A rigorous evaluation of spin-Hamiltonian parameters and linewidth from a polycrystalline EPR spectrum.

Details are given of a procedure to evaluate the spin-Hamiltonian (SH) parameters and the linewidth from a polycrystalline EPR spectrum by using a least-squares fitting (LSF) technique in conjunction with numerical diagonalization of the SH matrix. The required resonance line positions are computed rather quickly using a homotopy technique, in which the position at an external magnetic field (B) orientation (theta, phi) is used as the initial value in a LSF procedure to estimate the position at an infinitesimally close B-orientation, (theta + deltatheta, phi + deltaphi). The resonance line positions are calculated successively in this procedure for all orientations of B over a grid of (theta, phi) values for the unit sphere. The eigenvectors of the SH matrix are used to calculate the intensities of the EPR lines exactly for each orientation of B. Details are given of how to compute rigorously the first and second derivatives of the chi(2)-function with respect to the SH parameters and the linewidth using the eigenvalues and eigenvectors of the spin-Hamiltonian matrix for a polycrystalline spectrum required in the LSF procedure. It is explained how this technique is generalized to include two or more magnetically inequivalent paramagnetic species, as well as how it is used for the simulation of other EPR-related spectra. The procedure is illustrated by evaluation of the Mn(2+) SH parameters and Lorentzian linewidth from the 249.9-GHz EPR spectrum of Mn(gamma-picoline)(4)I(2).     

EPR and optical spectroscopy of Yb<Superscript>3+</Superscript> ions in CaF<Subscript>2</Subscript>: an analysis of the structure of tetragonal centers

CaF₂ crystals doped with Yb³⁺ ions have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy. EPR spectra of paramagnetic centers (PCs) for cubic (T_c) and tetragonal (T_tet) symmetries were identified. Empirical energy level diagrams were established and crystal field parameters were determined. Information on the CaF₂∶Yb³⁺ phonon spectra was obtained from the electron-vibrational structure of the optical spectra. The crystal field parameters were used to analyze the crystal lattice distortions in the vicinity of the Yb³⁺ ion. Within the framework of a superposition model, it is established that four F⁻ ions located symmetrically with respect to the fourfold axis from the side of the ion-compensator approach the impurity ion and deviate from the PC axis. The second set of four fluorine ions also approaches the Yb³⁺ ion and the PC axis. The ion-compensator F⁻ also approaches considerably the impurity ion.     

Observation of electric quadrupole spin resonance of Ho<Superscript>3+</Superscript> impurity ions in synthetic forsterite

The anomalous dependence of the electron paramagnetic resonance (EPR) line shape on the microwave power in the resonator has been found when studying the continuous-wave EPR spectra of impurity holmium ions in synthetic forsterite on an ELEXSYS E 580 EPR spectrometer. The power-threshold transition from the conventional lines being the derivatives of the spectral line contours to the spectral line contours themselves has been observed as the power increased. The properties of the anomalous EPR lines are qualitatively explained assuming that the resonance electric quadrupole transitions take place between the electron spin levels.     

Variable-frequency EPR study of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) single crystal at 9.6, 36, and 249.9 GHz: structural phase transition

Multifrequency electron paramagnetic resonance studies on the Mn(2+) impurity ion in a mixed single crystal NH(4)Cl(0.9)I(0.1) were carried out at 9.62 (X-band) in the range 120-295 K, at 35.87 (Q-band) at 77 and 295 K, and at 249.9 GHz (far-infrared band) at 253 K. The high-field EPR spectra at 249.9 GHz are well into the high-field limit leading to a considerable simplification of the spectra and their interpretation. Three magnetically inequivalent, but physically equivalent, Mn(2+) ions with their respective magnetic Z-axes oriented along the crystallographic [100], [010], [001] axes were observed. Simultaneous fitting of EPR line positions observed at X-, Q-, and far infra-red bands was performed using a least-squares procedure and matrix diagonalization to estimate accurately the Mn(2+) spin-Hamiltonian parameters. The temperature variation of the linewidth and peak-to-peak intensities of the EPR lines indicate the presence of lambda-transitions in the mixed NH(4)Cl(0.9)I(0.1) crystal at 242 and 228 K consistent with those observed in the pure NH(4)Cl and NH(4)I crystals, respectively. A superposition-model analysis of the spin-Hamiltonian parameters reveals that the local environment of the Mn(2+) ion is considerably reorganized to produce axially symmetric crystal fields about the respective Z-axes of the three magnetically inequivalent ions as a consequence of the vacancy created due to charge-compensation when the divalent Mn(2+) ion substitutes for a monovalent NH(4)(+) ion in the NH(4)Cl(0.9)I(0.1) crystal. This reorganization is almost the same as that observed in NH(4)Cl and NH(4)I single crystals, although the latter two are characterized by different, simple cubic and face-centered cubic, structures.     

Local structure of titanium pair centers in SrF2 crystals: EPR and ENDOR spectroscopic studies

The local structure of titanium pair centers in SrF₂: Ti crystals is investigated using electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy. It is found that titanium pair centers with spin moment S=2 and tetragonal symmetry of the magnetic properties are formed in SrF₂: Ti cubic crystals under certain growth conditions and during annealing. The tensor components of the fine and ligand hyperfine structures in the EPR and ENDOR spectra are determined. A model of the Ti⁺-Ti³⁺ paramagnetic dimer is proposed. This model provides an adequate interpretation of both the ferromagnetic nature of the exchange interaction and the observed displacements of four ligands in the first coordination sphere of titanium impurity ions in directions perpendicular to the impurity ion-ligand bonds.     

The migration of Mn2+ ions in Cd1−xMnxS nanocrystals: Thermal annealing control

This work reports evidence of the induced migration of Mn²⁺ ions in Cd_(1?x)Mn_xS nanocrystals (NCs) by selecting a specific thermal treatment for each sample. The growth and characterization of these magnetic dots were investigated by atomic force microscopy (AFM), optical absorption (OA), and electronic paramagnetic resonance (EPR) techniques. The comparison of experimental and simulated EPR spectra confirms the incorporation of Mn²⁺ ions both in the core and at the dot surface regions. The thermal treatment of a magnetic sample, via selected annealing temperature and/or time, affects the fine and hyperfine interaction constants which modify the shape and the intensity of the EPR transition spectrum. The identification of these changes has allowed tracing the magnetic ion migration from core to surface regions of a dot as well as inferring the local density of the magnetic impurity ions.     

Superhyperfine structure in the EPR spectra and optical spectra of impurity f ions in dielectric crystals: A review

The results of observation and simulation of the superhyperfine (ligand hyperfine) structure (SHFS) of the electron paramagnetic resonance (EPR) spectra of rare-earth and uranium impurity ions in dielectric crystals have been systematized. The resolved SHFS of the EPR spectra of doped cubic crystals (with the fluorite and perovskite structures) has been observed for orientations of a constant magnetic field along the crystallographic axes. Most attention has been paid to tetragonal double fluorides LiRF₄ (R = Y, Lu, Tm), in which the SHFS of the EPR spectra has also been found for intermediate orientations of the magnetic field. For the LiYF₄: Nd³⁺ single crystal, the splitting of optical spectral lines due to the interaction of Nd³⁺ ions with nuclear magnetic moments of the nearest neighbor fluorine ions has been observed for the first time. The Van Vleck paramagnet LiTmF₄: U³⁺ is characterized by the SHFS with clearly distinguishable components due to the interaction of uranium ions both with nuclei of the fluorine ions and with enhanced magnetic moments of the thulium nuclei. The SHFS envelopes of the EPR spectra of Yb³⁺, Ce³⁺, Nd³⁺, and U³⁺ ions in LiYF₄ and LiLuF₄ crystals are well reproduced by numerical calculations based on the microscopic model using only three fitting parameters: the width of transitions between the electron-nuclear sublevels of the complex containing the paramagnetic ion and nuclei of the ligands and two constants of covalent bonding of the f electrons with 2s and 2p electrons of the nearest neighbor fluorine ions.     

用光谱和EPR谱确定CsMgBr3:Ni2+的局域结构

本文采用半自洽场(semi-SCF)自由Ni2 的3d轨道波函数、点电荷—偶极子模型和Ni2 -6X-(X=F,Cl,Br,I)络合物的μ-κ-α模型,建立了结构参数与光谱、EPR谱之间的定量关系,利用完全对角化方法,由光谱和电子顺磁共振(EPR)谱,确定了CsMgBr3:Ni2 晶体在77K温度时的局域结构参数,统一解释了CsMgBr3:Ni2 晶体的局域结构、光谱和EPR谱。所得理论结果与实验值符合得很好。此外,还讨论了晶体局域结构发生畸变的原因。     

EPR spectra of a GdMnO3 thin film on a SrTiO3 substrate

Electron paramagnetic resonance (EPR) spectra of a GdMnO₃/SrTiO₃ thin film in the X band have been measured in the temperature interval from 200 to 450 K. Signals from two types of paramagnetic centers have been observed in the spectra. The first paramagnetic center is a subsystem of Gd³⁺ ions, in the EPR spectrum of which the fine structure lines are resolved below 350 K. The second paramagnetic center is a system of manganese and gadolinium ions, in the EPR spectrum of which an exchange-narrowed line is observed with the width ΔH several times less than the width ΔH of an exchange-narrowed line observed in the GdMnO₃ single crystal. Unusual magnetic properties are due to the mismatch of the lattice parameters of the GdMnO₃ thin film and the SrTiO₃ substrate.     

EPR and optical studies of Cu doped ammonium dihydrogen phosphate single crystals

Electron paramagnetic resonance (EPR) spectra of Cu²⁺ ion in ammonium dihydrogen phosphate are studied at liquid nitrogen temperature (77 K). Four magnetically inequivalent Cu²⁺ sites in the lattice are identified. The angular variation spectra of the crystal in the three orthogonal planes indicate that the paramagnetic impurity, Cu²⁺ enters the lattice substitutionally in place of NH₄⁺ ions. The spin Hamiltonian parameters are determined with the fitting of spectra to rhombic symmetry crystalline field. The ground state wave function of Cu²⁺ ion is constructed and found to be predominantly |x²-y²〉. The cubic field parameter (Dq) and tetragonal parameters (Ds and Dt) are determined from optical spectra at room temperature. By correlating EPR and optical absorption spectra, the bonding coefficients are calculated and nature of bonding of metal ion with different ligands in the crystal is discussed.     

Effect of heat treatment and concentration of Mn and Fe on the structure of borate glass

We have studied the magneto-optic Faraday effect (FE) and electron paramagnetic resonance (EPR) in an aluminum potassium borate glass containing Fe oxides as an impurity in a concentration of 1.5 mass % and Mn impurity in variable concentration from 0 to 1.2 mass %. When manganese oxide is added to the glass composition, the paramagnetic contribution to the Faraday effect increases more slowly than the change in the total concentration of paramagnetic ions, which allows us to hypothesize the appearance of clusters in which the paramagnetic ions are coupled by antiferromagnetic interactions. Formation of clusters upon addition of manganese oxide is confirmed by the change in the nature of the EPR spectra, where we observe a manganese concentration dependence of the distribution of iron atoms with respect to the different positions in the glass matrix. Heat treatment leads to a strong increase in the Faraday effect and a change in the spectral dependences of the Faraday effect and the EPR, which is explained by enlargement of the clusters and appearance of nanoparticles. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 354–358, May–June, 2006.     

Application of High-Frequency Electron Paramagnetic Resonance/Electron Spin Echo for the Identification of the Impurity Composition and Electronic Structure of Ceramics Based Garnets

Physics of the Solid State - Electron paramagnetic resonance (EPR) spectra of Ce3+, Yb3+, Cr3+, and Gd3+ impurity ions in yttrium aluminum garnet Y3Al5O12 (YAG) ceramics were detected and...     

Electron paramagnetic resonance of Ce<Superscript>3+</Superscript> and Nd<Superscript>3+</Superscript> impurity ions in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6.13</Subscript>

The electron paramagnetic resonance (EPR) spectra of Ce³⁺ and Nd³⁺ impurity ions in unoriented powders of the YBa₂Cu₃O_6.13 compound are observed and interpreted for the first time. It is demonstrated that, upon long-term storage of the samples at room temperature, the EPR signals of these ions are masked by the spectral line (with the g factor of approximately 2) associated with the intrinsic magnetic centers due to the significant increase in its intensity.     

A correlation between manifestations of the magnetoplastic effect and changes in the electron paramagnetic resonance spectra after quenching of NaCl: Eu single crystals

The electron paramagnetic resonance (EPR) spectra of Eu²⁺ impurity ions in NaCl: Eu single crystals are investigated. It is found that the intensity of the EPR spectra undergoes prolonged (～200 h) multistage variations after quenching of NaCl: Eu single crystals. The variations observed in the EPR signal intensity are explained by the aggregation of impurity-vacancy dipoles into complexes. It is revealed that the magnetoplastic effect (a change in the microhardness in a magnetic field with an induction of 6 T) in these crystals manifests itself at an intermediate stage of impurity aggregation when all individual impurity-vacancy dipoles are temporarily stabilized in the sample. This can be associated with the thermally activated transformation of the internal atomic structure in the majority of already existing complexes.     

EPR Spectroscopy of Impurity Thulium Ions in Yttrium Orthosilicate Single Crystals

The frequency-field and orientation dependences of the electron paramagnetic resonance (EPR) spectra are measured for impurity Tm³⁺ ions in yttrium orthosilicate (Y₂SiO₅) single crystals by stationary EPR spectroscopy in the frequency range of 50–100 GHz at 4.2 K. The position of the impurity ion in the crystal lattice and its magnetic characteristics are determined. The temperature dependences of the spin–lattice and phase relaxation times are measured by pulse EPR methods in the temperature range of 5–15 K and the high efficiency of the direct single-phonon mechanism of spin–lattice relaxation is established. This greatly shortens the spin–lattice relaxation time at low temperatures and makes impurity Tm³⁺ ions in Y₂SiO₅ a promising basis for the implementation of high-speed quantum memory based on rare-earth ions in dielectric crystals.     

EPR diagnostics of laser materials based on ZnSe crystals doped with transition elements

The electron paramagnetic resonance (EPR) spectra observed in laser materials based on zinc selenide (ZnSe) crystals doped with transition elements have been analyzed and identified. It has been shown that, in addition to working impurities (Cr²⁺, Co²⁺, or Fe²⁺), the diffusion layer exhibits EPR spectra of accompanying impurities due to the diffusion of transition elements (chromium, cobalt, or iron) used in the preparation of active materials for quantum electronics (lasers, switches) operating in the mid-infrared range. EPR diagnostics of these impurities can be used in the development of appropriate regimes for minimizing concentrations of accompanying impurities that adversely affect the performance characteristics of laser materials. It has been found that, during the diffusion of transition metals, ions of the accompanying impurity Mn²⁺, which is characterized by extremely informative EPR spectra, are embedded in the crystal lattice. It has been proposed to use these ions as ideal markers to control, on the electronic level, the crystal structure of the active diffusion layer.     

A Study of Mechanochemical Doping of Fluoride Crystals with a Fluorite Structure by Er3+ Ions via Electron Paramagnetic Resonance Spectra

Using electron paramagnetic resonance (EPR) spectroscopy, we have shown that, upon mecha- noactivated doping of powders of compounds CaF₂, SrF₂, and BaF₂ with Er³⁺ ions, impurity centers of single erbium ions with cubic symmetry are formed. Investigations of dependences of EPR spectra intensities on the particle size show that the process of mechanochemical doping with Er³⁺ ions proceeds differently for CaF₂, SrF₂, and BaF₂ host matrices. In the case of CaF₂, impurity centers are localized in a very thin near-surface layer of CaF₂ particles, in SrF₂, the impurity is distributed over the volume of particles, while, in BaF₂, there is a layer of a finite thickness for which the probability of doping in the course of mechanosynthesis is very small and the impurity of the rare-earth element is localized in the core of large particles. These data can be explained assuming that the result of mechanosynthesis of particles of fluorides with a fluorite structure doped with Er3+ ions at room temperature is governed by two processes—mechanoactivated diffusion of rare-earth ions into particles and segregation of impurity ions at grain boundaries. In this case, the typical scales for compounds CaF₂, SrF₂, and BaF₂ considerably differ from each other.     

EPR Studies of DOPA–Melanin Complexes with Fe(III)

Paramagnetic centers in 3,4-dihydroxyphenylalanine–melanin and its complexes with Fe(III) were examined by electron paramagnetic resonance (EPR) spectroscopy. Paramagnetic centers of melanin play an important role in detoxification of environment and they reveal high activity in binding of metal ions. Two different signals were observed in EPR spectra: lines of o-semiquinone free radicals and lines of paramagnetic Fe(III). Amplitudes of EPR lines of both free radicals and iron ions decrease with increasing Fe(III) content in melanin–metal ion complexes. Free radical concentrations in the melanin samples, g-factors, amplitudes and line widths of EPR spectra were determined. It was stated that fast spin–lattice relaxation processes exist in both free radical system and paramagnetic iron ions in melanin complexes.     

EPR characterization of Mn impurity ions in PbWO4 single crystals

The electron paramagnetic resonance (EPR) properties of the Mn²⁺ ions in PbWO₄ single crystals grown by the Czochralski method have been investigated in the X-band microwave frequency, at T=20 K. The angular dependence of the EPR line positions obtained by rotating the magnetic field in the main crystallographic planes shows that the local symmetry at the Mn²⁺ impurity ions is tetragonal, strongly suggesting that the Mn²⁺ ions substitute for the Pb²⁺ lattice cations, without charge compensation. The resulting spin Hamiltonian parameters compare well with the corresponding values for the Mn²⁺ ions in other isomorphous tungstates. The observed strong angular variation of the EPR linewidth has been quantitatively described considering a random distribution of lattice strains.     

晶体CsMgCl3:Ni2+的局部结构、光谱和EPR谱的理论研究

本文采用半自洽场(semi-SCF) 自由Ni2+的3d轨道波函数、点电荷-偶极子模型和Ni2+-6X-(X=F,Cl,Br,I)络合物的μ-κ-α模型,建立了结构参数与光谱、EPR谱之间的定量关系,利用完全对角化方法,由光谱和电子顺磁共振(EPR)谱,确定了CsMgCl3:Ni2+晶体的局部结构参数,统一解释了CsMgCl3:Ni2+晶体的吸收光谱和EPR 谱.此外,还讨论了高阶微扰方法、参量拟合方法等问题.理论计算结果与实验值符合得很好.