Ab Plane Of Crystal Research Articles

Investigation of the evolution of magnetic structure of multiferroics Tb1−x Ce x Mn2O5 (x = 0, 0.2) by polarized neutron diffraction

The evolution of multiferroics TbMn2O5 and Tb0.8Ce0.2Mn2O5 magnetic structure was studied by means of polarized neutron diffraction. It is shown that in all magnetically ordered phases there exists nonequilibrium population of domains with “right” and “left” spirals. It is revealed that in Tb0.8Ce0.2Mn2O5 in all magnetic phases and in TbMn2O5—in low-temperature magnetic phases incommensurate as well as in commensurate — the orientation of the rotation plane of magnetic moments remains the same and makes an angle of ~10° with the ab-plane of crystal. At the transition to the high temperature incommensurate phase in TbMn2O5 the orientation transition takes place.

Crystal and molecular structure of a second, high-density polymorph of silver malonate

A new orthorhombic polymorph of silver malonate ( II) has been synthesized and structurally characterized. Compound II crystallizes in space group Pnma, with a = 12.8180(11), b = 9.2479(8), c = 4.0219(3) Å; V = 476.75(7) Å 3; Z = 4; ρ calc = 4.427 g cm −3. Full-matrix least-squares refinement converged to R 1 = 0.0099 ( I > 2 σ( I), 765 data) and w R 2 = 0.0264 ( F 2, 785 data, 51 parameters). The familiar eight-membered Ag 2(RCO 2) 2 ring, characteristic of most silver(I) carboxylate complexes, has a Ag–Ag distance of 2.977(1) Å. Puckered sheets in the crystal ab plane are connected along c to form a three-dimensional coordination polymer. The density of II is >30% higher than that of the monoclinic polymorph ( I), first characterized in 1981. A survey of the density ratios of polymorphs in the Cambridge Structural Database indicates that virtually all of the pairs of entries having a density ratio >1.2 involve at least one form with significant void volume, as estimated using PLATON. However, neither I nor II have significant void volume, which suggests that the silver malonate polymorphs represent one of the largest density differences observed to date for a polymorphic pair. To date, it has not been possible to prepare I in our laboratories.

Anisotropy of second-order nonlinear optical susceptibilities of arsenic triiodide–sulfur addition complex: AsI 3 · 3S 8

We report the anisotropic linear and second-order nonlinear optical (NLO) properties of arsenic triiodide–octa-sulfur (1:3) adduct, AsI 3 · 3S 8, which spontaneously crystallizes in the trigonal rhombohedral non-centrosymmetric space group R3 m. The trigonal symmetry of the AsI 3 · 3S 8 molecule coincides with the crystal symmetry. The crystals are optically uniaxial with n o/ n e of about 1.2 and show dichroism at the UV-visible wavelengths. Second harmonic generation (SHG) tensor elements were determined from Maker fringes measured with an Nd:YAG laser (∼10 ns pulse, 1064 nm). The coefficient d 222,eff = 32.0 pm/V for the light polarized parallel to the layers of iodine and sulfur atoms in the AsI 3 · 3S 8 crystal ab plane is markedly larger than d 333 = 11.6 pm/V for the polarization of light parallel to the crystal c axis. The anisotropy parameter, defined as the d 222,eff/ d 333 ratio, is about 2.7 for the AsI 3 · 3S 8 crystal, smaller than that for the isomorphous CHI 3 · 3S 8 crystal (7.3) but larger than for the SbI 3 · 3S 8 crystal (0.7). Highly anisotropic components of the first hyperpolarizability tensor of an AsI 3 · 3S 8 molecule, β, were derived from the quadratic nonlinear susceptibility tensor of the crystal.

Nonresonant microwave absorption in Bi2212 single crystal: Second peak and microwave power dependence

Nonresonant microwave absorption (NMA) measurements were carried out at liquid-nitrogen temperature on a high quality Bi2212 single crystal, as a function of microwave power in three mutual orientations of crystal ab plane, dc field (Hdc), and microwave magnetic field (Hw). NMA line shapes in Bi2212 crystal are complicated with a narrow peak (P1 peak) located near zero field, followed by a much broader second peak (P2 peak) in the particular orientations. More excitingly, we show that the P2 peak qualitatively evolves as a function of microwave power in the orientation of Hdc ⊥ ab plane, $$H_W | {ab}.$$ plane, and Hdc ⊥ Hw. In this configuration, as the microwave power is progressively increased, the broad P2 peak first gets smeared off and then a multiple peak structure appears, which develops into another narrower second peak (Ps-peak) at high enough microwave powers. In the orientation of $$H_{dc} | {ab}.$$ plane, Hw ⊥ ab plane, and Hdc ⊥ Hw, we report for the first time the appearance and disappearance of a new second peak (P2-like peak) as a function of microwave power.

Quantum collective creep: Effects of anisotropy, layering, and finite temperature.

We determine the creep rates for classical and quantum motion in uniaxially anisotropic and layered superconductors within the framework of weak collective-pinning theory. In particular, we concentrate on the low- and intermediate-magnetic-field regime where single-vortex collective pinning is relevant. For a field aligned with the crystal c axis, we find that both the classical and the quantum creep rates are enhanced as compared with the isotropic results due to the increased elasticity of the vortices. For anisotropic superconductors the creep rates do not depend on the angle \ensuremath{\vartheta} between the magnetic field and the crystal ab plane and are also independent of the direction of motion. Identical results are obtained for layered superconductors within the large-angle region \ensuremath{\vartheta}>\ensuremath{\epsilon}, where ${\mathrm{\ensuremath{\epsilon}}}^{2}$=m/M1 denotes the mass anisotropy ratio. A more complex behavior is obtained in the small-angle region \ensuremath{\Vert}\ensuremath{\vartheta}\ensuremath{\Vert}, where the structure of the vortex cannot be approximated by a simple rectilinear object. Here the creep rates depend both on the angle \ensuremath{\vartheta} and on the direction of motion. We discuss the finite-temperature corrections to the quantum motion and determine the crossover temperature to the classical thermally activated behavior.

Ultrasonic study of microstructure thermal dynamics in YBCO ceramic

The marked changes in slope and the hysteresis are observed for ultrasound velocity temperature dependences in the granular orthorhombic YBCO compound below room temperature. Those fenomena can be interpreted as the first-order phase transition consisting in ferroelastic domains reordering in crystal ab-plane. The reordering is initiated by thermal stresses and depends on ceramic granularity.