Effects of nitrogen and vanadium on the57Fe hyperfine field of RFe12−x V x N y (R=Y,Nd)

Magnetization and⁵⁷Fe Mössbauer measurements were carried out on RFe_12–x V _x N _y compounds (R=Y and Nd,x=1.7 and 2.2) and the effects of nitrogen and vanadium atoms on the⁵⁷Fe hyperfine fields at the different iron crystallographic sites were investigated. The hyperfine field decreases with increasing number of vanadium neighbour atoms at all the iron sites. The hyperfine field is strongly enhanced in the nitrogen composition withy>1 where the compound tends to transform into an amorphous-like solid. The iron moment deduced from the hyperfine field increases more upon nitrogenation for the 8i-site than for the other sites, and exceeds the moment of bcc iron.     

Hyperfine interaction of166Er impurities implanted in iron and nickel

Sources of¹⁶⁶Ho implanted in iron and nickel foils have been studied by means of Mössbauer spectroscopy on the 80.6 KeV transition in¹⁶⁶Er. The spectra could be fitted with a unique hyperfine interaction in the temperature range studied (4.2–78 K). At 4.2 K the hfi parameters wereB _hf=7.68(13) MG and 1/4e ² qQ=+0.288(9) cm/s=+187(6) MHz. The temperature dependence of the hyperfine interaction could be described reasonably with a localized moment model with an exchange field of 3.7 MG acting on the Er electron spin. The spectra could be decomposed into 2 components of about equal intensity, component 1 withB _hf=7.01 (14) MG, 1/4e ² qQ=+0.20(3) cm/s =+130(20) MHz and component 2 withB _hf=4.76(9) MG and 1/4e ² qQ=+0.114(11) cm/s=+74(7) MHz. From a measurement on an annealed source it is concluded that component 2 is associated with ions in substitutional sites, whereas the ions contributing to component 1 probably are associated with vacancies. Internal oxidation of the rare earth impurities, which was suggested as the origin of the non-substitutional fraction in these systems, is completely absent in our samples.     

Observation ofμ − spin precession in ferromagnetic Ni and giant hyperfine anomaly

A ^–SR signal in nickel was found representing the first observation of ^–SR in ferromagnetic materials, and the hyperfine anomaly was determined to be –2.82±0.08% in comparison with the hyperfine field at dilute Co in Ni known from NMR.     

Magnetic hyperfine fields of Zr in nickel and iron measured by the DPAD method

The magnetic hyperfine fields of Zr in nickel and iron were measured by the DPAD method. Using the 8⁺ isomeric states in⁹⁰Zr and⁸⁸Zr these fields were found to beH _hf(ZrNi)=–4.65(10) T andH _hf(ZrFe)=–27.4(4) T, respectively.     

Knight shift,hyperfine field,NMR frequency and magnetization of a Neel-type nickel single crystal

The field dependence of the NMR line center frequency of naturally abundant⁶¹Ni has been studied with Néel-type nickel single crystals at 4.2 K. For internal fields H_i lower than H_is, which is the field necessary for complete magnetic saturation, a nonlinear correlation between and H_i was found due to changes of the orientation of the hyperfine field with H_i. For fields larger than H_is the linear variation lead to K=111.10^–4 for the Knight shift. Using available susceptibility data, we find _p=28.10^–6 emu/mole and _vv=92.10^–6 emu/mole.     

Mössbauer and EPR study of nitrosyl hemoglobin

Nitrosyl hemoglobin was prepared by bubbling fresh⁵⁷Fe-enriched rat hemoglobin with NO. S- and X-band EPR spectra at 77 K are typical for anS=1/2 system with an anisotropicg-tensor and exhibit hyperfine interactions of¹⁴N with the electronic spin. Mössbauer spectra at 4.2 and 100 K consist of a superposition of spectra from high- and low-spin Fe(III), deoxygenated hemoglobin and a component corresponding toS=1/2,g=2, hyperfine constantsA _xx /g _{n n} =A _yy /g _{n n} =–19.6 T,A _zz /g _{n n} =6.8 T, quadrupole splitting E _Q=1.5 mm s^–1, isomer shiftI _s=0.42 mm s^–1 and linewidth 0.4 mm s^–1. The spin-lattice relaxation rate at 100 K is <2×10⁶ s^–1.     

The magnetic hyperfine field of lutetium in iron by NMR/ON

Nuclear magnetic resonance of oriented¹⁷⁷Lu in iron has been found with a sample prepared by on-line implantation of¹⁷⁷Lu in iron at T<0.2 K. The broad resonance, FWHM=20.5 (1.3) MHz, has a centre frequency of _L=355.06 (51) MHz at zero external field. With the g-factor of¹⁷⁷Lu g=0.637 (3) from literature the magnetic hyperfine field of Lu in Fe is derived as B_hf=–73.12(36) T. Static nuclear orientation data are not compatible with a two site model where the nuclei which are oriented experience the hyperfine interaction found in NMR/ON. A fraction with a lower hyperfine field is necessary to explain the data.     

Isotope shift and hyperfine structure measurements at the242f Am fission isomer

Istope shift and hyperfine structure measurements have been performed for the^242fAm fission isomer with target production rates of only a few per second. The method is based on resonance ionization spectroscopy (RIS) in a buffer gas cell with radioactive decay detection of the ionization process (RADRIS). A relative isotope shift ratioX _exp=IS^242f,241/ IS^243,241=41.7±0.9 has been measured for the 500.02 nm transition corresponding to a nuclear parameter ^242f,241=5.4±0.3 fm². The analysis of the quadrupole moment based on the deformed Fermi-model of the nuclear charge distribution including second order corrections results inQ ₂₀=38.2 ±1.4( _–0.8 ^+0.4 )_model eb. The measurement of the hyperfine structure splitting of the transition at 466.28 nm yields a negativeg-factor and a nuclear spin ofI=2 orI=3.Work supported by the Bundesministerium für Bildung und Forschung under contract 06 MZ 5661.     

Mössbauer Spectroscopy Study of Iron Nickel Alloys

Three samples of Fe_100–x Ni _x (with x=30, 35 and 40) were prepared by arc melting technique. The Mössbauer spectra of the three samples were collected and analyzed. The spectrum of the sample with x=30 consists of a singlet and a sextet. The singlet component which has isomer shift (IS=–0.08 mm/s) is attributed to a superparamagnetic phase. The value of the magnetic hyperfine field associated with the sextet component, 34.0 T, is consistent with that of -Fe–Ni alloy. In the spectra of the other samples the central line disappears. The magnetic component, used in fitting the spectrum of the sample with x=40 has a hyperfine magnetic field B _hf=30.0 T. This component is assigned to the high-spin -FCC Fe–Ni phase. Two magnetic components of 16.3 T and 27.3 T are used to fit the spectrum of the sample with x=35. The 27.3 T component is associated with the typical high-spin -FCC Fe–Ni phase while the 16.3 T component is associated with a -FCC Fe–Ni phase with magnetic relaxation.     

Correlation of57Fe hyperfine interactions with Fe-Fe distance in Laves phase compounds RFe2 (R=rare earth)

The⁵⁷Fe Mössbauer isomer shifts and magnetic hyperfine fields in Laves phase compounds RFe₂ (R=Pr, Nd and Sm) are studied with particular reference to the effect of the Fe–Fe interatomic distance on the hyperfine interactions. It is shown that the charge density at the Fe nuclei scales linearly with fractional volume change up to 20%. The⁵⁷Fe hyperfine field corrected for the influence of rare-earth moment shows a systematic variation with the distance, which can be understood in terms of the Bethe-Slater curve arguments. The similarity of the atomic volume dependence of the⁵⁷Fe hyperfine interactions in Lves phase compounds to those in iron with close-packed structure is emphasized.This paper is based on a paper presented at the 5th Int. Conf. on hyperfine interactions, Berlin, July 21–25, 1980.     

Influence of Fe ions in characteristics and optical properties of mesoporous titanium oxide thin films

Fe-doped mesoporous titanium dioxide (M-TiO₂-Fe) thin films have been prepared on indium tin oxide (ITO) glass substrates by sol–gel and spin coating methods. All films exhibited mesoporous structure with the pore size around 5–9 nm characterized by small angle X-ray diffraction (SAXRD) and further confirmed by high resolution transmission electron microscopy (HRTEM). Raman spectra illustrated that lower Fe-doping contributed to the formation of nanocrystalline of M-TiO₂-Fe thin films. X-ray photoelectron spectroscopy (XPS) data indicated that the doped Fe ions exist in forms of Fe³⁺, which can play a role as e⁻ or h⁺ traps and reduce e⁻/h⁺ pair recombination rate. Optical properties including refractive indices/n, energy gaps/E_g and Urbach energy width/E₀ of the thin films were estimated and investigated by UV/vis transmittance spectra. The presence of Fe content extended the light absorption band and decreased the values of n, implying enhanced light response and performance on dye-sensitized solar cells (DSSC). The optimum Fe content in M-TiO₂-Fe thin films is determined as 10 mol%, for its compatibility of well crystalline and well potential electron transfer performance.     

NMR on oriented54Mn in nickel

The NMR/ON of thin foil polycrystalline⁵⁴MnNi was measured at 16 mK. From zero field resonance frequencyv ₀₀=273·1 (1) MHz the hyperfine fieldB _hf=–32·55 (6) T was deduced, the slope beingdv/dB=0·935 MHz/T.Dedicated to the 25th anniversary of the Joint Institute for Nuclear Research.     

Magnetic properties of U (Fe x Al1−x )2 and U(Fe y Ni1−y )2 compounds

The results of magnetic measurements and ferromagnetic resonance studies performed on U(Fe _x Al_1–x )₂ and U(Fe _y Ni_1–y )₂ compounds over a large temperature range are reported. The saturation magnetization decreases nearly linearly when substituting Fe by Al or Ni. In the composition range x<0.84 and y<0.81, the compounds are Pauli paramagnets, except in the region with y0.10. For UNi₂ two types of magnetic behaviours are shown. This compound can be both a ferromagnet withT _c =23.5 K and a Pauli paramagnet, depending on the crystal structure. Above the Curie temperatures, the reciprocal susceptibility for the compounds with x>0.84 and y>0.81 obeys a temperature dependence of the formX=X _o+C(T-) ^–1. The effective iron moments decrease when substituting iron by nickel or aluminium. The ferromagnetic resonance measurements show that theg values are not composition-dependent. A linear variation of the mean iron magnetization with the exchange field is observed. Finally, the magnetic behaviour of iron in these compounds is analysed.     

Annealing effect on the superconductivity of In2O3–ZnO thin films

We have investigated the relation among ρ–T characteristics, superconductivity, annealing conditions and the crystallinity of polycrystalline (In₂O₃)_1−x–(ZnO)_x films. We annealed as-grown amorphous films in air by changing annealing temperature and time. It is found that the films annealed at 200 °C or 300 °C for a time over 0.5 h shows the superconductivity. Transition temperature T_c and the carrier density n are T_c < 3.3 K and n ≈ 10²⁵–10²⁶ m⁻³, respectively. Investigations for films with x = 0.01 annealed at 200 °C have revealed that the T_c, n and crystallinity depend systematically on annealing time. Further, we consider that there is a suitable annealing time for sharp resistive transition because the transition width becomes wider with longer annealing times. We studied the upper critical magnetic field H_c2(T) for the film with different annealing time. From the slope of dH_c2/dT for all films, we have obtained the resistivity ρ dependence of the coherence length ξ(0) at T = 0 K.     

The183Re ground state dipole moment and nuclear spin-lattice relaxation of Re in Fe

The hyperfine interaction of the system¹⁸³Re(70d)Fe has been investigated with the NMR/ON technique. With the hyperfine field valueB _hf(ReFe)=–76.0(1.5) T the ground state magnetic moment was determined as: (5/2⁺,¹⁸³Re)=+3.12(6) _N. The field dependent nuclear spin-lattice relaxation time has been measured. The result for the high-field relaxation rateR _exp=1.65(5)·10^–15 T ²s K^–1 is explained in terms of indirect spin-wave interaction.     

Magnetic characteristics of thin Ni films electrodeposited on n-Si(1 1 1)

The nanocrystalline Ni films were grown on n-Si(1 1 1) substrate by pulsed electrodeposition in non-aqueous NiCl₂ + methanol solution. The frequency of potential pulse was modulated during the deposition of Ni onto Si substrates. When the frequency varies from 20 to 900 Hz, the average size of Ni nanocrystallites varied in the ranges from 48 to 130 nm. In these cases, all Ni films have grown through a three-dimensional instantaneous nucleation followed by diffusion-limited growth. From X-ray diffraction measurement, it has been found that Ni(1 1 1) grows preferentially on the Si(1 1 1) substrates. The magnetic hysteresis loops for as-deposited films were measured by using VSM. As the angle θ between film plane and applied magnetic field varies from 0 to 90, the coercivity (H_c) and squareness (S) obtained from the magnetic hysteresis loops showed an opposite behavior. With the increase in θ, H_c increased but S decreased near linearly. We have also investigated the variation of H_c as a function of Ni nanocrystallite’s size. From VSM measurement, we could observe that the coercivities for the magnetic field applied perpendicular and parallel to the film plane increase up to the average size of 86 nm but begin to decrease over this size.     

Temperature and pressure dependence of magnetic and electric hyperfine interactions in metallic Samarium

The magnetic and electric hyperfine interaction at¹¹¹Cd impurities in Samarium has been investigated by TDPAC measurements. The quadrupole frequency is _Q=20.0(2) MHz at 290 K and has a linear temperature dependence with the same slope (dln_Q/dT)_290K=–7.3(2) 10^–4 K^–1 in the rhombohedral and the hcp phase. The pressure dependence up to 7 kbar is (dln _Q/dT)=+8.7(1.4) 10^–3 kbar^–1. The magnetic hyperfine field of¹¹¹Cd in Sm is H_hf=242(6) kG at 4.2 K. Its temperature dependence confirms the existence of 2 different magnetic phases in Sm. The crystal field parameters B ₂ ⁰ and B ₄ ⁰ have been estimated from a comparison of H_hf(T) with molecular field models. The TDPAC spectra in the magnetic phases suggest that the impurities preferentially occupy the hexagonal Sm sites.     

Dispersive optical constants of a-Se100−xSbx films

Thin films of amorphous Se_100−xSb_x (x=5,10 and 20 at%) system are deposited on a silicon substrate at room temperature (300 K) by thermal evaporation technique. The optical constant such as refractive index (n) has been determined by a method based on the envelope curves of the optical transmission spectrum at normal incidence by a Swanpoel method. The oscillator energy (E_o), dispersion energy (E_d) and other parameters have been determined by the Wemple–DiDomenico method. The absorption coefficient (α) has been determined from the reflectivity and transmitivity spectrum in the range 300–2500 nm. The optical-absorption data indicate that the absorption mechanism is a non-direct transition. We found that the optical band gap, E_g^opt, decreases from 1.66±0.01 to 1.35±0.01 eV with increase Sb content.     

Nonlinear Optical Characteristics of BSO and BGO Photorefractive Crystals in Visible and Infrared Ranges

Nonlinear refraction, nonlinear absorption and optical limiting in photorefractive crystals Bi₁₂SiO₂₀(BSO) and Bi₁₂GeO₂₀(BGO) at the wavelengths of 1064 and 532 nm were investigated. It was shown that both BSO and BGO crystals possess by positive nonlinear refraction in two investigated spectral ranges (n ₂ ^BSO=(2.5 ± 0.5)× 10^–12 esu, n ₂ ^BGO=(6.3 ± 1.3)× 10^–12 esu at equals 1064 nm; n ₂ ^BSO=(4.4 plusmn; 0.9)× 10^–12 esu, n ₂ ^BGO=(7.4 ± 1.5)× 10^–12 esu at = 532 nm). The nonlinear absorption was due to three-photon absorption at the wavelength of 1064 nm ( ⁽³⁾ _BSO=(2.5 ± 0.8)× 10^–20cm³W^–2, ⁽³⁾ _BSO=(4.4 ± 1.3)× 10^–20cm³W^–2) and two-photon absorption at the wavelength of 532 nm ( ⁽²⁾ _BSO=(2 ± 0.4)× 10^–9cm W^–1, ⁽²⁾ _BGO=(3.7 ± 0.7)× 10^–9cm W^–1).