), 8443â€“8449
 Kamita G. et al. (2016). Biocompatible and Sustainable Optical Strain Sensors for Large-Area Applications Adv. Opt. Mat. DOI: 10.1002/adom.201600451
On: April 21, 2017 From: 10h00 To: 11h00View talk
Speaker: Makoto Fujita (Tokyo)
Coordination Self -Assembly: From the Origins to the Latest Advances Makoto Fujita
Department of Applied Chemistry, The University of Tokyo firstname.lastname@example.org -tokyo.ac.jp
Molecular self -assembly based on coordination chemistry has made an explosive development in recent years. Over the last >25years, we have been showing that the simple combination of transition -metal’s square planer geometry (a 90 degree coordination angle) with pyridine -based bridging ligands gives rise to the quantitative self -as sembly of nano -sized, discrete organic frameworks. Representative examples include square molecules (1990), 1 linked -ring molecules (1994), 2 cages (1995), 3 capsules (1999), 4 and tubes (2004) 5 that are self -assembled from simple and small components. Origin ated from these earlier works, current interests in our group focus on i) molecular confinement effects in coordination cages, 6 ii) solution chemistry in crystalline porous complexes (as applied to “crystalline sponge method”), 7 and iii) and giant self -ass emblies (Figure 1), 8 as disclosed in this lecture.
Figure 1. The latest giant self - assembly from 144 small components. 8b The network topology is described as a “tetravalent Goldberg polyhedron” that has never been discussed to describe real 3D objects.
1. M. Fujita, J. Yazaki, and K. Ogura, J. Am. Chem. Soc. 1990 , 112 , 5645 -5647 2. M. Fujita, F. Ibukuro, H. Hagihara, K. Ogura, Nature 1994 , 367 , 720. 3. M. Fujita, D. Oguro, M. Miyazawa, H. Oka, K. Yamaguchi, K. Ogura, Nature 1995 , 378 , 469 -471 4. M. Fujita, N. Fujita, K. Ogura, and K. Yamaguchi Nature 1999 , 400 , 52 -55. 5. T. Yamaguchi, S. Tashiro, M. Tominaga, M. Kawano, T. Ozeki, and M. Fujita, J. Am. Chem. Soc. 2004 , 126 , 10818 - 10819. 6. (a) M. Yoshizawa, J. K. Klosterman, and M. Fujit a, Angew. Chem. Int . Ed. 2009 , 48 , 3418 -3438 (review). (b) M. Yoshizawa, M. Tamura, and M. Fujita, Science 2006 , 312 , 251 -254. 7. (a) Y. Inokuma, S. Yoshioka, J. Ariyoshi, T. Arai, Y. Hitora, K. Takada, S. Matsunaga, K. Rissanen, M. Fujita Nature 2013 , 495 , 461 -466. (b) M. Hoshino, A. Khutia, H. Xing, Y. Inokuma, M. Fujita, IUCrJ , 2016 , 3, 139 -151 . 8. (a) D. Fujita, Y. Ueda, S. Sato, H. Yokoyama, N. Mizuno, T. Kumasaka, M. Fujita, Chem 2016 , 1, 91 -101. (b) D. Fujita, Y. Ueda, S. Sato, N. Mizuno, T. Kumasaka, M. Fujita, Nature 2016, 540 , 563 –566 . Download PDF
On: May 19, 2017 From: 15h30 To: 16h30View talk
History of Mathematics
Speaker: Professor Malcolm Longair (Cavendish Laboratory, University of Cambridge)
Professor Longair, a former Astronomer Royal for Scotland and now at the Cavendish Laboratory in Cambridge, is an expert on the famous 19th century Scottish physicist, James Clerk Maxwell. The lecture will be aimed at a wide audience, and all are welcome.Professor Longair will be receiving an honorary DSc at the Mathematics graduation ceremony in the afternoon.
On: June 23, 2017 From: 10h30 To: 11h30View talk
Speaker: Simon Redfern (Cambridge)
Zeolitic imidazolate frameworks (ZIFs) are a class of metal organic frameworks that have structural similarities to aluminosilicate zeolites but show much greater framework flexibility. By tuning these structures selective guest incorporation can be achieved. In the case of ZIF -7, we have used neutron and synchrotron X -ray methods to understand the relationship between structural transformations of the host framework and CO2 incorporation. The potential for recycle CO2 capture and release from this material is remarkable, and further applications of these materials, from ferroelectric properties to their potential for drug delivery, are gaining wider appreciation. Here, I discuss the structural response of these materials to external and interna l pressure, to temperature, and to guest molecule incorporation. Download PDF
On: October 11, 2017 From: 15h30 To: 16h30View talk