Mössbauer spectra of Fe3+ and Fe2+ ions in hexagonal ferrite with w-structure

The hexagonal ferrite Fe₂W = BaFe₂²⁺Fe³⁺₁₆O₂₇ exhibits a sharp ⁵⁷Fe Mössbauer spectrum at 300 and 78 K. All seven sublattices in this complicated crystal structure are detected. Fast electron exchange between Fe²⁺ and Fe³⁺ ions gives rise to sharp lines and makes them indistinguishable. At 5 K the exchange is slow and the Fe²⁺ ions are detected from the presence of a weak subspectrum with broadened lines separated from the main spectrum of the Fe³⁺ ions. Analysis shows that the Fe²⁺ ions reside exclusively on one of the seven sublattices, which is occupied statistically by Fe²⁺ and Fe³⁺ ions in the ratio of 2 : 1. For SrFe²⁺₂Fe³⁺₁₆O₂₇ the situation is the same.     

Synthesis,crystal structure and magnetic characterization of Pr3+ and Zn2+ ions co-doped hexagonal ferrites via the ceramic process

M-type hexaferrites Ca_0.2Sr_0.8-xPr_xFe_12-yZn_yO₁₉ (0.00?≤?x?≤?0.40, 0.00?≤?y?≤?0.30) were synthesized by the ceramic process. The X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and a vibrating sample magnetometer (VSM) were used to investigate microstructure and magnetic properties of the M-type hexaferrites. The single-phase with hexagonal structure was obtained in all Pr–Zn substituted M-type hexaferrites, and with increasing Pr–Zn content, the 2θ values of (107) and (114) peaks shifted towards higher angles. With increasing Pr–Zn content, the lattice constant a basically kept unchanged, while the lattice constant c decreased. FESEM images of the hexaferrites showed that the hexagonal platelets had formed in the hexaferrites and the average grain size increased with increasing Pr–Zn content. The saturation magnetization (M_s), remanent magnetization (M_r) and M_r/M_s ratio first increased with increasing Pr–Zn content (0.00?≤?x?≤?0.24, 0.00?≤?y?≤?0.18), and then decreased with further increasing Pr–Zn content. The coercivity (H_c), magnetic anisotropy field (H_a) and effective magnetic anisotropy constant (K_eff) increased with increasing Pr–Zn content (0.00?≤?x?≤?0.16, 0.00?≤?y?≤?0.12), and then decreased with further increasing Pr–Zn content.     

Estimation of 4s covalent bonding of Fe2+ and Fe3+ ions in NiO

The charge densities of the 4s electrons in Fe²⁺ and Fe³⁺ ions in the ionic compound, NiO, were measured from an internal conversion experiment and compared with some predicted values on the basis of different theoretical methods.     

ESR of Fe3+ -Rhombic,Fe2+ -Vo and Fe1+ -Vo complexes in SrTiO3

Three new Fe-defect complexes have been identified by ESR in Fe doped crystals of SrTiO₃. These are an Fe³⁺ center with rhombic fine structure in the “as-grown” crystals, and the vacancy associated complexes Fe²⁺ -V_o and Fe¹⁺ -V_o in “reduced” crystals. Photo-excited charge transfer effects are observed for these centers.     

Exchange-coupled pairs of Fe3+ ions in beryl

The EPR spectrum of first nearest neighbour pairs of Fe³⁺ ions substituting for Al³⁺ ions in beryl is reported. The form of the pair spin Hamiltonian is discussed, and operator equivalent factors for fourth-order terms are tabulated. The Fe³⁺ pair interionic coupling corresponds to isotropic antiferromagnetic exchange with J = + 1.7 cm^-1 plus anisotropic dipolar coupling. The pair value of the zero-field splitting parameter D is + 0.0206 cm^-1 and shows a substantial shift from the single-ion value. It is proposed that resonance lines previously attributed to Fe³⁺ ions in Be²⁺ or Si⁴⁺ sites are due to Fe³⁺ pairs.     

Electron exchange between Fe2+ and Fe3+ ions on octahedral sites in spinels studied by means of paramagnetic Mössbauer spectra and susceptibility measurements

Mössbauer spectra were obtained of the paramagnetic spinels $\text{Zn}{}^{\mathrm{2+}}\text{|}\text{Zn}{}^{\mathrm{2+}}{}_{\mathrm{<mtext>(1?x)</mtext><mtext>2</mtext>}}\text{Ti}{}^{\mathrm{4+}}{}_{\mathrm{<mtext>(1+x)</mtext><mtext>2</mtext>}}\text{Fe}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>(1?</mtext><mtext>x)</mtext>}}\text{Fe}{}^{\mathrm{2+}}{}_{\mathrm{x}}\text{|}\text{O}{}_4$ and susceptibilities were measured. The strong difference between the paramagnetic Fe²⁺ and Fe³⁺ spectrum, due to the different quadrupole splitting, is used for the distinction between the two species. At 300 K a superposition of the Fe³⁺ and the Fe²⁺ spectra is found for most of the iron and, in addition, some continuous absorption. The latter is strongest for equal Fe³⁺ and Fe²⁺ concentration $\text{(x =}\text{1}\text{2}\text{)}$ while it disappears towards the end members (Fe³⁺ only or Fe²⁺ only) as well as with decreasing temperature (between 78 and 200 K). From this it is concluded that it arises from thermally activated electron exchange, the frequency of which passes a “critical” value of ～10⁸ sec^?1 for increasing temperature. Paramagnetic susceptibilities are found to obey a Curie-Weiss law down to low temperatures. From the dependence of the asymptotic Curie temperature on the composition the magnetic interaction parameters J₁₁ = ?1.4 K, J₂₂ = ?3.3 K and J₁₂ = + 1.6 K for the Fe³⁺Fe³⁺, Fe²⁺Fe²⁺ and Fe³⁺Fe²⁺ interactions are derived. The experimental results are discussed in terms of a hopping model with an activation energy q ～- 0.12eV and a non-equivalence of the octahedral sites expressed by a varying potential energy difference U₀ between neighbouring sites. The continuous absorption at 300 K for $\text{x =}\text{1}\text{2}$ is attributed to about 17% of the iron on sites with U₀ running from 0 to ??0.06 eV. The ferromagnetic Fe³⁺, Fe²⁺ interaction (J₁₂) is attributed to electron transfer from localized Fe²⁺ ions to Fe³⁺ neighbours via a transfer integral b of the order of 0.05 eV. The magnitudes of J₁₂ and b are tentatively explained.     

ESR study of Fe3+ and Mn2+ ions on trigonal sites in ilmenite structure MgTiO3

Electron spin resonance has been observed for Fe³⁺ and Mn²⁺ ions occupying sites with trigonal symmetry in undoped and doped Verneuil-grown crystals of the ilmenite type compound MgTiO₃. At 300 K, the fine structure parameters in the spin Hamiltonian are (in 10^?4cm^?1) D = +844 (± 1), (a? F) = +118 (± 1), a = 69 (± 7) for Fe³⁺ and D = +164 (± 1), (a ? F) = +10.2 (± l), a = 7.0 (± 1) for Mn²⁺. These values are compared with literature data for Fe³⁺ and Mn²⁺ in other oxides, especially Al₂o₃, with particular reference to the recent “superposition” theory of the effect of a trigonal distortion. From the orientation of the axes of cubic pseudosymmetry of the spin Hamiltonian, and with the assumption that a has the same sign for both ions, it is proposed that Fe³⁺ and Mn²⁺ occupy the same octahedral site, namely the Mg²⁺ site. Anomalous line splittings observed for one sample were attributed to twinning on (0001) or {1120} planes.     

On the Fe2+ ion contribution to induced anisotropy and magnetic after-effect in several Mn ferrites

After a brief survey of the relaxation phenomena of permeability in Mn mixed ferrites we present new results concerning induced anisotropy Ku and viscosity field in four samples of composition Mn_xFe_3?xO_{4 + y} with x = 0.2, 0.4, 0.6 and 0.8.The first important result shows that Ku is proportional to the iron content, the extrapolation giving Ku = 0 at x = 1.The other data obtained from more fundamental properties indicate that the elementary coupling energy of Fe²⁺ to the lattice, w, is of the order of 3 to $\text{4 × 10}{}^{\mathrm{?16}}\text{erg}\text{ion}\text{Fe}{}^{\mathrm{2+}}$ and seems to be related to the Curie point, that is to the exchange energy. Finally we can conclude that the Fe²⁺ ion is responsible first for the well-known ‘effect II” at 100–300°C in the thermal spectra of permeability disaccomodation and also for the strong induced anisotropy Ku created by magnetic annealing in this temperature zone. It is shown once more that Fe²⁺ plays an important role even above room temperature in spite of the Fe²⁺ ? Fe³⁺ hopping process.     

Effects of Eu3+  Fe3+ exchange interaction on the spin Hamiltonian parameters of Fe3+ in EuGaG

The anisotropic exchange $\text{1}\text{3}\text{a}{}_{\mathrm{\mu \nu }}\text{Y}{}_{\mathrm{\mu \nu }}\text{(L}{}_{\mathrm{<mtext>Eu</mtext>}}\text{)S}{}_{\mathrm{<mtext>Eu</mtext>}}\text{· S}{}_{\mathrm{<mtext>Fe</mtext>}}\text{(0 < μ ? 6)}$ is incorporated with the isotropic exchange ?2 a₀₀S_Eu · S_Fe to interpret the observed spin-Hamiltonian parameters g and D of Fe³⁺ doped into EuGaG. Calculations from the observed g shifts yield a value of a₀₀ equal to 0.01 K. In order to explain the observed D shift, it is concluded that the spherical harmonics Y_μν(L_Eu) with μ > 2 are of dominant importance.     

Mössbauer study of spin-spin relaxation of Fe3+ ions in the presence of other paramagnetic ions

Mössbauer spectroscopy has been used to study the influence of paramagnetic ions, viz. Cu²⁺, Cr³⁺, Co²⁺ Mn²⁺, Gd³⁺ and Dy³⁺ on the spin-spin relaxation time of Fe³⁺ ions in amorphous frozen aqueous solutions. It is found that these ions shorten the relaxation time, but the effect is much smaller than suggested earlier on the basis of measurements of relaxation of Fe³⁺ in an α-Al₂O₃ matrix. It is also found that S-state ions have a greater influence on the relaxation time than other paramagnetic ions. The spectra obtained in presence of S-state impurity ions could only be fitted by allowing the individual transition probabilities to vary independently.     

Magnetic properties of paramagnetically doped crystals Fe3+, Nd3+ and Ho3+ in various compounds

In this work we calculate the energy levels, wave functions and transition probabilities for a number of compounds whose crystal field parameters have been determined. We introduce a convergence criterion in the diagonalization of the Hamilton matrices dependent upon a self consistency test on the eigenvectors. This assures us of numerically accurate wave functions.First we calculated energy level and susceptibility differences in (Nd³⁺)PbMoO₄ dependent on the multiplicative constants θ_n, used with the published A_l^m to determine the crystal field parameters B_l^m, (B_l^m = θ_nA_l^M). Calculated energy levels as a function of external magnetic field strength and orientation are compared with experimental results for three different sets of published crystal field parameters, B_l^m, for (Fe³⁺)TiO₂. The ground state energy levels, and wave functions, have been calculated for the non-Kramers Ho³⁺ ion in the crystals PbMoO₄, LaCl₃ and HoCl₃. Easily distinguishable variations in the temperature dependence of the X_zz component of the susceptibility are found as a function of the host crystal. It is pointed out that susceptibility calculations, based upon measured crystal field parameters, in conjunction with subsequent susceptibility measurements, provide a good check on the validity of the crystal field parameters.     

Far-infrared absorption of MgO: Fe2+ in magnetic fields

We have measured the far-infrared absorption of iron-doped MgO in the wavenumber region 10–200 cm^?1 and in magnetic fields up to 6 T. Absorption peaks found at 107.0 and 110.5 cm^?1 are assigned to magnetic dipole transitions between the spin-orbit Г_5g groundstate (J = 1) and the Г_3g, Г_4g excited states (J = 2) of the Fe²⁺ -ion at a cubic site. The observed magnetic field dependence shows that Г_4g is the higher excited level, so that the crystal field order of the levels is not changed by the reduction of the spin-orbit splitting attributed to a dynamic Jahn-Teller effect. An additional absorption peak at 33.4 cm^?1 is found to split in magnetic field.In iron-doped KMgF₃ absorption peaks at 52 and 87 cm^?1 that have previously been attributed to the same transitions of Fe²⁺ are found to remain unshifted and unsplit in magnetic fields up to 6 T.     

Theoretical simulations of emission spectra of Fe^7＋ and Fe^＋8

The energy levels, oscillator strengths, spontaneous radiative decay rates, and electron impact collision strengths are calculated for Fe VIII and Fe IX using the recently developed flexible atomic code （FAC）. These atomic data are used to analyse the emission spectra of both laboratory and astrophysical plasmas. The nf-3d emission lines have been simulated for Fe VIII and Fe IX in a wavelength range of 6-14 nm. For Fe VIII, the predicted relative intensities of lines are insensitive to temperature. For Fe IX, however, the intensity ratios are very sensitive to temperature, implying that the information of temperature in the experiment can be inferred. Detailed line analyses have also been carried out in a wavelength range of 60-80 nm for Fe VIII, where the solar ultraviolet measurements of emitted radiation spectrometer records a large number of spectra. More lines can be identified with the aid of present atomic data. A complete dataset is available electronically from http：//www.astrnomy.csdb.cn/EIE/.     

Identification of Fe4+ and Fe5+ charge-transfer photochromic absorption bands in SrTiO3

Optical absorption and the enhancement and bleaching of Fe³⁺ and Fe⁵⁺ electron paramagnetic resonance in SrTiO₃: Al measured as a function of wavelength and time show that the photochromic absorption bands are due to electron transfer from O^2- valence states to Fe⁴⁺ and Fe⁵⁺. They occur at 2.09 and 2.82 eV for Fe⁴⁺ and at 1.99 and 2.53 eV for Fe⁵⁺.     

The sign of Fe3+OCr3+ superexchange determined from Fe57 hyperfine field measurements

The sign of the super-transferred hyperfine field at an impurity site is shown to depend on the sign of the impurity-host superexchange interaction. This fact is used to determine that the Fe³⁺OCr³⁺ superexchange in YCrO₃ is antiferromagnetic.     

Mössbauer study of Zn2+ and Sn4+ additives in Nickel ferrites

The Mössbauer study of Fe⁵⁷ in polycrystalline solid solutions of Ni_{1 + x ? y}Zn_ySn_xFe_{2 ? 2x}O₄ (y = 0.1, 0.3, 0.5 and x = 0.1 to 0.5 with x varying in steps of 0.1) has been made. The present work has been aimed at investigating the variation of isomer shift, nuclear magnetic field at Fe⁵⁷ nuclei and ionic distribution at tetrahedral and octahedral sites when the concentration of Zn²⁺ and Sn²⁺ ions is successively increased in nickel ferrites. The ionic distribution in samples having low tin concentration has been explained on the basis of Neel's molecular field model whereas the ionic distribution of samples having high tin and zinc concentration has been explained on the basis of formation of isolated superparamagnetic clusters at the octahedral site. It has been inferred that a larger substitution of zinc and tin ions enhances relaxation effects.     

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.     

电气石中离子对(Fe2+—Fe3+跃迁

本文在晶体场理论的基础上,采用Fe²⁺的自洽场解析近似3d轨道,考虑到电气石中b,c两位置的实际对称性(C_s,C₁),计算了属于3d⁶组态的Fe²⁺在该两位置的自旋允许能谱:用离子对跃迁的观点,从理论上探讨了前人尚未处理过的离子对的(Fe²⁺(g)-Fe³⁺)→(Fe²⁺(e)-Fe²⁺)跃迁;并对偏振依赖性很大的三条谱:9000cm^-1,13800cm^-1,15000cm^-1作了强度估计,较为满意地解释了电气石的近红外光谱。 关键词：     

Far infrared absorption of Fe2+ in KMgF3

Far infrared absorption in cubic KMgF₃ doped with Fe²⁺ is reported . A line is observed at 87cm^?1, which is assigned to the (Γ_5g → Γ_3g, Γ_4g) transition in the Fe²⁺. The reduction in the spin-orbit coupling from the free ion value has been predicted by Ham, Schwarz and O'Brien.