Cu2MnAl-type Structure Research Articles

In search of coloured alloys resembling gold: Structure and optical properties of LiCu2Ga1−xAlx and Li(Cu1–yNiy)2Ga

The Li-containing solid solutions LiCu2Ga1–xAlx and Li(Cu1–yNiy)2Ga were prepared by induction heating. LiCu2Ga1–xAlx retains the Cu2MnAl-type (full Heusler) structure of LiCu2Ga for x = 0–0.7 and then adopts the CsCl-type structure for x = 0.9–1.0. The solid solution Li(Cu1–yNiy)2Ga forms for y = 0–0.5 with the Cu2MnAl-type structure. Solid-state 7Li NMR spectra for LiCu2Ga1–xAlx suggest that Li atoms occupy unique sites, but there is some uncertainty about the intermediate members of this solid solution. These compounds show high reflectivity in the yellow region and an absorption edge caused by interband transitions from filled Cu 3d states to empty bands. The yellow colour of LiCu2Ga gradually changes to red as Ga is substituted by Al because the absorption edge shifts to lower energy, and it becomes lighter yellow as Cu is substituted by Ni because the relative reflectivity decreases. For low levels of substitution by Al (x = 0.1) or Ni (y = 0.1), the chromaticity coordinates are close to those of elemental gold.

Structural, mechanical, electronic, thermal, and optical properties of the inverse-Heusler compounds X2RuPb(X = La, Sc): A first-principles investigation

Topological insulators are novel quantum material states with insulating bulk band gaps and topologically protected metallic surface states that have been extensively studied owing to their intriguing properties for spintronic and quantum-computing applications. The structural, mechanical, electronic, thermal, and optical properties of inverse Heusler compounds La2RuPb and, Sc2 RuPb in two Hg2CuTi, Cu2 MnAltype structures were calculated using the full potential linear muffin-tin orbital simulation methodology as implemented in the computer code,which is based on density functional theory.We employed the local-density approximation for the exchange and correlation potential (XC) terms. Consequently, the optical characteristics of La2 RuPb, Sc2 RuPb and elastic constants Cij and their corresponding elastic moduli were computed for the first time. According to our structural calculations, La2 RuPb is more stable in its Hg2 CuTi-type structure than Sc2 RuPb in its Cu2 MnAl-type structure. However, the mechanical characteristics demonstrate their stability in the final stages of elastic deformation.

A DFT study of new full Heusler compound Li2MgC insights into the structural, electronic and thermoelectric properties: A high efficiency performance thermoelectric material

Structural, electronic and thermoelectric properties for full Heusler compound Li2MgC were studied using the full potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT), implemented in the Wien2k package. The term of the exchange and correlation potential (XC) is treated by the generalized gradient approximation GGA and Trans-Blaha-modified Becke–Johnson (mBJ-GGA). From the various calculations, it emerges that the Cu2MnAl type structure is more suitable for this compound than that of the Hg2CuTi type structure; moreover, this compound is stable in the non-magnetic (NM) state. Furthermore, this compound exhibits a semi -conductor behavior with an indirect band gap at Γ-X direction. The calculated formation and cohesion energies are negative, which clearly and unequivocally indicates the thermodynamic stability of the compound studied and that it can be synthesized experimentally. Otherwise, this compound is characterized by a high figure of merit (ZT) (close to unity), making it a promising candidate for thermoelectric applications.

Phase stability, mechanical, electronic, magnetic and thermodynamic properties of the Pd2PrX(X=Cl, F) compounds: An Ab-initio study

Many of the known examples of half-metallic ferromagnets HMF are oxides, sulfides, or Heusler alloys have attracted some interest for their potential use in spintronics. In order to achieve such understanding we have performed an ab-initio calculations with spin polarization using plane-wave pseudo potential technique based on the density-functional theory (DFT), the exchange-correlation potential was treated with the generalized gradient approximation (PBE-GGA), whereas for the treatment of on-site electron-electron correlations the PBE-GGA+U approximation (where U is the Hubbard Coulomb energy term) are applied for the calculation of the structural, electronic, elastic and magnetic properties of Pd2PrX (X=Cl, F). The results showed that for Pd2PrCl and Pd2PrF, Hg2CuTi-type structure is energetically more stable than Cu2MnAl-type structure at the equilibrium volume. Electronically, Pd2PrCl and Pd2PrF exhibit half-metallicity with small band gaps of 0.06 and 0.25eV respectively with GGA-PBE+U in the spin-down channels whereas spin-up channels are conducting. The calculated total magnetic moment of 2.00 μB per formula unit is very close to integer value and agree well with the Slater-Pauling rules ( Mtot=34-Ztot), where the magnetic moment is basically carried by Pr atoms. However, the elastic properties show that Pd2PrX (X=Cl, F) compounds are ductile and anisotropic according to the analysis of B/G and Cauchy’s pressure. The Thermodynamic properties were also analyzed using the quasi-harmonic Debye model. Both the compounds are found structurally stable.

Cobalt-based full Heusler compounds Co2FeZ (Z = Al, Si, and Ga): A comprehensive study of competition between XA and L21 atomic ordering with ab initio calculation

To study the structural properties of Co2FeZ (Z = Al, Si, Ga) (CFZ) alloys, we will use the approximation method GGA-PBE based on the method of plane waves increased by linear waves at full potential using the theory of functional density in both the Hg2CuTi and Cu2MnAl-type structures. From the most stable state we determine the other properties such as the magnetic, elastic and thermoelectric properties. The band structure calculation reveals indirect band gap in spin down channel and zero band gap in spin up channel of valence and conduction bands confirming the spin gapless semiconducting nature of these compounds. Calculated Seebeck coefficient in spin up and spin down channel reveals that the CFZ behaves as both n and p type thermoelectric materials with better output efficiency. The transport properties of these materials are discussed on the basis of Seebeck coefficient, electrical conductivity coefficient, thermal conductivity and figure-of-merit coefficient. By analyzing the nature of the bonding between the different atoms that form CFZ that each of them has a strong covalent character.

A potential full Heusler thermoelectric material CO2ZrZ (Z=Al, Si, Ga and Sn) in low temperature: An Ab-initio investigation

The structural, electronic, magnetic, elastic and thermoelectric properties of full-Heusler alloys Co2ZrZ (Z = Al, Si, Ga and Sn) are investigated using the augmented plane wave method (FP-LAPW) based on the framework of spin density functional theory. The term of the exchange and correlation potential (XC), is treated by the generalized gradient approximation GGA and Trans-Blaha-modified Becke–Johnson (TB-mBJ). The results obtained showed that the Cu2MnAl-type structure has more stable energy than the Hg2CuTi-type structure for all the full-Heusler studied. From electronic calculations, it is found that all the compounds studied have an indirect band gap with a half-metallic behavior. Furthermore, we also found that all materials have integral magnetic moments which are mainly due to 100% spin polarization at Fermi energy. The calculated elastic constants and the anisotropy shear factors indicate that these compounds have a ductile character and are mechanically stable. Finally, we calculated the thermoelectric properties by applying Boltzmann theory as implemented in the BoltzTraP code. The results obtained for the merit factor (ZT) and Seebeck coefficient (S) make these materials promising candidates in thermoelectric applications and in spintronics devices.

Structural, electronic, magnetic and mechanical properties of the full-Heusler compounds Ni2Mn(Ge,Sn) and Mn2NiGe

Abstract Mn-Ni based full-Heusler alloys belong to novel half-metallic compounds with a promising set of physical properties for applications as functional materials. Based on first principles calculations, the electronic structures, the magnetic and mechanical properties of Ni2Mn(Ge,Sn) and Mn2NiGe full-Heusler alloys have been investigated in detail. The results revealed that the Mn2NiGe with Hg2CuTi type structure is more stable; on the other hand, for Ni2Mn(Ge,Sn), the Cu2MnAl type structure is more stable. The Mn2NiGe alloys are found to be half-metallic with an integer value of total magnetic moment of 4 μB which makes them interesting materials in the field of spintronics. The Ni2Mn(Ge,Sn) alloys exhibit metallic character in both Hg2CuTi and Cu2MnAl type structures. The calculated B/G ratios for all the considered compounds Ni2Mn(Ge,Sn) and Mn2NiGe are greater than 1.75; therefore, these alloys are ductile, and the calculated Cauchy’s pressure is positive, which also classified these compounds as ductile materials.

First-principles investigation of half-metallic ferromagnetism of Fe2YSn (Y = Mn, Ti and V) Heusler alloys

In this paper, we use the first-principles calculations based on the density functional theory to investigate structural, electronic and magnetic properties of Fe2YSn with (Y = Mn, Ti and V). The generalized gradient approximation (GGA) method is used for calculations. The Cu2MnAl type structure is energetically more stable than the Hg2CuTi type structure. The negative formation energy is shown as the evidence of thermodynamic stability of the alloy. The calculated total spin moment is found as 3μB and 0μB at the equilibrium lattice constant for Fe2MnSn and Fe2TiSn respectively, which agrees with the Slater-Pauling rule of Mt= Zt-24. The study of electronic and magnetic properties proves that Fe2MnSn and Fe2TiSn full-Heusler alloys are complete half-metallic ferromagnetic materials.

Theoretical Study of the Electronic Properties of X2YZ (X = Fe, Co; Y = Zr, Mo; Z = Ge, Sb) Ternary Heusler: Abinitio Study

Abstract In the purpose of exploring new Heusler alloys with different magnetic applications, we have employed first principles calculations method within density functional theory. After checking the structural stability of X2YZ Heusler alloys (X = Fe, Co; Y =Zr, Mo and Z = Ge, Sb), we found that Cu2MnAl type structure is more favorable for most compounds except for X2MoGe and Co2MoSb, were the Hg2CuTi structure is energetically more stable. The trends in magnetic and electronic structures can be predicted by the structure types as well as the different kinds of hybridizations between the constituents. Among the two series only two compounds were identified to be true half metals with potential applications in spintronic devices. While one compound was classified as a nonmagnetic semiconductor with a small band gap. For the rest of materials, we found that the metallic behavior is dominant. These materials show possible interesting features in technical applications as well. The effect of distortion on the magnetic properties of Co2ZrGe and Fe2ZrSb showed that the half metallic character was preserved within a moderate range of volume changes, which makes it possible to grow these materials as thin films with modern techniques.

Insight view of Hf2CrZ (Z = B, Ga, In, Si, Ge, Sn) Heusler materials via DFT calculations: A study on structural, electronic and magnetic properties

In this study, we have investigated the structural, electronic and magnetic properties of the Hf2CrZ (Z = B, Ga, In, Si, Ge, Sn) full Heusler materials in both Hg2CuTi and Cu2MnAl type structures. These investigations have been carried out by employing the first-principles computational method - full potential (FP) linearized (L) augmented plane-wave plus local orbital (APW + lo) - framed within the density functional theory (DFT) and embodied in WIEN2k computational package. Our investigations show that Cu2MnAl-type structures of the Hf2CrZ (Z = B,Ga,In, Si, Ge, Sn) Heusler compounds are more stable than that of Hg2CuTi-type ones. Our investigations also show that Hg2CuTi type structure of Hf2CrZ Heusler alloys demonstrates half-metallic character for Hf2CrZ (Z = B,Ga, In) with a value of the magnetic moment 1 μB and lower value for Hf2CrZ (Z = Si, Ge, Sn).

First-Principles Calculations to Investigate Structural, Electronic, Elastic, Magnetic, and Thermodynamic Properties of Full-Heusler Rh2MnZ (Z = Zr, Hf)

The structural, electronic, elastic, magnetic, and thermodynamic properties of two new Heusler alloys Rh2MnZ (Z = Zr, Hf) are studied based on the first principal calculation using the scheme of the generalized gradient approximation (GGA) of density function theory. The investigation was carried out in ferromagnetic (FM), anti-ferromagnetic (AFM), and the non-magnetic (NM) phases of the Cu2MnAl-type structure (regular structure) and Hg2CuTi-type-structure (inverse structure). Both alloys were found to be more stable in the ferromagnetic phase of the Cu2MnAl-type structure. The equilibrium lattice parameter in this structure is equal to 6.39 Ǻ for Rh2MnZr and 6.35 Ǻ for Rh2MnHf. The electronic properties reveled the metallic nature of the Heusler Rh2MnZ (Z = Zr, Hf) alloys. The interpretation of the elastic properties confirmed the elastic stability of the two alloys in the studied structure with a good agreement between the resulting bulk modulus from the structural properties and that of resulting from the elastic properties. Other elastic parameters such as modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio (ν) and Pugh’s ratio B/G, and the Zener anisotropy parameter A showed that the Rh2MnZ (Z = Zr, Hf) alloys are slightly deformed. They show high rigidity, anisotropic, and little deformation and behave in ductile way. The magnetic properties confirmed the ferromagnetic state of both compounds with computed total magnetic moment equal to 4.76 μB for Rh2MnZr and 4.60 μB for Rh2MnHf. The thermodynamic parameters were evaluated with various temperatures between 0 and 1200 K and a pressure from 0 to 50 GPa using the quasi-harmonic Debye model.

Electronic structure and magnetic properties of a full-Heusler Mn2NiSb: Cu2MnAl type structure

Manganese (Mn) based full-Heusler alloys have been shown to be the most promising materials due to their excellent magnetic behaviors for applications in magneto resistance, magnetic tunnel devices, spin valve and spin injection devices. Here, we report the study of crystal structure, electronic structure and magnetic properties of Mn2NiSb full-Heusler alloy. XRD investigation of Mn2NiSb followed by Rietveld refinement reveals the material to be successfully crystallized in a well-ordered Cu2MnAl prototype structure manifested by the existence of super-lattice diffraction peaks of (111) and (220). The experimental lattice parameter is estimated to be 6.01 Å which is larger than the available reports. Magnetic measurement (M-H) performed by applying external magnetic field up to 1.8 Tesla reveals the saturated magnetic moment (MS) of 4.07μB/formula unit and 2.50μB/formula unit at temperature 5 K and 300 K respectively which is the highest value reported so far at 5 K for Mn2NiSb stabilized in Cu2MnAl type structure. Further, magnetization versus temperature (M-T) curve with zero-field cooled (ZFC) and field-cooled (FC) up to 300 K indicates that Mn2NiSb crystallized in a single phase. However, the square of magnetization and temperature curve was best fitted with linear fitting supporting to Stoner like ferromagnetism. In order to have a better understanding of magnetic behavior, the First principal calculation has also been performed. Interestingly, our experimental observations were found to be well corroborated with the theoretically estimated magnetic behavior.

Effect on Annealing Temperature (Ta) of Ternary Full Fe2CrSi Heusler Alloy Nanoparticles for Spin-Based Device Applications

The ternary full Heusler alloy nanoparticle Fe2CrSi compounds were prepared using mechanical alloy method. The as-prepared sample was observed as amorphous in nature and further increases various annealing temperatures (like 700 °C, 800 °C, and 900 °C) in nitrogen gas atmosphere for 5 h in tubular furnace using quartz tube. X-ray diffraction studies confirmed the formation of Cu2MnAl-type structure instead of the conventional L21 disordered structure. Through Williamson-Hall plot (W-H plot), the uniform deformation model was used to get low value of strain-induced broadening. In the surface morphology, elemental composition studies were carried out using HRSEM with EDS. The presence of Fe2CrSi with the particle size of ~ 35 nm was also observed using high-resolution scanning electron microscopy and elemental composition study confirmed the presence of Fe, Cr, and Si. The magnetic properties of Fe2CrSi nanoparticles were studied showing ferromagnetic behavior and low coercivity of soft magnetic nature. Half metallic ferromagnetic Heusler alloys have wide range of applications from medical imaging to data storage for its profound performance on spintronics.

A Critical Study of Phase Stability and Electronic, Magnetic, and Elastic Properties in the Inverse Heusler Cr2MnSi Alloy: a First-Principles Calculations

Ab initio calculations were systematically investigated for nonmagnetic (NM), ferromagnetic (FM), and antiferromagnetic (AFM) states of new full-Heusler alloy Cr2MnSi in Hg2CuTi and Cu2MnAl-type structures. The calculations are based on the density functional theory, with the full potential linear muffin-tin orbital (FP-LMTO) method. The results show that the ferromagnetic Hg2CuTi prototype structure is the most stable. The optimized lattice parameter is found to be 5.643 A, with the total magnetic moment 0.30 μB. The electronic band structure calculations revealed that Cr2MnSi exhibits a metallic ferromagnet behavior. Using the Mehl method, we have also calculated the elastic constants and their related parameters such as Poisson’s ratio, Young modulus, Zener anisotropy, shear modulus, Kleinman parameter ξ, Lame constants (λ, μ), Cauchy pressure Pc, microhardness parameter, and the melting temperature Tm. Our calculation validates the conditions of mechanical stability in the cubic crystal. The estimation of the Curie temperature shows that the Cr2MnSi compound is a good candidate for the spintronic application.

Structural stability, mechanical, electronic and thermal behaviour of Ru2CrZ (Z=Sb, Si, Pb, Ge) Heusler alloys

In this paper, the structural, elastic, electronic properties of Ru2CrZ (Z=Si, Ge, Pb, Sn) are explored using the generalized gradient approximation based on ab initio plane-wave pseudopotential density functional theory. With the help of the quasi-harmonic Debye model, we also investigate the variation of normalized volume V/V0, the heat capacities CV and CP, thermal expansivity, and Debye temperature of Ru2CrZ (Z=Si, Ge, Pb, Sn). Results show that the Cu2MnAl type structure is more stable then Hg2CuTi type structure. The four compounds in the ground state are predicted to be nearly half-metal behavior with total magnetic moment near to the integer value. To provide a comparative and complementary study to future researches, we investigated the elastic and thermodynamic properties.

First-principles search for half-metallic ferromagnetism in CsCrZ2 (Z = O, S, Se or Te) Heusler alloys

Exploring highly spin-polarized materials is crucial for the development of spin-based devices. In this paper, we investigate the atomic structure, electronic, half-metallic and magnetic properties of the CsCrZ2 (Z = O, S, Se or Te) Heusler alloys, by performing first-principles calculations based on density functional theory (DFT). The geometry optimization process shows that the alloys are more stable in Cu2MnAl type structure than in Hg2CuTi one. To find a magnetic ground state, the total energy of the alloys is calculated in the non-magnetic (NM), ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering. We find that, the FM ordering yields the lowest energy, thereby confirming that the alloys are FM in the ground state. On computing the cohesive and formation energy in the ground state, it is found that alloys are chemically and thermodynamically stable, respectively. Spin polarized band structures and density of states (DOS) demonstrate that the CsCrO2, CsCrS2 and CsCrSe2 alloys are true half-metals with 100% spin-polarization at the Fermi level, while the CsCrTe2 alloy is predicted as highly spin polarized material. Furthermore, the CsCrO2, CsCrS2 and CsCrSe2 alloys possess 2.529, 2.250 and 2.050 eV gaps in the spin down band structure, respectively. The calculated total magnetic moments reveal that half-metallic alloys have an integral total magnetic moment of 3.000 μB, which satisfies the Slater-Pauling rule Mt = Zt-16. The main contribution to the total magnetic moment comes from the Cr atoms (about 3.9 μB). Furthermore, the Curie temperature TC calculated within classical Heisenberg model is estimated to be about 822 K (CsCrO2), 685 K (CsCrS2), 753 K (CsCrSe2) and 636 K (CsCrTe2). The obtained high spin polarization and above room temperature FM ordering make the materials as promising materials to be used in spintronic technology.

Investigation of Full-Heusler compound Mn2MgGe for magnetism, spintronics and thermoelectric applications: DFT study

First principle method based Density functional theory calculations are used to investigate electronic, magnetic, thermoelectric and lattice-dynamical properties of Full-Heusler compound Mn2MgGe. We considered the energetic, thermodynamical and lattice-dynamical stability criteria for Mn2MgGe by evaluating the total energy, formation energy, and phonon density of states respectively, which thereby suggest that the synthesis of Full-Heusler compound Mn2MgGe is possible. Half metallic spin-polarized nature from electronic band structure and total magnetic moment (2μB) of Hg2CuTi type structure of Mn2MgGe potentially facilitate its spintronics applications. The results of electronic structure and magnetism predicts that Hg2CuTi type structure of Mn2MgGe is an indirect band gap semiconductor with half-metallic ferrimagnetic behaviour. Antiparallel and equal magnetic moment of Mn atoms cancel out the magnetization in Cu2MnAl type structure of Mn2MgGe, making its total magnetic moment 0 μB/cell. The electronic and magnetic properties for Cu2MnAl type structure of Mn2MgGe has not been previously reported. Positive and negative value of Seebeck coefficient for spin up and spin down channel indicate the presence of P-type and N-type charge carriers in the compound. Mn2MgGe exhibits high Seebeck coefficient −38 μV/K and 180 μV/K in spin-up and spin-down channel at room temperature (300 K) along with huge power factor of 4.23×1011 w/mK2s at 600 K, predicting Mn2MgGe as a potential candidate for thermoelectric applications.

Structural, electronic, magnetic and thermoelectric properties of inverse Heusler alloys Ti2CoSi, Mn2CoAl and Cr2ZnSi by employing Ab initio calculations

ABSTRACT The inverse Heusler alloys such as Ti2CoSi, Mn2CoAl and Cr2ZnSi were studied in the framework of density functional theory using FP-LAPW linearised augmented plane wave method in order to determine the different physical properties such as structural, electronic, magnetic and thermoelectric. The generalised gradient approximation (GGA) was used to treat the exchange–correlation energy and the Beck-Johnson (mBJ) approach was used to calculate the electronic properties. In all studied compounds, the stable type Hg2CuTi was energetically more favourable than Cu2MnAl type structure. The results show that two compounds (Ti2CoSi and Mn2CoAl) are both ferromagnetic (FM) while Cr2ZnSi is antiferromagnetic (AFM). The compounds Ti2CoSi and Mn2CoAl have a total magnetic moment of 3 and 2 μB, respectively, whereas the Cr2ZnSi alloy has a total magnetic moment equals zero. The Ti2CoSi, Mn2CoAl and Cr2ZnSi compounds exhibit half-metallic (HM) character with 100% spin polarisation at the Fermi level. Finally, the semi-classical Boltzmann theory implicit in the BoltzTraP code was used to calculate the electronic transport coefficients such as thermal and electrical conductivity, the Seebeck coefficient and the factor of merit.

Computational discovery of the novel half-metallic full-Heusler alloys Mn2LiAs and Mn2LiSb

The structural, elastic, electronic and magnetic properties of the novel full-Heusler alloys Mn2LiAs and Mn2LiSb are determined to explore their structural stability and half-metallicity. The method used is the first-principles method based on density functional theory. Calculations show that the Hg2CuTi-type structure is more energetically favourable than the conventional Cu2MnAl-type structure and is thermodynamically and mechanically stable for both alloys. The Hg2CuTi-type Mn2LiAs and Mn2LiAs alloys are half-metallic ferrimagnets and have a total magnetic moment of 2.000 μB per formula unit. They follow the Slater-Pauling rule and have an indirect energy gap in the spin-down channels with values of 1.176 and 1.269 eV at equilibrium lattice constants of 5.793 and 6.132 Å, respectively. The half-metallicity is kept within the limits of a wide lattice constant range. The spin polarisation ratio is 100% and the total magnetic moment is 2.000 μB. Mn2LiAs and Mn2LiSb alloys, which can be synthesised via experiments, are promising candidates for spintronic applications.

The surface effect on the thermodynamic stability, half-metallic and optical properties of Co2MnGa(001) films: a DFT study

In this study, the half-metallic properties, thermodynamic stability and optical parameters of the full-Heusler Co2MnGa compound and its four different terminations of Co–Co, Co–Mn, Mn–Ga and Co–Ga from the surface of Co2MnGa (001) have been calculated based on the density functional theory (DFT). The results confirm the ferromagnetic half-metallic behavior with a magnetic moment of 4.08 mu_{text{B}} and a gap of 0.32 eV at the Fermi level of Co2MnGa bulk phase having a Cu2MnAl-type structure. The density of states curves showed that all possible terminations from the Co2MnGa (001) surface eliminate the half-metallic behavior except the termination of Mn–Ga case. Moreover, the results indicate that the termination of Mn–Ga with the lowest surface energy is the most stable termination for the application in spintronics. The optical coefficients such as real and imaginary dielectric function, refraction, extinction, energy loss function, optical conductivity and reflections of the bulk and Mn–Ga termination have been calculated and compared.