Orientation Of Electric Field Gradient Research Articles

Strong magnetoelectric coupling at an atomic nonmagnetic electromagnetic probe in bismuth ferrite

Isolated nonmagnetic substitutional defect ions experience huge coupled electric magnetic interaction in the single-phase multiferroic ${\mathrm{BiFeO}}_{3}$. In the ferroelectric state above the magnetic N\'eel temperature ${T}_{N}$, the electric environment generates a single symmetric electric field gradient (EFG) parallel to the electric polarization direction. Below ${T}_{N}$, a distinct magnetic interaction arises, monitored by the probe nuclei via their magnetic moment. Two magnetic environments arise, given by the relative angle of the local magnetic moment within its easy magnetic plane with respect to the EFG orientation. The angle between field gradient orientation and magnetic field direction is the most stable fitting parameter. The magnetic interaction concomitantly increases the EFG dramatically which reflects an outstandingly large local magnetoelectric coupling. In the set of best fits, two different electric environments form concurrently with two distinctly different local magnetic fields. The magnetic ordering in ${\mathrm{BiFeO}}_{3}$ thus completely distorts the electric environment of the nonmagnetic probe nucleus. The implications for the local effect of dopants in ${\mathrm{BiFeO}}_{3}$ are discussed. A third probe environment arising independent of temperature is identified and associated with an iron vacancy.

Determination of hyperfine fields orientation in nuclear probe techniques

One of the most popular nuclear probes, 57Fe is used for the investigation of orientations of hyperfine fields and also for the determination of other important properties. In particular, the orientation of iron magnetic moments can be unambiguously determined, including its signs. Experiments with polarized radiation are presented with regard to selected systems. Orientation of electric field gradient is used for acquiring information about the shape of the texture-free spectra. Applications on the analysis of iron-based superconductors are presented.

First-principles and time-differentialγ−γperturbed-angular-correlation spectroscopy study of structural and electronic properties of Ta-dopedTiO2semiconductor

The, time-differential $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ perturbed-angular-correlation (TDPAC) technique using ion-implanted $^{181}\text{H}\text{f}(\ensuremath{\rightarrow}^{181}\text{T}\text{a})$ tracers was applied to study the hyperfine interactions of $^{181}\text{T}\text{a}$ impurities in the rutile structure of ${\text{TiO}}_{2}$ single crystals. The experiments were performed in air in the temperature range of 300--1273 K, allowing the electric-field-gradient (EFG) tensor characterization (in magnitude, asymmetry, and orientation) at $^{181}\text{T}\text{a}$ probe atoms located in defect-free cation sites of the structure. The measured EFG is parallel to the [001] crystal axis, as occurs at Ti sites, but normal to the EFG orientation observed at $^{111}\text{C}\text{d}$ impurities in ${\text{TiO}}_{2}$ single crystals [L. A. Errico et al., Phys. Rev. Lett. 89, 055503 (2002)]. In addition, ab initio calculations were performed using the full-potential augmented plane wave plus local orbital method that allow us to treat the electronic structure of the doped system and the atomic relaxations induced by the Ta impurity in a fully self-consistent way. We considered different dilutions of the doped system (using the supercell approach) and studied the electronic properties and structural atomic relaxation dependence on the charge state of the impurity. The accuracy of the calculations and the excellent agreement of the predicted magnitude, asymmetry, and orientation of the EFG tensor with the experimental results enable us to infer the EFG sign, not accessible with conventional TDPAC experiments. The comparison of the measured EFG at Ta sites with experimental and ab initio theoretical results reported in the literature at Cd, Ta, and Ti sites in ${\text{TiO}}_{2}$ allowed us to obtain a deeper insight on the role played by metal impurities in oxide semiconductors.

Orientation of electric field gradient and chemical shift tensors in BiVO4 at room temperature by51V NMR

Orientation of electric field gradient and chemical shift tensors in BiVO4 at room temperature by51V NMR

Method for the simultaneous characterization of texture, orientation of electric field gradient, and/or magnetic field from the57Fe/57Co M�ssbauer spectrum of pellets having a cylindrical texture typical of YBa2Cu3O7?x superconductors

A method using Mossbauer spectroscopy has been developed for estimating the degree of cylindrical texture in pellets of materials exemplified by the superconductor YBa2Cu3O7−x.The procedure can also be used to determine unambiguously the sign and orientation of the electric field gradient of a nonmagnetic species coexisting with a magnetically ordered one (or coexisting with another nonmagnetic species for which the sign and the orientation of the electric field gradient are known).

Structure and C–Cl bond in 1-Cl-3-NO2C6H4

AbstractThe crystal structure of metachloro-nitrobenzene, C6H4C1(1)(NO2)(3)was redetermined atT= 298 K: Space groupPna21,Z= 4,a= 2114.90(40) pm,b= 593.20(10) pm,c= 529.00(10) pm,Rw(F) = 0.038. The molecule is almost planar, with a small out of plane bending of the NO2group. Measurements of Zeeman-split35Cl NQR spectra give a nuclear quadrupole coupling constante2ϕzzQh−1= (69.745 ± 0.002) MHz atT= 298 K and (70.608 ± 0.002) MHz atT= 129 K. The asymmetry parameter is 0.1091 ± 0.0015 at 298 K (0.1066 ± 0.0040 at 129 K).ϕzzis within 0.45° parallel to the bond direction C(1)– Cl(1);ϕyyandϕxxare almost in the C(1 … 6)-plane and perpendicular to it, respectively. The temperature dependencev(35Cl) =f(T) was studied from 77 K up to the melting point. Structure and electric field gradient orientation are discussed.

Numerical solutions for single passage NMR on nuclei experiencing small electric quadrupole interactions

The adiabatic rapid-passage NMR equations are numerically solved for a small additional quadrupole interaction. The full range of the ratio of rf interaction strengths to quadrupole interactions strengths is considered for any electric field gradient orientation. The results forI=1 are particularly easy to describe and are used to predict the single-passage results for different orientations of the electric field gradient with respect to the static magnetic field.

Pureley nuclear diffraction of resonant gamma-rays due to hyperfine quadrupole interaction

A purely nuclear diffraction of the resonant 14.4 keV gamma-quanta has been observed from the set of (003) planes of a soudium nitroprusside single crystal. It originates from the quadrupole hyperfine splitting of the 57Fe nuclear levels and different orientations of electric field gradient on these nuclei.