xGax Alloys Research Articles

Multifaceted investigation into the impact of Ga substitution for Al in V[formula omitted]MnAl inverse Heusler alloys

This study investigates the impact of Ga substitution for Al in V2MnAl inverse Heusler alloys, focusing on lattice parameter variations. Despite similar valence electrons, Ga’s distinct size and surface energy prompt questions about its role in alloy characteristics. Experimental synthesis of V2Mn1Al1−xGax alloys (x = 0 to 0.60) reveals crystal parameter changes. Theoretical exploration using density functional theory (DFT) probes how Ga doping at the Al site influences the density of states, altering the half-metallic properties of V2MnAl. Additionally, machine learning, with a dataset of 391 entries, predicts lattice constants based on atomic properties, enhancing our ability to maneuver material characteristics. This multifaceted approach aims to deepen our understanding of Ga’s impact on Heusler alloys, bridging experimental and theoretical realms for comprehensive insights into materials design and behavior.

Magnetostructural Transition and Magnetocaloric Effect with Negligible Magnetic Hysteresis in MnCoGe1.02−xGax Alloys

The behavior of magnetostructural transition and the magnetocaloric effect in the MnCoGe1.02−xGax (x = 0, 0.02, 0.04, 0.06) alloys are investigated in this study. The addition of Ga changes the crystal structure of MnCoGe1.02−xGax alloys at room temperature and reduces the phase transition temperatures with increasing Ga content. The coupling of magnetostructural transition and negligible magnetic hysteresis is observed in the Mn-Co-Ge-Ga alloy. At 305 K, under the action of a 5 T magnetic field, the MnCoGeGa0.02 alloy exhibits 23.47 J/kg∙K magnetic entropy change, and its refrigeration capacity reaches 387 J/kg. The large magnetic entropy change near room temperature and the high refrigeration capacity in the Mn-Co-Ge-Ga alloy make it a promising new type of refrigeration material.

Twinning‐induced large tensile strains in directionally-solidified Fe100−xGax oligocrystals

Fe100−xGax alloys require highly textured samples for optimal magnetostrictive performance, which is often accomplished through directional solidification. In this study, we measure the mechanical properties of commercial Fe81.6Ga18.4 oligocrystals using sub-sized tensile specimens and digital image correlation (DIC). While many samples fractured around 360 MPa (the literature yield/tensile stress), most had discontinuous yielding as low as 186 MPa. Many of the samples also exhibited surprisingly large tensile strains, up to 5%, with substantial specimen-to-specimen variability. In all specimens, DIC showed high strain bands that develop at very defined angles, in agreement with electron back-scattered diffraction, which revealed significant deformation twinning.

Comparative investigation of linear and nonlinear optical properties of As–70 at% Te thin films: influence of Ga content

Thin films (~ 150 nm) of amorphous As30Te70−xGax (where x = 0, 1, 3, 6, and 10 at%) are prepared through thermal evaporation of As30Te70−xGax bulk samples on glass substrates. X-ray powder diffraction (XRD) analysis reveals the amorphous nature of the as-prepared As30Te70−xGax thin films. The influence of Ga content on the As30Te70−xGax thin films’ linear and nonlinear optical properties is determined based on the optical reflectance and transmittance spectra. The estimated (direct or indirect) optical bandgap decreases with an increase in Ga content up to 3 at% and then increases, whereas the Urbach energy exhibits an opposite trend. The linear and nonlinear refractive indices, extension coefficient, optical conductivity, electrical conductivity and nonlinear susceptibility, optical density, inter-band transition strength, etc., are found to be significantly influenced by Ga content and the energy of incident waves. The As30Te67Ga3 composition can be considered as a puzzling compound as most of the investigated parameters in As30Te70−xGax alloys demonstrate opposite behaviors around that composition. Moreover, the optical surface resistance and thermal emission of As30Te70−xGax thin films are estimated from the investigated optical parameters and it was found that they are dependent on Ga content. The obtained results enhanced basic understanding and showed that the As–Te–Ga system qualifies for various optoelectronic applications.

Martensitic transformation and shape memory effect in Pd50Mn50−xGax alloys

Martensitic transformation behaviors, microstructures, magnetic properties, and the shape memory effect (SME) were investigated for Pd50Mn50−xGax (0≦x≦25) alloys. Samples were prepared by arc melting, and they were found to have a single phase after solution heat treatments at 1473 K for 3 days followed by quenching. Though the martensitic transformation temperature for equiatomic Pd50Mn50 binary alloy being as high as about 1000 K, it drastically decreases upon doping with Ga, which is similar to Ni50Mn50−xGax alloys. The Pd50Mn25Ga25 alloy with B2 structure was found to be antiferromagnetic with Néel temperature of 198 K. A magnetic phase diagram was constructed and compared with those for Ni–Mn–Ga, Pd–Mn–Sn, and Ni–Mn–Sn alloys. The crystal structures of the martensite phase were investigated using an X-ray diffractometer and a transmission electron microscope. From these investigations, one of the long-period stacking-ordered structures, 14 M, was found at room temperature in the Pd50Mn35Ga15 alloy. SMEs were investigated for polycrystalline Pd50Mn35Ga15 and Pd50Mn40Ga10 samples by compression tests, and an SME up to 3.47% was observed for the Pd50Mn35Ga15 sample. This is the first observation of SME for Pd–Mn-based alloys.

Ab initio calculations of temperature-dependent magnetostriction of Fe and A2Fe1−xGax within the disordered local moment picture

The fully relativistic disordered local moment (DLM) theory is used to perform calculations of the magnetic torque of tetragonally distorted Fe and fully disordered (A2) Fe1−xGax (0≤x≤0.2) alloys to describe the temperature-dependence of their magnetoelasticity. The finite temperature magnetoelasticity, in particular the magnetoelastic constant B1, is obtained within DLM theory by studying the response of the magnetic torque generated by the magnetocrystalline anisotropy to the application of a tetragonal strain. Calculations of B1 have been performed on bcc Fe across its ferromagnetic temperature range. Our results show good qualitative agreement with experiment, in particular reproducing the anomalous, non-monotonic thermal behavior of bcc Fe’s magnetostriction, which has been largely unexplained for more than 50 years. The method has also been used to calculate the finite temperature magnetoelasticity of the A2 phase of Fe1−xGax alloys as a starting point for further investigations into the giant magnetostriction of Galfenol alloys. Our calculations show that homogeneously doping bcc Fe with Ga does not produce an enhancement in magnetostriction and that the non-monotonic temperature dependence and significant volume dependence are suppressed by increasing Ga content.

Magnetic phase diagram, magnetocaloric effect, and exchange bias in Ni43Mn46Sn11−xGax Heusler alloys

Abstract In this work, the effect of Ga substitution on the crystal structure, phase transitions, magnetocaloric effect, and exchange bias properties, was systematically investigated in Ni43Mn46Sn11−xGax alloys. With increasing Ga content, the Curie temperature of austenite slightly decreases, while the martensitic transformation temperature shifts to a higher temperature and finally disappears, due to the emergence of γ phase. Large low-field magnetic entropy changes around the martensitic transformation were observed as the transition from a paramagnetic martensitic phase to a ferromagnetic austenitic phase took place. Ni43Mn46Sn11 has a reentrant-spin-glass ground state, and Ga doping can enhance the antiferromagnetic interaction arising from lattice contraction, leading to close of intermediate ferromagnetic windows and establishment of canonical spin-glass for x > 2. Prominently, the zero-field-cooled exchange was achieved in the spin-glass region with 5 ⩽ x ⩽ 10 .

Thermoelectric properties of Heusler-type Ru2VAl1−xGax alloys

Electrical and thermal transport properties of the Heusler-type alloys, Ru2VAl1−xGax (x = 0.0–1.0) were studied by means of the electrical resistivity, Seebeck coefficient, and thermal conductivity measurements. All studied compounds show weak metallic characteristics with a low residual resistivity ratio. In addition, the Ru2VAl1−xGax alloys with x ≤ 0.75 show an n-type thermoelectric conduction from 10 to 300 K, while Ru2VGa displays p-type conduction. The estimated Fermi energy of these materials is higher than 0.5 eV, endorsing their metallic character. From the thermal conductivity study, we noticed that low-temperature thermal conductivity decreases with increasing Ga content for x ≤ 0.5 and then increases with further Ga substitution. This observation is essentially due to the change in the phonon scattering processes as a result of the substitution of heavier Ga atoms into the Al sites of Ru2VAl. It is important that an enhanced thermoelectric figure of merit ZT was found in Ru2VAl0.25Ga0.75, about seven times higher than that in Ru2VAl.

Alloying effects of Ga on the Co-V-Si high-temperature shape memory alloys

Co64V15Si21−xGax (x=4, 6, 8, 10) alloys have been prepared to investigate the alloying effects of Ga on various properties of Co-V-Si high-temperature shape memory alloys, including crystal structure, transformation behavior, thermal cycle stability, microstructure evolution, mechanical property and shape memory behavior. Results show that the D022-type martensite single-phase is transformed from the L21-type parent phase in Co64V15Si17Ga4 alloys. With the increase of Ga content, R phase appears along grain boundaries of martensite and martensitic transformation temperatures decrease rapidly. Furthermore, the Co64V15Si17Ga4 alloy exhibits excellent thermal cycle stability and stable microstructure even after heated to high temperatures of ~800°C repeatedly. On the other hand, for the (martensite+R) dual-phase alloys (i.e., Co64V15Si15Ga6, Co64V15Si13Ga8 and Co64V15Si11Ga10), (εCo) phase precipitates during thermal cycle process, with respective thermal cycle stabilities enhanced at different temperatures simultaneously. In addition, although excess Ga addition deteriorates the mechanical property significantly, it is still concluded that the doping of Ga has a positive effect on the development of shape memory effect of Co-V-Si high-temperature shape memory alloys.

Magnetostrictive iron gallium thin films grown onto antiferromagnetic manganese nitride: Structure and magnetism

We report structural and magnetic properties of magnetostrictive Fe100−xGax (x ≈ 15) alloys when deposited onto antiferromagnetic manganese nitride and non-magnetic magnesium oxide substrates. From X-ray diffraction measurements, we find that the FeGa films are single crystalline. Scanning tunneling microscopy imaging reveals that the surface morphologies are dictated by the growth temperature, composition, and substrate. The magnetic properties can be tailored by the substrate, as found by magnetic force microscopy imaging and vibrating sample magnetometry measurements. In addition to pronounced tetragonal deformations, depositing FeGa onto manganese nitride leads to the formation of stripe-like magnetic domain patterns and to the appearance of perpendicular magnetic anisotropy.

Effect of annealing on the devitrification behavior and mechanical properties of rapidly quenched Ce-based glassy alloys

This study deals with the effect of controlled crystallization of melt spun Ce75Al25−xGax (x=0, 2, 4 and 6at.%) and Ce60Cu25Al15−xGax (x=0, 1, 2 and 4at.%) metallic glasses on the formation of nano-composites. It has been found that the substitution of Ga significantly affects the devitrification behavior of these alloys. The Ce75Al25−xGax alloys with x=0 shows the formation of hexagonal phase (AlCe3 type) while the alloys with x≥2 give rise to the formation of tetragonal phase (Al2CeGa2 type). Contrary to this, for the Ce60Cu25Al15−xGax alloys, hexagonal phase of AlCeCu type for x=0 transforms to hexagonal phase of Al2Cu3Ce type for x≥1. The indentation behavior of nano-composites permitted us to understand the nature of microhardness, yield strength and strain hardening constant. They are compared for the above two alloy systems. The load dependent hardness values of annealed ribbons of Ce75Al19Ga6 and Ce60Cu25Al13Ga2 alloys have been found to be ~2.80GPa and ~2.96GPa, respectively. The absence of cracks around the indentation area up to 200g of load for Ce60Cu25Al15−xGax alloys suggests better capability to resist crack propagation in comparison to Ce75Al25−xGax alloys. Latter display cracks at 200g load. The formation of shear bands around the periphery of the indenter has been observed. The number of visible shear bands in a given area for the Ce75Al25−xGax alloys is higher in comparison to those of Ce60Cu25Al15−xGax alloys. The values of yield strength and Meyer exponent of these alloys are also compared.

Formation of nano-amorphous domains in Ce75Al25 − xGax alloys with delocalization of cerium 4f electrons

The formation of nano-amorphous domains in melt spun ribbons of Ce75Al25 − xGax alloys with x = 0, 0.01, 0.1, 0.5 and 1 is reported. For x = 0, a homogenous metallic glass feature is observed. Ga substitution has led to phase separation giving rise to nano-amorphous domains in a glassy matrix. The rationale of phase separation could not be explained in terms of enthalpy of mixing of the three possible binaries in this system. The Ce L3-edge XAS spectra of melt-spun ribbons for x = 0, 0.5 and 4 have shown appearance of 4f0 delocalized states in Ga substituted alloy. Such a substitution has led to shortening of Ce–Ce distance in the alloys owing to chemical pressure. This work, therefore, opens up new direction of research for delineating issues pertaining to phase separation in amorphous systems.

Magnetic properties of the selected phases from the Eu–Ag–Al and Eu–Ag–Ga systems

Magnetic properties are presented for the Eu2Ag15−xAl2+x (x = 1.92 and 2.51), Eu3Ag13–xAl8+x (x = 0.64), EuAg6+xAl7–x (x = 0.46), EuAg5–xAlx (x = 0.5 and 1.5), EuAg15–xGa2+x (x = 1.4 and 2) and EuAg5–xGax (x = 0.5 and 1) alloys. In all investigated compounds a divalent state of Eu ions was deduced from the results obtained for temperature dependencies of their magnetic susceptibilities, as well as the results derived for their field dependencies of isothermal magnetizations recorded at 1.9 K. At low fields, and low temperatures, magnetic phase transitions to magnetically ordered states occur for all compounds under study except of EuAg6.46Al6.54, which stays in the paramagnetic state down to 1.9 K. Six compounds orders antiferromagnetically while further three reveal ferrimagnetic–like ordering with uncompensated net moments.

Giant magnetocaloric effect in MnCoGe with minimal Ga substitution

The effects of Ga-doping on the phase transition behaviors and magnetocaloric properties of MnCoGe alloys are systematically investigated through calorimetry and magnetic measurements. The magneto-structural coupling between the structural and magnetic transitions is achieved in the MnCoGe1–xGax alloys by decreasing the structural transition temperature via Ga substitution. An 80K Curie-temperature window is established between Curie temperatures of austenite and martensite phases. Within the window, a magnetic entropy change of 34Jkg−1K−1 can be obtained near room temperature under the application of a 5T magnetic field.

Ab-initio study of structural, electronic, elastic and mechanical properties of RuAl1−xGax (x=0, 0.25, 0.50, 0.75 and 1)

We have used special quasirandom structure to study the structural, electronic, elastic and mechanical properties of RuAl1−xGax alloys for different compositions (x=0, 0.25, 0.50, 0.75 and 1) using a FP-LAPW method based on Density Functional Theory. The exchange and correlation potential is treated within the generalized gradient approximation. Ground state properties such as lattice constant (a0), bulk modulus (B), its pressure derivative (B′) and elastic constants are calculated. The ductility of these alloys has been analyzed by calculating the ratio of B/GH, Cauchy pressure (C12–C44) and Frantsevich rule. From this study RuAl and RuGa are found to be brittle, but their alloys show ductile behavior; RuAl0.50Ga0.50 is found to be most ductile. Mechanical properties such as Poisson's ratio (σ), Young's moduli (E), and the ratio of elastic anisotropy factor (A) are estimated. We have also correlated the ductility and bonding behavior of these alloys.

Growth and characterization of Fe1−xGax thin films from citrate-based electrolytes

In this work we report on the growth of Fe1−xGax films by means of the electrodeposition technique in baths containing sodium citrate as an antioxidant agent. We have investigated the effect of the electrolyte composition in terms of its Ga content on the structural and magnetic properties. Our experimental results indicate that for the optimized bath composition, O-free Fe1−xGax alloys can be achieved for a potential of E = −1.4 V and magnetic stirring at 500 rpm. Both the composition and the coercivity of the samples deposited from this electrolyte can be tuned by means of the duration of the rest pulse at E = −1.12 V. However, when the composition of the bath is not optimized the films exhibit a large amount of O that cannot be dissolved during the rest pulse. Our experimental results show that O-free Fe1−xGax alloys with a Ga content of around 19 at% and optimum magnetic properties can be deposited on Au substrates when using an optimized electrolyte and long rest pulses.

Strain-induced polarity switching of magnetic vortex in Fe1−xGax alloys with different compositions

The strain-induced polarity switching of magnetic vortex in the Fe1−xGax nanodots with different compositions is demonstrated by a real-space phase-field model, which explicitly includes the cross-coupling between magnetization and mechanical strain. The composition of Fe1−xGax nanodots has significant influence on the critical shear strain that induces the polarity switching of magnetization vortex. The critical shear strain in the Fe71Ga29 nanodot is one order of magnitude smaller than that of the Fe19Ga81 nanodot, which makes the polarity switching much easier under a mechanical shear strain. In addition, we elucidate that both the magnetostrictive coefficient and exchange stiffness that changes with compositions play the decisive role in the critical behavior; the higher magnetostrictive coefficient (or lower exchange stiffness) decreases critical shear strain.

Intrinsic Nanoscience of δ Pu–Ga Alloys: Local Structure and Speciation, Collective Behavior, Nanoscale Heterogeneity, and Aging Mechanisms

δ Pu–Ga alloys and their response to self-irradiation are important scientifically because of the unique complexity of Pu and technologically because of their importance in Science Based Stockpile Stewardship. The local order and structure and the role of the Ga are crucial to understanding the phase stability and the aging effects. X-ray diffraction that gives the long-range average structure of the periodic component of the materials and pair distribution functions analysis and X-ray absorption fine structure that give the overall and the element specific local structure have been used to examine a variety of new and aged materials, including a set of high purity δ Pu1–xGax alloys with 1.7 ≤ x ≤ 6.4 atom % Ga that span the low [Ga] portion of the δ region of the phase diagram across the ∼3.3 atom % Ga metastability boundary, a ∼1.7 atom % Ga alloy that was enriched with Pu238 to accelerate the aging process, and others. We find that metastable alloys contain tens of percents of a novel, “σ”, Pu structure that we attribute to rearrangement of the Ga-depleted regions after the self-organization of the Ga to form quasi-intermetallic Pu25–35Ga. This collective and cooperative behavior involving the Ga and other defects in terms of a tendency to aggregate into domains with structures that differ from the δ host and the resulting nanoscale heterogeneity also appears to play an important role in the observation of analogous locally ordered structures in aged materials. This description of these materials and their aging is radically different from current conceptual basis derived from other experiments that are insensitive to ordering on the angstrom–nanometer length scale.

Near room-temperature magnetocaloric properties of Gd–Ga alloys

The magnetocaloric properties of Gd–Ga alloys were examined with the aim to explore their potential application as magnetic refrigerants near room-temperature. A series of Gd100−xGax (x=0, 5, 10, 15, and 20at%) alloys were prepared by conventional melting and rapid solidification. Both as-cast and melt-spun alloys are comprised of α-Gd and Gd5Ga3 with differing microstructural characteristics. While the as-cast alloys have proeutectic α-Ga and eutectic α-Ga+Gd5Ga3 (grain size ~50–100µm), the melt-spun alloys have nanostructured (~50–100nm) α-Ga and Gd5Ga3. The Curie temperature (TC) derived from M–T curves indicates that alloying of Ga with Gd decreases TC. The decrease in TC for melt-spun alloys is gradual—~0.5K per at% of Ga, and the as-cast alloys (5≤x≤20) have similar TC (~286K). The saturation magnetization (MS) derived from M–H curves (260K), show that alloying of Ga with Gd decreases MS. MS for melt-spun alloys decreases from ~108emu/g for Gd to ~42emu/g for Gd80Ga20 and for as-cast alloys MS decreases from ~120emu/g for Gd to ~62emu/g for Gd80Ga20. Both maximum magnetic entropy change (−ΔSM)max and refrigerant capacity (RC) for as-cast and melt-spun alloys are lower than Gd. (−ΔSM)max decreases by ~1.55% and ~3.0% per atomic percent of Ga in as-cast and melt-spun alloys, respectively. A steeper decrease in RC is observed in melt-spun alloys than is observed for as-cast alloys—~433J/kg for Gd to ~235J/kg for Gd80Ga20 for melt spun alloys and ~462J/kg for Gd to ~306J/kg for Gd80Ga20 for as-cast. As-cast alloys appear to have better magnetocaloric properties than the melt-spun alloys. Alloying of diamagnetic Ga with Gd provides superior magnetocaloric properties compared to other diamagnetic elements in Group 13. The near room-temperature magnetocaloric properties of Gd–Ga alloys were comparable to a few first-order-transition based magnetic refrigerants.

The structural and magnetic properties of rapidly solidified Fe100−xGax alloys, for 12.8≤x≤27.5

This work presents the findings from structural, magnetic, and thermal investigations of melt-spun ribbons of Fe100−xGax alloys where 12.8≤x≤27.5at%. X-ray diffraction analysis from the as-spun samples indicates that all of the compositions form the disordered bcc A2 phase. Thermo-magnetic observations of the Fe-rich compositions where x=12.8, 17.5 and 19.5 show temperature dependent magnetisation curves where the A2 bcc phase is retained through the heating and cooling cycles. However, the compositions of x=22.5 and 27.5 both show anomalies, where a marked increase in magnetisation is detected at high temperatures indicating a substantial structural reconfiguration. Repetition of these measurements confirm that both structural and magnetic hysteresis occurs in both these compositions; however, in the x=22.5 composition these changes are eventually removed but not so for the x=27.5 sample. Repetitive thermal measurements using differential scanning calorimetry of the x=27.5 sample coupled with direct comparison to the thermo-magnetic measurements ascertain excellent evidence for the structural and magnetic transitions that are observed. In agreement with phase diagrams, X-ray diffraction of both annealed and quenched samples confirms the proposed structural transformations involving D03, L12 and D019 phases.