Crystal Growth with Oxygen Partial Pressure of the BaCuSi₂O₆ and Ba_1–xSr_xCuSi₂O₆ Spin Dimer Compounds

Abstract

BaCuSi2O6 is a quasi-two dimensional spin dimer system and a model material for studying Bose-Einstein condensation (BEC) of magnons in high magnetic fields. The new Ba1-xSrxCuSi2O6 mixed system, which can be grown with x ≤ 0.3, and BaCuSi2O6, both grown by using a crystal growth method with enhanced oxygen partial pressure, have the same tetragonal structure (I41/acd) at room temperature. The mixed system shows no structural phase transition, so that the tetragonal structure is stable down to low temperatures. The oxygen partial pressure acts as control parameter for the growth process. A detailed understanding of the crystal structure depending on the oxygen content will enable the study of the spin dynamics of field-induced order states in this model magnetic compound of high current interest with only one type of dimer layers, which shows the same distance between the Cu atoms, in the structure.

Floating Zone Growth of Sr Substituted Han Purple: Ba0.9Sr0.1CuSi2O6

“…Recently, we reported on the substitution series of (Ba,Sr)CuSi 2 O 6 , which stabilizes the tetragonal room temperature structure of BaCuSi 2 O 6 down to lowest temperatures already with 5% substititution [12]. In a following study, we could show the growth conditions of BaCuSi 2 O 6 single crystals and its Sr-substituted variant [13] by self melt growth in oxygen pressure. The resulting crystals have a typical size of 2 × 1 × 0.5 mm 3 .…”

“…Afterwards, the melting turns it to a viscous mass that glazes when cooled in air. However, upon applying oxygen pressure, the decomposition is shifted up further than the melting temperature seen in a DSC experiment performed in air compared to one in oxygen flow with a partial pressure of 1.3 bar [13] (see Figure 2). Using a linear interpolation, the difference between decomposition and melting would meet at around 2 bar.…”

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

“…45 However, the latter method cannot be applied to the substituted system, Ba 0.9 Sr 0.1 CuSi 2 O 6 , because the metaborate flux reacts with the SrO reagent. 56 Thus two methods were employed to grow the single crystals used in the present work. All of the high-field experiments were performed using small single crystals (sizes of order 10 mg) grown from the congruent melt in a tube furnace with an oxygen flow at a pressure under 1 bar.…”

“…All of the high-field experiments were performed using small single crystals (sizes of order 10 mg) grown from the congruent melt in a tube furnace with an oxygen flow at a pressure under 1 bar. 56 The INS experiments were performed using one rod-shaped single crystal of mass 1.3 g grown by a floating-zone method. While this method was developed 57 for BaCuSi 2 O 6 , it could not be applied directly to Ba 0.9 Sr 0.1 CuSi 2 O 6 because large oxygen bubbles from the reduction of CuO disconnected the two rods and terminated the crystal growth.…”

“…1a, down to the lowest temperatures. However, it is a significant challenge to grow single crystals of the substituted material, 56 and particularly to grow large single crystals suitable for inelastic neutron scattering (INS) experiments. 57 We have solved these problems, enabling the detailed study of the ground state and phase diagram of Ba 0.9 Sr 0.1 CuSi 2 O 6 that we present.…”