Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSpin-Coupling Topology in the Copper Hexamer Compounds A$_2$Cu$_3$O(SO$_4$)$_3$ (A=Na, K)
434
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The compounds A$_2$Cu$_3$O(SO$_4$)$_3$ (A=Na, K) are characterized by copper hexamers which are weakly coupled to realize antiferromagnetic order below TN=3 K. They constitute novel quantum spin systems with S=1 triplet ground-states. We investigated the energy-level splittings of the copper hexamers by inelastic neutron scattering experiments covering the entire range of the magnetic excitation spectra. The observed transitions are governed by very unusual selection rules which we ascribe to the underlying spin-coupling topology. This is rationalized by model calculations which allow an unambiguous interpretation of the magnetic excitations concerning both the peak assignments and the nature of the spin-coupling parameters.
rate research
Read More
Magnetic properties and underlying magnetic models of the synthetic A$_2$Cu$_3$O(SO$_4)_3$ fedotovite (A = K) and puninite (A = Na) minerals, as well as the mixed euchlorine-type NaKCu$_3$O(SO$_4)_3$ are reported. We show that all these compounds contain magnetic Cu$_6$ hexamer units, which at temperatures below about 100 K act as single spin-1 entities. Weak interactions between these magnetic molecules lead to long-range order below $T_N$ = 3.4 K (A = Na), 4.7 K (A = NaK), and about 3.0 K (A = K). The formation of the magnetic order is elucidated by ab initio calculations that reveal two-dimensional inter-hexamer interactions within crystallographic $bc$ planes. This model indicates the presence of a weakly distorted square lattice of $S=1$ magnetic ions and challenges the earlier description of the A$_2$Cu$_3$O(SO$_4)_3$ minerals in terms of Haldane spin chains.
Fedotovite K$_2$Cu$_3$O(SO$_4$)$_3$ is a candidate of new quantum spin systems, in which the edge-shared tetrahedral (EST) spin-clusters consisting of Cu$^{2+}$ are connected by weak inter-cluster couplings to from one-dimensional array. Comprehensive experimental studies by magnetic susceptibility, magnetization, heat capacity, and inelastic neutron scattering measurements reveal the presence of an effective $S$ = 1 Haldane state below $T cong 4$ K. Rigorous theoretical studies provide an insight into the magnetic state of K$_2$Cu$_3$O(SO$_4$)$_3$: an EST cluster makes a triplet in the ground state and one-dimensional chain of the EST induces a cluster-based Haldane state. We predict that the cluster-based Haldene state emerges whenever the number of tetrahedra in the EST is $even$.
K$_3$Cu$_3$AlO$_2$(SO$_4$)$_4$ is a highly one-dimensional spin-1/2 inequilateral diamond-chain antiferromagnet. Spinon continuum and spin-singlet dimer excitations are observed in the inelastic neutron scattering spectra, which is in excellent agreement with a theoretical prediction: a dimer-monomer composite structure, where the dimer is caused by strong antiferromagnetic (AFM) coupling and the monomer forms an almost isolated quantum AFM chain controlling low-energy excitations. Moreover, muon spin rotation/relaxation spectroscopy shows no long-range ordering down to 90~mK, which is roughly three orders of magnitude lower than the exchange interaction of the quantum AFM chain. K$_3$Cu$_3$AlO$_2$(SO$_4$)$_4$ is, thus, regarded as a compound that exhibits a Tomonaga-Luttinger spin liquid behavior at low temperatures close to the ground state.
The compounds A2Cu3O(SO4)3 (A=Na,K) are characterized by copper hexamers which are weakly coupled along the b-axis to realize one-dimensional antiferromagnetic chains below TN=3 K, whereas the interchain interactions along the a- and c-axes are negligible. We investigated the energy-level splittings of the copper hexamers by inelastic neutron scattering below and above TN. The eight lowest-lying hexamer states could be unambiguously assigned and parametrized in terms of a Heisenberg exchange Hamiltonian, providing direct experimental evidence for an S=1 triplet ground-state associated with the copper hexamers. Therefore, the compounds A2Cu3O(SO4)3 serve as novel cluster-based spin-1 antiferromagnets to support Haldanes conjecture that a gap appears in the excitation spectrum below TN, which was verified by inelastic neutron scattering.
Strongly correlated electrons in layered perovskite structures have been the birthplace of high-temperature superconductivity, spin liquid, and quantum criticality. Specifically, the cuprate materials with layered structures made of corner sharing square planar CuO$_4$ units have been intensely studied due to their Mott insulating grounds state which leads to high-temperature superconductivity upon doping. Identifying new compounds with similar lattice and electronic structures has become a challenge in solid state chemistry. Here, we report the hydrothermal crystal growth of a new copper tellurite sulfate Cu$_3$(TeO$_4$)(SO$_4$)$cdot$H$_2$O, a promising alternative to layered perovskites. The orthorhombic phase (space group $Pnma$) is made of corrugated layers of corner-sharing CuO$_4$ square-planar units that are edge-shared with TeO$_4$ units. The layers are linked by slabs of corner-sharing CuO$_4$ and SO$_4$. Using both the bond valence sum analysis and magnetization data, we find purely Cu$^{2+}$ ions within the layers, but a mixed valence of Cu$^{2+}$/Cu${^+}$ between the layers. Cu$_3$(TeO$_4$)(SO$_4$)$cdot$H$_2$O undergoes an antiferromagnetic transition at $T_N$=67 K marked by a peak in the magnetic susceptibility. Upon further cooling, a spin-canting transition occurs at $T^{star}$=12 K evidenced by a kink in the heat capacity. The spin-canting transition is explained based on a $J_1$-$J_2$ model of magnetic interactions, which is consistent with the slightly different in-plane super-exchange paths. We present Cu$_3$(TeO$_4$)(SO$_4$)$cdot$H$_2$O as a promising platform for the future doping and strain experiments that could tune the Mott insulating ground state into superconducting or spin liquid states.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
