83 research outputs found
Magnetic interactions in the S = 1/2 square-lattice antiferromagnets Ba2CuTeO6 and Ba2CuWO6: parent phases of a possible spin liquid
The isostructural double perovskites Ba2CuTeO6 and Ba2CuWO6 are shown by theory and experiment to be frustrated square-lattice antiferromagnets with opposing dominant magnetic interactions. This is driven by differences in orbital hybridisation of Te6+ and W6+. A spin-liquid-like ground state is predicted for Ba2Cu(Te1-xWx)O6 solid solution similar to recent observations in Sr2Cu(Te1-xWx)O6
Tuning the square-lattice antiferromagnet SrCu(TeW)O from N\'eel order to quantum disorder to columnar order
The spin-1/2 square-lattice Heisenberg model is predicted to have a quantum
disordered ground state when magnetic frustration is maximized by competing
nearest-neighbor and next-nearest-neighbor interactions (). The double perovskites SrCuTeO and SrCuWO are
isostructural spin-1/2 square-lattice antiferromagnets with N\'eel (
dominates) and columnar ( dominates) magnetic order, respectively. Here we
characterize the full isostructural solid solution series
SrCu(TeW)O () tunable from N\'eel order to
quantum disorder to columnar order. A spin-liquid-like ground state was
previously observed for the = 0.5 phase, but we show that the magnetic
order is suppressed below 1.5 K in a much wider region of 0.1-0.6.
This coincides with significant -linear terms in the low-temperature
specific heat. However, density functional theory calculations predict most of
the materials are not in the highly frustrated region
square-lattice Heisenberg model. Thus, a combination of both magnetic
frustration and quenched disorder is the likely origin of the spin-liquid-like
state in = 0.5.Comment: 20+5 pages, 6+4 figures. Accepted for publication in PR
Quality Changes and Freezing Time Prediction During Freezing and Thawing of Ginger
Effects of different freezing rates and four different thawing methods on chemical composition, microstructure, and color of ginger were investigated. Computer simulation for predicting the freezing time of cylindrical ginger for two different freezing methods (slow and fast) was done using ANSYSÂŽ Multiphysics. Different freezing rates (slow and fast) and thawing methods significantly (P \u3c 0.05) affected the color and composition of essential oil in ginger. Fresh ginger was found to contain 3.60% gingerol and 18.30% zingerone. A maximum yield of 7.43% gingerol was obtained when slow frozen gingers when thawed by infrared method. Maximum zingerone content of 38.30% was achieved by thawing slow frozen gingers using infrared-microwave method. Microscopic examination revealed that structural damage was more pronounced in slow frozen gingers than fast frozen gingers. Simulated freezing curves were in good agreement with experimental measurements (r = 0.97 for slow freezing and r = 0.92 for fast freezing). Slow freezing damaged gingerâs cellular structure. Data obtained will be helpful in selecting appropriate thawing method to increase desirable essential oil components in ginger. Computer simulation for predicting freezing time may help in developing proper storage system of ginger
Conductivity and redox stability of new double perovskite oxide Sr 1.6 K 0.4 Fe 1+ x Mo 1â x O 6â δ (x= 0.2, 0.4, 0.6)
A series of new perovskite oxides Sr1.6K0.4Fe1+xMo1âxO6âδ (x = 0.2, 0.4, 0.6) were synthesised by solid state reaction method. Synthesis of Sr1.6K0.4Fe1+xMo1âxO6âδ (x = 0.2, 0.4, 0.6) was achieved above 700 °C in 5 % H2/Ar, albeit with the formation of impurity phases. Phase stability upon redox cycling was only observed for sample Sr1.6K0.4Fe1.4Mo0.6O6âδ. Redox cycling of Sr1.6K0.4Fe1+xMo1âxO6âδ (x = 0.2, 0.4, 0.6) demonstrates a strong dependence on high temperature reduction to achieve high conductivities. After the initial reduction at 1200 °C in 5 %H2/Ar, then re-oxidation in air at 700 °C and further reduction at 700 °C in 5 %H2/Ar, the attained conductivities were between 0.1 and 58.4 % of the initial conductivity after reduction 1200 °C in 5 %H2/Ar depending on the composition. In the investigated new oxides, sample Sr1.6K0.4Fe1.4Mo0.6O6âδ is most redox stable also retains reasonably high electrical conductivity, ~70 S/cm after reduction at 1200 °C and 2â3 S/cm after redox cycling at 700 °C, indicating it is a potential anode for SOFCs
Structure, spin correlations, and magnetism of the S = 1/2 square-lattice antiferromagnet Sr2CuTe1âxWxO6 (0 ⤠x ⤠1)
Quantum spin liquids are highly entangled magnetic states with exotic properties. The S = 1/2 square-lattice Heisenberg model is one of the foundational models in frustrated magnetism with a predicted, but never observed, quantum spin liquid state. Isostructural double perovskites Sr2CuTeO6 and Sr2CuWO6 are physical realizations of this model but have distinctly different types of magnetic order and interactions due to a d10/d0 effect. Long-range magnetic order is suppressed in the solid solution Sr2CuTe1âxWxO6 in a wide region of x = 0.05â0.6, where the ground state has been proposed to be a disorder-induced spin liquid. Here, we present a comprehensive neutron scattering study of this system. We show using polarized neutron scattering that the spin liquid-like x = 0.2 and x = 0.5 samples have distinctly different local spin correlations, which suggests that they have different ground states. Low-temperature neutron diffraction measurements of the magnetically ordered W-rich samples reveal magnetic phase separation, which suggests that the previously ignored interlayer coupling between the square planes plays a role in the suppression of magnetic order at x â 0.6. These results highlight the complex magnetism of Sr2CuTe1âxWxO6 and hint at a new quantum critical point between 0.2 < x < 0.4
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