Strain wave in Cr rich CrFe alloys

Satellite reflections due to the strain wave were observed in Cr rich CrFe alloys by X-ray diffraction. The magnitude of the wave number vector of the strain wave decreases whenever the temperature approaches the ISDW-CSDW transition. From the temperature and concentration dependences of the strain wave and the lattice parameter observed by X-ray diffraction the magnetic phase diagram of CrFe was determined.     

The spin-density waves in thin films of Cr in the Fe/Cr/Sn/Cr multilayers

Magnetism of Fe/Cr/Sn/Cr multilayers have been studied by the first-principles density-functional theory. Calculations by the full-potential linearized augmented plane waves (FP LAPW) and screened Korringa–Kohn–Rostoker (SKKR) methods have shown that two types of solutions may be found in these systems: a high-spin (HS) and a low-spin (LS) ones in accordance with the Cr magnetic moment magnitudes. In this work, we have concentrated our attention on the LS solution. The calculation has shown that the LS solution has a phase slip of antiferromagnetic ordering in Cr and is classified as an incommensurate spin density wave (ISDW). The dependence of the ISDW solution on the thickness of Cr, lattice parameter and boundary conditions has been investigated.     

Electron spin resonance of Cr5+ in TeO2:Cr

A Cr⁵⁺ ion in a substitutional cation site is studied by ESR following a 1.5 MeV electron irradiation of Cr-doped paratellurite (α-TeO₂) at room temperature. The radiation is presumed to generate Cr⁵⁺ by charge transfer from Cr³⁺ ions present in the as-grown crystal. The principal values of g and their eigenvectors are reported for the Cr⁵⁺ impurity ion. A comparison of this g tensor with those reported for nd¹ ions in the more symmetric rutile-like crystal structures is made. Also, a comparison of the g values of Cr⁵⁺ in various host lattices is provided. Hyperfine interactions with the ⁵³Cr isotope and with the ¹²⁵Te isotopes in several neighboring cation sites are detected. However, only the A tensor for the largest ¹²⁵Te hyperfine interaction could be determined completely because of the low Cr concentration. These findings permit the assignment of a possible model for the Cr⁵⁺ ion in paratellurite.     

Superconductivity in amorphous Cr films

Superconducting transition has been observed for the first time in amorphous Cr films prepared by co-sputtering of Cr and BN. Superconducting transition temperatures (Tc) up to 1.14 K have been observed with an orbital contribution (i.e.(dH_c2⊥/dT)_Tc) as large as 49 kOe K^-1. The electronic specific heat coefficient (γ) has been estimated to be about 1.6 times as large as that of amorphous Mo-BN (or Mo-metalloid) alloys. This finding, i.e. the low Tc with the large γ for amorphous Cr is inconsistent with data reported for amorphous alloys of 4d and 5d transition elements. This inconsistency implies a formation of local magnetic moments or spin fluctuation in the amorphous Cr film.     

Gamma-ray spectra and level structure of Cr from thermal neutron capture in Cr

Gamma-ray measurements have been made of the ⁵⁴Cr(n, γ)⁵⁵ Cr reaction at the Livermore reactor. Spectra were taken with Ge(Li) Compton-suppression and pair-coincidence spectrometers. A total of 83 observed γ-rays are attributed to capture in ⁵⁴Cr, of which 26 are assigned to specific transitions among 10 inferred levels in ⁵⁵Cr. The neutron binding energy is determined to be 6246.3 ± 0.4 keV.     

Sub‐ppm determination of Hg and Cr in water: Cr speciation

A sensitive and alternative analytical procedure for the determination of chromium and mercury content in natural waters by coprecipitation with APDC and determination using an absolute thin layer EDXRF method is described. The use of ¹⁰⁹Cd and ²³⁸Pu annular radioisotope sources, the influence of the chromium oxidation states and the elemental concentration were studied. At pH 4, 100% recovery was found for mercury. The coprecipitation of Cr(VI) was not quantitative (75%) but constant for the selected concentration range (5–100 µg/l). On the other hand, Cr(III) did not precipitate at the same pH. The relative standard deviations (RSD) were lower than 9.0% for mercury (10 µg/l) and 5.0% for chromium (50 µg/l). The detection limits (DLs) for mercury and chromium were 0.4 and 0.6 µg/l when the ²³⁸Pu source was employed. Nevertheless, higher DL values were achieved using ¹⁰⁹Cd (0.6 and 3.3 µg/l). The proposed method was applied to the analysis of surface water samples. An alternative and simple chromium speciation procedure without chemical separation of Cr species is recommended. Copyright © 2007 John Wiley & Sons, Ltd.     

First-principles study of spin-density waves in Fe/Cr and V/Cr multilayers

A first-principles electronic structure calculation for Fe/Cr and V/Cr multilayers is performed, and spin-density wave order in the Cr layer is investigated. It is found that for a sufficiently large spacer thickness of the Cr layer the spin-density wave order grows spontaneously and becomes similar to that in bulk Cr in the vicinity of the middle of the Cr layer.     

Fe/Cr and Cu/Cr film pressure-sensitive elements

A pressure-sensitive element based on Fe/Cr or Cu/Cr film composition is described. The role of interdiffusion and phase formation is discussed, and the interface stability is studied.     

High spin states in48Cr

The self-consistent finite Fermi-system theory with three different parameter sets is used to calculate decay energies and Gamow-Teller strength distributions of neutronrich short-lived nuclides near shell closures Z=50, N=82. Among the parameters, the role of a strong surface neutron-proton attraction and an isovector spin-orbit force is discussed. The obtainedβ-decay half-lives are compared with large-scale calculation results and with available experimental data. Some predictions for the ground state properties of other unstable closed-shell nuclei are presented.     

A model of Cr in GaAs

We have developed a model of Cr in GaAs which is consistent with a large body of experimental data. It relies or recent spectroscopic models and on our interpretation of redistribution and electrical data, all of which indicate the existence of Cr complexes. The existence of rapidly diffusing interstitial Cr donors is assumed and justified. The model offers a unified picture of the effects of implantation on the Cr profile. It contains mechanisms for compensation and redistribution, which offer an explanation of the semi-insulating properties of Cr doped GaAs and of the two apparently incompatible classes of diffusion and anneal data. The redistribution depends on how the Cr was incorporated and on the vacancy concentration profiles. A study of representatives of the two classes of redistribution data allows us to estimate a lower limit of interstitial Cr diffusion constant and of the vacancy diffusion lengths in GaAs.     

High-frequency properties of Fe/Cr superlattices with thin Cr layers in the millimeter-wavelength range

Microwave properties of Fe/Cr multilayer nanostructures with thin chromium layers (with thickness t _Cr < 1 nm) are analyzed. Experiments are performed by the method of penetration of microwaves in the frequency range from 26 to 38 GHz. The dependence of the transmission coefficient for microwaves on the constant magnetic field strength exhibits the microwave magnetoresistive effect and magnetic resonance. The resonance spectrum is reconstructed from measurements at various frequencies. The results of microwave measurements are analyzed together with the results of magnetic and magnetoresistive measurements.     

Localization of nonequilibrium current carriers close to Cr ions in ZnSe:Cr single crystals

The photoluminescence (PL) of Cr-doped ZnSe single crystals is investigated in a temperature interval from 83 up to 297 K and in a wavelengths region from 440 up to 2700 nm. The doping was carried out during a high-temperature annealing of ZnSe crystals in CrSe vapors and in chrome chlorides medium. It is revealed that the doping results in an appearance of both luminescence bands located at 0.54, 0.97, and 2.15 μm and edge luminescence bands located at 454, 457, and 460 nm at 83 K. It is shown that the PL bands located at 457 and 460 nm are caused by the radiative recombination with the participation of holes located on hydrogen-like orbits close to Cr⁺ centers, having a binding energy of 99 meV. The excitons bound with centers responsible for the radiation located at 0.54 μm and having a binding energy of 65-68 meV are considered. The energy of a lattice relaxation at recharge of centers responsible for green radiation is estimated and equals 40-170 meV.     

The examination of the Faraday effect and location of the Cr level in Cr doped PbTe

Faraday effect, absorption coefficient and Hall effect have been examined in Cr doped PbTe single crystals. The effective masses of carriers m_F and then values of effective masses at the bottom of conductivity band m_F(0) have been calculated. It is shown that m_F in Cr doped PbTe is comparable with m_F in n-type PbTe not doped with chromium, with the same free carrier concentration, and the relative temperature variation of m_F(0) corresponds to relative variation of Eg. In the absorption spectrum the additional absorption maximum is found at the energy 0.11–0.14 eV. The long-wave side of the peak is shifted towards longer waves as the temperature is increased. Calculation shows that chromium level is located in the conduction band at ΔE = 0.11 eV in the limit T → 0, and is shifted down towards the bottom of the conduction band with a constant rate of $\text{0.8 × 10}{}^{\mathrm{?4}}\text{eV}\text{K}$ within the temperature range of 4.4–300 K and $\text{3.3 × 10}{}^{\mathrm{?4}}\text{eV}\text{K}$ within the temperature range 300–800 K.     

Role of disorder in Mn:GaAs, Cr:GaAs, and Cr:GaN

We present calculations of magnetic exchange interactions and critical temperature T(c) in Ga1-xMnxAs, Ga1-xCrxAs, and Ga1-xCrxN. The local spin-density approximation is combined with a linear-response technique to map the magnetic energy onto a Heisenberg Hamiltonion, but no significant further approximations are made. We show the following: (i) configurational disorder results in large dispersions in the pairwise exchange interactions; (ii) the disorder strongly reduces T(c); (iii) clustering in the magnetic atoms, whose tendency is predicted from total-energy considerations, further reduces T(c), while ordering the dopants on a lattice increases it. With all the factors taken into account, T(c) is reasonably predicted by the local spin-density approximation in Mn:GaAs without the need to invoke compensation by donor impurities.     

Study of the effects of Cr ions on Yb in Cr,Yb:YAG crystal

The absorption and fluorescence spectra of Cr,Yb:YAG crystal were measured. There are two absorption bands at 940 nm and 968 nm although the absorption coefficient is lower than that of the absorption peak of Yb:YAG superimposed in Cr:YAG absorption peak. The emission peak intensity is 4 times lower than that of Yb:YAG, which may be caused by the existence of the ground state absorption of Cr⁴⁺ which quenches the Yb³⁺ emission intensity. Although the emission peak of Cr,Yb:YAG is lower than that of Yb:YAG, there is an advantage of this crystal which combines the saturable absorber and gain medium into one and can be a self-Q switching laser crystal if Cr,Yb:YAG crystal is pumped with high energy power.