Electron spin echo of CH2OH radicals adsorbed in A-type zeolites

Data on the trapping site of radicals in zeolite α-cages have been obtained by the analysis of modulation effects in the electron spin echo of CH₂OH radicals produced by irradiation in A-type zeolite with adsorbed methyl alcohol.     

Connections on manifolds and new characteristic classes

We give an extension of Maslov-Arnold classes to a certain class of symplectic manifolds. It is proved that any such generalized class of minimal surfaces is equal to zero for a large class of stable minimal surfaces. We describe some applications to pseudo-Riemannian geometry and to the investigation of completely integrable Hamiltonian systems.     

Features of EPR Application to Systems Containing Paramagnetic Centers and Ferromagnetic Nanoparticles

The scope of the electron paramagnetic resonance (EPR) technique in catalysis is often limited because of the presence of the ferromagnetic nanoparticles in many catalytic systems. The present work gives an effective method to discriminate solid-state EPR spectra in the microwave resonance absorption while investigating such systems. The approach is based on the different features of the EPR spectra and ferromagnetic resonance absorption that are simultaneously observed in the system.     

Superinsulator–superconductor duality in two dimensions

For nearly a half century the dominant orthodoxy has been that the only effect of the Cooper pairing is the state with zero resistivity at finite temperatures, superconductivity. In this work we demonstrate that by the symmetry of the Heisenberg uncertainty principle relating the amplitude and phase of the superconducting order parameter, Cooper pairing can generate the dual state with zero conductivity in the finite temperature range, superinsulation. We show that this duality realizes in the planar Josephson junction arrays (JJA) via the duality between the Berezinskii–Kosterlitz–Thouless (BKT) transition in the vortex–antivortex plasma, resulting in phase-coherent superconductivity below the transition temperature, and the charge-BKT transition occurring in the insulating state of JJA and marking formation of the low-temperature charge-BKT state, superinsulation. We find that in disordered superconducting films that are on the brink of superconductor–insulator transition the Coulomb forces between the charges acquire two-dimensional character, i.e. the corresponding interaction energy depends logarithmically upon charge separation, bringing the same vortex-charge-BKT transition duality, and realization of superinsulation in disordered films as the low-temperature charge-BKT state. Finally, we discuss possible applications and utilizations of superconductivity–superinsulation duality.     

Stepwise magnetization of dispersed ferromagnets due to magnetic interparticle interactions

The main features of stepwise magnetization of dispersed ferromagnets caused by magnetic interparticle interactions are studied using a two-particle model. The ranges of values of the magnetic anisotropy constants of particles and of the dipole-dipole interaction between them are determined over which a reproducible jumpwise change in the magnetization of the system occurs in an external positive magnetic field. The proposed model is shown to explain the main specific features of the fine structure of the ferromagnetic resonance spectra.     

Four-Step Spin Crossover in a New Cyano-Bridged Iron-Silver Coordination Polymer

Spin-crossover complexes with multistep transitions attract much attention due to their potential applications as multi-switches and for data storage. A four-step spin crossover is observed in the new iron(II)-based cyanometallic guest-free framework compound Fe(2-ethoxypyrazine)₂{Ag(CN)₂}₂ during the transition from the low-spin to the high-spin state. A reverse process occurs in three steps. Crystallographic studies reveal an associated stepwise evolution of the crystal structures. Multiple transitions in the reported complex originate from distinct Fe^II sites which exist due to the packing of the ligand with a bulky substituent.