The electron structure and site preferences of Zn and Fe cations in Y hexaferrite system were calculated. The hyperfine magnetic fields on Fe-57 nuclei were determined using WIEN2k and corrections for hyperfine contact interaction. The calculated fields were compared to Fe-57 nuclear magnetic resonance (NMR) experiment in Ba2Zn2Fe12O22 single crystal with an aim of interpretation of experimental NAIR spectrum.

This work describes the design of a tuned NMR probehead that was developed for measurement of very broad spectra in fully impedance matched mode The probehead is constructed as an insert of continuous flow cryostat to allow operation down to helium temperatures Properties of the probehead are demonstrated on (57)Fe NMR in magnetic oxide with spinel structure

Series of lutetium doped yttrium iron garnet films is studied by means of Fe-57 nuclear magnetic resonance Satellite spectral lines are resolved and identified in the spectra and concentrations of lutetium in dodecahedral sites as well as yttrium/lutetium antisite defects in octahedral sites are estimated Compared to yttrium, lutetium cations are found to have stronger disposition towards creating the antisite defects

Silicon nanocrystals are an extensively studied light-emitting material due to their inherent biocompatibility and compatibility with silicon-based technology. Although they might seem to fall behind their rival, namely, direct band gap based semiconductor nanocrystals, when it comes to the emission of light, room for improvement still lies in the exploitation of various surface passivations. In this paper, we report on an original way, taking place at room temperature and ambient pressure, to replace the silicon oxide shell of luminescent Si nanocrystals with capping involving organic residues. The modification of surface passivation is evidenced by both Fourier transform infrared spectroscopy and nuclear magnetic resonance measurements. In addition, single-nanocrystal spectroscopy reveals the occurrence of a systematic fine structure in the emission single spectra, which is connected with an intrinsic property of small nanocrystals since a very similar structure has recently been observed in specially passivated semiconductor CdZnSe nanoparticles. The organic capping also dramatically changes optical properties of Si nanocrystals (resulting ensemble photoluminescence quantum efficiency 20%, does not deteriorate, radiative lifetime 10 ns at 550 nm at room temperature). Optically clear colloidal dispersion of these nanocrystals thus exhibits properties fully comparable with direct band gap semiconductor nanoparticles.

The perovskite compounds of LaMn1-xCoxO3(0.2⩽x⩽0.5) have been studied by means of NMR spectroscopy in powder samples prepared by the solid state reaction and sol–gel methods. The NMR signals were observed in the frequency range 250–650MHz at 4.2K in zero external magnetic field. A relatively narrow spectral line assigned to 55Mn in Mn4+ is situated around 270–320MHz in all spectra. Additional spectral lines are observed at higher frequencies. Line intensities and forms are dependent on the cobalt concentration and preparation techniques.

Nuclear Magnetic Resonance/Near Quadupole Resonace specra of Lu175 in lutetium iron garnet (LuIG) were measured in the range of 10–500MHz in zero external magnetic field at a temperature of 4.2K. Experimentally observed spectra had complicated structure and a theory was needed to interpret them. To this end we calculated the electronic structure of LuIG and from it the values of magnetic hyperfine fields and the components of electric-field-gradient tensor at the lutetium nuclei were determined. These parameters were used to simulate the theoretical spectra of Lu175 in LuIG. Simulated spectral lines of Lu175 at dodecahedral sublattice correspond reasonably well with the system of measured lines in the range of 10–200MHz. Several spectral lines in the range of 300–500MHz can be interpreted as the resonance of Lu175 at the octahedral sites that are nominally occupied by the ferric cations.

Alcohols with nuclear spins highly polarized due to the polarization transfer from stable nitroxyl radicals are suitable materials for polarized nucleon targets. In this work the ethanol-TEMPO system was studied by H-1 and C-13 high resolution NMR in a liquid phase. The concentration and temperature dependences of spin-lattice relaxation rates, linewidths and chemical shifts were measured. The highest impact of doping was seen for protons of OH group as a result of hydrogen bonds to the oxygen of TEMPO. For the other nuclei the relaxation enhancement corresponds to the diffusion-controlled regime above 210 K.

Fe nuclei situated in tetrahedral and octahedral sites inmagnetic domains as well as in domain walls at several temperatures within the range of 4.2-344 K. Comparing the simulated lineshapes to the experimental ones we found that the maincontribution to the observed spectra from walls originated from nuclei in 70:5

Magnetite single crystals with Al, Ga and Ti substitutions were measured by means of 57Fe nuclear magnetic resonance (NMR) technique. Satellite structure of NMR spectra well above the Verwey temperature was detected and analyzed to obtain information on the distribution of substituting cations on iron sublattices. It was confirmed that Al and Ti enter iron octahedral B-sites. Ga strongly prefers tetrahedral A-sites, nevertheless a low presence of Ga cations in B-sites was detected.

We present an NMR study of hyperfine fields at 5 7 F e nuclei in polycrystalline yttrium iron garnet. We measured spectra of 5 7 F e nuclei situated in tetrahedral and octahedral sites in magnetic domains as well as in domain walls at several temperatures within the range of 4.2-344 K. Comparing the simulated lineshapes to the experimental ones we found that the main contribution to the observed spectra from walls originated from nuclei in 70.5 degrees Bloch walls.

57Fe NMR spectra of lutetium iron garnet (LuIG) and yttrium iron garnet (YIG) samples prepared by liquid mix process were measured at 4.2 and 77K. We detected and identified patterns of satellite lines induced by lutetium antisite defects Lu(a) in LuIG and yttrium antisite defects Y(a) in YIG. Frequency shifts of satellite lines induced by Lu(a) were smaller compared to shifts of corresponding satellite lines induced by Y(a). Concentration of the defects determined from intensities of spectral lines was significantly higher for Lu(a) in LuIG than for Y(a) in YIG.

We report the NMR spectra of gallium substituted magnetite measured at temperatures 4.2, 77 and 273 K. A single crystal of Fe3−xGaxO4, x=0.05 has been prepared by a floating zone technique. The Ga-lines found in the NMR spectrum above Verwey temperature TV∼117K indicate a preferency of Ga substitution into the tetrahedral A-sites. The well-resolved structure of Ga-lines has been identified and assigned to both Ga isotopes below TV. A weak quadrupolar interaction contributes only to the line broadening.

NMR on a gadolinium iron garnet was measured in zero and nonzero external magnetic field at 4.2K. 24 well separated lines of 155Gd and 157Gd nuclei were found in the zero field spectrum. From the spectral line positions we determined the EFG tensor and both isotropic and anisotropic components of hyperfine magnetic interaction on gadolinium nuclei. The experimental hyperfine interaction parameters were compared with the ‘ab initio’ calculations of the EFG tensor.

Temperature dependence of 57Fe NMR spectra was measured below and around the Verwey transition in Fe3−xAlxO4 (x=0, 0.005, 0.01, 0.02, 0.03) single crystals. All lines of substituted samples were broadened with increasing Al concentration, but we have found no change in their positions. The Verwey temperature TV decreases with increasing Al concentration in agreement with electric conductivity measurements. The satellite structure found in the vicinity of the A-line above TV disappears below TV, on the other hand a broad spectrum in the spectral region 35–45MHz at temperature 4.2K was detected.

Effect of Ca2+ substitution on the 57Fe NMR spectra and relaxations was measured in YIG epitaxial films. A satellite line caused by the presence of Ca2+ was identified in the spectra of d-sites of YIG:Ca, Ca–Ge and Ca–Si films. In a YIG:Ca series, after an initial constant region a decrease of a spin–lattice relaxation rate was observed in a dependence on the increasing Ca2+ content. The onset of the relaxation rate decrease is supposed to correspond to the induced decrease of an amount of Fe2+ ions, while charge compensation is reached by other mechanisms for lower calcium content.

The known macroscopic data for the temperature dependence of the normalized spontaneous magnetization, m(s)(T), of iron, cobalt and nickel are reconsidered and compared with our normalized zero-field hyperfine field data, h(hf)(T), obtained by Mossbauer spectroscopy or nuclear magnetic resonance. It is observed that for all three metals h(hf)(T) is not proportional to m(s)(T) and systematically smaller than m(s)(T). This is attributed to smaller magnetic interactions in the domain walls compared to the volume of the domains. The temperature dependence of m(s)(T) and h(hf)(T) can be described in the whole range 0 < T < T-C by a few temperature power functions with analytical changes (crossovers) at the intersections of these functions. Below the critical power law, m(s) similar to (T-C - T)(beta), further power functions of the absolute temperature according to m(s)(T) = A - cT(epsilon), follow. From the observed rational exponents epsilon it can be concluded whether the effective spin is integer or half-integer. Using additionally the known data for the saturation magnetic moments and the effective paramagnetic Bohr magneton numbers it is suggested that for nickel the effective spin is S = 1/2 for T --> 0 but S = 1 for higher temperatures including the paramagnetic phase. For iron and cobalt the corresponding values are S = 3/2 and 2. (C) 2003 Elsevier B.V. All rights reserved.

Using 55Mn nuclear magnetic resonance (NMR), the magnetic phase separation into antiferromagnetic and ferromagnetic phases was found in Ca0.95La0.05MnO3 manganite. At 4.2K, distinct NMR signals from ferromagnetic domains, antiferromagnetic matrix, and from the domain walls were detected. Predominant relaxation mechanism in the ferromagnetic phase is the Suhl-Nakamura interaction. This suggests that ferromagnetic domains in Ca0.95La0.05MnO3 have mesoscopic rather than nanoscopic dimensions.