14High-field magnetization of the spin-1/2 antiferromagnet α-Cu2V2O7 was measured in pulsed magnetic fields of up to 56 T in order to study its magnetic phase diagram. When the field was applied along the easy axis (the a-axis), two distinct transitions were observed at Hc1 = 6.5 T and Hc2 = 18.0 T. The former is a spin-flop transition typical for a collinear antiferromagnet and the latter is believed to be a spin-flip transition of canted moments. The canted moments, which are induced by the Dzyaloshinskii-Moriya interactions, anti-align for Hc1 < H < Hc2 due to the anisotropic exchange interaction that favors the antiferromagnetic arrangement along the a-axis. Above Hc2, the Zeeman energy of the applied field overcomes the antiferromagnetic anisotropic interaction and the canted moments are aligned along the field direction. Density functional theory was employed to compute the exchange interactions, which were used as inputs for quantum Monte Carlo calculations and then further refined by fitting to the magnetic susceptibility data. Contrary to our previous report in Phys. Rev. B 92, 024423, the dominant exchange interaction is between the third nearest-neighbor spins, which form zigzag spin-chains that are coupled with one another through an intertwining network of the nonnegligible nearest and second nearest-neighbor interactions. In addition, elastic neutron scattering under the applied magnetic fields of up to 10 T reveals the incommensurate helical spin structure in the spin-flop state.

We report the results of magnetization and specific heat measurements of Ba2CoTeO6 composed of two subsystems A and B, which are magnetically described as an S = 1/2 triangular-lattice Heisenberg-like antiferromagnet and a J1 − J2 honeycomb-lattice Ising-like antiferromagnet, respectively. These two subsystems were found to be approximately decoupled. Ba2CoTeO6 undergoes magnetic phase transitions at TN1 = 12.0 K and TN2 = 3.0 K, which can be interpreted as the orderings of subsystems B and A, respectively. Subsystem A exhibits a magnetization plateau at one-third of the saturation magnetization for the magnetic field H perpendicular to the c axis owing to the quantum order-by-disorder, whereas for H c, subsystem B shows three-step metamagnetic transitions with magnetization plateaus at zero, one-third and one-half of the saturation magnetization. The analysis of the magnetization process for subsystem B shows that the classical ground states at these plateaus are infinitely degenerate within the Ising model.

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Rigid closed-cell polyurethane (PU) foam is well-known for its ability to withstand external force. On the other hand, due to the closed-cell nature, its ability to absorb sound is doubtful since hollowed materials are supposed be better in sound absorption. However, the composites fabrication with non-reactive fillers was thought to improve sound absorption ability since it might prohibit the formation of closed cell in the process. In this research, rigid polyurethane foam was prepared from polyether polyol and polymeric methylene di-isocyanate (p-MDI) formulated with water as a blowing agent. Natural rubber-wood sawdust was used as a filler. The percentages of rubber-wood sawdust in the polyurethane foam composites were varied by 0, 1, 3, 5 and 7%. The measurement of sound absorption coefficient has been done using impedance tube technique. The results showed that the rigid closed-cell polyurethane foam with 0% filler exhibits poor acoustic absorption. Additionally, sound absorption coefficient results showed that a sample with higher amount of rubber-wood sawdust allowed the sound wave to be absorbed at wider frequency range. This could be explained that the rubber-wood sawdust filler played an important role in sound absorption property.

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