EPR study of interlayer interaction in Gd2O3/Fe nanostructure

In this work, a nanoscale structure consisting of contacting layers of a metal of the iron subgroup and a rare earth metal oxide (REM) is considered. Such nanostructures have an interesting feature, which is that as a result of the contact of these layers, an increase in the galvanomagnetic, magneto-optical and kinetic properties of ferromagnetic metals are observed. Presumably, the enhancement is due to an increase in the magnetization of these metals, caused by the exchange f - d interaction between the unfilled f- and d-electron shells of the atoms that make up the contacting layers. The aim of this work is to find the possibility of such f - d exchange interaction by the EPR method. To compose the studied nanostructure, Fe used as it has the strongest magnetic properties in its subgroup. Gd2O3 was used as an REM oxide as one of the few oxides giving a significant signal in the EPR region. The Gd2O3/Fe nanostructure created by sequential electron-beam deposition of Gd2O3 and Fe layers on a sitall substrate. The thickness of the oxide and metal layers was 68 and 112 nm, respectively. EPR spectra were recorded at room temperature on a computerized spectrometer Radiopan 2547 SE / X at the frequency of 9.3 GHz. The set of the obtained spectra was processed using the OriginPro and MatLab programs, which confirmed their compliance with the Lorentz model. From the experimentally obtained EPR linewidth, the parameter of the exchange f - d interaction is determined under the condition of a number of assumptions. The value of the g-factor is also found. Comparison of the EPR parameters of the spectra of individual layers of Gd2O3 and Fe with the spectra of the Gd2O3/Fe nanostructure composed of them, including the value of the g factor and the exchange interaction parameter, suggests that the presence of an iron layer affects the EPR spectrum of the REM oxide layer Gd2O3. The exchange interaction parameter increases from 985 to 4685 (rel. units), the g-factor decreases from 3.5 to 2.4. The most probable reason for the change in the spectrum is the exchange f - d interaction between atoms with unfilled f- and d-electron shells that are parts of the contacting layers.

Studies of local structures for Cu2+ centers in M2Zn(SO4)2·6H2O (M = NH4 and Rb) crystals

The electron paramagnetic resonance (EPR) parameters (g factor g i , and hyperfine structure constants A i , with i = x, y, z) and local structures for Cu2+ centers in M2Zn(SO4)2·6H2O (M = NH4 and Rb) are theoretically investigated using the high order perturbation formulas of these EPR parameters for a 3d 9 ion under orthorhombically elongated octahedra. In the calculations, contribution to these EPR parameters due to the admixture of d-orbitals in the ground state wave function of the Cu2+ ion are taken into account based on the cluster approach, and the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the studied EPR parameters with the local structures of the Cu2+ centers. Based on the calculations, the Cu–H2O bonds are found to suffer the axial elongation ratio δ of about 3 and 2.9% along the z-axis, meanwhile, the planar bond lengths may experience variation ratio τ (≈3.8 and 1%) along x- and y-axis for Cu2+ center in (NH4)2Zn(SO4)2·6H2O and Rb2Zn(SO4)2·6H2O, respectively. The theoretical results show good agreement with the observed values.

Theoretical studies of the electron paramagnetic resonance parameters and local structures for Cu2+ in (100-2x)TeO2-xAg2O-xWO3 glasses

The electron paramagnetic resonance (EPR) parameters and local structures for Cu2+ in (100-2x)TeO2-xAg2O-xWO3 (TAW) (7.5 ≤ x ≤ 30 mol %) glasses are quantitatively studied for distinct modifier concentrations x. The octahedral Cu2+ centers are subject to the medium tetragonal elongations of about 2% along the C4 axis due to the Jahn-Teller effect. By utilizing only three adjusted coefficients a, b and ω, the quantities (Dq, k, t and κ) can be suitably characterized by the Fourier type functions, which reasonably account for the experimental concentration dependences of the d-d transition bands and EPR parameters. The calculation results are discussed, and the mechanisms of the above concentration dependences of these quantities are illustrated by the modifications of the local structures and the electron cloud distribution around the Cu2+ dopant with the variations of the concentration x.

An investigation of a series of layered Zn-1,4-diazabicyclo[2.2.2]octane metal–organic frameworks: local structure and adsorption properties of mixed-metal centre

The mixed-metal pillar-layered metal–organic frameworks of Zn(bdc)(DABCO)0.5, Zn0.5Cu0.5(bdc)(DABCO)0.5 and Cu(bdc)(DABCO)0.5 (bdc = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane) are investigated for their local structures and gas adsorption properties. According to the obtained electron paramagnetic resonance (EPR) spectra, the distorted structures around Cu2+ are proposed to be tetragonally and orthorhombically elongated [CuO4N] with the well fitted high-order perturbation formulae of the EPR parameters. Due to the doped Cu2+, the adsorption isotherms of industrially relevant gases (CO2, CO, CH4 and N2) and lower alkanes (CH4, C2H6, C3H8, C4H10 and C5H12) are different, especially at different temperatures. By combining the structural properties and adsorption isotherms, a comprehensive study suggests that the ZnDABCO series can be a controllable tool in gas storage and separation.