Spin Frustration and Orbital Order in Vanadium Spinels

We present the results of our theoretical study on the effects of geometrical frustration and the interplay between spin and orbital degrees of freedom in vanadium spinel oxides $A$V$_2$O$_4$ ($A$ = Zn, Mg or Cd). Introducing an effective spin-orbital-lattice coupled model in the strong correlation limit and performing Monte Carlo simulation for the model, we propose a reduced spin Hamiltonian in the orbital ordered phase to capture the stabilization mechanism of the antiferromagnetic order. Orbital order drastically reduces spin frustration by introducing spatial anisotropy in the spin exchange interactions, and the reduced spin model can be regarded as weakly-coupled one-dimensional antiferromagnetic chains. The critical exponent estimated by finite-size scaling analysis shows that the magnetic transition belongs to the three-dimensional Heisenberg universality class. Frustration remaining in the mean-field level is reduced by thermal fluctuations to stabilize a collinear ordering.Comment: 4 pages, 4 figures, proceedings submitted to SPQS200

Orbital and spin chains in ZnV2O4

Our powder inelastic neutron scattering data indicate that \zvo is a system of spin chains that are three dimensionally tangled in the cubic phase above 50 K due to randomly occupied $t_{2g}$ orbitals of V$^{3+}$ ($3d^2$) ions. Below 50 K in the tetragonal phase, the chains become straight due to antiferro-orbital ordering. This is evidenced by the characteristic wave vector dependence of the magnetic structure factor that changes from symmetric to asymmetric at the cubic-to-tetragonal transition

Rehydration of CTMA modified DNA powders observed by NMR

The rehydration of salmon sperm deoxyribonucleic acid (DNA) and cetyltrimethylammonium chloride $(C_{19}H_{42}ClN)$ complexes was observed using hydration kinetics, sorption isotherm, and high power proton relaxometry (at 30 MHz). The hydration kinetics shows (i) a very tightly bound water not removed by incubation over silica gel ($A_0^{h}$ = 0.061 ± 0.004), (ii) a tightly bound water saturating at $A_1^{h}$ = 0.039 ± 0.011, with the hydration time $t_1^{h}$ = (1.04 ± 0.21) h, a loosely bound water fraction (iii) with the hydration time $t_2^{h}$ = (19.1 ± 3.2) h and the contribution progressively increasing with the air humidity. For the hydration at $p//p_0$ = 100%, after $t_0$ = (152.6 ± 2.5) h of incubation the swelling process begins. The swelling time was $t_3^{h}$ = (12.5 ± 5.4) h, and the swelling amplitude $A_3^{h}$ = 0.140 ± 0.016. The sorption isotherm is sigmoidal in form and is fitted by the Dent model with the mass of water saturating primary binding sites Δ M/$m_0$ = 0.102 ± 0.021. Proton free induction decay is a superposition of the immobilized proton signal (Gaussian, with $T_{2S}$* ≈ 30 μs) and two liquid signal components coming from tightly bound ($T_{2 L_1}$* ≈ 100 μs) and loosely bound water fraction with the amplitude proportional to the mass of water added ($T_{2 L_2}$* ≈ 1000 μs)

Spin Driven Jahn-Teller Distortion in a Pyrochlore system

The ground-state properties of the spin-1 antiferromagnetic Heisenberg model on the corner-sharing tetrahedra, pyrochlore lattice, is investigated. By breaking up each spin into a pair of 1/2-spins, the problem is reduced to the equivalent one of the spin-1/2 tetrahedral network in analogy with the valence bond solid state in one dimension. The twofold degeneracy of the spin-singlets of a tetrahedron is lifted by a Jahn-Teller mechanism, leading to a cubic to tetragonal structural transition. It is proposed that the present mechanism is responsible for the phase transition observed in the spin-1 spinel compounds ZnV$_2$O$_4$ and MgV$_2$O$_4$.Comment: 4 pages, 3 eps figures, REVTeX, to appear in Phys. Rev. Let

Application of silver nanostructures in laser desorption/ionization mass spectrometry and mass spectrometry imaging

Metallic nanoparticles, especially silver nanoparticles, have attracted much attention due to their unique physical, chemical and opto-electronic properties. Silver nanoparticles have been successfully applied as a matrix replacement for the laser desorption/ionization time-of-flight mass spectrometry (LDI-ToF-MS). Silver nanoparticles (AgNPs) can efficiently absorb ultraviolet laser radiation, transfer energy to the analyte and promote analyte desorption, but also constitute a source of silver ions suitable for analyte cationisation. Nanoparticles, producing spectra with highly reduced chemical background in the low m/z region, are perfectly suited for low-molecular weight compound analysis and imaging. AgNPs have been demonstrated to allow efficient capture of different chemical compounds (including amino acids, cholesterol, fatty acids) on their surface, thus efficiently promoting their desorption and gas phase cationisation. The minimum detectable amount for those organic and biological molecules is often in the fmol range [23]. Despite the fact that scientists have developed a variety of methods for the synthesis of silver nanoparticles, there are still problems with obtaining surfaces with nanoparticles of high durability and chemical purity. Recently, a successful application of cationic silver nanoparticles (AgNPs), which were placed on MALDI targets for highly sensitive detection of d-ribose at attomolar levels as well as analysis of biological samples such as urine and blood serum [51] was shown. The application of new 109AgNPET surface has been presented with examples of analysis of nucleosides and nucleic bases [60]. One of the main directions of development of LDI-MS is the imaging mass spectrometry (MSI), enabling the visualization of surface distribution of biological samples. The critical limitations of the spatial resolution of MALDI-MSI are the size of the organic matrix crystals and the analyte migration during the matrix application process. To overcome these problems, researchers tried to use nanoparticles as substitutes of organic matrices. In 2013 Ruman group presented that direct contact of the analysed object with Ag nanoparticle-covered target permits direct surface transfer of chemical compounds. The active surface becomes then a “chemical photograph” of an object and allows MS analysis and MS imaging [68]

White noise excited vibrations of viscoelastic shallow shells

The paper presents the results of the analysis of randomly excited vibrations of viscoelestic shallow shells. The parameter of interest is the dispersion of velocity normal to the element surface. The choice of parameter is motivated by estimation of the noise generated by a vibrating panel.Drgania lepkosprężystych powłok małowyniosłych poddanych wymuszeniu losowemu typu białego szumu W artykule omówiono rezultaty analiz drgań powłok małowyniosłych wykonanych z materiału lepkosprężystego i poddanych wymuszeniu losowemu typu białego szumu. Jako parametr opisujący drgania przyjęto dyspersję składowej prędkości normalnej do powierzchni środkowej powłoki. Wybór tego parametru jest uzasadniony faktem, iż jego wartość może być miarą wartości mocy akustycznej promieniowanej przez drgający element

Initial phases of DNA rehydration by NMR and sorption isotherm

T*he initial stages of rehydration of salmon sperm deoxyribonucleic acid (DNA) lyophilizates were observed using hydration kinetics, sorption isotherm, and high power proton relaxometry (at 30 MHz). T*he hydration kinetics reveals (i) a very tightly bound water not removed by incubation over silica gel ($A_0^{h}$ = 0.057 ± 0.010), (ii) a tightly bound water [saturating at $A_1^{h}$ = 0.149 ± 0.007, hydration time $t_1^{h}$ = (0.27 ± 0.08) h], a tightly bound water (iii) [saturating at $A_2^{h}$ = 0.694 ± 0.039, with the hydration time $t_2^{h}$ = (9.8 ± 3.2) h], and (iv) a loosely bound water fraction for the samples hydrated at p/$p_{0}$ ≥ 76% [with the hydration time $t_3^{h}$ = (44 ± 14) h, and the contribution progressively increasing with the air humidity]. For the hydration at p/$p_{0}$ = 100%, after $t_{0}$ = (244 ± 22) h of incubation the swelling process begins. T*he amount of additional water uptake at swelling depended on the macrostructure of the sample. Sorption isotherm is sigmoidal in form and is fitted well by the Dent model with the mass of water saturating primary binding sites Δ M/$m_{0}$ = 0.114. Proton free induction decay is a superposition of the immobilized proton signal (Gaussian, with $T_{2S}^\ast$ ≈ 20 μs) and two liquid signal components coming from tightly bound ($T_{2L_1}^\ast$ ≈ 100 μs, with the mass saturating at Δ m/$m_{0}$ = 0.111 ± 0.044) and loosely bound water fraction (with the amplitude proportional to the mass of water added)

Kinetic characterisation of catalysts for methanol synthesis

The results of activity studies of four catalysts in methanol synthesis have been presented. A standard industrial catalyst TMC-3/1 was compared with two methanol catalysts promoted by the addition of magnesium and one promoted by zirconium. The kinetic analysis of the experimental results shows that the Cu/Zn/Al/Mg/1 catalyst was the least active. Although TMC-3/1 and Cu/Zn/Al/Mg/2 catalysts were characterised by a higher activity, the most active catalyst system was Cu/Zn/Al/Zr. The activity calculated for zirconium doped catalyst under operating conditions was approximately 30% higher that of TMC-3/1catalyst. The experimental data were used to identify the rate equations of two types – one purely empirical power rate equation and the other one - the Vanden Bussche & Froment kinetic model of methanol synthesis. The Cu/ZnO/Al2O3catalyst modified with zirconium has the highest application potential in methanol synthesis

Magnetic and Transport Properties of (Fe1−x\text{}_{1-x}Nix\text{}_{x})2\text{}_{2}P in View of KKR-CPA Results

We present results of the electronic structure study for the solid solution (Fe$\text{}_{1-x}$Ni$\text{}_{x}$)$\text{}_{2}$P (space group P6̅2m). The samples were synthesized for x=0.0 up to 0.15. From the electrical conductivity measurements on these materials, it was verified that resistivity increases with increasing temperature up to the Curie point T$\text{}_{C}$ and changes the slope at T$\text{}_{C}$ decreasing when temperature is raised above T$\text{}_{C}$. To get insight into the possible origin of such observations, we carried out the Korringa-Kohn-Rostoker-coherent potential approximation electronic structure calculations for (Fe$\text{}_{1-x}$Ni$\text{}_{x}$)$\text{}_{2}$P in the range of concentration x=0.0 up to 1.0. It was found that alloying with Ni in Fe$\text{}_{2}$ P causes vanishing of spin band splitting and non-rigid band behaving of electronic valence states near the Fermi level. The polarization factor for electrons at E$\text{}_{F}$ changes in (Fe$\text{}_{1-x}$Ni$\text{}_{x}$)$\text{}_{2}$P with increasing x, and interestingly, it reaches maximum at x=0.1, closely to the concentration (x=0.08), when the largest value of T$\text{}_{C}$ and a kink in temperature dependent resistivity were detected

Neutron Diffraction Studies of MnFeAsy\text{}_{y}P1−y\text{}_{1-y} System

Magnetic structures of the MnFeAs$\text{}_{y}$P$\text{}_{1-y}$ system were examined by means of the neutron diffraction technique in the 1.5-300 K temperature range. Atomic ordering in the metal sublattices, temperature dependence of the incommensurate (y = 0.2 and y = 0.275) and of the ferromagnetic (y = 0.275, y = 0.3, y = 0.5) ordering is discussed