EPR and magnetic susceptibility studies of the interaction between Cu2+ and Mn2+ ions in x(CuO·MnO)(1−x)[2B2O3·K2O] glasses

EPR and magnetic susceptibility experiments have been performed on x(CuO·MnO)(1?x)[2B₂O₃·K₂O] glasses with x varying in the range 0?x?50 mol.%. For x?3 mol.% both Cu²⁺ and Mn²⁺ ions are present mostly as the isolated species. The increase of the g-tensor values and bonding parameters (α², β², δ²) for Cu²⁺ ions together with the increase of TM ions concentration in the 0.2–1 mol.% range was noticed. In the case of 5 ? x ? 30 mol.% the dipole-dipole and superexchange interactions occur between transition metal ions, the first type of interactions prevailing in this range of concentration. For x30 mol.% the superexchange interaction prevail. The strong interaction between Cu²⁺ and Mn²⁺ gives rise to the exchange coupled Cu²⁺Mn²⁺ pairs in the studied glasses with x 3 mol.%.     

Absorption spectra of Cu2+ in azurite

EPR and optical absorption studies in azurite have been carried out at room and low temperatures. The EPR spectrum reveals that the ground state for Cu²⁺ ion is ²B₁. Peak to peak linewidth of EPR spectrum is calculated (ΔH_p = 76 G) and found to be close with the observed value. The Cu²⁺ ion situated in D_4h symmetry with spin-orbit interaction exhibits bands at 11,806, 16,484, 17,952 and 19,793 cm^?1. The tetragonal field parameters are calculated to be Ds = ? 3364 cm^?1 and Dt = ? 604 cm^?1. The crystal field splitting parameter is found to be Dq = ? 1175 cm^?1.     

EPR studies of Gd3+-doped Ce2(SO4)3.8H2O and La2(SO4)3.9H2O single crystals

EPR spectra of Gd³⁺-doped Ce₂(SO₄)₃.8H₂O and La₂(SO₄)₃.9H₂O single crystals have been measured with an X-band spectrometer at room and low temperatures. The absolute signs of spin Hamiltonian parameters have been determined for the La₂(SO₄)₃.9H₂O host from intensities of lines at liquid helium temperature; for the Ce₂(SO₄).8H₂O host the lines broaden considerably below 60 K, not permitting the determination of absolute signs of spin Hamiltonian parameters. The data are analysed using a rigourous least-squares procedure, fitting simultaneously all lines obtained for several orientations of the external magnetic field. The zero-field splittings have been computed for both the hosts. The characteristics of EPR spectra of Gd³⁺ in these hosts are compared with those obtained in other rare-earth trisulphate octahydrate hosts.     

EPR of Mn2+ doping unannealed single crystal of (La2O3)0.95(CeO2)0.05

X-band room temperature EPR spectra have been recorded for Mn²⁺ ion doping unannealed (La₂O₃)_0.95(CeO₂)_0.05 host crystal. The data are analysed using a rigorous least-squares fitting procedure in which a large number of lines characterized by ΔM = ± 1, Δm = 0 transition, obtained for several orientations of the static magnetic field, are simultaneously fitted. Combined with the knowledge of the absolute sign of the hyperfine interaction parameter. A, the hyperfine Hamiltonian parameters A, B, Q as reported in this paper, are given with their correct signs. The information on the linewidth is used to deduce the deviation of the crystal-field axes of different Mn²⁺ ions from the c axis; on the basis of the model proposed here these deviations are found to be between 0 and 10°.     

EPR of V2+ in SrCl2

The X-band EPR spectrum of SrCl₂:V has been measured at liquid nitrogen temperature. A signal associated with V²⁺ in a site of trigonal symmetry is observed. The EPR data have been explained using the spin hamiltonian $\textcolor{red}{}\text{= μ}{}_{\mathrm{\beta }}\text{H}\text{g}\text{?}\text{S}\text{+ D[S}{}^2{}_{\mathrm{z}}\text{?}\text{1}\text{3}\text{S(SH)] +}\text{S}\text{A}\text{?}\text{I}$, with D ? hv, g_∥ = 1.957 ± 0.004, g₆ = 1.954 ± 0.004, A_∥ = 230 ± 5 MHz, A₆ = 235 ± 5 MHz. This V²⁺ defect is similar to those previously reported in fluoride crystals with the fluorite structure.     

EPR evidence of pair formation of V4+ ions and their motion in a quasi-one-dimensional conductor β-Na0.33V2O5

Precise measurements of anisotropy of g-value and linewidth of the EPR absorption signal in β-Na_0.33V₂O₅ have revealed the presence of pair formation of magnetic V⁴⁺ ions in site-I chains. The anisotropy of the linewidth can be understood on the basis of the pairing model, by considering motions of pairs. The depairing time is estimated as of the order of 10^?11 sec.     

EPR of Fe3+ ion and symmetry of [AIF5·H2O]2? complex ion in (NH4)2AIF5·H2O single crystals

We used the spin-Hamiltonian method for the analysis of the electron paramagnetic resonance (EPR) spectrum of Fe³⁺ as a probe ion in (NH₄)₂AlF₅·H₂O single crystalline basic material. The theoretical expressions for the magnetic field (at which the fine structure transition lines appear) versus the angle between the magnetic field and the axis of symmetry of the magnetic complex are also given. These values were calculated by applying the perturbation theory to the second-order terms. From the experimental results (at 300 K and 9.21 GHz), the spin-Hamiltonian parameters were deduced:D=(668±10)·10⁻⁴ T,E=(−56±10)·10⁻⁴ T,a=(−54±10)·10⁻⁴ T,F=(30±10)·10⁻⁴ T. An isotropic superhyperfine structure was evidenced for the five fluorine ions. The obtained EPR data were used to determine the local symmetry of the Al³⁺ ion. A good agreement with X-ray diffraction measurements was found.     

Champs hyperfins magnetiques sur les noyaux de 121Sb5+ dans Cr2O3

The magnetic hyperfine interactions of the impurity Sb⁵⁺ in Cr₂O₃ have been examined by the Mössbauer effect of ¹²¹Sb.The magnetic field on the nucleus of ¹²¹Sb⁵⁺ (Cr₂O₃) measured at 77° K, H(0) = 170 ± 15 koe.The comparison of the results obtained for the impurity ¹²¹Sb⁵⁺ with those for the ¹¹⁹Sn⁴⁺ ions, occuring in the same matrix, suggests the preponderant effect of the decoupling of the electron spins of 5s valency on the values of the internal fields observed for those ions.     

EPR and magnetic susceptibility studies of iron ions in ZnO-Fe2O3-SiO2-CaO-P2O5-Na2O glasses

Room temperature electron paramagnetic resonance (EPR) spectra and temperature dependent magnetic susceptibility data have been obtained on bulk x(ZnO,Fe₂O₃)(65−x)SiO₂20(CaO, P₂O₅)15Na₂O (6≤x≤21 mole%) glasses prepared by melt quenching method. EPR spectra of the glasses revealed absorptions centered at g≈2.1 and 4.3. The variations of the intensity and line width of these absorption lines with composition have been interpreted in terms of the variation in the concentration of the Fe²⁺ and Fe³⁺ ions in the glass and the interaction between the iron ions. EPR and magnetic susceptibility data of the glasses reveal that both Fe²⁺ and Fe³⁺ ions are present in the glasses, with their relative concentration being dependent on the glass composition. The studies reveal superexchange type interactions in these glasses, which are strongly dependent on their iron content.     

EPR investigation on exchange coupled Mn2+ pairs in (CH3)4NCdCl3

EPR experiments were performed at Q-band and 300 K on Mn²⁺ doped (CH₃)₄NCdCl₃. Beside the single ion resonance many weak lines could be observed which can be attributed to nearest neighbour pairs of Mn²⁺ lying along the crystallographic c-axis. The spectra can be described using a Hamiltonian for strongly exchange coupled pairs. The obtained data show that the ionic separation varies in the different spin states. So an additional interaction occurs on the Mn²⁺ dimer, which can be interpreted as an exchange striction effect.     

EPR of orthorhombic Gd3+-M+ complexes in SrF2

In this paper we report new results of EPR experiments on orthorhombic Gd³⁺-M⁺ complexes (M = Na, K, Rb and Ag) in SrF₂. Special attention is payed to the second degree crystal field parameters B⁰₂ and B²₂ and a comparison with earlier results on corresponding complexes in CaF₂ and BaF₂ is made. We conclude that the main contributions to these crystal field parameters are of electrostatic nature.     

Cr5+ in SrTiO3: An example of a static Jahn-Teller effect in A d1 system

The effect of uniaxial stress on the EPR spectrum of Cr⁵⁺ in SrTiO₃ has been studied. It is concluded that SrTiO₃:Cr⁵⁺ is a static Jahn-Teller system. The strain-coupling coefficient V₂ is found to be 2 × 10⁴ cm^?1. Our results show that in the absence of external stress the intensity ratio of the EPR lines, at temperatures below the cubic-to-tetragonal phase transition, is related to the macroscopic strain, present in SrTiO₃ at these temperatures.     

EPR and magnetic susceptibility studies of xCuO·(1−x)[2B2O3·Li2O] glasses

The results of EPR and magnetic susceptibility studies on xCuO·(1?x)? [2B₂O₃·Li₂O] glasses with $\text{0?x?30 mol \%}$, are reported. The modification of EPR spectra with the increasing of CuO content are explained supposing that these are the result of the superposition of two EPR signals, one showing the hyperfine structure typical for isolated Cu²⁺ ions and other consisting from a broad line centered at g ～ 2 typical for the clustered Cu²⁺ ions. The values of the EPR parameters prove that the coordination of isolated Cu²⁺ -complexes remains approximately the same and show that Cu²⁺ ions are situated in axially distorted octahedral vicinities. EPR measurements have shown that the Cu²⁺ ions are present mostly as the isolated species when $\text{x?5 mol \%}$. Beside the dipole-dipole coupling between Cu²⁺ ions, the magnetic measurements suggest that for x>10 mol % superexchange interactions appear, too. From Curie constant is established that in this glass system the copper ions are in Cu²⁺ and Cu⁺ valence states. Also, the amounts of the copper ions in bivalent state are determined.     

EPR observation of phase transitions in calcium cadmium acetate hexahydrate: Using Mn2+ and Cu2+ ions as probe

Results of temperature dependence of EPR spectra of Mn²⁺ and Cu²⁺ ions doped calcium cadmium acetate hexahydrate (CaCd(CH₃COO)₄·6H₂O) have been reported. The investigation has been carried out in the temperature range between room temperature (～ 300 K) and liquid nitrogen temperature. A I-order phase transition at 146 ± 0.5 K has been confirmed. In addition a new II-order phase transition at 128 ± 1 K has been detected for the first time. There is evidence of large amplitude hindered rotations of CH₃ groups which become frozen at ～ 128 K. The incorporation of Cu²⁺ and Mn²⁺ probes at Ca²⁺ and Cd²⁺ sites respectively provide evidence that the phase transitions are caused by the molecular rearrangements of the common coordinating acetate groups between Ca²⁺ and Cd²⁺ sites. In contradiction to the previous reports of a change of symmetry from tetragonal to orthorhombic below 140 K, the symmetry of the host is concluded to remain tetragonal in all the three observed phases between room temperature and liquid nitrogen temperature.     

Al2O3:V3+晶体局域结构及其自旋哈密顿参量研究

提出了解释掺杂离子局域结构畸变的配体平面移动模型，建立了此模型下晶体微观结构与自旋哈密顿参量之间的定量关系.在考虑自旋与自旋、自旋与另一电子轨道和轨道与轨道作用等微小磁相互作用的基础上，采用全组态完全对角化方法，对Al₂O₃晶体中V³⁺的局域结构和自旋哈密顿参量进行了系统的研究.结果表明，V³⁺掺入Al₂O₃晶体后，上下配体氧平面间距离增大了0.0060 nm.从而成功地解释了Al₂O₃:V³⁺晶体的自旋哈密顿参量.在此基础上，研究了三角晶场下3d²离子自旋哈密顿参量的微观起源.研究发现，自旋三重态对自旋哈密顿参量的贡献是主要的，微小磁相互作用对自旋哈密顿参量的贡献只与自旋三重态有关.     

Pulsed magnetic field study of Fe2+ in some fluosilicates

Pulsed field experiments up to 450 kOe have been performed on FeSiF_6.6H₂O. We interpret the data: (i) in terms of spin hamiltonian constants: D = 12.3± 0.2 cm^-1 (E = 0.54cm^-1 being known from EPR data); (ii) in terms of axial-crystal-field parameters: $\text{δ}\text{λ}\text{=}\text{orbital trigonal splitting/spin-orbit coupling}\text{= 15 ± 2; λ = -100 ± 7cm}{}^{\mathrm{?1}}$. The magnetic axis is found to deviate from the cristallographie c axis by an angle 1° < θ < 2°. The adiabatic cooling obtained during the pulse is discussed.Similar experiments on Fe_0.15Zn_0.85SiF_6.6H₂O and Fe_0.30Zn_0.70SiF_6.6H₂O single crystals are reported; in both cases we measure $\text{D}\text{g}{}_{\mathrm{\parallel }}\text{= 6.0 ± 0.1cm}{}^{-1}$. Using EPR data, we obtain D = 14.3cm^-1, λ ～ ?75cm^-1, δ ～ 195cm^-1; using Mössbauer data, we obtain D = 15.3cm^-1, λ ～ ?88cm^-1, δ ～ 185cm^-1.     

Crystal field investigations of Yb(C2H5SO4)3. 9H2O and Er: YA1G

Using the spectroscopically derived crystal field parameters for Yb(C₂H₅SO₄)₃. 9H₂O and Er³⁺: YA1G, the temperature dependence of Schottky specific heat, paramagnetic susceptibility, magnetic anisotropy and μ_eff has been calculated over a temperature range 5–400°K. The hyperfine interaction parameters for ¹⁷¹Yb³⁺, ¹⁷³Yb³⁺ and ¹⁶⁷Er³⁺ systems are also obtained and in turn used to estimate the nuclear specific heat. The nice agreement obtained for susceptibility and specific heat of Yb(C₂H₅SO₄)₃. 9H₂O at very low temperatures confirms the accuracy of CEF parameters employed and the neglect of exchange interaction. However, for Er³⁺: YA1G, the CEF parameters are adequate to explain the bulk thermal and magnetic properties but not the g-values.     

Fourth-order spin Hamiltonian terms for Fe2+ in rutile structure antiferromagnet FeF2

The paper deals with the spectroscopic and magnetic properties of Fe²⁺ ions in FeF₂. The microscopic spin Hamiltonian theory for Fe²⁺ in crystalline environments with second-kind orthorhombic symmetry is considered. Explicit formulas for the parameters B₀⁽²⁾(D),B₂⁽²⁾(E), g_x, g_y, g_z and, for the first time in the literature, the fourth-order parameters B₀⁽⁴⁾, B₂⁽⁴⁾ and B₄⁽⁴⁾, are derived. Using semi-empirical data for the ⁵D-term energy levels of Fe²⁺ ion in FeF₂, the pressure dependence of the parameters B_q^(k) in the region from 0 to 133 kbar is discussed. The relative role of the fourth-order parameters with respect to the second-order ones is found to increase strongly with pressure (e.g. in the region studied, D increases only by a factor of 3, whereas B₀⁽⁴⁾ increases by a factor of nearly 20). The magnetocrystalline anisotropy of FeF₂; is considered in the strong anisotropy model taking into account the fourth-order spin Hamiltonian terms. The uniaxial anisotropy constants K₁ and K₂ are derived theoretically and their pressure dependence is discussed quantitatively. The theory and numerical results of this paper are useful with regard to Fe²⁺ in other isomorphic fluorides, namely: MgF₂, ZnF₂, VF₂ and MnF₂. It is found that the fourth-order spin Hamiltonian parameters are accessible to experimental detection from spectroscopic studies on Fe²⁺ in non-magnetic fluorides and magnetic studies on Fe²⁺ : MnF₂ and FeF₂, preferably under high pressure.     

Exchange interaction and spin dynamics in pentanuclear clusters, Cu3Ln2(ClCH2COO)12(H2O)8 (Ln = Nd3+, Sm3+, Pr3+)

New compounds, [Cu₃Ln₂(ClCH₂COO)₁₂(H₂O)₈]·2H₂O with Ln = Nd³⁺ (I), Sm³⁺ (II), Pr³⁺ (III), built up of pentanuclear clusters were synthesized and studied by means of X-ray analysis and electron paramagnetic resonance (EPR). X-ray data show that all compounds are isostructural and the pentanuclear clusteres may be considered as a linear system with alternating Cu(II) and Ln(III) ions: Cu(2)-L¹-Ln-L²-Cu(1)-L²-Ln-L²-Cu(2) with L¹ and L² being bridging fragments and Cu(1) and Cu(2) being structurally nonequivalent copper complexes. EPR studies demonstrate that in the temperature range of 100–293 K the signals due to only one type of the copper complexes are observed in the spectra of I–III. AtT<100 K the spectral temperature dependence is nontrivial. AtT<30 K new signals are detected in the spectra of I and II. The temperature dependence of the EPR spectra is interpreted under the assumption that the parameter of the exchange interaction Cu(2)-Ln considerably exceeds the parameter of the interaction Cu(1)-Ln. EPR spectra are calculated for the fragments of five paramagnetic centers in the frames of the model taking into account the nonequivalence of two copper complexes, short longitudinal and transverse paramagnetic relaxation times of the rare-earth ions at room temperature and the change of the relaxation rates when the temperature decreases. The results of the calculations show that it is possible to obtain information about the interactions in the system on the basis of the analysis of the temperature dependence of the EPR spectra of the central copper complex. The parameter of the isotropic part of the exchange interaction between copper and neodymium ions (for the interaction Cu(2)-Nd) is estimated as about 15 cm⁻¹. A considerable rearrangement of the spin states when the temperature changes is found for all complexes.     

EPR and optical absorption studies on VO ions in KZnClSO4·3H2O single crystals—an observation of superhyperfine structure

EPR spectra of VO²⁺ ions doped in KZnClSO₄·3H₂O single crystals have been studied at different temperatures. The EPR spectrum shows a well-resolved hyperfine and superhyperfine structure patterns. The angular variation of EPR spectra reveals the presence of more than three magnetic complexes, which correspond to distinct sites of VO²⁺ ion. From the angular variation EPR data, the spin-Hamiltonian parameters are evaluated and discussed. The optical absorption spectrum studied at room temperature shows bands corresponding to C_4v symmetry. From the EPR and optical data, the molecular-orbital bonding coefficient ε² and β² are evaluated and discussed. The observed five-line superhyperfine structure has been attributed to four protons (with I=1/2) from the surrounding water molecules of one of the vanadyl sites.