The impurity resistivity and resistivity minima in AlCr and AlMn alloys

The impurity resistivity of $\text{Al}$Cr between 1.5 and 50°K was determined with a characteristic temperature for the T² variation θ₁=960±40°K. The behaviour of the resistivity minimum both in $\text{Al}$Cr and $\text{Al}$Mn alloys with impurity concentration provides evidence that a T³ phonon resistivity is found also in aluminium with anomalous impurity resistivity.     

Structure relations in the x-ray photoelectron spectra of three chromium compounds

The chemical shift in electron binding energy, magnetic splitting of electron shells, and structures in the valence band are examined for chromium in the 3 + and 6 + oxidation states.The splitting of the Cr 3s energy level is associated with the appearance of a sharp Cr 3d line in the valence band. The relative chemical shift in the Cr 2p_{$\text{3}\text{2}$} line between Cr₂O₃ and K₂Cr₂O₇ is verified in the mixed compound KCr₃O₈ which contains both types of Cr ions, and the structure of this compound is verified by the X-ray photoelectron spectra. The spin-orbit intensity ratio of the 2p doublet of Cr⁶⁺ is 3, instead of the theoretical value of 2, and the spin-orbit splitting is less than for Cr³⁺. In the 3p level of Cr the relative chemical shift is 3.5 eV whereas for the 2p_{$\text{3}\text{2}$} level the shift is only 2.4 eV. The differences in chemical shift and intensity ratio can not be explained.     

Spectrométrie électronique (ESCA) appliquée à la caractérisation de dérivés oxygénés de chrome et de sodium,NaxCryOz.

A series of compounds of chromium and sodium (Na₂CrO₄, Na₃CrO₄, Na₄CrO₄, NaCrO₂) and for comparison Cr₂O₃ and chromium metal were examined by ESCA. The binding energy values for Cr 2p, Cr 3s, Cr 3p levels increase with the oxidation number of chromium for the Na_xCr_yO_z derivatives. The separation, Δ, between Cr 2p $\text{1}\text{2}$ and Cr 2p $\text{3}\text{2}$ increases with the number of unpaired 3d electrons. The splitting of the Cr 3s peak is observed for NaCrO₂ and Cr₂O₃. For the O 1s, Na 2s and Na 2p levels, the binding energies vary little in the series. Chromium is in a tetrahedral environment of oxygens in all the compounds Na_xCrO₄ (x = 2, 3, 4), as shown by IR absorption spectroscopy.     

Superconducting properties of ZnCr and ZnMn alloys

Measurements on the superconducting critical temperature T_c and critical field, H_c, of $\text{Zn}$Cr and $\text{Zn}$Mn alloys, down to 0.037°K are presented.The variation of T_c with increasing concentration depends strongly on T_cp/θ, with θ a characteristic temperature, while effects of H_c are similar to previously studied alloys.     

Surface energy bands observed in photoemission from a (1 × 1)-N structure on Cr (100)

The surface structure obtained on Cr (100) by diffusion of nitrogen from the bulk is studied by angle resolved photoemission. It is found that nitrogen is bonded in an ordered (1 × 1) configuration with a crystallographic point group C_4v. The data display a strongly dispersive two dimensional Bloch character for the N2p derived resonances. For these bands the symmetry at the $\text{Γ}$ point and the dispersion along the $\text{Δ}$ and $\text{Σ}$ lines of the surface Brillouin zone are determined. The results indicate a strong interaction of the nitrogen atoms with the substrate and favor the intersticial fourfold hollow position.     

The surface cation densities of iron oxide-chromium oxide solid solutions

The surface cation densities of Fe_xCr_{2 ? x}O₃ solid solutions were determined for x = 0.5, 1, and 1.5 using Auger Electron Spectroscopy on samples that had been equilibrated in air at 798 or 973 K. Cr(VI) was found to be present on the surface by iodometric titration. The results indicated that the $\text{Cr(VI)}\text{Cr(III)}$ ratio was constant, independent of composition. Compared to the bulk densities, Fe was found to be enriched on the surface for x = 0.5 and 1, but depleted for x = 1.5.     

The 52Cr(t,p)54 reaction at Et = 15 MeV

Using the ⁵²Cr(t, p)⁵⁴Cr reaction at a bombarding energy of 15 MeV, excitation energies have been measured for 30 levels up to E_x = 5.583 MeV in ⁵⁴Cr. Angular distributions were obtained for all but one of these levels; these have been compared with distorted-wave Born approximation (DWBA) calculations to determine the L-transfer (and hence J^π). The measured cross sections have been compared to the predictions of DWBA calculations that use two-neutron transfer amplitudes from a shell-model calculation with the active neutrons restricted to the $\text{(2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{,}\text{If}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{, 2}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}$ orbitals.     

Impurity lattice dynamics of Fe in Cr from precision Mössbauer fraction measurements

Precision 〈x²〉-values and their anharmonicity been measured for ⁵⁷Fe in Cr between 80 K and 600 K. At 294 K. $\text{? = 0.798 ± 0.005}$. A theoretical analysis based upon Cr neutron scattering data yields 0.8 for the impurity/host force constant ratio.     

Mössbauer effect study of charge and spin transfer in Fe-Cr

The influence of temperature and time of annealing on hyperfine fields and isomer shifts has been studied for a range of Fe–Cr alloys containing 1–45 at% Cr. It has been revealed that up to 15at% Cr neither time nor temperature of annealing practically does affect the hyperfine parameters. For more concentrated samples, however, both temperature and time of annealing are important. In particular, the Mössbauer spectrum of Fe–45.5 at% Cr annealed at 700°C for 5 h was a single-line indicating that the sample was paramagnetic. The observed changes of the hyperfine fields and the isomer shifts have been interpreted in terms of a spin and charge trasfer, respectively.Strong linear correlations between the following quantities have been revealed: the hyperfine field H(0,0) and the isomer shift IS(0,0); the average hyperfine field $\text{H}$ and the average isomer shift $\text{IS}$; the average hyperfine field $\text{H}$ and the average number of Cr atoms in the first two coordination spheres, $\text{N}$. It has been calculated from the first two correlations that a) a change of polarization of itinerant s-like electrons of one electron is equivalent to a change of the hyperfine field of 1602 kOe, and b) on average, a unit change of s-like electron polarization is equivalent to 3277 kOe. The two constant are very close to theoretical estimations, which can be found in literature. Correlation between the hyperfine field and the isomer shift led to a conclusion that the substitution of Fe atoms by Cr ones decreases the density of spin-up electrons on average by 0.026 electrons per one Cr atom in a unit cell. These electrons are most likely trapped by Cr atoms, because the hyperfine field at neighbouring Fe nuclei decreases and the density of charge at those nuclei increases at the rate of 0.029 electrons per one Cr atom in a unit cell.Based on the results obtained, a formula describing the dependence of the average hyperfine field on Cr contents and on the heat treatment has been postulated for Fe–Cr alloys.     

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.     

Hall effect in dilute magnetic alloys

We review the theory and the experimental results on the Hall effect in noble metals containing magnetic impurities of transition metals. In order to illustrate the various types of observed effects, we focus succesively on selected systems: $\text{Cu}$Mn, with only enhancement of the ordinary Hall effect due to the existance of different spin-up and spin-down currents; $\text{Au}$Fe and $\text{Au}$Cr, with skew scattering by magnetic impurities; $\text{Cu}$MnT ternary alloys (where T is a non-magnetic impurity), with skew scattering effects due to combined spin—orbit scattering by non-magnetic impurities and spin scattering by Mn impurities. The skew scattering in $\text{Au}$Fe and $\text{Au}$Cr can be ascribed to the orbital character of the impurity moments and accounted for in an orbitally degenerate virtual bound state model. However, the anomalous temperature dependence of the skew scattering in Kondo alloys at low temperature is not well understood. We also present some magnetoresistance data in order to describe the links between the Hall effect and the magnetoresistance in magnetic alloys. In particular, we relate the skew scattering and the magnetoresistance anisotropy observed in $\text{Au}$Cr alloys.     

Estimates of the s-d interaction in CdCr from superconducting transition temperature and magnetic susceptibility

Cr has a well developed magnetic moment in a Cd host and the superconducting transition temperature, T_c, is strongly depressed. We estimate a spin, S = 1.5 leading to a depression rate - $\text{dT}{}_{\mathrm{c}}\text{dc}\text{= 140 K/at.\%}$. The s-d interaction strength is estimated to 0.5–0.7 eV leading to a Kondo temperature in the milliKelvin range.     

Diffusion of 51Cr in Cr-doped MgO

An arc fusion technique was used to grow single crystals of MgO and Cr-doped MgO. Diffusion coefficients for ⁵¹Cr in Cr-doped single crystals were measured at three temperatures 1383, 1444 and 1495°C using a high specific activity isotope ⁵¹Cr. An approximately linear relationship between the concentration of Cr-ions in MgO and diffusion coefficients of ⁵¹Cr was obtained.It is shown that the activation energy of 19.6 $\text{kcal}\text{mole}$ obtained for the doped crystals is the difference between the energy for motion and the energy for association of the Cr-vacancy complexes. Using a previously determined value of 39.9 kcal/mol for the energy of motion, the energy of association for the Cr-vacancy complex is calculated to 20.3 ± 3 kcal/mol or 0.88 ± 0.13 eV.     

Resonance neutron capture in 52Cr

Neutron capture γ-ray measurements have been performed upon a natural sample of Cr. Twenty-six γ-rays were observed from the 1626 eV resonance of the ⁵²Cr(n, γ)⁵³Cr reaction, and twenty-four of them were assigned to a level scheme. A value of $\text{3}\text{2}$^? was determined for the spin-parity of this resonance. The neutron separation energy, derived from a separate thermal measurement with an enriched (99.9 %) ⁵²Cr sample was determined to be 7939.1 ± 0.2 keV. The high (n, γ) (d, p) correlation found for thermal capture is absent for the p-resonance, however the γ-ray intensities from thermal and resonance capture are correlated, with r = 0.86_?0.11^+0.06.     

The susceptibility maximum in paramagnetic α-Mn and its dilute alloys

The magnetic susceptibility was measured in paramagnetic $\text{α-Mn}$, dilute $\text{α-Mn}$ V, $\text{α-Mn}$ Cr, $\text{α-Mn}$ Fe and α-Mn Co alloys. The susceptibility maximum phenomena in these alloys were found to vary systematically with impurity atoms.     

Electromagnetic properties of levels in 55Mn

Excited levels of ⁵⁵Mn were produced by the reaction ⁵²Cr(α, p) at 10.5 and 11.1 MeV beam energy. A series of γ-ray measurements was made, all in coincidence with protons detected near 180°. A Ge(Li) γ-ray detector was used at 4 angles, and extensive angular-correlation measurements were made with an array of NaI(Tl) detectors. Excitation energies of 25 levels up to 3161 keV were determined, including a new level at 2215 keV. Only the level at 2285 keV and the $\text{1}\text{2}{}^{\mathrm{?}}$ state near 1290 keV were not observed in this range. From Doppler-shift attenuations, the mean lifetimes of 14 levels up to 2565 keV were deduced. Branching ratios and multipole mixing ratios were obtained for most of these levels. The following spin assignments were determined: 1530 keV, $\text{J =}\text{3}\text{2}$; 1885 keV, $\text{J =}\text{7}\text{2}$ or $\text{5}\text{2}$; 2565 keV, $\text{J =}\text{3}\text{2}$. Reduced transition probabilities, B (M1) and B (E2), of many transitions were calculated from these experimental results and are compared with the available theoretical values.     

On the magnetic properties of transition metal substituted MnAs

The properties of Mn_1?tT_t As phases (T: V, Cr, Fe or Co; 0<t$\text{\$}\text{?}$= 0.10) are studied in external magnetic fields up to 250 kOe, and temperatures between 80 and 400 K. The results are presented and discussed in terms of phase diagrams comprising concentration, temperature, and magnetic field axes.     

Interpretation of 3p-core-excitation spectra in Cr,Mn, Fe,Co, and Ni

Recent measurements of the 3p-core-excitation spectra of Cr, Mn, Fe, Co, and Ni are interpreted with an atomic model. The dispersion like line shape observed in these metals is attributed to the interference of 3p⁶3d^N → 3p⁵3d^N+1, which decays to 3p⁶3d^N?1?f via a super Coster-Kronig transition, with the direct excitation of 3p⁶3d^N → 3p⁶3d^N?1?f. The overall width of the line and some weaker features associated with it are related to the multiplet splittings of 3p⁵3d^N+1. The more symmetric line shape found for Cr, which is thought to be due to the absence of a large local moment, is explained in terms of the greater number of multiplets that contribute for a small moment ($\text{S=}\text{1}\text{2}$) as compared to a large moment ($\text{S=}\text{5}\text{2}$).     

Nuclear spin-lattice relaxation of dilute V,Cr and Mn in iron at very low temperatures

We report determinations of the spin-lattice relaxation rates of dilute ⁴⁸V, ⁵¹Cr and ⁵⁴Mn nuclei in polycrystalline Fe host at very low temperatures. The high-field limiting rates for $\text{FeV}$ and $\text{FeMn}$ agree well with earlier spin-echo results. The rate for $\text{Fe}$Cr fits the systematics and is in agreement with a recent ab initio calculation. A dependence of the relaxation rates on applied magnetic field was observed, similar to that seen for other impurity nuclei in Fe.     

High resolution proton inelastic scattering from 50Cr

Resonances in the ⁵⁰Cr(p, p′γ) reaction were investigated with the TUNL high resolution system. All previously observed p-wave resonances between Ep = 2.00 and 3.03 MeV were studied. Measurement of the p' and the γ-ray angular distributions provides sufficient information to determine unambiguously the J-value of the resonance and the magnitude and relative phase of the inelastic decay amplitudes. Expressions are given for the appropriate angular distributions and for the transformation between the channel spin and the total angular momentum representation. Experimental results are presented for 24 p-wave resonances in ⁵¹Mn including decay amplitudes and relative phases for $\text{16}\text{3}\text{2}{}^{\mathrm{?}}$ resonances. Six resonances formerly assigned $\text{1}\text{2}{}^{\mathrm{?}}$ are reassigned $\text{3}\text{2}{}^{\mathrm{?}}$. Inelastic spectroscopic factors were determined for two analogue states. Proton strength functions were evaluated from both the elastic and inelastic data.