Dilute Cr Alloys Research Articles

Newly developed EMF cell with zirconia solid electrolyte for measurement of low oxygen potentials in liquid Cu-Cr and Cu-Zr alloys

In order to measure the very low oxygen potential by use of stabilized zirconia solid electrolyte emf method, a new cell construction was devised. The idea was based on Janke but a zirconia rod was used instead of the zirconia crucible which contacts liquid alloy electrode. The cell was used for determination of the oxygen potentials in liquid dilute Cu-Cr and Cu-Zr alloys. The reference electrode was Cr,Cr2O3. Emf measurements were performed in the temperature range of 1400-1580K and composition range of 0.198-3.10at%Cr-Cu alloys, and 1380-1465K, 0.085-0.761at%Zr-Cu alloys. The composition of liquid alloys were determined by picking up from the liquid alloys and ICP analysis. By use of the newly devised cell construction in this study, stable emf values were obtained at each temperature and alloy composition. Emf values were corrected by using the parameter for electronic contribution of the YSZ. Activity of Cr obeys Henry?s law and activity coefficient at infinitely dilute alloys of Cr in Cu-Cr alloys are: lng0 Cr =(3.80 at 1423K), (3.57 at 1473K), (3.38 at 1523K) and (3.20 at 1573K). At 1423 K activity coefficient of Zr at infinitely diluted alloy is ln?o Zr = -4.0.

Electronic structure and magnetic properties of dilute Cr alloys with transition-metal impurities

By using full-potential linearized augmented plane wave (FLAPW) method based on the density function theory (DFT), we have performed ab initio calculations of electronic structure and magnetic properties for dilute alloys of Cr with transition metals. Here, we present our results for the local magnetic properties of $3d$ (Sc\char21{}Ni) and $4d$ (Y\char21{}Pd) impurities in Cr, as well as changes in macroscopic properties such as total magnetization and specific heat of Cr alloys, arising from impurity-induced host perturbations. Results obtained for nonmagnetic local density of states is analyzed within Stoner model, and the condition for local moment formation is found to be satisfied only for Fe, Co, and Ni. For all other cases including Mn, the impurity moments are predicted to be induced by Cr host. Systematic trends for the impurity local moments and hyperfine fields in antiferromagnetic Cr host have been established. The trends show remarkable similarity with those observed in ferromagnetic Fe, Co, and Ni hosts. While the impurity moments for Sc, Ti, V, and Mn are found to be antiparallel with respect to the near neighbor Cr moment, self-consistent solutions for Fe, Co, and Ni show ferromagnetic coupling. For $4d$ impurities, except for Rh and Pd, the exchange interaction remain antiferromagnetic. The calculated changes of the total moment due to host perturbations show qualitative agreements with data from magnetization measurements. A detailed comparison is made for the impurity-induced changes in the total density of states at Fermi energy ${E}_{F}$ and experimentally measured electronic specific heat of Cr alloys. The results presented in this work provide comprehensive and improved understanding of electronic and magnetic properties of dilute Cr alloys. They are also useful for a common understanding of local magnetic properties of transition metal impurities in ferromagnetic and antiferromagnetic hosts.

Atomic displacements in dilute alloys of Cr, Nb and Mo

Kanzaki lattice static method is used to calculate the atomic displacements due to substitutional impurities in 3d (Cr) and 4d (Nb, Mo) metals. Wills and Harrison interatomic potential is used to calculate dynamical matrix and the impurity-induced forces up to second nearest neighbors. The calculated atomic displacements for 3d, 4d and 5d impurities in Cr (V, Mn, Fe, Ni, Nb, Mo, Ta and W), Nb (V, Cr, Mn, Fe, Zr, Mo, Ta and W) and Mo (V, Cr, Mn, Fe, Zr, Nb, Ta and W) are tabulated up to 10 NN’s. The strain field due to 3d impurities is least in Cr metal while it is larger in Nb and Mo metals. For 4d and 5d impurities the strain is larger in Cr metal than in Nb and Mo hosts. Similar trend is found for relaxation energies also.

High-pressure ultrasonic properties of spin-density-wave Cr–Re alloy single crystals

The pressure dependence of the elastic constants ( c ij ) of Cr–Re alloy single crystals, containing 0.3 and 0.5 at.% Re, are reported. For 0.3 at.% Re the concentration ( c) is below the triple point concentration ( c t) on the ( c– T) magnetic phase diagram. This crystal therefore remains in the incommensurate (I) spin-density-wave (SDW) antiferromagnetic phase at all temperatures below the ISDW–paramagnetic (P) Néel transition temperature ( T N). The pressure derivatives of the elastic constants, d c ij /d p, were measured for the Cr+0.3 at.% Re crystal as a function of temperature through T N. The Cr+0.5 at.% Re crystal has c> c t and exhibits an incommensurate–commensurate (I–C) SDW phase transition at a temperature T IC< T N on heating. In the case of this crystal d c ij /d p was studied at temperatures close to and above T IC. The acoustic mode Grüneisen parameters ( γ n ), which quantify the lattice vibrational anharmonicity, were calculated as a function of temperature from the d c ij /d p data for each crystal. These calculations indicate much larger coupling of the SDW to the long-wavelength longitudinal phonons than to the shear modes for both Cr–Re crystals. Longitudinal mode softening under applied pressure, due to strong magnetoelastic interactions between the SDW and the longitudinal acoustic phonons, in Cr+0.3 at.% Re at T< T N, gives nearly discontinuously way to extremely large mode stiffening as the crystal is heated through T N. γ n in the CSDW and pressure-induced ISDW phases of the Cr+0.5 at.% Re crystal shows unusual behaviour with temperature. This is particularly so for the shear mode Grüneisen parameters which are relatively large and negative just above T IC, implying significant shear mode softening under applied pressure. γ n (shear) then increases on further increasing the temperature of this crystal. In comparison, γ n (shear) for both the CSDW and pressure-induced ISDW phases of other Cr alloys, with c> c t, for instance Cr–Ru and Cr–Ir alloys, is near zero, slightly positive, and remains constant with temperature. The measurements on the Cr+0.5 at.% Re crystal suggest the existence of a new phase line, separating the ISDW phase present at atmospheric pressure from that induced from the CSDW phase by applying high pressure, on the pressure–temperature magnetic phase diagrams of dilute Cr alloys with c> c t. More experimentation, particularly high pressure neutron diffraction studies, are needed to verify this point.

Sound propagation anomalies and phase diagram of chromium alloys

Calculations of the complex elastic moduli Ĉ(T) in dilute Cr alloys are compared to measurements of the velocity and damping of sound near TN and at high temperatures T>TN (TN — Neel temperature). The thermodynamic calculation is based on the covalent bond model of 3d ions in a state with different numbers n of covalent electrons. The parameters Aij(n) of indirect exchange between the ions of the i and j sublattices are expressed in terms of the covalent bond energy Γij(n). The stability of the charge and spin density waves (CDWs and SDWs) is found by a variational method and is determined by the dispersion of Γij(n) and by the Coulomb parameters Un. For a small structural vector Q the phase diagram contains a superantiferromagnetic phase (SAFM) at temperatures TN TN make it possible to determine the magnetostriction constants λ(T) of Ce alloys in the SAFM phase on the basis of the SAFM theory.

Influence of a magnetic field on the magnetoelasticity of commensurate spin-density-wave Cr–Ru and Cr–Si alloy single crystals

Previously reported attempts to produce a single-Q commensurate (C) spin-density-wave (SDW) state in a dilute Cr alloy by magnetic field cooling through the Néel temperature (TN), were unsuccessful. In the present study the influence of a cooling field of 4.5 T on the magnetoelasticity of Cr+0.3 at.% Ru and Cr+1.6 at.% Si alloy single crystals, both having CSDW phases below TN, are reported. The results show that cooling the Cr+0.3 at.% Ru crystal through TN in a field of 4.5 T has no influence on the first-order commensurate–incommensurate SDW magnetic phase transition. On the other hand, cooling the Cr+1.6 at.% Si crystal in a field of 4.5 T through TN noticeably affects the elasticity in the CSDW state, suggesting a condensation of part of this crystal into a single-Q CSDW phase.

Magnetovolume and magnetoelastic properties of Cr and Cr alloys

Spin-density-wave effects on the magnetoelasticity of Cr and dilute Cr alloys are discussed. Emphasis is placed on the effects of vibrational anharmonicity of each acoustic phonon mode of a Cr alloy and on establishing which acoustic modes interact strongly with the spin-density-wave.

Charge-density wave and magnetic phase diagram of chromium alloys

The magnetic phase diagrams of all dilute Cr alloys can be explained by a simple theoretical model with coupled spin- and charge-density waves and a finite electron reservoir. If the charge-density wave and electron reservoir are sufficiently large, then the paramagnetic to commensurate spin-density wave transition becomes strongly first order, as found in Cr1−xFex and Cr1−xSix alloys. The observed discontinuity of the slope dTN/dx at the triple point and the bending of the configuration interaction phase boundary are also natural consequences of this model.

Orientation dependence of interlayer coupling and interlayer moments in Fe/Cr multilayers

The relationship between indirect exchange coupling and interlayer d-electron magnetic moments is studied using magnetometry and x-ray magnetic circular dichroism (XMCD) in Fe/Cr multilayers. Multilayers are simultaneously prepared with growth axes along different crystallographic orientations to determine the orientation dependence of these properties. We find the Cr moments are antiparallel to the Fe, and that a Cr thickness (${\mathrm{t}}_{\mathrm{Cr}}$) of 1 ML has a moment of \ensuremath{\approx}-0.7${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$, 50% larger than the Cr moment developed in Fe-based dilute Cr alloys. For larger ${\mathrm{t}}_{\mathrm{Cr}}$ the Cr moment decays very quickly with distance from the Fe interface, while the Fe moment remains bulklike at all Cr thicknesses. It is found that for ${\mathrm{t}}_{\mathrm{Cr}}$10 \AA{} there are slight differences in the indirect (oscillatory) exchange coupling between Fe layers depending on crystallographic orientation. Intuitively, one would also expect an orientation dependence to the induced Cr moments, but we find them to be orientation independent. The orientation independence of the Cr moments correlates well with the orientation independent coupling which has been previously observed for ${\mathrm{t}}_{\mathrm{Cr}}$&gt;10 \AA{}.

A high-pressure ultrasonic investigation of the Néel transition in a Cr + 0.07 at.% Ir alloy single crystal

Measurements of the ultrasonic wave velocity, ultrasonic attenuation, thermal expansion and electrical resistivity of a Cr + 0.07 at.% Ir alloy single crystal are reported as functions of temperature through the Néel point. Ultrasonic wave velocities were also measured as a function of temperature at different constant applied pressures and as a function of pressure at different constant temperatures. The pressure derivative of the Néel temperature corresponds closely to that observed for pure Cr and for several other dilute Cr alloys exhibiting a phase transition from an incommensurate spin-density wave to a paramagnetic phase at the Néel point. Hysteresis effects were observed in the temperature and pressure dependences of the ultrasonic wave velocity below the Néel temperature. These effects probably originate from a difference in the antiferromagnetic domain pattern existing in the alloy on cooling or heating through the Néel transition. No firm conclusions could be reached on whether the addition of 0.07 at.% Ir to Cr is enough to drive the first-order Néel transition of Cr

High pressure ultrasonic study of the Néel transition in a Cr + 3.0 at% Al alloy single crystal

The pressure dependence of the commensurate spin density wave to paramagnetic Néel transition temperature ( T N) of a Cr + 3.0 at% Al alloy single crystal is determined from sound velocity measurements. T N varies linearly with pressure giving d T N/d P = −(370 ± 10) K GPa −1. The value of |d T N/d P| for the Cr + 3.0 at% Al alloy single crystal is among the largest recorded values for dilute Cr alloys with a second order CSDW-P phase transition. A value of d T N/d P calculated from bulk modulus and thermal expansion data by using a thermodynamic model, compares well with the directly measured result.

Spin-density-wave antiferromagnetism in chromium alloys

The account given here of the macroscopic and microscopic physical properties of antiferromagnetic (AFM) chromium alloys supplements the previous review of spin-density-wave (SDW) antiferromagnetism in pure Cr. The existence of an incommensurate spin-density wave results from Fermi-surface nesting, which changes with electron concentration as atoms of different valence are introduced into Cr. This gives rise for most impurities to a prototypical composition-temperature ($x\ensuremath{-}T$) magnetic phase diagram, which is described quite well by a model of nesting electron-hole octahedra and electron reservoir, with changes in the amplitude of the spin-density wave and its wave vector corresponding to the changes with impurity concentration of the N\'eel temperature. There are, however, numerous cases of idiosyncratic behavior in the $x\ensuremath{-}T$ phase diagram, some of which appear to correspond to unusual features in the pressure-temperature ($p\ensuremath{-}T$) phase diagram, e.g., in the CrFe, CrAl, and CrSi alloy systems. With these exceptions and a few others, the effect of impurities in the same group of the periodic table is fairly similar, so that this classification is used for the description of both the $x\ensuremath{-}T$ and $p\ensuremath{-}T$ phase diagrams. The properties of the alloy systems for each group of impurities are first summarized in the context of the $x\ensuremath{-}T$ phase diagram. The general features of the various physical properties are then considered: (1) magnetic susceptibility, whose temperature dependence signals the existence of local moments in some cases; (2) transport properties, in particular, electrical resistivity and thermopower, which show characteristic temperature dependence corresponding to the occurrence of spin fluctuations around the N\'eel temperature ${T}_{N}$, and in some cases well into the paramagnetic phase, followed below ${T}_{N}$ by effects due to the electron-hole condensation in the ordered AFM phase, and in some cases at lower temperatures to the formation of local impurity states; and (3) magnetoelastic properties, which show large effects associated with the spin-density wave and with SDW fluctuations in Cr alloys just as in pure Cr. Analysis of magnetic anomalies in the thermal expansion and bulk modulus in terms of magnetic Gr\"uneisen parameters is employed for some Cr alloy systems to describe the large body of experimental data. The empirical correspondence between increasing volume and increasing electron concentration is illustrated for several systems. The study of dilute Cr alloys provides insight into the reason for pure Cr having a weak first-order N\'eel transition, and provides examples of other phase transitions, including the incommensurate-commensurate SDW, the spin-glass, and AFM-superconducting phase transitions. The similarities between the incommensurate SDW fluctuations in Cr and Cr alloys and in the high-temperature superconducting cuprates strongly motivates, in particular, the examination of the inelastic neutron-scattering results. Optical properties provide an interesting picture of the relation between the magnitude of the energy gap at the Fermi surface and the N\'eel temperature, which is quite different in the incommensurate and commensurate SDW alloys. Local probes providing microscopic information about the environment of an impurity are clearly of great potential value in Cr alloy systems. The M\"ossbauer effect has, however, yielded disappointingly little information, but other probes such as perturbed angular correlation and nuclear magnetic resonance have provided interesting results.

High-pressure ultrasonic study of the commensurate-incommensurate spin-density-wave transition in an antiferromagnetic Cr-0.3 at. % Ru alloy single crystal.

A comprehensive experimental study has been made of the elastic and nonlinear acoustic behavior of a dilute Cr alloy as it undergoes a commensurate (C)-incommensurate (I) spin-density-wave transition. Simultaneous measurements of the temperature dependence of ultrasonic wave velocity and attenuation of longitudinal and shear 10-MHz ultrasonic waves propagated along both the [100] and the [110] direction of Cr-0.3 at.% Ru alloy single crystal have been made in the temperature range 200-300 K

Neutron Diffraction Study on the Magnetic Phase Diagram of Cr-Be Alloy

The change in the antiferromagnetic properties of chromium caused by alloying with a small amount of beryllium (less than 6 at.%) was studied br neutron diffraction for powder and single crystal specimens and also by electrical resistivity measurements at temperatures above 80 K. The results indicate that addition of Be causes a decrease of the Néel temperature, spin flip temperature, magnetic moment and the wave vector of the spin density wave. This behavior is quite different from that observed in the dilute Cr alloys containing other species of non-transition elements.

Antiferromagnetism and electrical resistivity of dilute chromium-germanium alloys

Electrical resistivity from 4 to 700 K is reported for dilute Cr alloys containing 0.35, 1.1, 1.4, and 2.2 at.% Ge. The implications of this study for the magnetic phase diagram of Cr-Ge alloys are compared with recent results from thermal expansion measurements by Suzuki, and agree with the existence of a magnetic triple point at \ensuremath{\sim}0.35 at.% Ge. Contrary to the rigid-band hypothesis, Ge acts as an electron donor when substituted into the Cr matrix. We argue that this puzzling result can be understood in terms of virtual impurity levels lying above the Fermi level of Cr. Identical considerations are shown to hold for Si impurities in Cr, and may account for the anomalous residual resistance and pronounced resistivity enhancements seen at the N\'eel temperatures of these alloys.

Neutron diffraction studies of dilute Cr-Re single crystal alloys

Neutron diffraction studies have been performed on five Cr-Re single crystal alloys with a Re content from 0 to 0·8 at. %. It was found that the wave vector of the sinusoidally modulated spin arrangement increases uniformly with temperature and concentration until a critical value of about 0·97. (2π/ a) when it changes abruptly to 2π/ a. This agrees with earlier experiments on Cr-Mn alloys. For dilute Cr alloys there is thus no essential difference between the addition of 5 d-electrons and 3 d-electrons. It was furthermore found that the most dilute alloys undergo a first order transition at the Néel temperature in agreement with earlier observations on pure Cr. Due to experimental difficulties the order of the transition at the Néel temperature cannot be determined unambiguously for the more concentrated alloys.

Hyperfine fields in concentrated FeCr alloys

AbstractMössbauer spectra of alloys in the range Fe–24 at% Cr to Fe–60 at% Cr have been analyzed using an extension to high concentrations of the results for dilute alloys. The decrease in hyperfine field at an Fe nucleus due to the presence of one Cr near or next near neighbor was found to be 7.5%, concentration independent over the range studied, and in excellent accord with the value of 7.6% found for dilute alloys of Cr in Fe. The isomer shift per Cr neighbor was found to be −0.02 mm/s, also independent of concentration and in good agreement with the value of −0.03 mm/s found for dilute alloys. The same parameters gave equally satisfactory fits to the spectra for randomly polarized absorbers and for high field experiments with the absorber magnetization saturated parallel to the direction of γ‐ray propagation.

Magnetic Properties of Dilute Alloys of Cr, Mn, and Ni in4dand5dTransition Metals

Magnetic-susceptibility measurements between 4 and 300\ifmmode^\circ\else\textdegree\fi{}K of dilute magnetic alloys of Cr, Mn, and Ni in various $4d$ and $5d$ transition metals are reported. Mn in Mo and Rh shows a localized magnetic moment with Kondo-type behavior. Below the Kondo temperature ${T}_{K}$, the susceptibility increases, by a term proportional to ($\frac{{T}_{K}}{T}$); faster than the Curie-Weiss law. This logarithmic term seems to be common to all dilute magnetic alloys of $3d$ solutes in transition metals. In addition to a localized moment, Mn causes a large change in the temperature-independent susceptibility of the order of ${10}^{\ensuremath{-}3}$ emu per mole of solute. Similar large changes are also observed for other dilute magnetic alloys. It seems to be quite general that the occurrence of localized moment in dilute alloys is accompanied by a large increase in the temperature-independent susceptibility. These increases are too large to be understood within the present theories of localized magnetic states. Large increases in the temperature-independent susceptibility are also observed for some alloys with no localized moments. For Mn in Re, this increase corresponds to about ${10}^{\ensuremath{-}2}$ emu per mole of solute.

Localized Impurity States in Liquid Metals: Magnetic Susceptibilities of Dilute Alloys of 3d-Transition Metals in Liquid Antimony

The experimental study of magnetic susceptibility of dilute alloys of 3 d -transition metals in liquid antimony is presented. The localized d -electrons of nickel, iron and cobalt atom in liquid antimony are non-magnetic. The temperature dependence of the susceptibility contributed from localized d -electrons of Ni and Co in liquid Sb is positive and that of Fe in liquid Sb is negative. This fact is explained by the Anderson scheme. The dilute alloys of Mn in liquid Sb obey the Curie law. The dilute alloys of Cr in liquid Sb also obey the Curie-Weiss law and their Weiss temperatures are negative.

Antiferromagnetism of Dilute Cr Alloys with Co and Ni

The magnetic properties of single crystals of Cr alloys containing a small amount of Co and Ni have been studied by neutron diffraction and thermal expansion. The alloy with less than 1 at%Co has the same magnetic structure as that of pure Cr. With increasing Co concentration, the Neel temperature decreases, and the wave vector of the S.D.W. increases, while the magnetic moment remains constant. For 2 at%Co-Cr, the commensurable antiferromagnetic structure becomes stable. The Neel temperature slightly increases and the magnetic moment still remains constant. With the further increase of Co concentration, the antiferromagnetic structure tends to be destroyed by Co-Co pairs. The alloys with Ni have been found to show the magnetic behavior as the alloys with impurities which decrease the electron to atom ratio. All of wave vector, Neel temperature and magnetic moment decrease with an increase of Ni concentration.