News
Browse Senn Group’s latest news, updates and papers.
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To Superspace and Beyond
Mark S. Senn, Acta Cryst. (2017). A73, 1-3. The significance of an algorithm developed by H. T. Stokes & B. J. Campbell [Acta Cryst. (2017), A73, 4-13] is discussed. The algorithm promises to be a key tool for understanding the structure-property relationships of the many technologically important materials that display incommensurate modulations in their atomic…
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Magnetostriction-driven ground-state stabilization in 2H perovskites
D. G. Porter, M. S. Senn, D. D. Khalyavin, A. Cortese, N. Waterfield-Price, P. G. Radaelli, P. Manuel, H.-C. zur-Loye, C. Mazzoli, and A. Bombardi The magnetic ground state of Sr3ARuO6 , with A=(Li,Na) , is studied using neutron diffraction, resonant x-ray scattering, and laboratory characterization measurements of high-quality crystals. Combining these results allows us…
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Directed Lifting of Inversion Symmetry in Ruddlesden–Popper Oxide–Fluorides: Toward Ferroelectric and Multiferroic Behavior
Ronghuan Zhang, Mark S. Senn, and Michael A. Hayward, Chem. Mater., DOI: 10.1021/acs.chemmater.6b03931 The cooperative tilting distortions of n = 2 Ruddlesden–Popper oxides can be utilized to break the inversion symmetry of the host lattice and induce ferroelectric behavior. Unfortunately the desired a–a–c+/a–a–c+ structural deformation is only stabilized in phases with extremely small structural…
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Emergence of long-range order in BaTiO3 from local symmetry-breaking distortions
M. S. Senn, D. A. Keen, T. C. A. Lucas, J. A. Hriljac, and A. L. Goodwin, Phys. Rev. Lett. 116 (2016), 207602. By using a symmetry motivated basis to evaluate local distortions against pair distribution function data (PDF), we show without prior bias, that the off-centre Ti displacements in the archetypal ferroelectric BaTiO3 are zone centred and rhombohedral-like in nature…
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Symmetry Switching of Negative Thermal Expansion by Chemical Control
Mark S. Senn, Claire A. Murray, Xuan Luo, Lihai Wang, Fei-Ting Huang, Sang-Wook Cheong, Alessandro Bombardi, Chris Ablitt, Arash A. Mostofi, and Nicholas C. Bristowe, J. Am. Chem. Soc., 10.1021/jacs.5b13192 The layered perovskite Ca3–xSrxMn2O7 is shown to exhibit a switching from a material exhibiting uniaxial negative to positive thermal expansion as a function of x.…
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Charge localization in the Verwey structure of magnetite
Mark S. Senn, Jon P. Wright, James Cumby, and J. Paul Attfield, Phys. Rev. B 92 (2015), 024104. The thermal evolution of electronic order in the complex Verwey ground state of magnetite (Fe 3 O 4 ) has been determined through 22 high-accuracy synchrotron x-ray structure refinements using three 10–40μm grains of stoichiometric magnetite. A robust fitting function is…
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Negative thermal expansion in hybrid improper ferroelectric Ruddlesden-Popper perovskites by symmetry trapping
M. S. Senn, A. Bombardi, C. A. Murray, C. Vecchini, A. Scherillo, X. Luo, and S. W. Cheong, Phys. Rev. Lett. 114 (2015), 035701. We present new results on the microscopic nature of the ferroelectricity mechanisms in Ca 3 Mn 2 O 7 and Ca 3 Ti 2 O 7 . To the first approximation, we confirm the hybrid improper ferroelectric mechanism recently proposed by Benedek and Fennie…
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B-Cation Order Control of Magnetism in the 1322 Perovskite CaCu3Fe2Nb2O12
Cation ordering in the 1322 perovskite CaCu3Fe2Nb2O12 has been investigated by synchrotron X-ray diffraction structure analysis, high-resolution electron microscopy, and magnetic measurements. All of the samples have full 1:3 ordering of Ca and Cu cations at the perovskite A-sites, but the Fe and Nb cations at the B sites show different degrees of ordering…
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Charge density wave fluctuations in La 2− x Sr x CuO 4 and their competition with superconductivity
T. P. Croft, C. Lester, M. S. Senn, A. Bombardi, and S. M. Hayden, Phys. Rev. B 89 (2014), 224513 We report hard (14 keV) x-ray diffraction measurements on three compositions (x=0.11,0.12,0.13) of the high-temperature superconductor La 2−x Sr x CuO 4 . All samples show charge density wave (CDW) order with onset temperatures in the range 51–80…
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A half-metallic A-and B-site-ordered quadruple perovskite oxide CaCu3Fe2Re2O12 with large magnetization and a high transition temperature
Wei-tin Chen, Masaichiro Mizumaki, Hayato Seki,Mark S. Senn, Takashi Saito, Daisuke Kan, J. Paul Attfield & Yuichi Shimakawa, Nature Communications 5 (2014), 3909. Strong correlation between spins and conduction electrons is key in spintronic materials and devices. A few ferro- or ferrimagnetic transition metal oxides such as La1−xSrxMnO3, Fe3O4, CrO2 and Sr2FeMoO6 have spin-polarized conduction…
