Transition from ferro- to ferrimagnetic ordering via Mn-disorder in (Ni,Co)MnGa quaternary Heusler alloy

An inclusive investigation of electronic and magnetic properties of ordered and disordered (Ni,Co)MnGa quaternary Heusler alloy has been undertaken using the density functional theory-based full potential linearized augmented plane wave method within generalized gradient approximation as exchange–correlation potentials. We observe that the increasing Mn concentration in Ni_1?x CoMn_1+x Ga (x = 0, 0.25, 0.50 and 0.75) lowers the ferromagnetic (FM) character of the parent (Ni,Co)MnGa alloy. This change creates two inequivalent Mn sites aligning antiparallel to each other and generates the ferrimagnetic (FiM) ordering in all resultant disordered alloys. Further, this replacement sets off a structural change from Y- to X_a-structure. The highest magnetic moment has been found to be 4.95 μ_B for ordered (Ni,Co)MnGa alloy, whereas it decreases with increase in Mn-concentration for disordered systems. The variation of half-metallicity with increasing Mn concentration is analysed. The stability of FM and FiM state for the present ordered and disordered alloys, respectively, is also examined.     

Effects of Transition Metal (TM = V,Cr, Mn,Fe, Co,and Ni) Elements on Magnetic Mechanism of LiZnP with Decoupled Charge and Spin Doping

The electronic structure and magnetism of a series of 111-type diluted magnetic semiconductors Li(Zn,TM)P (TM = V, Cr, Mn, Fe, Co, and Ni) are investigated on the basis of density functional theory. Our results indicate that V-, Cr-, Mn-, and Fe-doped LiZnP are magnetic while Co- and Ni-doped LiZnP systems show no magnetisms. But all TM-doped LiZnP systems prefer antiferromagnetic behavior by magnetic coupling calculations. In contrast, V/Li- and Cr/Li-codoped LiZnP prefer ferromagnetic ordering, and Mn/Li-, Fe/Li- and Co/Li-codoped LiZnP display antiferromagnetic spin ordering. Hence, Li dopant is very vital for the ferromagnetic formation of Li(Zn,TM)P materials. It is revealed that the magnetic moments come mainly from the TM 3d orbitals. The ferromagnetic coupling between the TM atoms is explained by through-bond spin polarization. Our work demonstrates that the magnetic properties of Li(Zn,TM)P can be mediated by doping different TM atoms. These results may provide theoretical guidance for further experimental research on DMS.     

Effect of transition metal (TM) on the crystallization and the magnetic properties of Fe<Subscript>62</Subscript>Co<Subscript>10</Subscript>Si<Subscript>10</Subscript>B<Subscript>13</Subscript>Nb<Subscript>4</Subscript>TM<Subscript>1 </Subscript>melt-spun ribbons

Crystallization and magnetic behavior of melt-spun Fe₆₂Co₁₀Si₁₀B₁₃Nb₄TM₁ amorphous ribbon where TM = Ni, Cr, V, Pd, Pt, Ti, Ta and Zr were examined. The alloy with Pt as transition metal showed the lowest crystallization temperature of 823 K among the studied alloys. Significant increase in crystallization temperature was observed when the atomic radius of the substituted transition metal was varied from that of Pt. High Curie temperature and high saturation magnetization were recognized for the alloys containing Pd, Pt or Ti. The amorphous alloys except the alloys containing Ti or V showed good soft magnetic properties.     

Mechanical and chemical properties of Ni3Si and Ni3(Si,Ti) alloys multiphased by chromium addition

Abstract

The alloying behaviour and microstructure of Ni–Si–Cr ternary and Ni–Si–Ti–Cr quaternary alloys were first characterised by optical microscopy, X-ray diffraction, and scanning electron microscopy with electron probe analysis. The microstructures of the Ni–Si–Cr ternary alloys consisted of large dispersed Ni₅Si₂ phase and finely precipitated Ni₃Si phase in nickel solid solution, while the Ni–Si–Ti–Cr quaternary alloys consisted of finely precipitated Ni₃(Si,Ti) phase and nickel solid solution. Then, the high temperature mechanical properties, bend strength, and oxidation and corrosion properties of the alloys were investigated. The Ni–Si–Cr ternary alloys showed significant strengthening over a wide range of temperatures, and also large compressive plastic deformation at high temperatures. The strength and fracture toughness at ambient temperatures were correlated with the volume fraction of Ni₅Si₂ phase. The Ni–Si–Ti–Cr quaternary alloys did not show increased yield strength, but exhibited improved tensile ductility and plasticity over a wide range of temperatures. Both Ni–Si–Cr ternary and Ni–Si–Ti–Cr quaternary alloys showed substantially improved oxidation resistance in air at 1173 K, compared with Ni₃Si and Ni₃(Si,Ti) alloys. Also, the Ni–Si–Cr ternary and Ni–Si–Ti–Cr quaternary alloys showed corrosion resistance comparable to that of the Ni₃Si and Ni₃(Si,Ti) alloys.     

Role of alloying elements in microstructures of beta titanium alloys with carbon additions

Abstract

The effect of 0.2 wt-%C on the microstructure of beta titanium alloys Ti-15X(Fe, Cr, Mn, Mo, Ni, Co, Cu, and V) has been studied using scanning and transmission electron microscopy. It has been found that coarse eutectic TiC_x tends to be formed in beta titanium alloys containing Fe, Cr, Mo, and Mn, and relatively finer homogeneous TiC_x is formed in alloys containing V, Ta, Co, Ni, or Cu. The volume fraction of TiC_x in alloys containing Cu, Co, and Ni is much less than that in other beta titanium alloys. The oxygen content of the matrix is lower than that of Ti₂C in Cr or alloys containing Mn and higher than that of Ti₂C in alloys containing Mo or Ni. These observations are discussed in terms of the role of phase diagrams and the effect of atomic radius of alloying elements on the dimension of interstitial sites in the host alloy and the sublattice of TiC_x.     

Study of Electronic Structure,Magnetism, and Half-Metallicity of New Heusler Compounds CsTmO<Subscript>2</Subscript> (Tm = Fe,Co, Ni,and Cu)

The density functional calculations were performed using the full-potential linearized augmented plane wave (FPLAPW) method for new Heusler alloys CsTmO₂ (Tm = Fe, Co, Ni, and Cu). All compounds were stable in FM AlCu₂Mn-type structure. Results revealed that these alloys can be experimentally synthesized according to the calculated cohesive and formation energies. CsTmO₂ (Tm = Fe, Co, Ni, and Cu) alloys in AlCu₂Mn-type and CuHg₂Ti-type structures were half-metallic ferromagnets. The origin of half-metallicity in CsNiO₂ alloy was also discussed. The total magnetic moment of CsTmO₂ (Tm = Fe, Co, Ni, and Cu) alloys in both structures were 3 μ_B per formula unit and obeyed the Slater-Pauling rule (M_tot =?22 ? Z_tot). The relationship between the magnetism and half-metallicity of all compounds and the lattice constants was also studied. The half-metallic character in combined alloys CsTmO₂ (Tm = Fe, Co, Ni, and Cu) improved in comparison with Heusler alloys including transition metals which indicated that they may be good candidates for practical applications in spintronics.     

Formation and microstructure of quasicrystals in suction cast Al‐6 wt.% Mn alloys with additions of nickel and iron elements

The formation and microstructure of quasicrystals in suction cast Al‐6 wt.% Mn‐2 wt.% TM (TM = Ni, Fe) alloys were investigated by transmission electron microscopy, scanning electron microscopy, energy dispersive spectrometry, and X‐ray diffraction. The suction cast Al‐6 wt.% Mn‐2 wt.% Ni alloy consists of a single decagonal phase of Al₅₆Mn₁₁Ni₂, whereas the Al‐6 wt.% Mn alloy with 2 wt.% iron addition comprises a primitive icosahedral phase and a decagonal phase of Al₄₀Mn₇Fe₂. Thus, the addition of nickel or iron favors quasicrystal formation in the suction cast Al‐6 wt.% Mn alloys. Based on a 4 : 1 matching ratio of aluminum atoms to heavier atoms, the approximate electron to atom ratio is 1.85 in two decagonal phases of Al₅₆Mn₁₁Ni₂ and Al₄₀Mn₇Fe₂. Various morphologies of quasicrystals with a size of more than 5 μm were observed in the microstructure of suction cast Al‐6 wt.% Mn‐2 wt.% TM (TM = Ni, Fe) alloys. The decagonal Al₄₀Mn₇Fe₂ phase nucleates epitaxially and grows on the icosahedral phase.     

Resistometric study on kinetics of reversible short-range ordering and crossover effect in Fe15Ni63Si8B14 metallic glass

The kinetics of reversible short-range ordering (SRO) and crossover effect in the fully stabilized Fe₁₅Ni₆₃Si₈B₁₄ metallic glass were examined by measurements of electrical resistivity change. The kinetic parameters for reversible SRO in the narrow temperature range from 240 to 280° C were determined to be 1.93eV for the activation energy, 8.6×10^–16sec for the preexponential factor and 2.3 for the width of the distribution of relaxation times on the assumption of a log-normal distribution. The crossover effect in reversible short-range ordering and disordering was clearly observed.     

Ni8X phases in the systems Ni-V,Ni-V-Nb,and Ni-V-Ta

In nickel-base alloys at the composition Ni₈X, where X may be combinations of V, Nb, and Ta, the ordering reactions have been investigated by employing electrical resistivity and electron diffraction techniques. The critical temperature for the order-disorder reaction is estimated to be 405° C for Ni₈V and is shown to decrease linearly with increasing vanadium content across the pseudo-binary sections Ni₈Nb-Ni₈V and Ni₈Ta-Ni₈V, in agreement with calculations based upon the Bragg-Williams model. A secondary ordering reaction between V and Nb atoms has been observed in nickel-base alloys at the composition Ni₈(V_0.5Nb_0.5).     

Mechanical properties of Ni3(Si,Ti) polycrystals alloyed with substitutional additions

The mechanical properties of the L1₂-type Ni₃(Si, Ti) polycrystals, which were alloyed with 1–2 at% of various transition metals and also doped with boron, were investigated over a wide range of temperatures. The addition of Hf enhanced the levels of yield stress whereas the addition of Cr, Mn and Fe reduced the levels of the yield stress over a wide range of temperatures. Ni₃(Si, Ti) alloyed with Cr, Mn and Fe showed a shallow minimum in the yield stress-temperature curves. This result was correlated with the modification of the micro-cross-slip process by the additives. At low temperatures, the addition of Hf and Nb slightly reduced the elongation, while the addition of Cr, Mn and Fe improved elongation. This elongation behaviour was interpreted as the alloying effect on the intergranular cohesive strength of L1₂ ordered alloys. At high temperatures, the elongation of Ni₃(Si, Ti) alloyed with Hf showed a particularly high value. This elongation behaviour is discussed based on the alloying effect on the competition between dynamic recrystallization and cavitation at grain boundaries. The fracture surfaces exhibited a variety of fracture patterns, depending on temperature and the alloy, and were primarily well correlated with the elongation behaviour. The ductilities of most of the alloys at high temperatures were reduced by the tests in air.     

Effect of Magnetic Transition Metal (TM = V,Cr, and Mn) Dopant on Characteristics of Copper Nitride

Pure and magnetic transition metal (TM = V, Cr, and Mn)-doped copper nitride (Cu₃N) films with a preferred orientation of (100) were successfully prepared by reactive rf magnetron sputtering with an appropriate optical band gap for potential application in solar energy conversion. The incorporation of V or Mn can make the lattice constant smaller while it becomes larger after the inset of Cr into Cu₃N. The calculated equilibrium structural parameters reveal that the unit cell of Cu₃N could expand by inserting TM in the center or Cu vacancy of Cu₃N. The SEM shows boundaries disappeared grains of V-doped sample, small spherical-like grains of Cr-doped sample, and greater glomerate crystal particles of Mn-doped Cu₃N. The band gap becomes minor (1.50 to 1.22 eV) after doping with V or Cr and larger (1.50 to 1.56 eV) for Mn-doped samples, which realized the adjustable optical band gap of Cu₃N films by doping with TM. What is more, TM in the center vacancy of Cu₃N can improve magnetic properties more effectively than that of TM in the Cu vacancy of Cu₃N. And Cr doping in the center gives the biggest magnetic moment of 0.2656 μ _B.     

Amorphous/crystalline Fe55Ni20Cu5P10Si5B5 composite produced by two-component melt–spinning

ABSTRACT

This work presents unique microstructure and thermal properties of the Fe₅₅Ni₂₀Cu₅P₁₀Si₅B₅ alloy produced by novel modification of the melt-spinning method, where two precursor alloys are simultaneously ejected i.e. Fe₄₀Ni₄₀P₁₀Si₅B₅ and Fe₇₀Cu₁₀P₁₀Si₅B₅, forming a composite ribbon. The investigation of melting the precursors by differential scanning calorimetry confirms the liquid miscibility of the Fe₇₀Cu₁₀P₁₀Si₅B₅ alloy. The two-component melt-spun composite obtained from the two alloys is compared to the alloys produced from a homogeneous liquid. The electron microscopy, X-ray diffraction and differential scanning calorimetry show different microstructure of the composite in comparison with the traditionally melt-spun alloys and our results reveal that the composite alloy inherits the thermal properties of the precursors.

This paper is part of a Thematic Issue on The Crystallographic Aspects of Metallic Alloys.     

Formation of metastable solid solutions of boron in nickel under mechanochemical synthesis from Ni-B and Ni-Nb-B mixtures

Using high-energy ball milling of Ni₈₇B₁₃ and Ni_{87 ? x} Nb _x B₁₃ component mixtures (x = 7, 10, 12, 14) for 2 h, nanocrystalline alloys containing fcc solid solutions of Ni〈B〉 and Ni〈Nb,B〉 were obtained. According to the results of X-ray analysis, oversaturated solid solutions of Ni〈B〉 are interstitial solutions; those of Ni〈Nb,B〉 are substitutional solutions or mixed substitutional-interstitial solutions. Upon heating of the alloys, exothermal effects appear on differential scanning calorimetry (DSC) curves; they are attributed to decomposition of metastable solid solutions and to crystallization of the amorphous phase appearing in mechanical alloying. After heating to 720°C, the Ni₈₇B₁₃ alloy contained stable phases of Ni and Ni₃B; the Ni₇₅Nb₁₂B₁₃ alloy contained a τ phase (Ni₂₁Nb₂B₆) and a metastable solid solution of Ni〈Nb〉.     

Crystallization behaviour of Ni-Co-base metallic glasses by isochronal and isothermal annealing

The crystallization behaviour of three amorphous alloys, Co₅₀Ni₂₅Si₁₅B₁₀, Ni₅₀Co₂₅Si₁₅B₁₀ and Ni₅₀Co₂₅P₁₅B₁₀, was studied by means of differential thermal analysis in conjunction with scanning transmission electron microscopy. Isochronal annealing showed a strong dependence of crystallization on scan rate over the range of 1.99 to 20.70 K min^–1. At high Co/Ni ratios, a sequential two-stage crystallization process involving primary MS-I phase followed by MS-II phase precipitation was observed. At low Co/Ni ratios MS-I and MS-II crystallization were concurrent and inseparable. Replacement of the metalloid Si with P as the glass-former dramatically reduced the activation energy for crystallization as well as the crystallization temperature. A mechanistic understanding of these findings was pursued in light of TEM/STEM microanalysis     

First-Principles Study of Structural,Electronic, Magnetic and Half-Metallic Properties of the Heusler Alloys Ti<Subscript>2</Subscript>ZAl (Z = Co,Fe, Mn)

Using the first-principles calculations based on density functional theory within the generalized gradient approximation (GGA), we investigate the structural, electronic and magnetic properties of the Ti₂ZAl (Z = Co, Fe, Mn) alloys with the CuHg₂Ti-type structure. The optimized equilibrium lattice constants were found to be 6.08 Å for Ti₂CoAl, 6.07 Å for Ti₂FeAl and 6.16 Å for Ti₂MnAl. The Ti₂ZAl (Z = Co, Fe, Mn) alloys are found to be half-metallic ferromagnets. The total magnetic moment of Ti₂ZAl (Z = Co, Fe, Mn) is 2, 1 and 0 µ _B, respectively, which is in agreement with the Slater–Pauling rule M _tot=Z _tot- 18. The Ti₂ZAl (Z = Co, Fe, Mn) have a band gap of 0.64745, 0.57795 and 0.39327 eV, respectively.     

Synthesis and structural characterization of nanocrystalline (Ni,Fe)3Al intermetallic compound prepared by mechanical alloying

Synthesis of (Ni, Fe)₃Al intermetallic compound by mechanical alloying (MA) of Ni, Fe and Al elemental powder mixtures with composition Ni₅₀Fe₂₅Al₂₅ was successfully investigated. The effects of Fe-substitution in Ni₃Al alloy on mechanical alloying process and on the final products were investigated. The structural changes of powder particles during mechanical alloying were studied by X-ray diffractometry, scanning electron microscopy and microhardness measurements. At the early stages, mechanical alloying resulted in a Ni (Al, Fe) solid solution with a layered nanocrystalline structure consisting of cold welded Ni, Al and Fe layers. By continued milling, this structure transformed to the disordered (Ni, Fe)₃Al intermetallic compound which increased the degree of L1₂ ordering upon heating. In comparison to Ni–Al system, Ni (Al, Fe) solid solution formed at longer milling times. Meanwhile, the substitution of Fe in Ni₃Al alloy delayed the formation of Ni (Al, Fe) solid solution and (Ni, Fe)₃Al intermetallic compound. The microhardness for (Ni, Fe)₃Al phase produced after 80 h milling was measured to be about 1170HV which is due to formation of nanocrystalline (Ni, Fe)₃Al intermetallic compound.     

On the formation of M2+ -Sb3+ -alkoxide precursors and sol-gel processing of M-Sb oxides with M = Cr,Mn, Fe,Co, Ni,Cu and Zn

Binary alkoxide complexes of compositions close to MSb(OEt)₅, with M = Mn, Fe, Co and Ni, have been prepared and characterized by their i.r. and u.v.-VIS spectra, while Cr, Cu and Zn do not form similar ethoxide complexes with Sb(OEt)₃. The Mn and Fe complexes must be prepared in inert atmosphere as they are very easily oxidized. The Fe complex is metastable and decomposes within a few hours. The Co complex can only be prepared in the presence of acetonitrile. X-ray amorphous gels were formed upon hydrolysis of solutions containing M to Sb species in the ratio 12 for M = Mn, Fe, Co and Ni. The gels consisted of agglomerated particles of sizes from 75 to 300 nm. The decomposition of the gels in air and in nitrogen has been monitored by means of thermogravimetric measurements. Samples of heated gels were quenched from various temperatures in the region 50–950°C, and the formed oxides were characterized by their X-ray powder patterns and by their infrared spectra. At 950 °C MSb₂O₆ was formed in air, while in nitrogen MSb₂O₄ (M = Mn, Co and Ni) was formed at intermediate temperatures. At higher temperatures the latter compound decomposed and Sb₂O₃ sublimated.     

Microstructure and martensitic transformation and mechanical properties of cast Ni rich NiTiCo shape memory alloys

Abstract

The influence of Co additions on the microstructure, second phase precipitates, phase transformation and mechanical properties of cast Ni_51?xTi₄₉Co_x (x?=?0, 0·5, 1·5 and 4 at-%) shape memory alloys was investigated. At the expense of Ni, Co added to NiTi alloy significantly increases the martensitic transformation temperature. The matrix phase in the microstructure of Ni₅₁Ti₄₉Co₀ alloy is the austenite phase (B2) in addition to martensite phase (B19′) and precipitates of NiTi intermetallic compounds. However, the parent phase in the other three alloys, Ni_50·5Ti₄₉Co_0·5, Ni_49·5Ti₄₉Co_1·5 and Ni₄₇Ti₄₉Co₄, is martensite. Ti₂Ni phase was found in the microstructures of the all investigated alloys; however, Ni₃Ti₂ phase precipitated only in the NiTi alloy with 0 at-%Co. The volume fraction of Ti₂Ni phase decreased by the additions of 0·5 and 1·5 at-%Co, while it is slightly increased with 4 at-%Co. The hardness value of NiTi alloy is affected by Co additions.     

Study of Electronic,Mechanical, Magnetic,and Optical Properties of Mg<Subscript>0.75</Subscript>TM<Subscript>0.25</Subscript>S/Se (TM = Fe,Co, Ni): A First Principle Approach

A systematic study of the magnetism, mechanical, and optical behaviors of Mg_0.75TM_0.25S/Se (TM = Fe, Co, Ni) ordered alloys was conducted using the full-potential linearized augmented plane wave plus local orbital method. The ferromagnetic (FM) and antiferromagnetic (AFM) ground state energy differences and enthalpy of formation scrutinized their dynamical stability in the FM state. The elastic parameters decided their mechanical stability, ductile behavior, and partial ionic and covalent characters. Moreover, the calculated band structures and density of states revealed the type and origin of magnetism in terms of exchange splitting energies and exchange constants. The Fe- and Ni-doped MgS/Se alloys exhibited half metallic ferromagnetic (HMF) characteristics, while the Co-doped MgS/Se alloy depicted ferromagnetic semiconducting characters. A reduction in the magnetic moments of the transition metals was observed compared with their free space value, which is due to strong p-d hybridization. Furthermore, the optical spectrum showed the maximum light absorbed in the visible and in the UV region of the electromagnetic spectrum, which makes them potential candidates for optoelectronic and spintronic device applications.     

The sensitization of SrTiO3 photoanodes by doping with various transition metal ions

The influence that various dopants exert on the behaviour of single crystalline SrTiO₃ electrodes in a photoelectrochemical cell for water decomposition has been investigated. The electrodes were surface doped with Sr₃MeNb₂O₉ (Me₂₊ = Mn, Fe, Co, Ni) and LaMeO₃ (Me³⁺ = V, Cr, Mn, Fe, Co, Rh). The results have been compared with those for the sensitization of single crystalline SrTiO₃ photoanodes homogeneously doped with LaCrO₃ or the oxides of the transition metals Cr, Mn, Fe, Co, Ni, Nb, Mo, Ta and W. The response to visible light is greatest for Cr³⁺ and decreases in the sequence Co²⁺, Ni²⁺, Mn²⁺, Rh³⁺. The dopant ions V³⁺, Mn³⁺, Fe²⁺, Fe³⁺, Co³⁺ and the oxides of Nb, Mo, Ta and W reveal hardly any or no photosensitization. This is discussed in terms of a simple model proposed recently by members of our group.