Magnetic field dependence of the 31P longitudinal nuclear-spin relaxation time in GdP at high temperatures

The magnetic field dependence of the longitudinal nuclear-spin relaxation time for ³¹P nuclei in paramagnetic GdP is expressed in terms of a wavevector frequency-dependent relaxation-shape function. A Gaussian representation of the memory function associated with the spin-velocity relaxation function is chosen that satisfies the first six frequency moments. The results are compared with the experimental data of Myers and Narath.     

Magnetic moments and structure of the nuclei3H,3He and of baryons

From a solution of the problem of magnetic moments of the nuclei³H and³He, two properties are obtained: - These nuclei have mixed orbital ground states. - These states are not charge symmetric. The first property is expected to hold also for baryons in the quark model, on account of recently measured magnetic moments. Supporting evidence and implications for baryon structure are discussed.     

Nitrogen-containing species in the structure of the synthesized nano-hydroxyapatite

Synthesized by the wet chemical precipitation technique, hydroxyapatite (HAp) powders with the sizes of the crystallites of 20–50 nm and 1 μm were analyzed by different analytical methods. By means of electron paramagnetic resonance (EPR) it is shown that during the synthesis process nitrate anions from the reagents (byproducts) could incorporate into the HAp structure. The relaxation times and EPR parameters of the stable axially symmetric NO ₃ ^2? paramagnetic centers detected after X-ray irradiation are measured with high accuracy. Analyses of high-frequency (95 GHz) electron-nuclear double resonance spectra from ¹H and ³¹P nuclei and ab initio density functional theory calculations allow suggesting that the paramagnetic centers and nitrate anions as the precursors of NO ₃ ^2? radicals preferably occupy PO ₄ ^3? site in the HAp structure.     

Superhyperfine structure in the EPR spectra and optical spectra of impurity f ions in dielectric crystals: A review

The results of observation and simulation of the superhyperfine (ligand hyperfine) structure (SHFS) of the electron paramagnetic resonance (EPR) spectra of rare-earth and uranium impurity ions in dielectric crystals have been systematized. The resolved SHFS of the EPR spectra of doped cubic crystals (with the fluorite and perovskite structures) has been observed for orientations of a constant magnetic field along the crystallographic axes. Most attention has been paid to tetragonal double fluorides LiRF₄ (R = Y, Lu, Tm), in which the SHFS of the EPR spectra has also been found for intermediate orientations of the magnetic field. For the LiYF₄: Nd³⁺ single crystal, the splitting of optical spectral lines due to the interaction of Nd³⁺ ions with nuclear magnetic moments of the nearest neighbor fluorine ions has been observed for the first time. The Van Vleck paramagnet LiTmF₄: U³⁺ is characterized by the SHFS with clearly distinguishable components due to the interaction of uranium ions both with nuclei of the fluorine ions and with enhanced magnetic moments of the thulium nuclei. The SHFS envelopes of the EPR spectra of Yb³⁺, Ce³⁺, Nd³⁺, and U³⁺ ions in LiYF₄ and LiLuF₄ crystals are well reproduced by numerical calculations based on the microscopic model using only three fitting parameters: the width of transitions between the electron-nuclear sublevels of the complex containing the paramagnetic ion and nuclei of the ligands and two constants of covalent bonding of the f electrons with 2s and 2p electrons of the nearest neighbor fluorine ions.     

Exchange magnetic moments of some odd-mass nuclei

The exchange magnetic moment has been calculated for the nuclei ⁹¹Zr, ⁸⁹Sr and ⁸⁷Kr in the ground state. By adding the core polarization contribution to the magnetic moments computed earlier, an improved value is obtained for the magnetic moments of these nuclei.     

<Superscript>23</Superscript>Na and <Superscript>27</Superscript>Al NMR Study of Structure and Dynamics in Mordenite

Temperature dependencies of ²⁷Al and ²³Na nuclear magnetic resonance spectra and spin–lattice relaxations in mordenite have been studied in static and magic angle spinning regimes. Our data show that the spin–lattice relaxations of the ²³Na and ²⁷Al nuclei are mainly governed by interaction of nuclear quadrupole moments with electric field gradients of the crystal, modulated by translational motion of water molecules in the mordenite channels. At temperatures below 200 K, the dipolar interaction of nuclear spins with paramagnetic impurities becomes an important relaxation mechanism of the ²³Na and ²⁷Al nuclei.     

Multifrequency EPR spectroscopy of Ho3+ ions in synthetic forsterite

Electron paramagnetic resonance (EPR) of Ho³⁺ single ions and Ho³⁺?Mg²⁺-vacancy-Ho³⁺ associates in holmium-doped forsterite single crystals are studied at 9.4, 37.3 and 65–250 GHz. Crystals were grown from melt by the Czochralski technique in slightly oxidizing atmosphere. For both centers, directions of the principal magnetic axes and parameters of the effective spin Hamiltonians describing dependences of electron-nuclear levels on applied magnetic field are obtained. For Ho³⁺ substituting Mg²⁺ in the M2 site as the single ion and for Ho³⁺ ions in dimer centers, values of crystal field parameters related to a real crystal lattice structure are estimated in the framework of the exchange charge model. The calculated crystal field energies, values of theg-factors of the ground Ho³⁺ quasi-doublet and the directions of the corresponding magnetic moments agree satisfactorily with the data obtained from measurements of EPR and optical absorption and site-selective luminescence spectra.     

Propriétés magnétiques et relaxation magnétique nucléaire de Be9 dans des composés intermétalliques de terres rares: GdBe13, TbBe13 et DyBe13

Be⁹ nuclear magnetic relaxation, magnetic susceptibilities and magnetic moments measurements of intermetallic compounds GdBe₁₃, TbBe₁₃ and DyBe₁₃ have been performed. The relaxation rate is mainly due to a dipolar interaction between the nuclear moments and the paramagnetic ions moments. Antiferromagnetic ordering was observed for all compounds. Curie-Weiss behaviour was observed at high temperature. The effective moments are comparable to that expected from the three positive ions.     

Neutron crystal-field spectroscopy of RNi 2 11 B2C (R = Ho,Er, Tm)

Inelastic neutron scattering experiments of the crystal-field (CEF) splitting of the R³⁺ ions (R = Ho, Er, Tm) in the superconductor RNi ₂ ¹¹ B₂C have been performed in the paramagnetic as well as in the magnetically ordered state in order to deduce the CEF parameters which in turn determine the thermodynamic magnetic properties of these systems. The calculated ordered magnetic moments are in agreement with magnetic neutron diffraction results, i.e. both the easy axis and the size of the zero-field moments are correctly reproduced. In addition, the entropy involved in the magnetic ordering obtained from specific heat measurements is in correspondence with the number of low-lying CEF states observed in this study. Our CEF parameter set also reproduces both the behavior and the anisotropy in M/H measured for single crystals.     

The deviation of the magnetic moments from the Schmidtlines induced by a nonlocal two-body potential

A unitary transformed two-body hard-core potential contains nonlocal terms, which will produce a deviation of the magnetic moments from the Schmidtlines. These deviations were calculated for several nuclei up to Ca⁴¹ using an oscillator basis, and they are positive for odd-neutron and negative for odd-proton nuclei. Thus it is not possible to describe the experimental deviation from the Schmidtlines; but for the magnetic moments of C¹³, O¹⁵ and N¹⁵, the only nuclei where the experimental values are outside of the Schmidtlines, these nonlocal terms yield the right magnitude in the right direction of the deviation.     

Electrically Detected HYSCORE on Conduction Band Tail States in ^{29}Si-Enriched Microcrystalline Silicon

Electrically detected hyperfine sublevel correlation (ED-HYSCORE) measurements are presented and employed to study spin-dependent transport in thin-film microcrystalline silicon solar cells. We explore the hyperfine coupling between paramagnetic conduction band tail states involved in hopping transport and neighboring ²⁹Si nuclei at low temperature ( \(T = 5\)  K). ED-HYSCORE measurements performed on solar cells with ²⁹Si-enriched absorber layers reveal that the hyperfine interaction between these current-influencing centers and ²⁹Si nuclei in the surroundings is dominated by isotropic couplings up to \(\sim\) 4 MHz, whereas the anisotropic contributions are small. This indicates that the wave function of the conduction band tail states is distributed over several nuclei. Our results demonstrate that the ED-HYSCORE technique can provide helpful insight into the microscopic structure of transport-relevant paramagnetic states and thus usefully complement the toolbox of electrically detected magnetic resonance spectroscopy.     

Magnetic relaxation and paramagnetic Mössbauer spectra: Influence of the off-diagonal hyperfine coupling

The influence of magnetic relaxation on paramagnetic Mössbauer spectra is considered in the case of non-diagonal hyperfine coupling. The Clauser and Blume stochastic theory is used to calculate paramagnetic spectra of⁵⁷Fe,¹⁶⁹Tm and¹⁶⁶Er nuclei for doublet or pseudo-doublet electronic states and various point symmetries. The influence of an external magnetic field is presented.     

Paramagnetic properties of ion-implanted polymer layers

Films of polyethylene, polyethylene terephthalate, and polyamine-6 implanted with B⁺ and N⁺ ions with an energy of 100 keV are investigated by an EPR method in a dose interval of 1·10¹⁴–1·10¹⁷ cm⁻². It is shown that paramagnetic centers with g=2.0025 formed in the implanted polymers have a nature similar to the nature of paramagnetic centers of pyrolized and initially conducting polymers. Correspondence of the character of the variation in paramagnetic characteristics of the modified polymers to the model proposed earlier for the formation of pyrocarbon “drops” in ion implantation is revealed. The relaxation times for paramagnetic centers in the implanted polymer films are calculated and assumptions are made about the formation of a quasi-two-dimensional electron gas as well as the possibility of magnetic ordering in polymer-film layers modified by high-dosage implantation. The effect of oxygen on the electron states of the implanted polymer specimens is studied. Belarusian State University, 4, Skorina Ave., Minsk, 220050 Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 562–567, July–August, 1998.     

Electronic structure and phase transitions of MnAs

On the basis of a two center tight binding approach the recursion method of Haydock et al. was applied for MnAs to calculate non-polarized and spin polarized local densities of states, magnetic moments and band energies for two different B8₁ crystal structures and two B31 structures. The itineracy of the Mn 3d-states was implied by allowing for hybridization of p-states centred at the As-sites with d-states centred at the Mn-sites. Self-consistency procedures were applied to determine the relative position of the paramagnetic p- and d-band centers (E_p - E_d = - 1 eV), and to calculate the magnetic moments (3.27 μ_B for the low temperature B8₁ phase and 3.14 μ_B for the corresponding B31 phase). Because of the similarities of the electronic structures of both phases it is argued that for the first-order B8₁ [rlarr2] B31 phase transition the usually applied model of a high spin-low spin transition of the Mn³⁺ ion is basically wrong. Instead of such an ionic model it is suggested to adopt an itinerant d-electron concept within that both phases are closely related but the B8₁ phase is favoured above a certain critical magnetic moment as supported by a very recent study of Kato et al. For the high temperature B8₁ phase occurring after the second-order B31 → B8₁ phase transition a magnetic moment of 3.37 μ_B was obtained.     

Paramagnetic resonance and off-center location of Cu<Superscript>2+</Superscript> ions in ferroelectric lead germanate

This paper reports on the results of investigations into the orientation behavior of the splitting of the electron paramagnetic resonance spectrum due to the location of paramagnetic ions in different domains of Cu²⁺-containing lead germanate. The off-diagonal components of the tensor g for Cu²⁺ quasi-monoclinic centers are determined. A model for off-central displacement of copper ions is proposed with due regard for the revealed symmetry of paramagnetic centers, their superhyperfine structure, and the orientation of the magnetic axes.     

Magnetic moments of K isomers as indicators of octupole collectivity

The relation between the quadrupole-octupole deformation and the structure of high-K isomers in heavy even-even nuclei is studied through a reflection asymmetric deformed shell model including a BCS procedure with constant pairing interaction. Two-quasiparticle states with K ^?? = 4^?, 5^?, 6^?, 6⁺ and 7^? are considered in the region of actinide nuclei (U, Pu and Cm) and rare-earth nuclei (Nd, Sm and Gd). The behaviour of two-quasiparticle energies and magnetic dipole moments of these configurations is examined over a wide range in the plane of quadrupole and octupole deformations (?? ₂ and ?? ₃. In all considered actinide nuclei, the calculations show that there is pronounced sensitivity of the magnetic moments to the octupole deformation. In the rare-earth nuclei, the calculations for ^{154, 156}Gd show stronger sensitivity of the magnetic moment to the octupole deformation than in the other considered cases.     

Magnetic moments of mirror nuclei with tilted-foil polarization

We report here on an ongoing experimental program initiated at the ISOLDE facility at CERN for the measurement of magnetic moments of short-lived radionuclides, with the emphasis on magnetic moments of mirror nuclei in far-from-stability regions. The nuclei are polarized by the tilted foil technique and the resulting 0–180^○ βasymmetry is monitored as a function of rf frequency applied in an NMR setup. In order to achieve sufficiently high energy for transmission through the foils, the experimental setup is mounted on a high voltage platform. The first experiment in this program was the measurement of the βasymmetry and the NMR resonance for the ground state of ²³Mg (I=3/2, T_1/2=11.3 s), yielding μ=−0.533(6) nm. Improvements to the experimental setup are presently being designed, to be used in conjunction with the new developments at ISOLDE for obtaining high charge-state ions from the EBIS (REX-ISOLDE) ion source. This will help pave the way for measurements of magnetic moments of T=3/2 nuclei in the s–d shell and of T=1/2 f-shell nuclei. The study of relaxation times and other solid-state phenomena in semiconductors and other materials of interest using this technique is also contemplated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Proton NMR of isomorphous paramagnetic and diamagnetic monohydrates MeSO4.1 H2O Me = Mn2+, Fe2+, Ni2+ AND Mg2+

Nuclear magnetic resonance of protons of crystallization water in isomorphous paramagnetic and diamagnetic monohydrates MeSO₄. 1 H₂O with Me = Mn²⁺, Fe²⁺, Ni²⁺ and Mg²⁺ is studied in the present paper. Proton NMR spectra in paramagnetic hydrates are asymmetric and their second moments, M₂, depend linearly on the square of the induction of the external magnetic field B₀. NMR spectrum of diamagnetic hydrate MgSO₄. 1 H₂O is symmetric and its shape and the second moment do not change with B₀. The parameters M₂₀ andK which characterize nuclear dipole-dipole interaction of protons and interaction of protons and paramagnetic ions, respectively, are derived from experimentally obtained dependences M₂ vs B ₀ ² and on the other hand, they are calculated by means of crystallographic data for substances studied. Calculations were realized in approximation where two nearest neighbour ions Me²⁺ to each water molecule are considered. The influence of the demagnetizing magnetic field of the sample was neglected.     

Trimers of bivalent copper impurity ions in CaF<Subscript>2</Subscript> crystals: The structure and mechanism of formation

Crystals of CaF₂: Cu (with a copper impurity content higher than 0.1 at. %) grown by the Czochralski method from a melt in a mixed helium-fluorine atmosphere are investigated using electron paramagnetic resonance (EPR) spectroscopy. It is found that the crystals contain paramagnetic centers whose magnetic properties at low temperatures are identical to those of [CuF₄F₄]^6? (S=1/2) single centers. The magnetic properties of the centers exhibit a qualitative change in the temperature range 77–300 K. These changes are described within a model according to which the center is treated as a cluster composed of three [CuF₄F₄]^6? impurity complexes involved in exchange interactions and interactions occurring in the field of Jahn-Teller lattice distortions.     

The effect of melting temperature on the glasses from B2O3Na2OCuO system studied by EPR and NMR

The influence of the preparation temperature of copper doped soda-borate glasses on their structure and properties was investigated by means of the electron paramagnetic resonance of the Cu²⁺ ions and of the nuclear magnetic resonance of the ¹¹B nuclei. The melting temperature varied in the range 900–1300°C. The shape and parameters of EPR and NMR spectra show that due to the increase of thermal agitation, there is a greater degree of disorder in the glasses melted at higher temperatures. Consequently the microenvironmental amplitudes of the two magnetic resonance centers also increase, which is reflected in the poorer resolution of the resonance lineshapes. Both the fraction of tetracoordinated boron atoms and the paramagnetic center density decrease, the phase separation process is diminished and also the covalent character of CuO bonds decreases.A mechanism based on these results is suggested, that could describe the structural modifications which take place in these glasses as a result of the increase of their preparation temperature.