Role of antisymmetric exchange in selecting magnetic chirality in Ba3NbFe3Si2O14

Tuning the Langasite, La3SbZn3Si2O14, towards white light emission: synthesis, structure, SHG and photoluminescence studies

A series of single-phase color-tunable Langasite, La3SbZn3Si2O14:RE3+ (RE = Eu, Tb, and Tm) phosphors have been prepared and characterized employing X-ray diffraction (XRD), Raman, and photoluminescence (PL) studies. The substituted compounds, La3SbZn3Si2O14:Eu3+, La3SbZn3Si2O14:Tb3+ and La3SbZn3Si2O14:Tm3+ exhibit the characteristic emissions of Eu3+ (red), Tb3+ (green) and Tm3+ (blue), respectively. By carefully adjusting the concentration of Eu3+ ions in the La3SbZn3Si2O14:1% Tm3+, 2% Tb3+, x% Eu3+ system, we achieved a white emission with a reasonable quantum yield. The compounds are found to be SHG (second-harmonic generation) active with the highest values of 3.6 × KDP (potassium dihydrogen phosphate). In addition, the compounds exhibit reasonable dielectric constants with low loss. The present study demonstrates the color tunability of the Langasite family of compounds and establishes it as an adaptable structure.

First crystal structures of oxo-bridged [CrIIITaV] dinuclear complexes: spectroscopic, magnetic and theoretical investigations of the Cr–O–Ta core

The vibrational, electronic, structural and magnetic properties of dinuclear compounds with a Cr–O–Ta bridge were validated with DFT calculations.

X-ray natural circular dichroism in langasite crystal

Optical activity in the X-ray range stems from the electric-dipole-electric-quadrupole interference terms mixing multipoles of opposite parity, and can be observed exclusively in systems with broken inversion symmetry. The gyration tensor formalism is used to describe the X-ray optical activity in langasite La₃Ga₅SiO₁₄ crystal with the P321 space group. An experimental study of the X-ray natural circular dichroism (XNCD) near the Ga K-edge in La₃Ga₅SiO₁₄ single crystal was performed at ESRF beamline ID12, both along and perpendicular to the crystal optical axis. The combination of the quantum mechanical calculations and high-quality experimental results has allowed us to separate the contributions into X-ray absorption and XNCD spectra of Ga atoms occupying three distinct Wyckoff positions.

Experimental and Theoretical Investigation of the Anti-Ferromagnetic Coupling of CrIII Ions through Diamagnetic -O-NbV-O- Bridges

The synthesis and properties of a novel hetero-tetranuclear compound [Cr₂(bpy)₄(μ-O)₄Nb₂(C₂O₄)₄]·3H₂O (1; bpy = 2,2'-bipyridine), investigated by single-crystal X-ray diffraction, magnetization measurements, IR, UV/visible spectroscopy, electron paramagnetic resonance (EPR; X- and Q-bands and high-field), and density functional theory (DFT) calculations, are reported. Crystal structure of 1 (orthorhombic Pcab space group) consists of a square-shaped macrocyclic {Cr₂(μ-O)₄Nb₂} core in which Cr^III and Nb^V ions are alternately bridged by oxo ions and three uncoordinated water molecules. The intramolecular Cr^III···Cr^III distances through the -O-Nb^V-O- bridges are 7.410(2) and 7.419(2) Å, while diagonal separation is 5.406(2) Å. The temperature dependence of magnetization M(T) evidences an anti-ferromagnetic ground state, which originates from a magnetic interaction between two Cr^III ions of spin 3/2 through two triatomic -O-Nb^V-O- diamagnetic bridges. A spin Hamiltonian appropriate for polynuclear isolated magnetic units was used. The best-fitting curve for this model is obtained with the parameters g_Cr = 1.992(3), J = -12.77(5) cm^-1, and |D| = 0.17(4) cm^-1. The Cr^III···Cr^III dimer model is confirmed by EPR spectra, which exhibit a pronounced change of their shape around the temperature corresponding to the intradimer coupling J. The EPR spectra simulations and DFT calculations reveal the presence of a single-ion anisotropy that is close to being uniaxial, D = -0.31 cm^-1 and E = 0.024 cm^-1.

Effect of divalent Ba cation substitution with Sr on coupled 'multiglass' state in the magnetoelectric multiferroic compound Ba3NbFe3Si2O14

(Ba/Sr)₃NbFe₃Si₂O₁₄ is a magneto-electric multiferroic with an incommensurate antiferromagnetic spiral magnetic structure which induces electric polarization at 26 K. Structural studies show that both the compounds have similar crystal structure down to 6 K. They exhibit a transition, T_N at 26 K and 25 K respectively, as indicated by heat capacity and magnetization, into an antiferromagnetic state. Although Ba and Sr are isovalent, they exhibit very different static and dynamic magnetic behaviors. The Ba-compound exhibits a glassy behavior with critical slowing dynamics with a freezing temperature of ~35 K and a critical exponent of 3.9, a value close to the 3-D Ising model above T_N, in addition to the invariant transition into an antiferromagnetic state. The Sr-compound however does not exhibit any dispersive behavior except for the invariant transition at T_N. The dielectric constant reflects magnetic behavior of the two compounds: the Ba-compound has two distinct dispersive peaks while the Sr-compound has a single dispersive peak. Thus the compounds exhibit coupled ‘multiglass’ behavior. The difference in magnetic properties between the two compounds is found to be due to modifications to super exchange path angle and length as well as anti-site defects which stabilize either ferromagnetic or antiferromagnetic interactions.

Quantum interference oscillations of the superparamagnetic blocking in an Fe8 molecular nanomagnet

We show that the dynamic magnetic susceptibility and the superparamagnetic blocking temperature of an Fe(8) single molecule magnet oscillate as a function of the magnetic field H(x) applied along its hard magnetic axis. These oscillations are associated with quantum interferences, tuned by H(x), between different spin tunneling paths linking two excited magnetic states. The oscillation period is determined by the quantum mixing between the ground S=10 and excited multiplets. These experiments enable us to quantify such mixing. We find that the weight of excited multiplets in the magnetic ground state of Fe(8) amounts to approximately 11.6%.

Phase diagram and magnetic structures of the Co-bearing dugganites Pb3TeCo3A2O14 (A = V, P)

Exhibiting rich magnetic behaviour and potentially multiferroic properties, the dugganites, a Te(6+) containing subgroup of the langasite series, are an attractive family of compounds for future study. It was recently shown that Pb-bearing members of the dugganite series undergo distortions away from the P321 symmetry that is characteristic of the langasites. Here, we detail the consequences these distortions have on the magnetism exhibited by Pb3TeCo3V2O14 and Pb3TeCo3P2O14, solving the magnetic structures of both compounds with respect to a new supercell. Using neutron scattering and magnetic susceptibility measurements, we show that small applied magnetic fields can seriously perturb the delicate magnetic states in both of these systems. This is further demonstrated by presenting how doping P(5+) onto the nonmagnetic V(5+) site completely changes the magnetic structure from either of the end series members. Finally, it is shown using inelastic neutron scattering and magnetic susceptibility measurements that Pb3TeCo3V2O14 can be characterized using a model for isosceles trimers, which do not exist in the previously reported P321 subcell.