Stabilization of the tetragonal structure in(Ba1−xSrx)CuSi2O6

Abstract

We present a structural analysis of the substituted system (Ba1−xSrx)CuSi2O6, which reveals a stable tetragonal crystal structure down to 1.5 K. We explore the structural details with lowtemperature neutron and synchrotron powder diffraction, room-temperature and cryogenic highresolution NMR, as well as magnetic-and specific-heat measurements and verify that a structural phase transition into the orthorhombic structure which occurs in the parent compound BaCuSi2O6, is absent for the x = 0.1 sample. Furthermore, synchrotron powder-diffraction patterns show a reduction of the unit cell for x = 0.1 and magnetic measurements prove that the Cu-dimers are preserved, yet with a slightly reduced intradimer coupling Jintra. Pulse-field magnetization measurements reveal the emergence of a field-induced ordered state, tantamount to Bose-Einsteincondensation (BEC) of triplons, within the tetragonal crystal structure of I 41/acd. This material offers the opportunity to study the critical properties of triplon condensation in a simple crystal structure.

Revealing three-dimensional quantum criticality by Sr substitution in Han purple

“…By comparing H c1 , for a field applied along the ĉ-axis, with the value of the spin gap extracted from INS, ∆ = 3.00(1) meV, we deduce a g-factor of g c = 2.298 +0.008 −0.008 . This result is in agreement with both the value 2.32(2) determined for the Sr-doped material 55 and the value g c = 2.306(3) obtained for the parent compound. 74 Clearly the mean value of φ we obtain agrees spectacularly well with the 3D exponent of 2/3, although we stress that the CIs are broad (as one may expect from the number of data points in the analysis), and to interpret these results we turn to QMC modelling.…”

“…As to the density of this disorder, while the nominal substitution was x = 0.1 and a compatible value of x = 0.08(2) was determined by energy-dispersive x-ray spectroscopy (EDX), a somewhat lower value of x = 0.05(1) was obtained from Rietveld refinement of synchrotron diffraction data for crushed crystals. 55 We conclude that local magnetic effects arising from this disorder are negligible, and that only its qualitative and quantitative effects on the average structure are relevant.…”

“…Figures 1e-f and 2b-e make clear that these parameters provide an excellent account of all the measured data, leaving no evidence of any requirement for further terms in the spin Hamiltonian. The INS parameters also serve as a benchmark for the magnetic interactions estimated using electronic structure calculations based on measurements of the atomic structure, 55 from which one may deduce (using the notation in Table II of that work) that J 1 ≡ J is obtained to very high accuracy, J 3 − J 5 ≡ J is overestimated by approximately 30%, J 4 = 0 is identified correctly and J 2 ≡ J is surprisingly accurate in both size and sign, given its small value. On this point, we stress that the three terms we have deduced form a hierarchy of interactions whose strengths differ by at least an order of magnitude, and hence that each is responsible for physics at quite different energy scales.…”

“…Thus a possible route to the ideal quasi-2D material would be to suppress the orthorhombic transition. In pursuing this programme, a number of stoichiometric substitutions have been tested on the non-magnetic Ba site, and it was reported 55 that even a 5% Sr substitution is sufficient to stabilize the tetragonal structure, represented in Fig. 1a, down to the lowest temperatures.…”

Crystal Growth with Oxygen Partial Pressure of the BaCuSi2O6 and Ba1–xSrxCuSi2O6 Spin Dimer Compounds

“…To separate the influence of the substitution with Sr and the influence of the change of the ratio between Si and O (±δ), additional investigations of BaCuSi2O6±δ, grown under oxygen partial pressure are currently performed. The investigation of the stabilization of the tetragonal structure in will be published elsewhere 25 . …”