Determination of the orbital moment and crystal-field splitting in LaTiO3

Utilizing a sum rule in a spin-resolved photoelectron spectroscopic experiment with circularly polarized light, we show that the orbital moment in LaTiO3 is strongly reduced from its ionic value, both below and above the Ne el temperature. Using Ti L2,3 x-ray absorption spectroscopy as a local probe, we found that the crystal-field splitting in the t2g subshell is about 0.12-0.30 eV. This large splitting does not facilitate the formation of an orbital liquid.     

Multinuclear (27Al, 29Si, 47,49Ti) solid-state NMR of titanium substituted zeolite USY

Multinuclear solid-state NMR spectroscopy, employing 29Si MAS,27Al MAS/3Q-MAS and (47,49)Ti wide-line experiments, has been used for the structural characterization of titanium substituted ultra-stable zeolite Y (Ti-USY). 27Al MAS experiments show the presence of aluminum in four (Al(IV)), five (Al(V)), and six (Al(VI)) coordination, whereas the multiplicity within Al(IV) and Al(VI) is revealed by 27Al 3Q-MAS experiments. Two different tetrahedral and octahedral Al environments are resolved and their isotropic chemical shifts (delta(CS)) and second-order quadrupole interaction parameters (P(Q)) have been determined by a graphical analysis of the 3Q-MAS spectra. The emergence of signal with higher intensity at -101 ppm in the 29Si MAS spectrum of Ti-USY samples indicates the possible occurrence of Q4(3Si,1Ti) type silicon environments due to titanium substitution in the faujasite framework. High-field (11.74T) operation, using a probehead specially designed to handle a large sample volume, has enabled the acquisition of 47,49Ti static spectra and identification of the titanium environment in the zeolite. The chemical shielding and electric field gradient tensors for the titanium environment in the zeolite have been determined by a computer simulation of the quadrupolar broadened static 47,49Ti NMR spectra.     

Crystal field theory and electric field gradients at 49Ti nuclei sites in LaTiO3

The energy level diagram and the wave functions for the Ti³⁺ ions (3d ¹) in LaTiO₃ are calculated using modern crystal-field theory. The relative orbital ordering of these ions in the ground state is obtained. It turns out that the states of the ground triplet are considerably split and therefore the effect of the electronic-vibrational interaction is suppressed despite the fact that the distortions of the TiO₆ building block seem to be small. The components of the electric field gradient tensor at the Ti³⁺ nuclei sites are calculated using the wave functions of the ground states obtained. The calculated asymmetry parameter agrees well with the experimental values, which demonstrates the adequacy of the proposed orbital-ordering pattern of the Ti³⁺ ions in the ground state.     

The quadrupole moment of176Lu

The intrinsic quadrupole moment of¹⁷⁶Lu has been determined by Coulomb excitation with α-particles to be 6.98±0.10 b. Evidence for a new level at approximately 578 keV with presumably collective structure is presented.     

Nuclear electric quadrupole moment of41Ca by laser-RF spectroscopy

Zeitschrift für Physik A Hadrons and nuclei - The nuclear electric quadrupole moment of41Ca, which contains a single neutron outside closed proton and neutron shells (N=Z=20) has been...     

Atom movement in In3La studied via nuclear quadrupole relaxation

Jump frequencies of Cd tracer atoms in In3La were measured via nuclear quadrupole relaxation caused by stochastic reorientation of the electric field gradient using the method of perturbed angular correlation of gamma rays. Activation enthalpies of 0.53(1) and 0.81(1) eV were found at the two phase boundaries, which differ in composition by only about 0.1 at. %. The jump frequency was found to be higher at the more In-rich phase boundary, ruling out a simple In-vacancy diffusion mechanism. Possible diffusion mechanisms and general applicability of the method are discussed.     

Magnetic quadrupole moment of W-boson in Kobayashi-Maskawa model

Due to CP-invariance violation a vector particle can acquire a T- and P-odd electric dipole moment and a magnetic quadrupole one. The W-boson magnetic quadrupole moment is calculated in the Kobayashi-Maskawa model. This is the only known CP-odd moment arising in this model in two-loop approximation.     

Spin dynamics and orbital state in LaTiO3

A neutron scattering study of the Mott-Hubbard insulator LaTiO3 ( T(N) = 132 K) reveals a spin wave spectrum that is well described by a nearest-neighbor superexchange constant J = 15.5 meV and a small Dzyaloshinskii-Moriya interaction ( D = 1.1 meV). The nearly isotropic spin wave spectrum is surprising in view of the absence of a static Jahn-Teller distortion that could quench the orbital angular momentum, and it may indicate strong orbital fluctuations. A resonant x-ray scattering study has uncovered no evidence of orbital order in LaTiO3.     

Cross relaxation studied by β NMR

The dipole-dipole interaction between polarized β active probes implanted into a metal and the surrounding host nuclei may lead to a transfer of polarization from the probe to the host. As energy must be conserved in this cross-relaxation (CR) process, resonance-like dips show up at certainB values, if the polarization of the probes is measured as a function of magnetic inductionB. The probe isotope¹²B has been studied in several metallic stoppers. For¹²B in the fec crystals Al, Cu the three possible cubic implantation sites could easily be discriminated by means of the CR technique. The temperature dependence of the dips yielded information on the diffusion of the probes. In the case of¹²B, in Cu above 400 K a further CR structure was found due to trapping of the probe at another site. In the bcc metal VCR spectra belonging to two different¹²B trapping sites could be separately registered using a special radiofrequency technique. Both, static and dynamical properties of the CR could be quantitatively explained by theory.     

Fresco paintings studied by unilateral NMR

Unilateral NMR has been used to monitor the state of conservation of frescoes in the Vasari's house in Florence. The causes of deterioration of ancient frescoes are varied, which result in the detachment and crumbling of the painted film from the supporting plaster and in the outcropping of salts. Unilateral measurements of Hahn echo performed on such frescoes have allowed a perfect identification of the detachment of the painted film from the plaster. The presence of soluble salts on the pictorial film affects the spin-spin relaxation times, T(2). It is then possible using this technique, to characterize the effect of chemical treatments, of cleansing and consolidation procedures using the distribution of T(2) spin-spin relaxation times.     

Nuclear quadrupole effects in orientation-modulated NMR

A quantum-statistical method is used to study the structure of the NMR spectrum under adiabatic orientation-modulated (OM) magnetically anisotropic Hamiltonian of a nuclear system by rotational oscillation of a crystal about a fixed axis. A general expression is obtained for an NMR absorption signal, in phase with the OM, which reflects the main anomalies of such a spectrum. The results are used to interpret the OM NMR spectrum in spin systems with weak axisymmetric nuclear quadrupole interactions.Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 4, pp. 48–52, April, 1990.     

Electric quadrupole moment of the neutron-rich 33Al

The nuclear electric quadrupole moment (Q moment) of the neutron-rich nucleus ³³Al (I = 5/2 , T _1/2 = 41 ms) has been measured by the $ \beta$ -ray detected nuclear quadrupole resonance ( $ \beta$ -NQR) method for the first time. The ³³Al nucleus is considered to be on the border of the island of inversion within which a significant intrusion of the pf orbits occurs across the N = 20 shell gap and the intrusion causes an anomalous enhancement of the Q moment. Polarized ³³Al nuclei were produced from ³⁶S (77.5MeV/u beams through the fragmentation process and separated by LISE fragment separator at GANIL. The ³³Al nuclei were implanted into a Al₂O₃ single-crystal plate and the $ \beta$ -NQR spectrum was successfully obtained.     

Hyperfine interaction of 25Al in α-Al2O3 and its quadrupole moment

A brief review is presented of recent work with the Precision Penning Trap Mass Spectrometer, formerly at MIT, now at Florida State University. This includes atomic mass comparisons using single trapped ions; mass comparisons using two simultaneously trapped ions alternated between large and small cyclotron radii; and measurement of the dipole moment of a molecular ion using the polarizability-induced shift in cyclotron frequency.     

Photo-induced persistent internal quadrupole moment of a semiconductor

The persistent internal quadrupole moment which has been observed in Li-doped ZnO crystals is studied theoretically. The quadrupole moment is expressed in terms of relaxation coefficients and effective cross sections characterizing the scattering and capture processes of the photo carriers. Furthermore, it is related to the anisotropy of the mobility and of the persistent internal polarization.     

Giant quadrupole moment andproton halo discovered in8B

The nuclear quadrupole moment of⁸B(I =2⁺,T _1/2=769 ms) has been determined by use of a modified -NMR detection as |Q(⁸B)|=68.3±2.1 mb, which is twice the prediction of the Cohen-Kurath shell model calculation. The anomalous quadrupole moment which is carried mainly by the protons in the nucleus, has been accounted for by the proton halo effect.     

The electric quadrupole moment of theΩ −

We estimate the electric quadrupole moment of theΩ ^? within current non-relativistic quark models. With only one-gluon exchange as a source of tensor forces we get typically a valueQ _ω=0.004 fm² which is probably very hard to measure experimentally.     

The quadrupole interaction of57Fe in Ti

The quadrupole interaction of⁵⁷Fe in titanium was studied by Mössbauer spectroscopy and by the time-differential perturted angular correlation technique, using an implanted and diffused source of⁵⁷Co in titanium. From the latter measurements a quadrupole interaction frequencyv _Q = 2.22 ± 0.42 MHz was derived. The modulation amplitude of the delayed coincidence spectrum combined with the Mössbauer spectra indicate a high degree of substitutionality of the cobalt in the titanium.     

Magnetic moment and electric quadrupole moment of the anomalous186Ir ground state

The ground state nuclear moments of¹⁸⁶Ir (j ^π=5⁽⁺⁾) have been determined with NMR on oriented¹⁸⁶Ir in Ni as |μ|=3.80 _?0.02 ^+0.12 μ _n andQ=?3.00 (15)b. The quadrupole moment is consistent with an anamolousj ^π K=5⁺0 or 5⁺1 ground state configuration. The explanation of the magnetic moment in terms of pure 5⁺0 or 5⁺1 configurations would require a high collectiveg _R-factor ofg _R≧0.76. On the other hand the magnetic moment can be explained with a “normal”g _R and a mixed ground state configuration.