Description of spin reorientation transition in Au/Co/Au sandwich with Co film thickness within a simple phenomenological model of ferromagnetic film

Simple phenomenological model of ferromagnetic film characterized by equal energies of surface anisotropies at two sides of a film (symmetric film) is considered. The model is used to describe a two-step spin reorientation transition (SRT) in Au/Co/Au sandwich with Co film thickness: the SRT from perpendicular to canted noncollinear (CNC) state at N_⊥=6.3 atomic layers and the subsequent SRT from CNC to in-plane state at _N∥=10.05$N_{\parallel }=10.05$ atomic layers. Analytic expressions for the stability criterion of collinear perpendicular and in-plane states of a film are derived with account of discrete location of atomic layers. The dependence of borders that separate regions corresponding to various magnetic states of a film in the (k_B,k_S)-diagram on film thickness N is established. k_S(k_B) is surface (bulk) reduced anisotropy constant. The comparison of theory with experiment related to Au/Co/Au sandwich shows that there is a whole region in the (k_B,k_S)-diagram corresponding to experimentally determined values of threshold film thicknesses N_⊥=6.3 and _N∥=10.05$N_{\parallel }=10.05$. The comparison of this region with similar region determined earlier for a bare Co/Au film within the same model of asymmetric film and characterized by N_⊥=3.5, _N∥=5.5$N_{\parallel }=5.5$ shows that the intersection of these regions is not empty. Hence, both the SRT in Au/Co/Au sandwich and in bare Co/Au film with Co film thickness can be described within the same model using the same magnitudes of model parameters k_S, k_B. Based on this result we conclude that the energy of Neel surface anisotropy at free Co surface is negligible compared to the energy of Co–Au interface anisotropy. It is demonstrated that the destabilization of collinear states in symmetric film leads to occurrence of the ground CNC state and two novel metastable CNC states. These three CNC states exhibit different kinds of symmetry. In case of asymmetric film only ground CNC state occurs on destabilization of collinear states of a film.     

Spin-polarized current generated by magneto-electrical gating

We theoretically study spin-polarized current through a single electron tunneling transistor (SETT), in which a quantum dot (QD) is coupled to non-magnetic source and drain electrodes via tunnel junctions, and gated by a ferromagnetic (FM) electrode. The I–V characteristics of the device are investigated for both spin and charge currents, based on the non-equilibrium Green's function formalism. The FM electrode generates a magnetic field, which causes a Zeeman spin-splitting of the energy levels in the QD. By tuning the size of the Zeeman splitting and the source–drain bias, a fully spin-polarized current is generated. Additionally, by modulating the electrical gate bias, one can effect a complete switch of the polarization of the tunneling current from spin-up to spin-down current, or vice versa.     

Synthesis and characterization of two acetato-bridged dinuclear copper(II) complexes with 4-bromo-2-((4 or 6-methylpyridin-2-ylimino)methyl)phenol as ligand

The synthesis and characterization of two new acetato-bridged dinuclear copper(II) complexes are described. Both compounds have the general formula [Cu(L)(µ-O₂C–CH₃)]₂, in which L = 4-bromo-2-((4-methylpyridin-2-ylimino)methyl)phenol or 4-bromo-2-((6-methylpyridin-2-ylimino)methyl)phenol. The title compounds consist of dinuclear units with bridging acetato groups and a ligand linked to each copper via the phenol oxygen and nitrogen. Both compounds were synthesized in a one-step reaction and characterized by elemental analysis, Fourier transform infrared (FTIR), electron spin resonance (ESR), and electronic spectra and by room temperature magnetic moments. The compounds exhibit antiferromagnetic interactions at room temperature. UV-Vis spectra show four absorptions attributed to d–d transitions of copper, ligand → metal charge transfer and π → π* or n → π* transitions of ligand. The FTIR spectra indicate a Cu₂O₄C₂ ring vibration. Both complexes show room temperature magnetic moments of about 1.6 B.M. per copper. The X-band ESR studies indicate a weak half-field band, characteristic of the Cu(II)–Cu(II) dimer, observed at 1552 and 1558 G for the complexes, strongly suggesting that the hyperfine structure arises from a spin triplet species. The spectra of frozen samples in DMSO or DMF at liquid nitrogen temperature show a typical Δm = 1 transition.     

Iron(II) complexes containing the 2,6-bis-iminopyridyl moiety. Synthesis,characterization, reactivity,and DNA binding

Two iron(II) complexes, [Fe^II(py^tBuN₃)₂](FeCl₄) (1) and [Fe^II(py^tBuMe₂N₃)Cl₂] (2), with sterically constrained py^tBuN₃ and py^tBuMe₂N₃ chelate ligands (py^tBuN₃ = 2,6-bis-(aldiimino)pyridyl; py^tBuMe₂N₃ = 2,6-bis-(ketimino)pyridyl), have been synthesized and characterized by elemental analysis, IR, UV–vis spectra, and preliminary X-ray single-crystal diffraction. The latter revealed that Fe(II) in 1 is six-coordinate by six nitrogen donors from two bisiminopyridines in a distorted octahedron. Complex 2 reacts with thiourea with a second-order rate constant k₂ = (2.50 ± 0.05) × 10^?3 M^?1 s^?1 at 296 K, and the reaction seemed to be slow. In a similar way, the interaction of 2 and DNA was studied by fluorescence and absorption spectroscopy. The results revealed that 2 caused fluorescence quenching of DNA through a dynamic quenching procedure. The binding constants K_A, K_app, and K_SV as well as the number of binding sites between 2 and DNA were determined.     

Dipole Moment Studies of n-butanol,i-butanol and t-butanol with Chlorobenzene Complexes

Abstract

The dipole moments of H-bonded complexes of n-butanol, i-butanol and t-butanol with chlorobenzene in benzene were investigated from dielectric measurements at 455 kHz and at temperature 303.16 K. The dipole moment of the complex (μab), interaction dipole moment (Δμ) and induced polarization (Pab) for thermodynamically most favoured geometry of 1:1 complexes in these systems were determined. The results shows that the complexation is due to charge redistribution effect in all cases studied and the tendency of complex formation is maximum in n-butanol system.     

Evaluation of Excess Molar Polarization in Binary Mixtures of Amines in Nonpolar Solvents

Abstract

A new expression for the excess molar polarization in binary mixture of polar and nonpolar liquids has been proposed. An experimental assessment of the proposed equation has been made by comparison with an earlier equation in the binary mixtures of amines in nonpolar liquids. The proposed equation for excess molar polarization is found to be more appropriate for detailed study of molecular association in the liquid mixtures.     

Self-rotation of elliptically polarized light in Doppler-broadened rubidium atoms

We present a theoretical and experimental study of self-rotation of incident elliptically polarized light on a rubidium atomic vapor. We construct density matrix equations, which are then solved numerically, and further averaged over atomic transit times and a Maxwell-Boltzmann velocity distribution. We calculate the rotation angle as a function of detuning for various laser intensities and polarizations. We compare the calculated results with experimental results and find good agreement between them.     

Synthesis,structure, and magnetic property of Co(II)-based metal–organic framework with 4,4′-oxy bis(benzoate) ligand

A 2-D coordination polymer, [Co(OBA)₂]_∞ (OBA?=?4,4′-oxy bis(benzoate)), where OBA ligands bridge cobalt in a terminal fashion to build up a 2-D layer structure with strong hydrogen-bonding interaction was isolated and structurally characterized from the reaction of OBA with Co(OAc)₂?·?4H₂O. Magnetic data indicate the Co(II) centers in 1 are negligibly magnetically coupled to each other and the single-ion magnetic behavior of Co(II) in octahedral environment is dominated at low temperature to give an effective S?′?=?1/2 ground state from S?=?3/2 state due to spin–orbit coupling.