75 research outputs found
Magnetic pyroxenes LiCrGe2O6 and LiCrSi2O6: dimensionality crossover in a non-frustrated S=3/2 Heisenberg model
The magnetism of magnetoelectric = 3/2 pyroxenes LiCrSiO and
LiCrGeO is studied by density functional theory (DFT) calculations,
quantum Monte Carlo (QMC) simulations, neutron diffraction, as well as
low-field and high-field magnetization measurements. In contrast with earlier
reports, we find that the two compounds feature remarkably different, albeit
non-frustrated magnetic models. In LiCrSiO, two relevant exchange
integrals, 9 K along the structural chains and
2 K between the chains, form a 2D anisotropic honeycomb lattice. In
contrast, the spin model of LiCrGeO is constituted of three different
exchange couplings. Surprisingly, the leading exchange
2.3 K operates between the chains, while 1.2 K is about
two times smaller. The additional interlayer coupling
renders this model 3D. QMC simulations reveal excellent agreement between
our magnetic models and the available experimental data. Underlying mechanisms
of the exchange couplings, magnetostructural correlations, as well as
implications for other pyroxene systems are discussed.Comment: 11 pages, 8 figures, 3 tables + Supplementary informatio
Phenomenological Landau analysis of predicted magnetoelectric fluorides: KMnFeF and BaNiF
Recently, we predicted based on symmetry considerations that KMnFeF and
BaNiF are likely magnetoelectric multiferroic materials. In
this contribution, we investigate with Landau theory and crystal structure
considerations the polarization and the linear magnetoelectric effect in these
materials. Based on these two examples, we show that any magnetoferroelectric
will display additional electrical polarization below its magnetic ordering
temperature. This additional electrical polarization is not related to the
linear magnetoelectric effect. Its magnitude depends on the dielectric
susceptibility.Comment: 11 pages, accepted for publication in Journal of Physics: Condensed
Matte
Magnetic properties of the low-dimensional spin-1/2 magnet \alpha-Cu_2As_2O_7
In this work we study the interplay between the crystal structure and
magnetism of the pyroarsenate \alpha-Cu_2As_2O_7 by means of magnetization,
heat capacity, electron spin resonance and nuclear magnetic resonance
measurements as well as density functional theory (DFT) calculations and
quantum Monte Carlo (QMC) simulations. The data reveal that the magnetic Cu-O
chains in the crystal structure represent a realization of a quasi-one
dimensional (1D) coupled alternating spin-1/2 Heisenberg chain model with
relevant pathways through non-magnetic AsO_4 tetrahedra. Owing to residual 3D
interactions antiferromagnetic long range ordering at T_N\simeq10K takes place.
Application of external magnetic field B along the magnetically easy axis
induces the transition to a spin-flop phase at B_{SF}~1.7T (2K). The
experimental data suggest that substantial quantum spin fluctuations take place
at low magnetic fields in the ordered state. DFT calculations confirm the
quasi-one-dimensional nature of the spin lattice, with the leading coupling J_1
within the structural dimers. QMC fits to the magnetic susceptibility evaluate
J_1=164K, the weaker intrachain coupling J'_1/J_1 = 0.55, and the effective
interchain coupling J_{ic1}/J_1 = 0.20.Comment: Accepted for publication in Physical Review
Prediction for new magnetoelectric fluorides
We use symmetry considerations in order to predict new magnetoelectric
fluorides. In addition to these magnetoelectric properties, we discuss among
these fluorides the ones susceptible to present multiferroic properties. We
emphasize that several materials present ferromagnetic properties. This
ferromagnetism should enhance the interplay between magnetic and dielectric
properties in these materials.Comment: 12 pages, 4 figures, To appear in Journal of Physics: Condensed
Matte
Crystal structure and thermal behavior of Bi <sub>6</sub> Te <sub>2</sub> O <sub>15</sub>:Investigation of synthetic and natural pingguite
The previously unknown crystal structure of pingguite was determined and refined from laboratory X-ray powder diffraction data using a synthetic sample. Additional single crystal diffraction of natural pingguite confirms that the crystal structure of the synthetic sample is identical to the natural mineral. This new crystal structure calls for a revised chemistry of the rare mineral pingguite to Bi6Te2O15 instead of the previously reported formula Bi6Te2O13. Pingguite contains TeVI only and not TeIV as previously reported. Pingguite undergoes an irreversible phase transition around 840 ∘C which is characterized by a loss of oxygen and a reduction from TeVI to TeIV resulting in a δ-Bi2O3 like type structure. In addition, we report the Raman spectroscopic data on the natural pingguite
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