The rare-earth pyrosilicate family of compounds (RE$_{2}$Si$_{2}$O$_{7}$) hosts a variety of polymorphs, some with honeycomb-like geometries of the rare-earth sublattices, and the magnetism has yet to be deeply explored in many of the cases. Here we report on the ground state properties of C-Er$_{2}$Si$_{2}$O$_{7}$. C-Er$_{2}$Si$_{2}$O$_{7}$ crystallizes in the C2/m space group and the Er$^{3+}$ atoms form a distorted honeycomb lattice in the $a$-$b$ plane. We have utilized specific heat, DC susceptibility, and neutron diffraction measurements to characterize C-Er$_{2}$Si$_{2}$O$_{7}$. Our specific heat and DC susceptibility measurements show signatures of antiferromagnetic ordering at 2.3 K. Neutron powder diffraction confirms this transition temperature and the relative intensities of the magnetic Bragg peaks are consistent with a collinear Néel state in the magnetic space group C2'/m, with ordered moment of 6.61 $μ_{B}$ canted 13$^{\circ}$ away from the $c$-axis toward the $a$-axis. These results are discussed in relation to the isostructural quantum dimer magnet compound Yb$_{2}$Si$_{2}$O$_{7}$.
We study themagnetism of a spin-1 substance Li2Ni2Mo3O12. The spin system consists of distorted honeycomb lattices and linear chains of Ni2+ spins. Li+ ions enter about 25% and 50% of the honeycomb and chain Ni sites, respectively, creating disorder in both spin subsystems. A magnetic phase transition occurs at Tc = 8.0 K in the zero magnetic field. In low magnetic fields, the magnetization increases rapidly below Tc, decreases below 7 K, and finally becomes negative at low temperatures. We determine the magnetic structure using neutron powder diffraction results. The honeycomb lattices and li…
Coupled dimerized alternating-bond quantum spin chains in the distorted honeycomb-lattice magnet Cu$_5$SbO$_6$
Mahidol University（马希隆大学）；Thailand Center of Excellence in Physics, Commission of Higher Education（泰国物理卓越中心，高等教育委员会）；Tohoku University（东北大学）；Tokyo University of Science（东京科学大学）；National Taiwan University（台湾大学）；Taiwan Consortium of Emergent Crystalline Materials, National Science and Technology Council（台湾新兴晶体材料联盟，国家科学技术委员会）；Center of Atomic Initiative for New Materials, National Taiwan University（台湾大学新物质原子倡议中心）；J-PARC Center（J-PARC中心）；University of Maryland（马里兰大学）；National Institute of Standards and Technology（美国国家标准与技术研究院）
Magnetic excitation spectra of quantum spins of Na3Cu2SbO6 with the distorted honeycomb structure have been measured by neutron inelastic scattering. The intensity distribution and the dispersion curves of the excitations indicate that the spin system can be well understood by considering one-dimensional spin chains formed of Cu2+ ions on a lattice of the alternation of the shorter- and longer-spacings along the b axis. The exchange interactions between the neighboring spins with the shorter- and longer-spacings correspond to ferromagnetic and antiferromagnetic ones, respectively. These findin…
We report on the magnetic, thermodynamic, dielectric, and pyroelectric measurements on the hitherto unreported Fe${_4}$Ta${_2}$O${_9}$. This system is seen to exhibit a series of magnetic transitions, many of which are coupled to the emergence of ferroelectric order, making Fe${_4}$Ta${_2}$O${_9}$ the only genuine multiferroic in its material class. We suggest that the observed properties arise as a consequence of an effective reduction in the dimensionality of the magnetic lattice, with the magnetically active Fe${^{2+}}$ ions preferentially occupying a quasi 2D buckled honeycomb structure. T…
For temperatures T well above the ordering temperature T*=3.0+-0.2K the magnetic properties of the metal-organic material Mn[C10H6(OH)(COO)]2x2H20 built from Mn^2+ ions and 3-hydroxy-2-naphthoic anions can be described by a S=5/2 quantum antiferromagnet on a distorted honeycomb lattice with two different nearest neighbor exchange couplings J2 \approx 2J1 \approx 1.8K. Measurements of the magnetization M(H,T) as a function of a uniform external field H and of the uniform zero field susceptibility χ(T) are explained within the framework of a modified spin-wave approach which takes into account t…
The spin-1/2 Heisenberg antiferromagnet on the distorted honeycomb (DHC) lattice is studied by means of the tensor renormalization group method. It is unveiled that the system has a quantum phase transition of second-order between the gapped quantum dimer phase and a collinear Neel phase at the critical point of coupling ratio α_{c} = 0.54, where the quantum critical exponents ν= 0.69(2) and γ= 1.363(8) are obtained. The quantum criticality is found to fall into the O(3) universality class. A ground-state phase diagram in the field-coupling ratio plane is proposed, where the phases such as the…
We investigate the ground-state phase diagram of a spin-1/2 honeycomb-lattice antiferromagnetic (AF) Heisenberg model with three exchange interactions, $J_{\rm A}$, $J_{\rm B}$, and $J_{\rm C}$ that is realized in a distorted honeycomb-lattice antiferromagnet ${\rm Cu_2 (pymca)_3 (ClO_4)}$. We remeasured the magnetic susceptibility of its polycrystalline sample with special care, and determined the exchange parameters of this material through the comparison with numerical results based on a quantum Monte Carlo (QMC) method. The QMC method also provides a ground-state phase diagram in the $J_{\…
Keeping current interests to identify materials with intrinsic magnetodielectric behavior near room temperature and with novel pyroelectric current anomalies, we report temperature and magnetic-field dependent behavior of complex dielectric permittivity and pyroelectric current for an oxide, Li2Ni2Mo3O12, containing magnetic ions with (distorted) honey-comb and chain arrangement and ordering magnetically below 8 K. The dielectric data reveal the existence of relaxor ferroelectricity behavior in the range 160-240 K and there are corresponding Raman mode anomalies as well in that temperature ran…
Spin-1/2 chains with alternating antiferromagnetic (AF) and ferromagnetic (FM) couplings exhibit quantum entanglement like the integer-spin Haldane chains and might be similarly utilized for quantum computations. Such alternating AF-FM chains have been proposed to be realized in the distorted honeycomb-lattice compound Na$_2$Cu$_2$TeO$_6$, but to confirm this picture a comprehensive understanding of the exchange interactions including terms outside of the idealized model is required. Here we employ neutron scattering to study the spin dynamics in Na$_2$Cu$_2$TeO$_6$ and accurately determine th…
VI$_{3}$ is a ferromagnet with planar honeycomb sheets of bonded V$^{3+}$ ions held together by van der Waals forces. We apply neutron spectroscopy to measure the two dimensional ($J/J_{c} \approx 17$) magnetic excitations in the ferromagnetic phase, finding two energetically gapped ($Δ\approx k_{B} T_{c} \approx$ 55 K) and dispersive excitations. We apply a multi-level spin wave formalism to describe the spectra in terms of two coexisting domains hosting differing V$^{3+}$ orbital ground states built from contrasting distorted octahedral environments. This analysis fits a common nearest neigh…
Magnetization plateaus, spin-canted orders and field-induced transitions in a spin-1/2 Heisenberg antiferromagnet on a distorted diamond-decorated honeycomb lattice
Institute of Physics, Faculty of Science, P. J. Šafárik University（帕日·沙法里克大学理学院物理研究所）
We report on the experimental results of magnetic susceptibility, specific heat, electron spin resonance (ESR), and high-field magnetization measurements on a polycrystalline sample of the spin-$1/2$ distorted honeycomb-lattice antiferromagnet Cu$_2$(pymca)$_3$(ClO$_4$). Magnetic susceptibility shows a broad peak at about 25~K, which is typical of a low dimensional antiferromagnet, and no long range magnetic order is observed down to 0.6~K in the specific heat measurements. Magnetization curve up to 70~T at 1.4~K shows triple stepwise jumps. Assuming three different exchange bonds $J_{\rm A}$,…
