Papers by Keyword: Heusler Alloy

Abstract: Heusler alloys are intermetallic compounds formed in two combinations: Full-Heusler (X₂YZ) and Half-Heusler (XYZ). X and Y can be any transition element, and Z belongs to the main group. This shows that there can be a huge variation in the combinations, leading to various properties and applications. We aimed at predicting the combination leading to shape memory properties using machine learning tools and then synthesizing the same. The predictions are done by training the tool with input data. We employed the lattice strain, valence electron concentration ratio, mechanical stress, difference in entropy, and saturation magnetization as input features. The correlation between the martensitic and austenitic temperature was evaluated in terms of regression metrics. The random forest and decision tree modeling were executed. Test scores were obtained using frequency ordering, PCA, linear regression, and correlation matrix to forecast magnetically controlled shape memory effect. The silhouette score matched the transition temperature at which the material showed shape memory behavior. Additionally, from 70% of the training data, a combination of Iron (Fe), Nickel (Ni), and Aluminum (Al) as Full Heusler alloys stimulated the algorithms in gaining the accuracy of predictive modeling by minimizing the error. Through DFT-based bandgap and density of states calculations, the Fe₂NiAl Heusler compound is hypothesized to behave as a half-metallic ferromagnet by considering the atomic number, the number of valence electrons, and the local magnetic moment. The experimental validation will be done along with magnetization studies, magneto-transport, and magneto-caloric measurements.

Abstract: The spin-disorder resistivity (SDR) of a broad range of magneticmaterials, both ordered and disordered, is reviewed.We identify the SDR at the critical temperature with the residualresistivity of the corresponding system evaluated in the frameworkof the disordered local moment (DLM) model.The underlying electronic structure is determined in the frameworkof the tight-binding linear muffin-tin orbital method which employsthe coherent potential approximation to describe the DLM stateand chemical disorder.The DLM fixed-spin moment method is used in the case when the DLMmoment collapses.The Kubo-Greenwood approach is employed to estimate the resistivityof the DLM state.Formalism is applied to Fe and Ni and its alloys, Heusler alloys,and ordered ferromagnetic and antiferromagnetic alloys.Finally, the SDR of the Earth's core will be studied using thesame formalism.Calculations are compared with available experimental data.

Abstract: To obtain a larger spin signal for use in graphene-based spintronic devices, the spin injection efficiency needs to be enhanced. Previously researchers can increase the efficiency by inserting a tunnel barrier such as Al₂O₃ or MgO between ferromagnet and graphene. However, the key value in spin transport is still very low because of the conductance mismatch as well as the limit to fabricate a high-quality tunnel barrier at the junction surface. Here we use a highly spin-polarized ferromagnetic material—Heusler alloy Co₂MnGe as a substitutional scheme without the tunnel barrier. The spin injection efficiency of our Co₂MnGe (111)/graphene junction can be as high as 73% which is much higher than 1% of ferromagnet/graphene or 30% of ferromagnet/oxide/graphene using first-principles study. The large spin polarization can be explicated by analyzing the transmission spectrum at the nonequilibrium state.

Abstract: In this paper, the effect of substitution of Co by d-valent elements such as Ag and Pt on electronic structure and magnetic properties of full Heusler type Co₂FeSi alloys was investigated. Structural study reveals the presence of a small gap in the minority band structure around the vicinity of the Fermi level on Co₂FeSi resulting to half-metallic behaviour. However, CoFeSiAg and CoFeSiPt cannot preserved the half-metalicity due to disappearing of the gap in the minority band structure due to the creation of new states around the Fermi level in the minority density of states. The variation in the magnetic moment of Co₂FeSi with change of the atoms was attributed to the change in the local magnetic moment of atoms.

Abstract: The authors have been investigated structural, magnetic and electrical transport properties for CFAS/n-GaAs junctions. From cross sectional TEM image, RHEED and XRD patternz of thin CFAS films, CFAS films found to be grown epitaxially on GaAs, and shown L2₁-ordered structure for the films with substrate temperature (T_CFAS) of 300°C and 400°C. It is hard to find some additional phase around the interface between CFAS and GaAs. Magnetic moment (and magnetic anisotropy energy) of CFAS increased (and decreased) with increasing T_CFAS up to 300°C and decreased (and increased) at T_CFAS of 400°C, respectively. The asymmetry of current (J)-voltage (V) curve for the junction with T_CFAS =300°C was found to be larger than those for other junctions. It was found there is the relation between T_CFAS dependence of spin signal obtained by three terminal Hanle or four terminal non-local measurement and that of magnetic moment, magnetic anisotropy field or asymmetry of J-V curve.

Abstract: The massive tunnel magnetoresistane (TMR) is expected when Fe₃Al Heusler alloy are used for magnetic electrodes in magnetic tunnel junction (MTJ). We demonstrate the Fe₃Al/MgO/Fe₃Al MTJ, which have good lattice matching interfaces. The electronic and transport properties of these system are systematically investigated by first principle calculation. The electronic band structure of Fe₃Al Heusler alloy and MgO are represented for discussion spin filtering effect. Besides, the transmission conductance is calculated to study the spin tunneling effect. We found that the massive TMR is clearly achieved at zero-bias condition, and the TMR is decreased when the finite bias are applied. Thus, among ferromagnetic materials, the Fe₃Al Heusler alloy will be good alternative to bcc-Fe based electrodes with MgO barrier for the MTJs beyond.

Abstract: Dual-site doped half-Heusler ZrNiSn alloys were prepared by arc melting. In order to diminish thermal conductivity of the alloys, as-casted ingots were sintered again by spark plasma sintering (SPS) technique after pulverizing and milling for several different periods of time. The electrical resistivity, thermoelectric powers and thermal conductivity of the sintered samples were measured from 4 to 350 K. A drastic reduction of thermal conductivity was obtained. The thermal conductivity decreased from about 17 to 1.5 W/K m and from 8.8 to 6.3 W/K m at 30 and 350 K, respectively. The dimensionless figure of merit of the half-Heusler alloys increased about 10%

Abstract: We investigate the electronic structure and magnetism of DO3-type Heusler alloys Rh₃M (M = Al, Ga, In, Si) using the first-principle calculations. The Rh₃Si have been predicted to be half-metallic ferromagent at their equilibrium lattice constants. The effect of lattice parameters on the electronic structure and magnetic properties is also discussed in detail.

Abstract: Co₂FeAl full-Hesuler alloys show good soft magnetic properties, implying a promising high ferromagnetic resonance frequency. In this study, Co₂FeAl films were deposited on Si (100) substrates using an oblique sputtering method. As expected, a good high-frequency performance was achieved in the as-deposited Co₂FeAl films without any annealing. An obvious uniaxial magnetic anisotropy over 200 Oe with the magnetic hard axis along the radial direction of the sample turntable was obtained. As a result, the self-bias ferromagnetic resonance frequency reaches more than 4 GHz for the Co₂FeAl films prepared under an integrated circuits compatible process. These results indicate that the Co₂FeAl films are promising in integrated circuits RF/microwave devices.

Abstract: A series of (Co₂FeSi)_1-x(Al₂O₃)_x Heusler alloy films with various Al₂O₃-doping were prepared by an oblique sputtering method. It is exciting that the as-deposited films exhibit a very high in-plane uniaxial magnetic anisotropy (UMA) field up to 360 Oe and low coercivity of 12 Oe. Consequently, a very high self-bias ferromagnetic resonance frequency in excess of 5.02 GHz was obtained in as-deposited Co₂FeSi films without any annealing. The good microwave ferromagnetic performances and the integrated circuits compatible fabrication process of Co₂FeSi films make possible application in RF/microwave devices.