Berlin 2015 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 30: Correlated Electrons: Spin Systems and Itinerant Magnets – Frustrated Magnets 3 (jointly with MA)
TT 30.4: Vortrag
Dienstag, 17. März 2015, 10:15–10:30, H 0110
Stabilisation of the tetragonal structure in (Ba,Sr)CuSi2O6 — •Pascal Puphal1, Natalija Van Well1, Franz Ritter1, Wolf Assmus1, Denis V. Sheptyakov2, Christian Rüegg2,3, and Cornelius Krellner1 — 1Physikalisches Institut, Goethe-Uni. Frankfurt — 2Lab. for Neutron Scattering and Imaging, PSI, Switzerland — 3Dep. of Quantum Matter Physics, Uni. of Geneva, Switzerland
BaCuSi2O6 is a spin dimer system presenting a 2D Bose-Einstein condensation of triplons at low temperatures and high magnetic fields. BaCuSi2O6 undergoes a structural phase transition below 100 K into an orthorhombic structure with two different dimer layers, leading to a complex Hamiltonian. Presently, the role of frustration in the orthorhombic structure is under debate. We present results for strontium substitution on the barium side and investigate the structural transition with low temperature x-ray and neutron powder diffraction. In addition the results of magnetic and specific-heat measurements are discussed. Surprisingly, we found that already small amounts of Sr (x = 0.05) lead to a suppression of the structural phase transition and the higher symmetric tetragonal crystal structure with only one sort of Cu-dimers is stable down to lowest temperatures. With increasing Sr-content the unit cell volume decreases and the intra-dimer spacing increases. Therefore, (Ba1−xSrx)CuSi2O6 is a spin dimer system in a well-defined tetragonal crystal structure with the possibility to control the exchange interactions. Further manipulation is possible in substituting silicon by germanium (especially considering co-substitution) resulting in an increased cell volume and intra-dimer spacing.