Search

Abstract A polymorph of Cu2OSeO3 with the distorted kagome lattice is successfully obtained using the high‐pressure synthesis technique (Cu2OSeO3‐HP). The structural analysis using X‐ray and neutron powder diffraction suggests that the tetrahedral Cu2+ clusters [similar to those in Cu2OSeO3 ambient‐pressure phase (Cu2OSeO3‐AP)] exist in Cu2OSeO3‐HP but with three symmetry inequivalent sites. No structural change is observed between 1.5 K and the room temperature. The complex magnetic H‐T phase diagram is established based on the temperature‐ and field‐dependent magnetization data, indicating two distinct antiferromagnetic phases at low and intermediate temperatures, in addition to the higher‐temperature spin‐glass‐like phase. The low temperature phase is identified by neutron powder diffraction refinements as a canted noncollinear antiferromagnetic order with a weak ferromagnetic component along the b‐axis. Size of the refined ordered moment is ≈1.00(4) µB in Cu2OSeO3‐HP, indicating a large enhancement compared to that of Cu2OSeO3‐AP (≈0.61 µB). By applying a uniaxial stress, finite enhancement of weak ferromagnetic component in the noncollinear antiferromagnetic phase in Cu2OSeO3‐HP is observed, which is the clear evidence of the piezomagnetic effect. Interestingly, the sign of the induced magnetization changes on heating from the low‐temperature to the intermediate‐temperature phases, indicating a novel piezomagnetic switching effect in this compound.

Abstract A magnetic structure of the sawtooth-chain antiferromagnet $$\hbox {Fe}_2\hbox {Se}_2\hbox {O}_7$$ Fe 2 Se 2 O 7 was investigated by magnetization measurements, single crystalline and powder neutron diffraction experiments, and a further analysis on the Mössbauer spectra. These experiments revealed a nearly collinear antiferromagnetic structure with magnetic moments aligned along the b-axis, indicating dominant antiferromagnetic exchanges between Fe(1)–Fe(2) and Fe(2)–Fe(3) sites. The magnon dispersion relation derived from the linear spin wave approximation suggests the possible flat band nature of magnons.

Topological edge states can emerge not only in a fermionic electron system but also in a bosonic system. Here, Nawa et al. report topologically nontrivial triplon bands in a two-dimensional dimerized quantum antiferromagnet Ba2CuSi2O6Cl2, suggesting a bosonic realization of the coupled Su-Schrieffer-Heeger model.

The spin excitations of the S=1/2 anisotropic triangular antiferromagnet Ca_{3}ReO_{5}Cl_{2} were investigated by inelastic neutron-scattering experiments. The spin excitation spectrum exhibits sharp dispersive modes in addition to a spinonlike continuum. The sharp modes exhibit large and small dispersions along the intrachain (K) and interchain directions (L), respectively, reflecting a one-dimensional character modified by interchain interactions. The dispersion intensity along the interchain direction is enhanced at the wave vectors around (K, L)=(0.25,±1.0) and (0.75, 0.0) (in reciprocal lattice units, r.l.u.). This enhancement is well explained by the formation of bound spinon pairs. These features are reminiscent of the spin excitations observed in the prototypical compound Cs_{2}CuCl_{4} [Coldea, et al., Phys. Rev. Lett. 86, 1335 (2001)10.1103/PhysRevLett.86.1335; Phys. Rev. B 68, 134424 (2003)10.1103/PhysRevB.68.134424]. The consistency with the simulated spectrum based on the random-phase approximation is better for Ca_{3}ReO_{5}Cl_{2} than for Cs_{2}CuCl_{4}, indicating that the spin system in the former remains closer to a Tomonaga-Luttinger liquidlike disordered state. In addition, the low-energy modes exhibit a wave-vector shift along the ±K direction, suggesting that uniform intrachain Dzyaloshinskii-Moriya interactions are more relevant in Ca_{3}ReO_{5}Cl_{2}.

We have investigated magnetic properties of the rare-earth based intermetallic compound Yb3Ni11Ge4.63 (YNG), where Yb3+ ions form a breathing-kagome lattice. Single-site 4 f electron wavefunctions of the ground-state doublet are deduced from magnetization and heat capacity measurements. The Weiss temperatures are quite anisotropic as Θa = -0.01(2)K (H ‖ a) and Θc = -0.67(2)K (H ‖ c), indicating Ising-like spin-spin interactions dominating in this compound. Low-temperature neutron diffraction confirms absence of magnetic Bragg peaks down to 0.05 K, whereas enhancement of broad peaks below 0.8K was observed, a signature of short-range spin correlations. Competing interactions on the breathing-kagome lattice would suppress a magnetic long-range order in YNG. [ABSTRACT FROM AUTHOR]

A new spin-1/2 quasi-one-dimensional antiferromagnet KCuMoO4(OH) is prepared by the hydrothermal method. The crystal structures of KCuMoO4(OH) and the already-known Na-analogue NaCuMoO4(OH) are isotypic, comprising chains of Cu2+ ions in edge-sharing CuO4(OH)2 octahedra. Despite the structural similarity, their magnetic properties are quite different because of the different arrangements of dx²-y² orbitals carrying spins. For NaCuMoO4(OH), dx²-y² orbitals are linked by superexchange couplings via two bridging oxide ions, which gives a ferromagnetic nearest-neighbor interaction J1 of -51 K and an antiferromagnetic next-nearest-neighbor interaction J2 of 36 K in the chain. In contrast, a staggered dx²-y² orbital arrangement in KCuMoO4(OH) results in superexchange couplings via only one bridging oxide ion, which makes J1 antiferromagnetic as large as 238 K and J2 negligible. This comparison between the two isotypic compounds demonstrates an important role of orbital arrangements in determining the magnetic properties of cuprates. [ABSTRACT FROM AUTHOR]

In a frustrated J1-J2 chain with the nearest-neighbor ferromagnetic interaction J1 and the next-nearest-neighbor antiferromagnetic interaction J2, novel magnetic states such as a spin-nematic state are theoretically expected. However, they have been rarely examined in experiments because of the difficulty in obtaining suitable model compounds. We show here that the quasi-one-dimensional antiferromagnet NaCuMoO4(OH), which comprises edge-sharing CuO2 chains, is a good candidate J1-J2 chain antiferromagnet. The exchange interactions are estimated as J1 = -51K and J2 = 36K by comparing the magnetic susceptibility, heat capacity, and magnetization data with the data obtained using calculations by the exact diagonalization method. High-field magnetization measurements at 1.3K show a saturation above 26 T with little evidence of a spin nematic state expected just below the saturation field, which is probably due to smearing effects caused by thermal fluctuations and the polycrystalline nature of the sample. [ABSTRACT FROM AUTHOR]

The phase diagram of the quasi-one-dimensional magnet NaCuMoO4(OH) is established through single-crystal NMR and heat-capacity measurements. The 23Na and 1H NMR experiments indicate a spiral and a collinear spin density wave (SDW) order below and above Bc = 1.5–1.8 T, respectively. Moreover, in the paramagnetic state above the SDW transition temperature, the nuclear spin-lattice relaxation rate 1/T1 indicates anisotropic spin fluctuations that have gapped excitations in the transverse spectrum but gapless ones in the longitudinal spectrum. These static and dynamic properties are well described by a theoretical model assuming quasi-one-dimensional chains with competing ferromagnetic nearest-neighbor interactions J1 and antiferromagnetic next-nearest-neighbor interactions J2 (J1−J2 chains). Because of the excellent crystal quality and good one-dimensionality, NaCuMoO4(OH) is a promising compound to elucidate the unique physics of the frustrated J1−J2 chain. [ABSTRACT FROM AUTHOR]