Ga Nuclei Research Articles

Optically detected magnetic resonance study of defects in undoped, Be-doped, and Mg-doped GaN

Undoped, Be-doped, and Mg-doped GaN samples were investigated with photoluminescence-detected electron paramagnetic resonance (PL-EPR) and electron-nuclear double resonance (PL-ENDOR). Two types of shallow donors and a deep level Be-related complex were measured in Be-doped GaN. One type of shallow donors is probably due to Si contamination. In all investigated samples, distant gallium ENDOR lines were observed which were split by a quadrupole interaction. From this splitting the electrical field gradients (efg’s) at the Ga nuclei in all investigated samples could be determined very precisely. The efg’s were correlated with strain.

NMR determination of 2D electron spin polarization at nu = 1/2

Using a "standard" NMR spin-echo technique we determined the spin polarization P of two-dimensional electrons, confined to GaAs quantum wells, from the hyperfine shift of Ga nuclei located in the wells. Concentrating on the temperature ( 0.05 less, similarT less, similar10 K) and magnetic field ( 7 less, similarB less, similar17 T) dependencies of P at Landau level filling factor nu = 1/2, we find that the results are described well by a simple model of noninteracting composite fermions, although some inconsistencies remain when the two-dimensional electron system is tilted in the magnetic field.

Collective and broken pair states of65,67Ga

Excited states of 65Ga and 67Ga nuclei were populated through the 12C(58Ni,αp) and 12C(58Ni,3p) reactions, respectively, and investigated by in-beam γ-ray spectroscopic methods. The NORDBALL array equipped with a charged particle ball and 11 neutron detectors was used to detect the evaporated particles and γ rays. The level schemes of 65,67Ga were constructed on the basis of γγ-coincidence relations up to 8.6 and 10 MeV excitation energy, and Iπ=27/2 and 33/2+ spin and parity, respectively. The structure of 65,67Ga nuclei was described in the interacting boson-fermion plus broken pair model, including quasiproton, quasiproton-two-quasineutron, and three-quasiproton fermion configurations in the boson-fermion basis states. Most of the states were assigned to quasiparticle + phonon and three quasiparticle configurations on the basis of their electromagnetic decay properties.

Optically detected nuclear magnetic resonance from a single heterojunction in the fractional quantum Hall regime

We report a remarkably sensitive optical technique for detecting nuclear magnetic resonance from a single ultra-high mobility two-dimensional electron system at a GaAs heterojunction in the fractional quantum Hall regime. Resonant inter-band optical excitation of the 2DES provides a very high degree of dynamic nuclear polarization, three times greater than that previously achieved; this is detected by using inelastic light scattering to measure the Overhauser shift in the energy of the electron spin wave. Our optical detection scheme is sensitive only to the polarization of nuclei in the illuminated volume at the heterojunction. This factor, together with the highly resonant excitation, increases the sensitivity of the technique and has allowed us to measure Knight-shifted magnetic resonance bands of As and Ga nuclei within a single 2DES at filling factor ν=1/3 at temperatures <100 mK. These measurements can be made over a wide range of temperatures and filling factors and have great potential for the study of collective spin excitations in the fractional quantum Hall regime.

Calculated paramagnetic resonance parameters of a gallium arsenide cluster: Ga2As3

Dirac molecular-orbital calculations are reported for the trigonal bipyramid gallium arsenide Ga2As3 cluster, and comparisons are made to electron spin resonance spectra. The calculations show good agreement with the observed Δg and 71Ga hyperfine tensors. This theoretical study predicts both parallel and perpendicular components of the 75As hyperfine tensors, while experimentally only the perpendicular component was assigned. Furthermore, the calculated isotropic and anisotropic spin distributions show some discrepancy with the empirically deduced spin distributions. The discrepancy between the calculated and empirically deduced values may be traced back to the methodology used in the empirical treatment. The calculations predict that the single unpaired electron spin spend 31.4% of its time on each axial 71Ga nuclei, and, 12.4% of its time on each equatorial 75As nuclei.

69,71GaNMR in thekagomélattice compoundSrCr9−xGa3+xO19

We report the NMR site assignment of ${}^{69,71}\mathrm{Ga}$ in the kagom\'e lattice compound ${\mathrm{SrCr}}_{9\ensuremath{-}x}{\mathrm{Ga}}_{3+x}{\mathrm{O}}_{19},$ and discuss the couplings of the different Ga nuclei with Cr moments. We find that $\mathrm{Ga}(4e)$ is dominantly coupled to the triangular plane, and $\mathrm{Ga}(4f)$ is coupled to both the kagom\'e and triangular planes. The low-temperature behavior of the NMR signal in ${\mathrm{SrCr}}_{8}{\mathrm{Ga}}_{4}{\mathrm{O}}_{19}$ suggests that a slowing down of some spin degrees of freedom occurs first on the kagom\'e plane.

Location Of Residual Donors In GaN Epitaxial Layers

AbstractOptically-detected electron-nuclear double resonance (ODENDOR) studies at 24 GHz on high-resistivity GaN films grown on Al2O3 have been combined with x-ray diffraction measurements to obtain information on the location of the residual shallow donors. Strong ODENDOR assigned to 69,71Ga lattice nuclei was detected on the g=1.951 effective-mass donor resonance found on the 2.2 eV emission bands. The x-ray studies reveal that the layers are under biaxial compression with high values of strain (∼ 2–3 × 10−3). The quadrupole splittings for 69Ga are smaller than those reported for strain-free samples by 15–25 %. The dominant sources of the local electric field gradient (EFG) responsible for the splittings are attributed to the wurtzite crystal structure and the strain fields that arise from the lattice constant mismatch and the difference in thermal expansion coefficients. An EFG/strain relationship of 3 × 1022 Vm−2 per unit strain at the 69,71Ga nuclei is deduced. The ODENDOR can be described with asymmetry parameter η=0. This provides evidence that the donors are in the crystallites rather than near grain boundaries.

Electron paramagnetic resonance of the group-III deep acceptor impurities in SiC

In this letter we report the EPR observation of the group-III deep acceptor impurities: deep B, deep Al and deep Ga centres in SiC crystals. A direct identification of the B and Ga atoms involved in the defect centre, considered as deep B and deep Ga, has been established by the presence of hyperfine interaction with 11B and 10B nuclei in isotope enriched B doped crystals and 69Ga and 71Ga nuclei in Ga doped crystals. In contrast to the results for the group-III shallow acceptor impurities in SiC, the observed qualitative behaviour for Al and Ga deep level impurities is the same as that for B. No effective-mass-like behaviour was observed for deep group-III acceptors. Deep centres were shown from EPR spectra to have symmetry nearly axial around the hexagonal axis of the crystal. Evidence of strong thermally activated dynamic effects having common features for the EPR spectra of all deep centres have been observed. The structural model for deep centre as an impurity-vacancy pair are presented. For shallow B acceptor off-centre position of B which is induced by chemical rebonding was suggested and as a result no effective-mass-like behaviour was observed. It was indicated from ODMR of deep Al acceptors that deep Al level is about 0.1 eV shallower as compared to deep B.

NMR measurement of the spin magnetization and spin dynamics in the quantum Hall regimes

We review our recent measurements of the Knight shift ( K s( v, T)) and spin-lattice relaxation time ( T 1( v,T) of the 71Ga nuclei located in n-doped GaAs quantum wells using optically pumped NMR, for Landau-level filling 0.66 < v < 1.76 and temperature 1.55K< T <K. K s( v) (proportional to the electron spin polarization 〈 S z( v)〉)drops precipitously on either side of v = 1, which is evidence that the charged excitations of the v = 1 ground state are finite-size skyrmions. For v < 1, the data are consistent with a many-body ground state which is not fully spin-polarized, with a very small spin-excitation gap that increases as v → 2/3.

Bistability of the magnetic resonance of conduction electrons in gallium oxide

The EPR spectrum of {beta}-Ga{sub 2}O{sub 3} conduction electrons have different resonance fields in forward and backward magnetic field sweeps due to the dynamic polarization of Ga nuclei upon resonance saturation of conduction electron spins. This bistability results from a narrow line width and a strong isotropic hyperfine interaction that causes a large Overhauser shift. This phenomena is maximum at moderate electron spin system saturation. There is also evidence of a magnetic field memory. 25 refs., 9 figs.

Determination of gallium in H(Ga)ZSM5 zeolites by gallium-71 MAS NMR spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDetermination of gallium in H(Ga)ZSM5 zeolites by gallium-71 MAS NMR spectroscopyCees R. Bayense, Arno P. M. Kentgens, Jan W. De Haan, Leo J. M. Van de Ven, and Jan H. C. Van HooffCite this: J. Phys. Chem. 1992, 96, 2, 775–782Publication Date (Print):January 1, 1992Publication History Published online1 May 2002Published inissue 1 January 1992https://doi.org/10.1021/j100181a047RIGHTS & PERMISSIONSArticle Views431Altmetric-Citations66LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1020 KB) Get e-Alerts

NMR study of one dimensional ionic conductor A xGa 8Ga 8+ xTi 16− xO 56 (ACs, Rb)

Ionic conduction in a new type of one-dimensional ionic conductor, A x Ga 8Ga 8+ x Ti 16− x O 56 (AGGTO), was investigated using NMR. Mobile 87Rb and 133Cs nuclei and stationary 69Ga and 71Ga nuclei in the framework were used as the probes. Temperature dependence of the line shape of 87Rb indicates that Rb + ions are in a motionally averaged state with the asymmetry parameter η of about 0.1 and the quadrupole coupling parameter ν Q of −8.6 MHz. The fact that T ∗ 1 of the mobile 133Cs and the stationary 71Ga nucleus show similar temperature dependences in the measured temperature range in CGGTO indicates that the Ga nuclei are good probes for observing ionic motion in the channel. The slope d( lnT 1 ∗)/ d(1/kT) in the high temperature limit gives E NMR = 0.06 eV, which is about one half of that in KAl-priderite. The smaller value ( E NMR = 0.03 eV) in RGGTO corresponds to the result of ac conductivity that RGGTO shows the highest conductivity in AGGTO.

Superconductivity of amorphous Mg0.7Zn0.3-xGaxalloys

The authors report on low-temperature measurements (0.1K<or=T<or=1.5K) of the specific heat and electrical resistivity of amorphous Mg0.7Zn0.3-xGax alloys (0.06<or=x<or=0.20) prepared by melt spinning. Superconductivity is observed for all samples. The transition temperature increases from approximately=0.1K to approximately=0.3K as the Ga concentration increases towards x=0.20. This increase is accomplished by a 10% increase in the electron-phonon coupling constant lambda . The specific heat data show that these alloys are weak-coupling superconductors ( lambda approximately=0.3). The upper critical field measured for x=0.20 is analysed in terms of the WHH theory. Finally, the normal-state specific heat data taken in a magnetic field of 2 T show contributions from Ga nuclei.

Crystal-field effects in amorphous alloys containing praseodymium

Crystal-field (CF) effects on Pr in amorphous and crystalline La 3Al and La 3Ga compounds are investigated through superconducting and magnetic properties. Strong evidence is obtained for a Pr 3+ singlet ground state in amorphous as well as in crystalline alloys. In addition, the results suggest that the local symmetry around the lanthanide ions is the same in nature in the crystalline compounds and in their amorphous modifications, in good agreement with NMR studies on Al and Ga nuclei.

Composition and temperature dependence of the density of states at the Fermi level in vanadium-based A-15 compound systems

Abstract The nuclear spin-lattice relaxation time T1 of the V, Pt and Ga nuclei in the A-15 systems V1−xPtx, V1−xGa1−x and V1−xSix has been measured as a function of the composition x and the temperature in the normal state. The V and Pt respectively Ga states are found to be strongly admixed. The experimental results indicate that the major contribution to the density of states at the Fermi energy N(EF) originates from the V 3d conduction electrons. This contribution, NVd(EF), exhibits a maximal value for the stoichiometric composition (x=0.25) in the systems investigated. Moreover, the anomalous temperature dependence of N(EF), typical for A-15 compounds, is largest for x=0.25. Both composition and temperature dependence of NVd(EF) can be explained with a simple model, using the results of recent band structure calculations on stoichiometric A-15 compounds.

Erratum: Production of Ca, Ga, and Br nuclei having angular momenta equal to or greater than the calculated liquid drop limit

Erratum: Production of Ca, Ga, and Br nuclei having angular momenta equal to or greater than the calculated liquid drop limit

Production of Ca, Ga, and Br nuclei having angular momenta equal to or greater than the calculated liquid drop limit

A semiconductor detector telescope has been used to detect heavy recoil nuclei produced in the reactions of 157 and 262 MeV $^{14}\mathrm{N}$ projectiles with $^{27}\mathrm{Al}$, Cr, and Ni target nuclei. Cross sections have been determined for the production of heavy recoiling compound nucleus residues. The limiting angular momenta which have been derived from these cross sections indicate the production of nonfissioning compound nuclei with angular momenta which equal or exceed the critical limit calculated using the liquid drop model. A comparison of the data with limits calculated using a reaction potential model recently proposed by Bass suggests that a picture based on dynamic restrictions to the fusion process provides a reasonable explanation of the results. However, the saturation limit predicted by the Bass model has not been observed.NUCLEAR REACTIONS $^{14}\mathrm{N}$+$^{27}\mathrm{Al}$, $^{14}\mathrm{N}$+Cr, $^{14}\mathrm{N}$+Ni, $E=157 \mathrm{and} 262$ MeV, measured $\ensuremath{\sigma}(E)$ for compound nucleus residues. Deduced limiting $J$ for production of nonfissioning compound nucleus.

Hyperfine interaction of adsorbed O 2− with GaAs surface atoms

EPR measurement of the hyperfine interaction between Ga nuclei and O 2 − ions adsorbed on clean GaAs is reported. The surface Ga atomic orbital concerned has an almost purely p character.

High frequency space charge layer capacitance of strongly inverted semiconductor surfaces : M. J. McNutt and C. T. Sah. Solid St. Electron.17, 377 (1974)

The bimetallic [M1M2(tren)2(CAn−)]m+ series, where M = GaIII or CrIII and CA is the chloranilate ligand which can take on diamagnetic (CAcat,cat)4− or paramagnetic (CAsq,cat)3− forms, comprises an electronically diverse series of compounds ranging from the closed-shell [Ga2(tren)2(CAcat,cat)]2+ to the S = 5/2 ground state of [Cr2(tren)2(CAsq,cat)]3+. This report deals with the interpretation of the EPR and ENDOR spectra of [Ga2(tren)2(CAsq,cat)](BPh4)2(BF4) (2) and the related derivative [Ga2(tren)2(DHBQ)](BPh4)2(BF4) (2a) (where DHBQ is the fully deprotonated trianionic form of 2,5-dihydroxy-1,4-benzoquinone) in an effort to further characterize the electronic structure of this radical species. The X-band (∼9.5 GHz) EPR spectrum of complex 2 acquired in a butyronitrile/propionitrile glass at 4 K reveals a rhombic g-tensor with gxx = 2.0100, gyy = 2.0097, and gzz = 2.0060 with hyperfine interactions due to spin delocalization onto the two Ga nuclei (axx = 4.902 G, ayy = 4.124 G, azz = 3.167 G); the origin of the hyperfine coupling was confirmed by analysis of the room temperature spectra of complexes 2 and 2a. The low-temperature spectrum of complex 2 also indicates the presence of a triplet electronic state characterized by a g-value of 2.009 and axial zero-field splitting of D = 150 G (0.012 cm−1) as determined from measurements carried out at both X- and W-band (∼95 GHz) frequencies. This triplet state is believed to arise due to a weak intermolecular Heisenberg exchange interaction between two aggregating complexes. ENDOR measurements on complex 2a at 20 K allowed for a determination of the magnitude of hyperfine coupling to the protons associated with the radical bridge as well as providing a rare example of an ENDOR signal arising from coupling to a gallium nucleus. Finally, these results were combined with literature data on the free semiquinone form of the bridging ligand in order to assess the extent to which density functional theory can predict unpaired spin density distribution in a complex molecule of this type. Although differences between theory and experiment were noted, DFT was able to provide a reasonably accurate picture of the electronic structure of this system as well as provide insight into the spin polarization mechanism(s) responsible for the observed hyperfine interactions.

Coupling of a three-particle (hole) valence-shell cluster to quadrupole vibrations (Alaga model): The Z = 50 region: odd Ag and I isotopes; and the Z = 28 region: odd Mn and Ga isotopes

The present approach includes two important physical correlations: the interaction between single-particle degrees of freedom and the vibrational field and the Pauli principle for three particles or holes in the valence shell. No new parameters have been introduced. In this way, both the explicit appearance of broken and promoted pairs and the anharmonicities from the neighbouring doubly even nuclei are accounted for. The model is generally characterized b y the coexistence of quasivibrational and quasirotational features. Typical quasirotational elements are the quasiband pattern and the I = j − 1 anomaly, while a typical quasivibrational element is the multiplet structure. Both features are naturally introduced by the mechanism of the cluster field coupling. Nuclei with Z = 50 ± 3 and Z = 28 ± 3 are qualitatively discussed within the framework of the present approach. A detailed qualitative and quantitative description of the properties of low-lying states (energy spectra, electromagnetic properties, transfer reactions) as well as a comparison with experiment are given for 107, 109Ag, 127I, 55Mn, and 69Ga, which are typical and well-known representatives of odd Ag, I, Mn, and Ga nuclei, respectively.