Search

We report a detailed study of the magnetic properties of the buckled kagome compound Cu3Y(SeO3)2O2Cl using heat capacity, magnetization, powder neutron diffraction, electron spin resonance, and first-principles calculations. The crystal structure is confirmed to be isotypic with the mineral francisite, with orthorhombic space group symmetry Pmmn throughout the temperature range 5-300 K. Magnetization, heat capacity, and neutron diffraction confirm long range magnetic order below TN = 35 K. The electron spin resonance spectra reveal the presence of two modes corresponding to two different crystallographic Cu positions. The principal g values of the g tensor of Cul sites were found to be g1 = 2.18(4),g2 = 2.10(6), and g3 = 2.05(9), while the effective g factor of Cu2 sites is almost isotropic and is on average g = 2.09(5). At low temperatures, Cu3Y(SeO3)2O2Cl undergoes a metamagnetic transition, with a critical field Bc = 2.6 T at 2 K, due to the suppression of the interplane exchange interactions and saturates in modest magnetic field Bs ⩽ 8 T. The first-principles calculations allow an estimation of both intraplane and interplane exchange interactions. The weakness of the interplane exchange interaction results in low values of the critical fields for the metamagnetic transition, while the competition between intraplane exchange interactions of different signs results in a similarly low value of the saturation field. [ABSTRACT FROM AUTHOR]

In this combined experimental and theoretical paper, we study the properties of Cu3Sm(SeO3)2O2Cl belonging to the francisite family of compounds, which are novel frustrated layered compounds. Cu3Sm(SeO3)2O2Cl is synthesized through a solid state reaction. Characterizations through measurements of magnetization, specific heat, X-band electron spin resonance, and rare-earth optical spectroscopy, establish that the compound orders antiferromagnetically at TN=35K and undergoes a spin-reorientation phase transition at TC=8.5K due to the interplay of anisotropies in transition metal and rare-earth subsystems. The ground state Kramers doublet of Sm is found to split only at T

We present a comprehensive experimental and theoretical study of the electronic and magnetic properties of two quasi-two-dimensional (2D) honeycomb lattice monoclinic compounds A3Ni2SbO6(A = Li, Na). Magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long-range order with Néel temperatures of ~14 and 16 K for Li3Ni2SbO6 and NA3Ni2SbO6, respectively. The effective magnetic moments of 4.3µB/f.u.(Li3Ni2SbO6) and 4.4µB/f.u.(NA3Ni2SbO6), where f.u. is formula units, indicate that Ni2+ is in a high-spin configuration (S = 1). The temperature dependence of the inverse magnetic susceptibility follows the Curie-Weiss law in the high-temperature region and shows positive values of the Weiss temperature, ~8K (Li3Ni2SbO6) and ~12 K (NA3Ni2SbO6), pointing to the presence of nonnegligible ferromagnetic interactions, although the system orders antiferromagnetically at low temperatures. In addition, the magnetization curves reveal a field-induced (spin-flop type) transition below TN that can be related to the magnetocrystalline anisotropy in these systems. These observations are in agreement with density functional theory calculations, which show that both antiferromagnetic and ferromagnetic intralayer spin exchange couplings between Ni2+ ions are present in the honeycomb planes, supporting a zigzag antiferromagnetic ground state. Based on our experimental measurements and theoretical calculations, we propose magnetic phase diagrams for the two compounds. [ABSTRACT FROM AUTHOR]

The synthetic mineral urusovite CuAl(AsO4)O was prepared through the wet chemistry route and characterized over a wide temperature range in terms of studies of magnetization, specific heat, and X-band electron spin resonance. The basic structural units of the compound are distorted square pyramids CuO5 assembled into corrugated honeycomb layers separated by AsO4 and AlO4 tetrahedrons. Both thermodynamic and resonant measurements indicate that CuAl(AsO4)O is a spin gap system with a gap of ∼350K. The electronic structure calculations performed within the framework of density functional theory suggest a weakly interacting dimer model with antiferromagnetic signs for both intradimer and interdimer superexchange interactions. This establishes the valence bond solid as the quantum ground state of the title compound. The pronounced discrepancy between experimental data and calculations within the weakly interacting dimer model at elevated temperatures is ascribed in part to the steep increase of the intradimer exchange interaction parameter driven by the thermal expansion effects. [ABSTRACT FROM AUTHOR]

An antiferromagnetic ordering in Pb3TeCo3V2O14 takes place through formation of a short-range correlation regime with T* ~ 10.5 K and the succession of a second-order phase transition at TN1 = 8.9 K and a first-order phase transition at TN2 = 6.3 K. An external magnetic field rapidly destroys magnetic structure at T < TN2 and influences the magnetic order at TN2 < T < TN1, resulting in a complex magnetic phase diagram of Pb3TeCo3V2O14 as derived from magnetization and specific heat measurements. The first-principles calculations indicate that, in variance with a layered crystal structure, the magnetic subsystem of Pb3TeCo3V2O14 is quasi-one-dimensional and highly unusual, consisting of weakly coupled triangular tubes. [ABSTRACT FROM AUTHOR]

By means of thermodynamic and magnetic resonance measurements the S = 1/2 dimer system BaVSi2O7 is characterized. A broad maximum in the temperature dependence of the magnetic susceptibility and a Schottky- type anomaly in the specific heat allows estimating the main exchange interaction within V4+-V4+ dimers as J = 37 ± 1 K. This estimation is confirmed by pulsed magnetic field measurements of the magnetization, which is evidenced by the field-induced singlet-triplet transition at about 27 T. Both X-band and high-field terahertz electron spin resonance data qualitatively agree with the results of the specific heat and magnetization measurements. The electronic structure calculations, by using local density approximation, indicate that the magnetic properties of BaVSi2O7 can be interpreted within the weakly interacting dimer model. [ABSTRACT FROM AUTHOR]

We present the synthesis and the experimental and theoretical study of the new member of the francisite family, Cu3Yb(SeO3)2O2Cl. The compound reaches an antiferromagnetic order at TN=36.7K and experiences first-order spin-reorientation transition to weakly ferromagnetic phase at TR=8.7K evidenced in specific heat Cp and magnetic susceptibility χ measurements. Distinctly different magnetization loops in T

The magnetic structure of Li3Ni2SbO6 has been determined by low-temperature neutron diffraction, and the crystal structure has been refined by a combination of synchrotron and neutron powder diffraction. The monoclinic (C2/m) symmetry, assigned previously to this pseudohexagonal layered structure, has been unambiguously proven by peak splitting in the synchrotron diffraction pattern. The structure is based on essentially hexagonal honeycomb-ordered Ni2SbO6 layers alternating with Li3 layers, all cations and anions being in an octahedral environment. The compound orders antiferromagnetically below TN = 15 K, with the magnetic supercell being a 2a × 2b multiple of the crystal cell. The magnetic structure within the honeycomb layer consists of zigzag ferromagnetic spin chains coupled antiferromagnetically. The ordered magnetic moment amounts to 1.62 (2) µ B/Ni, which is slightly lower than the full theoretical value. Upon cooling below TN, the spins tilt from the c axis, with a maximum tilting angle of 15.6° at T = 1.5 K. Our data imply non-negligible ferromagnetic interactions between the honeycomb layers. The observed antiferromagnetic resonance modes are in agreement with the two-sublattice model derived from the neutron data. Orthorhombic anisotropy shows up in zero-field splitting of Δ = 198 ± 4 and 218 ± 4 GHz. Above TN, the electron spin resonance data imply short-range antiferromagnetic order up to about 80 K. [ABSTRACT FROM AUTHOR]

The magnetic phase diagram and low-energy magnon excitations of structurally and magnetically chiral MnSb2O6 are reported. The specific heat and the static magnetization are investigated in magnetic fields up to 9 and 30 T, respectively, while the dynamic magnetic properties are probed by X-band as well as tunable high-frequency electron spin-resonance spectroscopy. Below TN=11.5 K, we observe antiferromagnetic resonance modes which imply small but finite planar anisotropy showing up in a zero-field splitting of 20 GHz. The data are well described by means of an easy-plane two-sublattice model with the anisotropy field BA=0.02 T. The exchange field BE=13 T is obtained from the saturation field derived from the pulsed-field magnetization. A crucial role of the small anisotropy for the spin structure is reflected by competing antiferromagnetic phases appearing, at T=2 K, in small magnetic fields at BC1 ≈ 0.5 T and BC2=0.9 T. We discuss the results in terms of spin reorientation and of small magnetic fields favoring helical spin structure over the cycloidal ground state which, at B=0, is stabilized by the planar anisotropy. Above TN, short-range magnetic correlations up to ≳60 K and magnetic entropy changes well above TN reflect the frustrated triangular arrangement of Mn2+ ions in MnSb2O6. [ABSTRACT FROM AUTHOR]