Hyperfine structure of the ground state muonic <Superscript>3</Superscript>He atom

On the basis of the perturbation theory in the fine structure constant α and the ratio of the electron to muon masses we calculate one-loop vacuum polarisation and electron vertex corrections and the nuclear structure corrections to the hyperfine splitting of the ground state of the muonic helium atom (μ e ³ ₂He). We obtain total results for the ground state hyperfine splitting Δ ν ^hfs = 4166.648 MHz which improves the previous calculation of Lakdawala and Mohr due to new corrections of orders α ⁵ and α ⁶. The remaining differences between our theoretical result and experimental value of the hyperfine splitting lie in the range of theoretical and experimental errors and require the subsequent investigation of higher order corrections.     

Mössbauer effect study of Gadolinium Iron Garnet

The Mossbauer Effect study of polycrystalline Gadolinium Iron Garnet has been undertaken between 714K and 4.2K. The temperature dependence of the sublattice magnetization has been determined at the two iron sites and the direction of the hyperfine fields at each site is [111] over the entire temperature range. The saturation fields at the octahedral and tetrahedral sites are respectively 547 kOe and 477 kOe. The ferrimagnetic Neel temperature has been found to be 562.5K and above this temperature, the quadrupole splitting at the octahedral and tetrahedral sites are –0.43 mms^–1 and ¦0.89¦mms^–1 respectively.     

Shallow-Donor Hydrogen-Like Impurities in ZnO Studied by MuSR

Two species of Mu centers with extremely small hyperfine parameters have been observed in single crystalline ZnO below 40 K. Both Mu centers have an axial symmetric hyperfine structure along with the [0001] axis, indicating that they are located at AB_O,∥ and BC_∥ sites. It is inferred from their small ionization energy (≃6 meV and 50 meV) and hyperfine parameters (∼10⁻⁴ times the vacuum value) that these centers behave as shallow donors, strongly suggesting that hydrogen is one of the primary origins of n type conductivity in as-grown ZnO. This revised version was published online in September 2006 with corrections to the Cover Date.     

Low temperature1H NMR study of electronic structure parameters (T 1e T) in zirconium dihydride

Measurements of the proton-spin-lattice relaxation times (T ₁) are reported for zirconium dihydrides: ZrH_1.87, ZrH_1.93 and ZrH_2.00 at nominal frequency of 41 MHz, with emphasis on the low temperature (4.2–25 K) behaviour of theT ₁. The dominant contributions are originated from the hyperfine interactions of the protons with the conduction electrons and the paramagnetic impurities. The (T _1e T)^–1/2 values determined from the low temperature range (4.2–25 K) agree with those obtained in the extended range (4.2–300 K) as well as with the values reported by the other researches. The paramagnetic impurity contribution is found to be small and teperature independent.     

Muonium quantum diffusion and spin dynamics in solid xenon

We present measurements of the transverse (T ₂ ^–1 ) and longitudinal (T ₁ ^–1 ) spin relaxation rates of muonium (Mu) atoms in solid natural xenon (n-Xe) as well as pure¹³⁶Xe (which has no nuclear moments). The temperature dependences ofT ₂ ^–1 andT ₁ ^–1 in natural Xe belowT 115 K demonstrate the quantum character of Mu diffusion governed by one-phonon interactions. Taking into account both the polaron effect (PE) and the effect of fluctuational preparation of the barrier (FPB) makes it possible to consistently describe Mu diffusion in Xe. Mu spin relaxation in¹³⁶Xe at high temperatures is not due to nuclear hyperfine (NHF) interactions.     

NMR-ON on196,197m,198,198m,200mAu in Fe and Ni

The zero-field hyperfine splitting frequencies of a series of Au isotopes in Fe and Ni have been determined with nuclear magnetic resonance on oriented nuclei. The results are:. For¹⁹⁸Au(2^–) in Fe the quadrupole splitting could be resolved. The results are ¦g_NB_HF/h|=259.48 (3) MHz and e²qp/h=–2.08(4) MHz. Our measurements show that most hyperfine splittings published on these isotopes have been incorrect. The quadrupole splitting of¹⁹⁸AuFe disagrees in magnitudeand sign from the value reported by single-passage NMR on oriented nuclei. The following nuclear quantities are deduced: (^197mAu,11/2^–)=5.98(9) _N; (^198mAu, 12^–)=5.85(9) _N; (^200mAu, 12^–)=5.90(9) _N; Q(¹⁹⁸Au,2^–)/Q(¹⁹⁹Au, 3/2⁺)=1.37(3). Our measurements show further that the non-contact hyperfine field for Au in Ni is smaller than assumed previously, and that the magnetic hyperfine splitting frequency of¹⁹⁷AuFe known from NMR is inconsistent with the magnetic hyperfine splitting frequencies of^{198, 199}AuFe.     

Order–disorder transition in nanocrystalline Ni3Al prepared by a chemical route

Ni₃Al alloys of nanometer dimensions in the range 10–38 nm could be synthesized by reaction sintering of sol–gel-derived Ni/SiO₂ nanocomposite and commercially available micrometer-sized aluminum powder. The sintering was carried out at a temperature of 923 K and a pressure of 2.4 MPa. By a suitable choice of sintering conditions a disordered phase of Ni₃Al was stabilized. The disordered phase could be converted to an ordered one by an increase of heat treatment temperature.     

Temperature dependence of the muon and proton hyperfine constants of an \alpha‐muonium‐substituted methyl radical

Muon hyperfine constants A_μ have been measured by transverse field μSR for (CH₃)₃Si\mbox\.CHMu in hexane from 167 K to 332 K. In addition, avoided level‐crossing resonance was used to determine \alpha‐proton coupling constants A_p over a similar range of temperatures. The two hyperfine constants can be described by a common temperature dependence, d|A_i|/ dT=1.4\times 10^-3 MHz\,K^-1, where A_i represents A_p or the reduced muon constant A^\prime_μ=0.3141A_μ. There is a small isotope effect (A^\prime_μ is 2.2 % larger than A_p) consistent with zero‐point motion in the anharmonic C–H bond stretch. The common temperature dependence is tentatively attributed to a coupled deviation of the C–H and C–Mu bonds out of the nodal plane of the p orbital containing the unpaired electron. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dynamical behavior of muonium on silica surfaces

The behavior of muonium on the surface of finely divided silica (amorphous SiO₂) powder (mean grain diameter 70 Å) has been studied as a function of the surface concentration of hydroxyl groups. The temperature dependence of the Mu relaxation rate in transverse field was measured for samples prepared with 0%, 50% and 70% of the surface hydroxyl groups removed over the temperature range 4 K <T < 300 K. The relaxation rate shows a distinct maximum at about 25 K and a minimum at about 16 K for all three samples, and shows a dramatic decrease below 16 K as the concentration of surface hydroxyls is reduced. A three-state nonequilibrium model describing the diffusion and trapping of muonium on the silica surface is used to interpret the data.On leave from Department of Physics, University of Saskatchewan, Saskatoon, Sask. S7N OWO, Canada.     

Spin echo and nuclear orientation study of metallic glasses

Hyperfine fields on Co nuclei in amorphous as-quenched and heat-treated Co₇₅Fe₅B₂₀ samples were studied by conventional NMR and by very low temperature nuclear orientation techniques. The Co spin echo measurement at 1.4 K yielded broad spectra between 130 – 260 MHz, with narrow maxima at 145.5 MHz and 155.1 MHz for as-quenched sample and with a broad maximum at 227 MHz for heat-treated sample well below the recrystallization point. The⁶⁰Co nuclear orientation measurements gave the mean value of hyperfine field B_hf15 T nearly independent of the sample heat-treatment. The spin-lattice relaxation was studied by pulse NMR and also by nuclear orientation thermal cycling technique.     

Hyperfine interaction in Co2SiO4 investigated by high resolution neutron spectroscopy

We have investigated the hyperfine interaction in Co₂SiO₄ by inelastic neutron scattering with a high resolution back-scattering neutron spectrometer. The energy spectrum measured from a Co₂SiO₄ powder sample revealed inelastic peaks at at T=3.5 K on both energy gain and energy loss sides. The inelastic peaks move gradually towards lower energy with increasing temperature and finally merge with the elastic peak at the electronic magnetic ordering temperature . The inelastic peaks have been interpreted to be due to the transition between hyperfine-split nuclear level of the ⁵⁹Co isotopes with spin . The temperature dependence of the energy of the inelastic peak in Co₂SiO₄ showed that this energy can be considered to be the order parameter of the antiferromagnetic phase transition. The determined hyperfine splitting in Co₂SiO₄ deviates from the linear relationship between the ordered electronic magnetic moment and the hyperfine splitting in Co, Co-P amorphous alloys and CoO presumably due to the presence of unquenched orbital moment. These results are very similar to those of CoF₂ recently reported by Chatterji and Schneider [7].     

Mössbauer effect study of antiferromagnetic Fe–Mn–Si alloys

Antiferromagnetic Fe–30Mn–Si alloys containing 2.0–8.7 at.% Si are known to exhibit several attractive physical properties at Néel temperatures which render them candidate materials for functional alloys applications. The Néel transitions and anomalous transport phenomena have been studied extensively in a wide temperature range. In the present work, the hyperfine interactions are studied by Mössbauer spectroscopy measured at temperatures 95–623 K. It is found that the Mössbauer spectra are singlets at temperatures above the Néel temperature and doublets below the Néel temperature. The alloys have a small hyperfine field around the Fe nuclei below the Néel temperature and the hyperfine field increases linearly with increasing silicon concentration. This can be explained by the presence of a localised net magnetic moment on the Fe nuclei which is induced by the silicon atoms. A decrease in isomer shift with increasing silicon concentration is observed and this can be accounted for by the change in the occupation of the Fe 3d shell. There is a small quadrupole splitting, it increases with increasing silicon concentration, and is consistent with the lattice shrinking and magnetostriction.     

Zero-field μSR in crystalline C60

The C_o60Mu radical in polycrystalline C₆₀ has been studied in zero magnetic field between 9 K and 200 K, and at room temperature. At low temperatures, we observe three low-frequency oscillations which correspond to the intra-triplet transitions of a completely anisotropic muon-electron hyperfine interaction. These signals exhibit a strongly temperature-dependent T₁, attributed to thermally-activated jump rotational diffusion of the C₆₀Mu radical. A fit to an Arhenius law yields an activation energy of 200(20) meV for temperatures below the fcc-sc structural phase transition. At room temperature only the motionally-narrowed 325 MHz singlet-triplet transition is observed.     

X-ray and Mössbauer study of rapidly solidified Ce20Fe80 ribbons; effect of the quenching rate

Ce₂₀Fe₈₀ ribbons have been produced by planar flow casting under an He atmosphere at linear wheel velocities between 19 and 29 m s^–1. Analysis of ribbons by X-ray diffraction and⁵⁷Fe Mössbauer spectrometry in the temperature range 77–300 K shows that the ribbons are crystallized. For higher velocities, the ribbon is constituted of the two equilibrium phases CeFe₂ and Ce₂Fe₁₇, but, for lower velocities, there appears a third iron metallic phase, which can be explained by the quenching rate of the melt. A coherent hyperfine parameter set was deduced from fitting Mössbauer spectra in the whole temperature range.     

Dynamical studies of highly deuterated betaine phosphate near the antiferroelectric phase transition

The dielectric response and the Raman spectra of single crystals of deuterated betaine phosphate are studied around the antiferroelectric phase transition. The dielectric data between 10 MHz and 11 GHz can be explained on the basis of a simple Debye-relaxation with a critical slowing-down of the relaxation rate on approachingT _C . Using the Cole-Davidson form of the dielectric function we succeeded in fitting the data in the whole frequency range from 10 MHz to 11 GHz and from 64–400 GHz over a temperature range from 145–280 K. Raman spectra clearly indicate that the doubling of the unit cell does not take place at the antiferroelectric transition temperature, but some degrees below.     

High-Temperature Mössbauer Spectroscopy of Mechanically Milled NiFe2O4

Oxide spinels, in particular those containing iron, often exhibit technically important electrical- and magnetic-properties. We report here on X-ray powder diffraction and Mössbauer studies of nanostructured NiFe₂O₄ particles prepared by high-energy ball milling from bulk NiFe₂O₄, which is an inverse spinel. The Mössbauer spectra were recorded in situ at different temperatures in the range of 300–850 K. The Mössbauer spectra of the milled samples show a broad distribution of magnetic hyperfine fields together with a paramagnetic state at room temperature. Initially, at 700 K the spectrum is mainly paramagnetic, but during the process of annealing, magnetic sextets emerge. The treatment results in a significant change in the B/A area ratio of the ferrite. The Neél temperature of the samples is estimated from the B(T) relation to be in the range of 800–850 K.     

Mössbauer studies of dilute Au:Er alloys: Obervation of hyperfine structure of ground and excited CEF levels

The hyperfine structure of dilute ¹⁶⁶Er impurities in Au has been investigated between 1.8 and 60 K by Mössbauer spectroscopy. The hyperfine spectrum of the Γ₇ electronic ground state is clearly observed below 4.2 K while at higher temperatures there is an indication of the contribution from the excited CEF-states Γ⁽¹⁾₈ and Γ₆. Using Hirst's relaxation theory for the Γ₇ ground state the magnetic hyperfine coupling constant A=(247±3) MHz and the exchange coupling constant J_sf=(0.10±0.02)eV were derived. A quadruple coupling constant B of about 1 MHz was estimated from the hyperfine pattern of the Γ⁽¹⁾₈ quartet.     

Two-frequency quasi-optical radiospectrometer for substance investigations

In this paper two-frequency radiospectrometer is described: frequency of ESR is n _e =(120 GHz – 150 GHz); frequency of the nuclear magnetic resonance (NMR) is n _n =(180 MHz – 200 MHz).Radiospectrometer is operates in the temperature band T=(4.2 K 1.7 K) and in the magnetic field band H=5 T.     

Preparation of SiC nanowires with fins by chemical vapor deposition

SiC nanowires with fins have been prepared by chemical vapor deposition in a vertical vacuum furnace by using a powder mixture of milled Si and SiO₂ and gaseous CH₄ as the raw materials. The products were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). These investigations confirm that the nanowires with fins are cubic β-SiC. The diameter of the fins is about 100–120 nm and the diameter of the inner core stems is about 60–70 nm. The formation process of the β-SiC nanowires with fins is analyzed and discussed briefly.     

Nuclear magnetic moment of 12 d 11/2− 131mXe

NMR-ON measurements were performed on^131mXe (I=11/2^–; T_1/2=12.0 d) in Fe, the sample being prepared by recoil implantation after the¹³⁰Te(,3n)^131mXe compound reaction at E=40 Mev. The hyperfine splitting _NB_HF/h¦, extrapolated to zero external magnetic field, was found to be 209.9(1) MHz. Taking B_HF=+1523(8) kG for the hyperfine field of XeFe, the magnetic moment of^131mXe is deduced to be (–)0.994(5) _N. As a byproduct, the zero-field hyperfine splitting of^129mXe (I=11/2^–; T_1/2=8.9d) in Fe was measured as 188.1(1) MHz, with which a magnetic moment of (–)0.891(5) _N is deduced for^129mXe.