Effect of a weak dimer-dimer interaction on the EPR line shape of polycrystalline samples

The spectroscopic manifestations of a weak interaction between dimers in the EPR spectra of polycrystalline samples are analyzed. It is shown that, under specific conditions, the weak interaction between dimers can be responsible for the additional lines in the EPR spectrum. The appearance of these features is associated with the collapse of the spectral lines in orientations satisfying the condition of exchange narrowing for the components of the fine structure in the spectrum of the dimer.     

Specific features of the substitution of Fe<Superscript>3+</Superscript> impurity ions for Zr<Superscript>4+</Superscript> in NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> single crystals

The EPR spectra of Fe³⁺ impurity ions in NaZr₂(PO₄)₃ single crystals at 300 K are investigated, and the spin Hamiltonian of these ions is determined. A comparative analysis of the spin-Hamiltonian and crystal-field tensors is performed using the maximum invariant component method. It is demonstrated that Fe³⁺ impurity ions substitute for Zr⁴⁺ ions with local compensator ions located in cavities of the B type. It is revealed that the invariant of the spin-Hamiltonian tensor B₄ and the crystal-field tensor V ₄ ⁴⁴ depend substantially on the mutual arrangement of ions in the first and second coordination spheres. The corresponding dependences are analyzed.     

Low-symmetry spin hamiltonian and crystal field tensors analysis: Fe(3+) in natrolite

Electron paramagnetic resonance study of a natural single crystal of natrolite was carried out at the frequency nu=36.772 GHz at room temperature. The angular dependence of the four symmetry-related spectra of Fe(3+) in the three crystallographic planes was fitted to a spin Hamiltonian (S=5/2) of symmetry C(i). The rank 4 crystal field tensors at tetrahedral sites were calculated using the point-charge model to determine the principal axes orientations of their cubic and trigonal components. The analysis of zero-field splitting tensors and comparison with crystal field ones suggests that Fe(3+) substitutes for Al(3+) with no significant distortion of the coordination tetrahedron in natrolite. Comparison of data for several natural and synthetic crystals reveals that the 4-rank zero-field splitting tensor invariants for Fe(3+) at the tetrahedral oxygen-coordinated sites are distinguishably smaller than those for Fe(3+) at octahedral sites. Such comparative analysis may help to determine the substitutional sites in other crystals.     

Effect of the Landau–Zener Transitions on the ac Susceptibility Shape

Physics of the Solid State - A model spin system S = 1 with a strongly anisotropic g factor is considered. The response of the system on low-frequency ac magnetic field is calculated numerically....     

Plasma drift-anisotropy instability and anomalous transport processes

The author expounds a nonlinear theory of the instability of a weakly inhomogeneous plasma with hot ions when a”loss cone” is present in their velocity distribution. Flute-type instabilities (k_Z= 0) are considered, which for a strong enough irregularity may build up even in short traps with”magnetic mirrors.” It is shown that the total ion flux through the magnetic mirrors, which is caused by turbulent diffusion into the loss cone, exceeds by a factor of (2n/R_H ?n)^1/2 the ion flux across the magnetic field as a result of diffusion in coordinate space (here n, ?n, are the density and its gradient, R_H is the ion Larmor radius). The diffusion time of ions into the “loss cone” is of the order τ=10Ω_? ^? (2n/R ^??n)^3/2 (Ω_H is the ion Larmor frequency). A plasma contained in magnetic traps is always in a nonequilibrium thermodynamic state. The nature of the nonequilibrium is connected with the specific geometry of the containing magnetic field. Here we will consider open traps with magnetic mirrors in which the nonequilibrium of the plasma is caused by:

1. 1)
   the curvature of the magnetic field force lines and its associated effective gravity field;     

Aluminum avoids the central position in AlB9- and AlB10-: photoelectron spectroscopy and ab initio study

The structures and the electronic properties of two Al-doped boron clusters, AlB(9)(-) and AlB(10)(-), were investigated via joint photoelectron spectroscopy and high-level ab initio study. The photoelectron spectra of both anions are relatively broad and have no vibrational structure. The geometrical structures were established by unbiased global minimum searches using the Coalescence Kick method and comparison between the experimental and calculated vertical electron detachment energies. The results show that both clusters have quasi-planar structures and that the Al atom is located at the periphery. Chemical bonding analysis revealed that the global minimum structures of both anions can be described as doubly (σ- and π-) aromatic systems. The nona-coordinated wheel-type structure of AlB(9)(-) was found to be a relatively high-lying isomer, while a similar structure for the neutral AlB(9) cluster was previously shown to be either a global minimum or a low-lying isomer.