Temperature dependent scattering from Cr impurities in Pd

The incremental resistivity Δ?(T) associated with small amounts (between 0.05 and 0.3 at% Cr) of Cr in Pd has been measured between 1.4 and 300 K and has been assumed to contain two principle contributions. The first decreases monotonically with increasing temperature, while the second consists of a rapid increase in Δ?(T) with increasing temperature between 15 and 60 K and has been attributed to conventional deviations from Matthiessen's rule (DMR). With the latter assumed to temperature independent above 70 K, Δ?(T > 70 K) has been fitted to

$\text{Δ?(T) = Ac + Bc 1n(T}{}^2\text{+ T}{}^2{}_{\mathrm{s}}\text{)}{}^{\mathrm{1/2}}$

yielding a concentration independent estimate of T_s ? 44 K. By comparing the experimental data with the extention of the above equation at temperatures below 70 K it is possible to estimate both the conventional DMR and the coefficient of the T² term predicted at low temperatures. While the former are in reasonable agreement with DMR observed in dilute non-magnetic Pd alloys, the T² coefficients measured in Δ?(T ? T_s) differ from their predicted values. Sources for this discrepency are discussed.     

Magnetic properties of CrPd alloys

Magnetic susceptibility, resistivity, and neutron diffraction measurements have been obtained for a series of CrPd alloys containing up to 3 at.% Pd. The Néel temperature variation is irregular for a solute which is to the right of Cr in the periodic table.     

Xenon-beam-induced atomic transport through Cr/Al and Cr2N/Al interfaces

Cr layers (60–75 nm) on Al substrates and Cr₂N layers (40–120 nm) on Al+3 wt.% Mg substrates were irradiated at 80 K and 300 K with 150–900 keV Xe-ions. The ion-beam-induced interface mixing was analyzed by means of Rutherford Backscattering Spectrometry (RBS). Both systems exhibit fairly small mixing rates, with those of Cr/Al being enhanced at 300 K target temperature, due to radiation-enhanced diffusion. The observed interface broadening is compared with predictions of ballistic and thermal spike mixing models. The low-temperature mixing rates in the system Cr/Al are underestimated by the ballistic model, but are rather well reproduced by local spike models. Mixing in the Cr₂N/Al system at both temperatures, on the other hand, seems to be rather well described by the ballistic model.     

Some low temperature properties of PdCr and PtCr alloys: A comparison with PdNi

Values of the low temperature magnetic susceptibility and specific heat of PdCr and PtCr are presented and compared with the data for PdNi. It is concluded that the properties of PdCr and PtCr can be understood in terms of localized spin fluctuations, like in PdNi.     

Effects of heavy impurities on thermodynamic properties of solid hydrogen

The influence of a heavy substitutional impurity on the thermodynamics of the rotational sub-system of solid hydrogen is studied. A splitting of 3°K is found for the rotational level of the orthohydrogen molecule with the heavy impurity as the nearest neighbour on the assumption that the heavy isotopic impurity suppresses short-range dynamic correlations. The contribution of impurity-orthomolecule pairs to the thermodynamics of the rotational sub-system is also studied. The calculated values are in a fair agreement with experiment.     

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.     

Features of the magnetic properties of Pd/Fe/Pd films and nanodisks

The magnetic properties of Pd/Fe/Pd films and nanodisks with diameter 600 nm fabricated by focused ion beam milling were investigated. A fourth-order anisotropy of magnetization reversal in nanodisk arrays was observed during the experiment. It was demonstrated that the anisotropy occurs due both to the breaking of symmetry of dipole-dipole interactions at array boundaries and to the initiation of inhomogeneous configurations of magnetization in nanodisks.     

An estimation of the magnetic disorder at Fe/Cr interfaces in coupled and non-coupled Fe/Cr multilayers

The antiferromagnetic coupling at the Fe/Cr interfaces, inferred from the orientation of the Cr magnetic moments, is used to estimate the magnetic disorder resulting from the interfacial roughness in Fe/Cr multilayers. A crossover from in-plane to out-of-plane orientation of Cr moments depends on the energy cost in either case: (i) to break the interfacial Fe–Cr antiferromagnetic coupling or (ii) having sites with frustrated Cr–Cr antiferromagnetic coupling in the Cr interlayers. A quantitative model of the magnetic frustration due to interfacial disorder in Fe/Cr multilayer systems is described. The step edge density, or terrace size, required to break the interfacial Fe–Cr coupling and destroy the Fe–Fe interlayer exchange coupling is estimated.     

Effects of thermal annealing on structural and magnetic properties of thin Pt/Cr/Co multilayers

Thermal stability of thin Pt/Cr/Co multilayers and the subsequent changes in their structural, magnetic, and magneto-optical properties are reported. We observe CoCrPt ternary alloy phase formation due to annealing at temperatures about 773 K, which is accompanied by enhancement in the coercivity value. In addition, 360° domain wall superimposed on a monodomain like background has been observed in the pristine multilayer, which changes into a multidomain upon annealing at 873 K.     

Effects of Zn impurities on the electronic properties of Pr doped CaTiO3

Microcosmic investigations of weak red-emitting materials are crucial for their further development and application. In this work, we have focused on the band structures and electronic properties of Pr mono- and (Zn, Pr) co-doped CaTiO₃ using density functional theory. Zn substitution for Ca or Ti tends to form clusters energetically with Pr substituting for Ca in CaTiO₃. In Pr mono-doped CaTiO₃, the O_2p→Ti_3d transition in CaTiO₃ host corresponds to the centered 330 nm excitation spectra. The gap states above the valence band of ∼1.30 eV and ∼2.06 eV are hybridized by Pr_4f, O_2p and Ti_3d orbitals. They are mainly due to Pr_4f orbitals in CaTiO₃:Pr. The former gap level is related to red emission at 614 nm due to ¹D₂→³H₄ transition of Pr³⁺ activator. The latter is related to the excitation spectra centered at 380 nm due to the low-lying Pr-to-mental intervalence charge transfer transitions (Pr³⁺-O²⁻-Ti⁴⁺?Pr⁴⁺-O²⁻-Ti³⁺). The band structures of (Zn, Pr) co-doped CaTiO₃ keep the similar gap levels to those in Pr mono-doped CaTiO₃. The incorporation of Zn brings out the two stronger localized gap states, which are hybridized by Pr_4f, O_2p and Ti_3d orbitals, in comparison with those in Pr mono-doped CaTiO₃. Therefore, when Zn impurities are added into Pr doped CaTiO₃, the present calculations visualize the two enhanced levels and the distorted structures around Pr.     

Strain induced epitaxial relationships of Cr on Co/Pd(111)

The growth and structure of Co ultra-thin films on Pd(111) and Cr on Co/Pd(111) have been analyzed by grazing incidence X-ray diffraction and low energy electron diffraction. It is shown that the in-plane lattice constant of the epitaxial Co film depends on the growth temperature. Although the strain decreases as a function of the Co film thickness, it persists for 20 monolayer (ML) films or even thicker. When Cr is deposited at room temperature on a strained Co film (10 to 20 ML thick) a Kurdjumov–Sachs epitaxial relationship is observed, whereas when Cr is deposited on a Co(0001) single-crystal or on a very thick Co film on Pd(111), a Nishyama–Wassermann orientation is obtained.     

Superhard nitride-based nanocomposites: role of interfaces and effect of impurities

Recently, a hardness similar to that of diamond has been reported for a quasiternary, nitride-based nanocomposite. The related, quasibinary nanocomposite "nc-TiN/a-Si3N4," which may be regarded as the prototype of the family of superhard nc-metal-N/a-Si3N4 systems, also exhibits a significant hardness enhancement. Extensive density-functional theory calculations indicate that the superhardness is related to the preferential formation of TiN(111) polar interfaces with a thin beta-Si3N4-derived layer. The strength of TiN in the 111 direction is similar to that of the weakest bonding direction in diamond. Oxygen impurities cause a significant reduction of the interface strength.     

Geometric and magnetic properties of Co/Pd system

We measured geometric and magnetic properties of Co films on the Pd(1 1 1) surface by X-ray photoelectron diffraction (XPD), X-ray magnetic circular dichroism (MCD) at the Co L_2,3 edge, and the surface magneto-optical Kerr effect (SMOKE) measurements. Co thin films are found to grow incoherently with fcc island structure on the smooth Pd(1 1 1) substrate. Comparison of MCD and SMOKE measurements of Co thin films grown on rough and smooth Pd(1 1 1) surfaces suggests that perpendicular remnant magnetization and Co orbital moment are enhanced by the rough interface. Pd capping layer also induces perpendicular orbital moment enhancement. These observations indicate the influence of hybridization between Co 3d and Pd 4d at the interface on the magnetic anisotropy.     

Evidence for local orbital moments on Ni and Co impurities in Pd

The spontaneous magnetoresistance anisotropy has been measured for the ferromagnetic alloys PdNi, PdCo and PdFe. The results confirm the conclusion drawn from other data that in Pd, Ni and Co (but not Fe) possess local orbital moments.     

Effects and mechanism of ultrasonic irradiation on solidification microstructure and mechanical properties of binary TiAl alloys

In spite of their high temperature and reactivity, the binary TiAl alloys are successfully imposed by the ultrasonic irradiation and the microstructure evolution, solidification behaviors and mechanical properties are elaborately investigated. After ultrasonic irradiation, a high quality ingot without shrinkage defects and element segregation is obtained and the coarse dendrite structure is well modified into fine non-dendrite globular grains. The coarse lamellar colony and lamellar space of Ti44Al alloy is refined from 685 μm to 52 μm and 1185 nm to 312 nm, respectively (similarly, 819 μm to 102 μm and 2085 nm to 565 nm for Ti48Al alloy). For Ti48Al alloy, the α peritectic phase is simultaneously precipitated from the melt as well as the β primary phase before the peritectic reaction and the solidification is transformed into the mixed α-solidifying and β-solidifying. Ultrasonic irradiation promotes the peritectic reaction and phase transformation completely and the phase constituent becomes more close to the equilibrium level. The compressive strength of Ti44Al and Ti48Al alloys are increased from 623 MPa to 1250 MPa and 980 MPa to 1295 MPa, respectively. The grain refinement and dendrite transformation enhance the grain boundary sliding improving the plastic deformation ability. Ultrasonic irradiation significantly accelerates the melt flow and solute redistribution and the main grain refinement mechanism is the cavitation-enhanced nucleation by inclusion activation and heightened supercooling.     

The effect of strain and interfaces on the orbital moment in Fe/V superlattices

The dependence of the Fe orbital moment on strain and interfaces in Fe/V superlattices has been investigated by X-ray magnetic circular dichroism (XMCD). The orbital moment was determined to be lower at the interfaces than in the bulk, which we attribute to Fe–V hybridization. An enhancement of the orbital moment with increasing strain in the Fe layers was observed. This enhancement is attributed to an unquenching of the orbital moment. Consequently, the orbital moment of Fe in Fe/V is concluded to be influenced by two competing parameters. It is lowered by increasing interface density, and enhanced by increasing strain.