Axis Of Electric Field Gradient Research Articles

Magnetic States of Fe2+ Ions in FexMn1 – xS Induced by Chemical Pressure

Influence of the chemical pressure (x) in single crystals of FexMn1 – xS (0.12 ≤ x ≤ 0.29) on the spin state of iron ions was studied by Mossbauer spectroscopy in the temperature range from 4.2 to 300 K. Peculiarities of formation of the paramagnetic and antiferromagnetic phases of solid solutions were found. Substitution of Fe2+ cations in the high-spin state for Mn2+ was found to occur in FexMn1 – xS as x changes. A decrease in the distance between the ions in FexMn1 – xS induces changes in the state of the Fe2+ ions in the samples with x = 0.25 and 0.29. The asymmetry parameter of the electric field gradient (EFG) tensor and the angle between the directions of the magnetic moment and the principal axis of the electric field gradient were found to change in the magnetically ordered phase at 4.2 K; the angle between the magnetic moment and the electric field gradient axis changes from 21° in the sample with x = 0.12 to 33° when x = 0.29.

Magnetic field tuning of low-energy spin dynamics in the single-atomic magnet Li2(Li1−xFex)N

We present a systematic ${}^{57}\mathrm{Fe}$ M\"ossbauer study on highly diluted Fe centers in ${\mathrm{Li}}_{2}({\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x})\mathrm{N}$ single crystals as a function of temperature and magnetic field applied transverse and longitudinal with respect to the single-ion anisotropy axis. Below 30 K, the Fe centers exhibit a giant magnetic hyperfine field of ${\overline{B}}_{A}=70.25(2)\phantom{\rule{4pt}{0ex}}\mathrm{T}$ parallel to the axis of strongest electric field gradient ${\overline{V}}_{zz}=\ensuremath{-}154.0(1)\phantom{\rule{4pt}{0ex}}\mathrm{V}/{\AA{}}^{2}$. Fluctuations of the magnetic hyperfine field are observed between 50 and 300 K and described by the Blume two-level relaxation model. From the temperature dependence of the fluctuation rate, an Orbach spin-lattice relaxation process is deduced. An Arrhenius analysis yields a single thermal activation barrier of ${\overline{E}}_{A}=570(6)\phantom{\rule{4pt}{0ex}}\mathrm{K}$ and an attempt frequency ${\overline{\ensuremath{\nu}}}_{0}=309(10)\phantom{\rule{4pt}{0ex}}\mathrm{GHz}$. M\"ossbauer spectroscopy studies with applied transverse magnetic fields up to 5 T reveal a large increase of the fluctuation rate by more than one order of magnitude. In longitudinal magnetic fields, a splitting of the fluctuation rate into two branches is observed consistent with a Zeeman induced modification of the energy levels. The experimental observations are qualitatively reproduced by a single-ion effective spin Hamiltonian analysis assuming a ${\mathrm{Fe}}^{1+}\phantom{\rule{4pt}{0ex}}{d}^{7}$ charge state with the unquenched orbital moment and a $J=7/2$ ground state. It is demonstrated that a weak axial single-ion anisotropy $D$ of the order of a few Kelvin can cause a two orders of magnitude larger energy barrier for longitudinal spin fluctuations.

Modulated magnetic structure of Fe3PO7 as seen by Fe57 Mössbauer spectroscopy

The paper reports new results of the 57Fe M\"ossbauer measurements on Fe3PO4O3 powder sample recorded at various temperatures including the point of magnetic phase transition TN ~ 163K. The spectra measured above TN consist of quadrupole doublet with high quadrupole splitting of D300K ~ 1.10 mm/s, emphasizing that Fe3+ ions are located in crystal positions with a strong electric field gradient (EFG). In order to predict the sign and orientation of the main components of the EFG tensor we calculated monopole lattice contributions to the EFG. In the temperature range T < TN, the experimental spectra were fitted assuming that the electric hyperfine interactions are modulated when the Fe3+ spin (S) rotates with respect to the EFG axis and emergence of spatial anisotropy of the hyperfine field Hhf = S\~AI at 57Fe nuclei. These data were analyzed to estimate the components of the anisotropic hyperfine coupling tensor (\~A). The large anharmonicity parameter, m ~ 0.94, of the spiral spin structure results from easy-axis anisotropy in the plane of the iron spin rotation. The temperature evolution of the hyperfine field Hhf(T) was described by Bean-Rodbell model that takes into account that the exchange magnetic interactions are strong function of the lattice spacing. The obtained M\"ossbauer data are in qualitative agreement with previous neutron diffraction data for a modulated helical magnetic structure in strongly frustrated Fe3PO4O3.

A Long-Lived Fe(III)-(Hydroperoxo) Intermediate in the Active H200C Variant of Homoprotocatechuate 2,3-Dioxygenase: Characterization by Mössbauer, Electron Paramagnetic Resonance, and Density Functional Theory Methods.

The extradiol-cleaving dioxygenase homoprotocatechuate 2,3-dioxygenase (HPCD) binds substrate homoprotocatechuate (HPCA) and O2 sequentially in adjacent ligand sites of the active site Fe(II). Kinetic and spectroscopic studies of HPCD have elucidated catalytic roles of several active site residues, including the crucial acid-base chemistry of His200. In the present study, reaction of the His200Cys (H200C) variant with native substrate HPCA resulted in a decrease in both kcat and the rate constants for the activation steps following O2 binding by >400 fold. The reaction proceeds to form the correct extradiol product. This slow reaction allowed a long-lived (t1/2 = 1.5 min) intermediate, H200C-HPCAInt1 (Int1), to be trapped. Mössbauer and parallel mode electron paramagnetic resonance (EPR) studies show that Int1 contains an S1 = 5/2 Fe(III) center coupled to an SR = 1/2 radical to give a ground state with total spin S = 2 (J > 40 cm(-1)) in Hexch = JŜ1·ŜR. Density functional theory (DFT) property calculations for structural models suggest that Int1 is a (HPCA semiquinone(•))Fe(III)(OOH) complex, in which OOH is protonated at the distal O and the substrate hydroxyls are deprotonated. By combining Mössbauer and EPR data of Int1 with DFT calculations, the orientations of the principal axes of the (57)Fe electric field gradient and the zero-field splitting tensors (D = 1.6 cm(-1), E/D = 0.05) were determined. This information was used to predict hyperfine splittings from bound (17)OOH. DFT reactivity analysis suggests that Int1 can evolve from a ferromagnetically coupled Fe(III)-superoxo precursor by an inner-sphere proton-coupled-electron-transfer process. Our spectroscopic and DFT results suggest that a ferric hydroperoxo species is capable of extradiol catalysis.

Synthesis, X-ray Rietveld analysis, infrared and Mössbauer spectroscopy of R2FeSbO7 (R3+ = Y, Dy, Gd, Bi) pyrochlore solid solution

A few iron-antimonate pyrochlores R2FeSbO7 (R3+ = Y, Dy, Gd, Bi) were synthesized using the solid state reaction technique and characterized systematically through powder X-ray diffraction and its Rietveld analysis, SEM-EDAX, Fourier-transform infrared and Fe57 Mössbauer spectroscopy. Scherrer's analysis of the XRD pattern and SEM-EDAX analysis estimate particle size of the polycrystalline powder to be in the range of 30–40 nm. Using the Rietveld fitting of the XRD profile, a model for unit Bravais cell is constructed suitably choosing 4 R ions, 4 Fe/Sb ions, 12 O ions and 2 O′ ions. A very strong and broad band at high wavenumber end at 642.0 cm−1 followed by some low intensity bands at 490, 465, 447 and 432 cm−1 are observed in the mid-infrared region of 400–1000 cm−1 in FT-IR spectra of Y2FeSbO7. The bands at 642 and 490 cm−1 can be ascribed to the stretching vibrations of the smallest inter-atomic bond M(Fe/Sb)–O in MO6 octahedron and Y–O′ bond, respectively. Mössbauer spectra exhibit paramagnetic doublet and sextet magnetic splitting at 300 K and 9 K, respectively. Quadrupole splitting measured at 300 K decreases linearly with the decrease of the x-coordinate of the 48f oxygens, which measures the distortion of the FeO6 octahedron. The quadrupole splitting arises due to the electric field gradient at Fe3+ nucleus site, which is nearly one-half of the value found for high-spin Fe2+ nucleus. Quadrupole splitting in the magnetic ordered spectra taken at 9 K is reduced from its 300 K value due to random distribution of the hyperfine fields at Fe site with regard to the electric field gradient axis. The larger effective magnetic moment of cations causes higher hyperfine field at Fe nucleus and vice-versa in these compounds.

Magnetic structure of Sr2Fe2O5 brownmillerite by single-crystal Mössbauer spectroscopy

Abstract In order to determine orientation of the Fe3+ magnetic moments and electric field gradient (efg) axes in the brownmillerite-type strontium ferrite structure for both iron sublattices where the efg tensor is not axially symmetric, the Mossbauer spectra of powdered and oriented single-crystal Sr2Fe2O5 were analyzed by solving the complete Hamiltonian for hyperfine interactions in the excited and ground states of the 57Fe nuclei. The magnetic moments of both octahedrally and tetrahedrally coordinated iron cations lie on the ac-plane of the orthorhombic unit cell and are parallel to the shortest c-axis, whilst the main efg axes are parallel to the longest crystallographic axis, b. This orientation is similar to that in Ca2Fe2O5, in spite of the structural differences of strontium and calcium ferrite brownmillerites at low temperatures.

NMR study of the electric field gradient in the paramagnetic phase of M3V2O8 (M = Co, Ni) compounds

The NMR spectra and the decay of a spin echo signal from 51V nuclei in Kagome-staircase Co3V2O8 (CVO) and Ni3V2O8 (NVO) single crystals are measured in the temperature range 30–300 K and a magnetic field H0 = 20 kOe. The orientation dependences of the 51V NMR line shape are used to determine the electric field gradient (EFG) parameters, namely, quadrupole frequency νQ and asymmetry parameter η. These parameters for NVO and CVO are νQ = 180(10) kHz, η = 0.5(1) and νQ = 130(10) kHz, η = 0.6(1), respectively. A comparison of the results of calculating EFG tensors with a point charge model and the NMR data indicates that the crystallographically equivalent vanadium atoms in the Ni3V2O8 and Co3V2O8 compounds differ in the EFG axis orientation. M3V2O8 crystals are found to have vanadium positions (V1, V2) with different orientations of the z axis, which specifies the direction of the principal value of EFG (Vzz): these orientations lie in the bc plane and make an angle of either +51(5)° (V1) or −51(5)° (V2) with axis c. In the temperature range 30–300 K, the EFG tensor components and the local symmetry of the charge surrounding of the vanadium positions in NVO and CVO oxides are found to change insignificantly.

Microwave spectrum and molecular structure of the 1-chloro-1-fluoroethylene-hydrogen fluoride complex

Guided by ab initio calculations, Fourier transform microwave spectra in the 8–22 GHz region are obtained for six isotopomers of the complex formed between 1-chloro-1-fluoroethylene and hydrogen fluoride. These include both 35Cl- and 37Cl-containing CH 2CClF with HF and DF, as well as 13CH 2C 35ClF and CH 2 13C 35ClF with HF. Analysis of the spectra determines the rotational constants, the complete chlorine quadrupole hyperfine coupling tensors in both the inertial and principal electric field gradient axis systems, and where appropriate, the diagonal components of the deuterium quadrupole coupling tensors. Spin–spin hyperfine structure is resolved and analyzed for CH 2C 35ClF–HF and CH 2C 37ClF–HF. The inertial information contained in the rotational constants combined with the HF and DF hyperfine interaction constants provides the structure for CH 2CClF–HF: a primary, hydrogen bonding interaction existing between the HF donor and the F atom acceptor on the 1-chloro-1-fluoroethylene moiety, while a secondary interaction occurs between the fluorine atom on the HF molecule and the H atom cis to the hydrogen-bonded F atom on the substituted ethylene, which causes the hydrogen bond to deviate from linearity. This is analogous to the structure obtained for 1-chloro-1-fluoroethylene-acetylene [H.O. Leung, M.D. Marshall, D.D. Grimes, J. Chem. Phys. 134 (2011) 034303] and similar to that of 1,1-difluoroethylene–HF [H.O. Leung, M.D. Marshall, T.L. Drake, T. Pudlik, N. Savji, D.W. McCune, J. Chem. Phys. 131 (2009) 204301], and indeed as with the acetylene complexes, to within experimental uncertainty, the intermolecular interactions in CH 2CClF–HF and its 1,1-difluoroethylene counterpart are practically indistinguishable.

Rotational spectroscopy and molecular structure of the 1-chloro-1-fluoroethylene-acetylene complex

Guided by ab initio calculations, Fourier transform microwave spectra in the 6-21 GHz region are obtained for seven isotopomers of the complex formed between 1-chloro-1-fluoroethylene and acetylene. These include the four possible combinations of (35)Cl- and (37)Cl-containing CH(2)CClF with the most abundant acetylene isotopic modification, HCCH, and its H(13)C(13)CH analogue, as well as three singly substituted deuterated isotopomers. Analysis of the spectra determines the rotational constants and additionally, the complete chlorine quadrupole hyperfine coupling tensors in both the inertial and principal electric field gradient axis systems, and where appropriate, the diagonal components of the deuterium quadrupole coupling tensors. The inertial information contained in the rotational constants provides the structure for CH(2)CClF-HCCH: a primary, hydrogen bonding interaction existing between the HCCH donor and the F atom acceptor on the 1-chloro-1-fluoroethylene moiety, while a secondary interaction occurs between the acetylenic bond on the HCCH molecule and the H atom cis to the hydrogen-bonded F atom on the substituted ethylene, which causes the hydrogen bond to deviate from linearity. This is similar to the structure obtained for 1,1-difluoroethylene-HCCH [H. O. Leung and M. D. Marshall, J. Chem. Phys. 126, 154301 (2006)], and indeed, to within experimental uncertainty, the intermolecular interactions in CH(2)CClF-HCCH and its 1,1-difluoroethylene counterpart are practically indistinguishable, even though ab initio calculations at the MP2∕6-311G++(2d, 2p) level suggest that the former complex is more strongly bound.

Definitive solid-state 185/187Re NMR spectral evidence for and analysis of the origin of high-order quadrupole-induced effects for I = 5/2

Rhenium-185/187 solid-state nuclear magnetic resonance (SSNMR) experiments using NaReO(4) and NH(4)ReO(4) powders provide unambiguous evidence for the existence of high-order quadrupole-induced effects (HOQIE) in SSNMR spectra. Fine structure, not predicted by second-order perturbation theory, has been observed in the (185/187)Re SSNMR spectrum of NaReO(4) at 11.75 T, where the ratio of the Larmor frequency (ν(0)) to the quadrupole frequency (ν(Q)) is ∼2.6. This is the first experimental observation that under static conditions, HOQIE can directly manifest in SSNMR powder patterns as additional fine structure. Using NMR simulation software which includes the quadrupole interaction (QI) exactly, extremely large (185/187)Re nuclear quadrupole coupling constants (C(Q)) are accurately determined. QI parameters are confirmed independently using solid-state (185/187)Re nuclear quadrupole resonance (NQR). We explain the spectral origin of the HOQIE and provide general guidelines that may be used to assess when HOQIE may impact the interpretation of the SSNMR powder pattern of any spin-5/2 nucleus in a large, axially symmetric electric field gradient (EFG). We also quantify the errors incurred when modeling SSNMR spectra for any spin-5/2 nucleus within an axial EFG using second-order perturbation theory. Lastly, we measure rhenium chemical shifts in the solid state for the first time.

Rotational Spectroscopy and Molecular Structure of the 1,1,2-Trifluoroethylene−Hydrogen Chloride Complex

Fourier transform microwave spectra in the 6-20 GHz region are obtained for the complex formed between 1,1,2-trifluoroethylene and hydrogen chloride, including both (35)Cl and (37)Cl isotopomers. Analysis of the spectra provides rotational constants and additionally, the complete quadrupole hyperfine coupling tensor in both the inertial and principal electric field gradient axis systems. The inertial information contained in the rotational constants combined with the results of the hyperfine analysis provides the structure for CF(2)CHF-HCl. A primary, hydrogen bonding interaction exists between the HCl donor and the F atom geminal to the H atom on the substituted ethylene. The hydrogen bond is bent from linearity to allow a secondary interaction to form between this H atom and the Cl atom. Comparisons made to similar complexes involving both other protic acids (HF and HCCH) and fluoroethylenes (vinyl fluoride and 1,1-difluoroethylene) reveal the effects of varying gas phase hydrogen bond donor strength, of increasing fluorine substitution on fluorine atom nucleophilicity, and on the relative importance of steric versus electrostatic effects in determining the structures of these species.

Effect of Fe substitution on the magnetic ordering inCa3(Co1−xFex)2O6

M\"ossbauer studies over $4.2--550\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ of iron doped quasi-one-dimensional spin chain compounds ${\mathrm{Ca}}_{3}{({\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x})}_{2}{\mathrm{O}}_{6}$, crystallizing in rhombohedral structure (space group $R\overline{3}c$) for $x\ensuremath{\leqslant}0.2$, reveal that the iron resides only in the Co2 $(6a)$ site. The compounds are paramagnetic at $90\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and the iron exhibits slow spin relaxation phenomena even at room temperature. However, for the $x=0.5$ compound, the crystal structure is triclinic $(P\overline{1})$, and the iron resides almost equally in two different crystallographic sites and exhibits a very high magnetic ordering temperature ${T}_{N}\ensuremath{\sim}500\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Both iron sites exhibit quadrupole interactions of almost equal size; however, with opposite sign $(\frac{1}{4}{e}^{2}qQ\ensuremath{\approx}\ifmmode\pm\else\textpm\fi{}0.62\phantom{\rule{0.3em}{0ex}}\mathrm{mm}∕\mathrm{s})$. At ${T}_{\mathrm{sr}}=193\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a spin reorientation of the iron magnetic moments is observed. Below $150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ the magnetic moments are tilted at 20\ifmmode^\circ\else\textdegree\fi{} relative to the local electric field gradient axis and above $230\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ they are aligned perpendicular to this axis. These results agree well with magnetic susceptibility measurements, in which a sharp drop in magnetization is observed above $200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The magnetic hyperfine fields in the two sites at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ are 53.3 and $45.7\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, respectively. The net magnetic interaction is antiferromagnetic, however, with a small ferromagnetic component displaying hysteresis along with a saturation magnetization of about $0.02{\ensuremath{\mu}}_{B}∕\mathrm{f.u.}$ at $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

Hindered rotation and phase transition in sodium gallohydride according to the NMR data

Polycrystalline sodium gallohydrides with different hydrogen isotope compositions, NaGaH4, NaGaH2.56D1.44, and NaGaD4, were studied over the temperature range 100–375 K by the 2H, 23Na, and 69,71Ga NMR methods in magnetic fields of 1.4, 1.88, and 7.04 T. The data on spin-lattice deuteron relaxation T 1(2H) were used to determine the activation energy (∼35 kJ/mol) of anion rotational motions and quadrupole coupling constant (QCC) χ Q 0 (2H) = 90 kHz for the rigid lattice. To within measurement errors, the activation energy and 2H QCC were independent of the isotope composition. The low-temperature 2H NMR line was a doublet with 2H QCC χ(2H) = 70 kHz. The difference between χ 0 and χ(T) was interpreted in terms of the librational averaging of the electric field gradient (EFG) according to the Bayer equation. The frequency of librations at 113 K was estimated (31 cm−1). The shape of the 69,71Ga NMR line was indicative of second-order quadrupole interaction with a nonzero asymmetry parameter η of the EFG tensor. Temperature variations in the QCC and η parameter at gallium were considered using the distorted tetrahedron model. The η value changed from 0.65 to zero (axial EFG tensor symmetry characteristic of tetragonal lattices) over the temperature range 140–295 K and again increased to 0.3 at 300–365 K, which was evidence of a change in the orientation of the distorted tetrahedral anion in the lattice. Changes in the asymmetry parameter were in agreement with the phase transition in sodium gallohydride recorded as a heat capacity jump.

A Mössbauer spectral study of the GdCo4−xFexB compounds

The iron-57 Mössbauer spectra of the GdCo4−xFexB compounds, where x is 0.10, 0.15, 0.20, 0.25, 1, 2, 2.5, and 2.6, have been measured at room temperature and reveal relatively small iron hyperfine fields of approximately 12–18T, relatively large quadrupole interactions of approximately +0.9 and −1mm∕s, and three very different types of spectra for x=0.10 and 0.15, x=0.25, 1, and 2, and x=2.5 and 2.6. The differences result from both the different easy magnetization directions in these compounds and the different cobalt and∕or iron occupancies of the crystallographic 2c and 6i sites. The spectra have been fitted by calculating the spectral absorption with the complete iron-57 nuclear excited state Hamiltonian for the iron 2c and 6i sites. The fits have used an asymmetry parameter η and Euler angles θ and ϕ that relate the hyperfine field to the iron electric field gradient axes of each crystallographic site in an orientation that is consistent with the structural and magnetic properties of the site. The results of the fits indicate both that the full Hamiltonian approach is required for physically reasonable spectral fits and that the small observed fields result from the presence of large orbital contributions which subtract from the Fermi contact contributions to the magnetic hyperfine fields of the two sites. The iron 2c occupancy obtained from the Mössbauer spectral area has been used to model the compositional dependence of the magnetic anisotropy constant in the GdCo4−xFexB compounds.

A Mössbauer spectral study of theYCo4−xFexB compounds

The Mössbauer spectra of the YCo4−xFexB compounds, where x is 1, 2 and 3, have been measured at 78 and 295 K and reveal relatively small ironhyperfine fields of about 15 T, relatively large quadrupole interactions of about+1.0 and−1.0 mm s−1 and very differentspectra for YCo3FeB and YCo2Fe2B ascompared with YCoFe3B. As a consequence, the spectra have been fitted with a full Hamiltonianby adjusting the hyperfine parameters of the iron 2c and 6i sites foundin these compounds. The fits have used an asymmetry parameter,η, and Eulerangles, θ and ϕ, that relate the hyperfine field to the iron electric field gradient axes of each iron site in anorientation that is consistent with the structural and magnetic properties of the site. Thefits indicate that the relative areas of the spectral components assigned to the two iron 2cand 6i sites are in agreement with the iron occupancy of the sites as determined by neutrondiffraction. The results of the fits also indicate both that the full Hamiltonian approach isrequired for physically reasonable spectral fits and that the small observed fieldsresult from the presence of large orbital contributions which subtract from theFermi contact contributions to the magnetic hyperfine fields of the two sites.

Magnetic properties of GdNiSn studied by 155Gd Mössbauer spectroscopy

The magnetic and electronic properties of the GdNiSn compound have been studied by the 155Gd Mössbauer spectroscopy. The alignment of the electric field gradient axes system has been determined at the Gd site. The possible magnetic structures have been proposed in the whole range of temperatures below the Néel temperature. In the proposed magnetic structures the Gd magnetic moments are either collinear and lie in the crystallographic ab -plane ( cb -plane) or noncollinear and deviate for 54(2)° from the crystallographic b -axis.

Magnetic properties of silver lanthanide molybdates AgLnMo2O8 (Ln = lanthanide)

The magnetic properties of scheelite related compounds AgLnMo2O8 (Ln = lanthanide) are reported. Magnetic susceptibility measurements show that the compounds are paramagnetic down to 2 K with AgSmMo2O8 and AgEuMo2O8 showing Van Vleck paramagnetism. A 151Eu Mossbauer spectrum for AgEuMo2O8 indicates that the Eu ion is in the trivalent state and that an axial electric field gradient exists in this compound. Both magnetic susceptibility and electron paramagnetic resonance (EPR) measurements show that the Gd3+ ion is in the 8S7/2 state.

Local ordered magnetic fields in bismuth dielectrics. 209Bi NQR in Bi4Ge3O12 single crystal

The results of the 209Bi NQR experiments carried out on α-Bi2O3, Bi3O4Br, Bi2M4O9 (M=Al, Ga), Bi2Ge3O9, and Bi4Ge3O12 showed that these compounds are not diamagnets in the conventional sense. The Zeeman perturbed zero-field 209Bi NQR spectra gave an indication that local ordered magnetic fields of the order of 30–200G exist in these substances comprising neither transition nor rare earth elements. Further aspects of this principally new phenomenon of yet unknown nature were studied by the 209Bi NQR experiments on the Bi4Ge3O12 single crystal in external magnetic fields below 500Oe, applied at various orientations with respect to the crystal axes. The spectral patterns of dramatically increased intensity and multiplicity, caused by the unknown magnetism of the compound, were observed in applied fields and modeled. Based on the results of the modeling, the conclusions were made that at least four magnetically non-equivalent Bi sites characterized by antiferromagnetically ordered local fields of the order of 30G are present in the Bi4Ge3O12 crystal; the intensity increase was interpreted to arise from the change in orientation of the electric field gradient axes at the Bi site upon applying an external magnetic field.

Hyperfine Interactions and Dynamic Characteristics of 119Sn Dopant Atoms in Ca2Fe2O5

119Sn Mossbauer spectra of tin impurity ions located in the bulk of Ca2Fe2O5 particles have been investigated over the 77–1070 K temperature range. This study has allowed us to determine the sign of electric field gradient (EFG) as well as the angle between directions of the main EFG axis and magnetic field induced at 119Sn nuclei. The values obtained appear to be in a good accordance with distorted octahedral coordination of 119Sn4+ ions. Analysis of the asymmetry of the 119Sn quadrupole doublet at T>TN showed that the mean-square amplitudes of Sn4+ thermal vibrations along the EFG direction are greater than those in the perpendicular direction. The temperature behavior of the 119Sn spectra is described in terms of the Debye model.

2D EPR investigation of endohedral La@C 82 in solution

The analysis of a two-dimensional EPR spectrum gives direct evidence for a dominant nuclear quadrupole interaction at the site of the encapsulated La 3+ ion. From the observed nuclear spin transition rates we deduce eQV zz /[ I(2 I − 1) h] ≈ 0.5(3) MHz, assuming that the correlation time of the electric field gradient axes is determined by molecular reorientation of the molecule in solution. The non-vanishing value of the quadrupole interaction is further proof for an off-center position of the metal ion.