A first principles study on the full-Heusler compound Mn2CuSb

Electronic structure calculations from first-principles are employed to design half-metallic ferrimagnets susceptible of finding applications in spintronics. The electronic structure and magnetism properties of a new Mn-based Heusler alloy Mn₂CuSb are studied and both possible L2₁ structures (CuHg₂Ti and AlCu₂Mn types) are taken into account. It is found that the CuHg₂Ti-type structure is energetically more favorable than the AlCu₂Mn-type structure and presents half-metallic character. Calculations show that their total spin moment is ?2.00μ_B for a wide range of equilibrium lattice constants and the total spin magnetic moment is attributed mainly to the two Mn atoms. Simultaneously, the small spin magnetic moments of Cu and Sb atoms are parallel and the compound is ferrimagnets. The total spin moment mainly origins from the antiparallel configurations of the Mn partial moments. The CuHg₂Ti-type Mn₂CuSb alloy keeps a 100% of spin polarization of states at the Fermi level. Our findings suggest that Mn₂CuSb may be a promising material for future spintronic applications.     

Electronic,Elastic, and Magnetic Properties of the Full-Heusler with the 4d Transition Metal Element,Co<Subscript>2</Subscript>YSi,Co<Subscript>2</Subscript>ZrSi,and Co<Subscript>2</Subscript>Y<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>Si: a First-Principle Study

The full-potential all-electron linearized augmented plane wave plus local orbitals (FP-LAPW + lo) method, as implemented in the suite of software WIEN2K, has been used to systematically investigate the structural, electronic, elastic, and magnetic properties of the half-metallic ferromagnetic Heusler compounds with 4d transition elements Co₂YSi, Co₂ZrSi, and alloy Co2Y_0.5Zr_0.5Si presented. The theoretical formalism used is the generalized gradient approximation to density functional theory (GGA) with the Perdew–Burke–Ernzerhof (PBE) exchange-correlation functional. The calculated lattice parameters and magnetic moments agree well with the available theoretical results. The spin-polarized density of states (DOS) of Co₂YSi and Co₂ZrSi indicate a half-metallic behavior with vanishing electronic density of states for minority spin at the Fermi level, which yields a perfect spin polarization while for Co₂Y_0.5Zr_0.5Si shows a nearly half-metallic behavior with small spin-down electronic density of states at the Fermi level.     

Spin–Orbit Torque Switching in a Nearly Compensated Heusler Ferrimagnet

Ferrimagnetic materials combine the advantages of the low magnetic moment of an antiferromagnet and the ease of realizing magnetic reading of a ferromagnet. Recently, it was demonstrated that compensated ferrimagnetic half metals can be realized in Heusler alloys, where high spin polarization, zero magnetic moment, and low magnetic damping can be achieved at the same time. In this work, by studying the spin–orbit torque induced switching in the Heusler alloy Mn₂Ru_{1? x} Ga, it is found that efficient current‐induced magnetic switching can be realized in a nearly compensated sample with strong perpendicular anisotropy and large film thickness. This work demonstrates the possibility of employing compensated Heusler alloys for fast, energy‐efficient spintronic devices.     

Electronic Structure,Phase Stability,and Elastic Properties of Inverse Heusler Compound Mn<Subscript>2</Subscript>RuSi at High Pressure

The structural, magnetic, electronic, and elastic properties of the new Mn-based Heusler alloy Mn₂RuSi at high pressure have been investigated using the first-principles calculations within density functional theory. Present calculations predict that Mn₂RuSi in stable \(F\bar {4}3m\) configuration is a ferrimagnet with an optimized lattice parameter 5.76 Å. The total spin magnetic moment is 2.01 μ _B per formula unit and the partial spin moments of Mn (A) and Mn (B) which mainly contribute to the total magnetic moment are 2.48 and ?0.66 μ _B, respectively. Mn₂RuSi exhibits half metallicity with an energy gap in the spin-down channels. The study of phase stability indicates that the elastic stiffness coefficients of Mn₂RuSi with \(F\bar {4}3m\) structure satisfy the traditional mechanical stability restrictions until up to 100 GPa. In addition, various mechanical properties including bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio along with elastic wave velocitieshave also been obtained and discussed in details in the pressure range of 0–100 GPa based on the three principle elastic tensor elements C ₁₁, C ₁₂, and C ₄₄ for the first time.     

Study of the Structural,Electronic, Magnetic,and Optical Properties of Mn<Subscript>2</Subscript>ZrGa Full-Heusler Alloy: First-Principles Calculations

In this work, the structural, electronic, magnetic, and optical properties of Mn₂ZrGa full-Heusler alloy were investigated by using density functional theory (DFT) calculations. It is found that the spin-up states have a metallic character, but the spin-down bands have a pseudo-gap at the Fermi level. The total spin magnetic moment of Mn₂ZrGa (per formula unit) is 3.00 µ _B at an equilibrium lattice parameter of 6.15 Å. The calculations show that Mn₂ZrGa is a ferrimagnetic with 81% spin polarization at equilibrium lattice parameter. The effect of lattice parameter distortion on the magnetic properties and spin polarization is also studied. It is found that the total magnetic moment preserves its value for a lattice parameter range of 5.96–6.30 Å. The decreasing of the lattice parameter leads to improvement of spin polarization. The real and imaginary parts of dielectric function and hence the optical properties including energy absorption spectrum, reflectivity, and optical conductivity are also calculated. The value of plasma frequency for spin-up and down electrons is located at 1.78 and 0.74 eV, respectively.     

Synthesis of new (Bi,La)<Subscript>3</Subscript>MSb<Subscript>2</Subscript>O<Subscript>11</Subscript> phases (M = Cr,Mn, Fe) with KSbO<Subscript>3</Subscript>-type structure and their magnetic and photocatalytic properties

Synthesis and structure of new (Bi, La)₃MSb₂O₁₁ phases (M = Cr, Mn, Fe) are reported in conjunction with their magnetic and photocatalytic properties. XRD refinements reflect that Bi₃CrSb₂O₁₁, Bi₂LaCrSb₂O₁₁, Bi₂LaMnSb₂O₁₁ and Bi₂LaFeSb₂O₁₁ adopt KSbO₃-type structure (space group, Pn[`3])Pn\overline{3}). The structure can be described through three interpenetrating networks where the first is the (M/Sb)O₆ octahedral network and other two are the identical networks having Bi₆O₄ composition. The magnetic measurements on Bi₂LaCrSb₂O₁₁ and Bi₂LaMnSb₂O₁₁ show paramagnetic behaviour with magnetic moments close to the expected spin only magnetic moments of Cr^+ 3 and Mn^+ 3. The UV-Visible diffuse reflectance spectra are broad and indicate that these materials possess a bandgap of ∼ 2 eV. The photocatalytic activity of these materials has been investigated by degrading Malachite Green (MG) under exposure to UV light.     

Full-potential study of Fe2NiZ (Z = Al,Si, Ga,Ge)

The first-principles calculations using full-potential in the stable F-43m phase have been performed to investigate the structural, elastic, magnetic, nature of chemical bonding and electronic properties of Fe₂-based inverse Heusler alloys. The structural stability and the lattice constants match well with the experimental results. We have further reported other mechanical, elastic and thermophysical properties for the first time of these Fe₂NiZ (Z = Al, Si, Ga, Ge) materials. Cauchy's pressure and Pugh's index of ductility label these materials as ductile. The spin magnetic moment distributions show that these materials are ferromagnetic in stable F-43m phase. Further, spin resolved electronic structure calculations show that the discrepancies in magnetic moments of Fe-I and Fe-II depend upon the hybridization of Fe with the main group element. The charge density distribution plots present a clear picture of the stronger covalent bonding in Fe₂NiSi and the decreasing trend of covalent bonding in these materials. The main group electron concentration is predominantly responsible in establishing the magnetic properties, formation of magnetic moments and the magnetic order for these alloys. Spin resolved band structure calculations show that these materials are metallic in stable F-43m phase at ambient conditions.     

Hyperfine field distributions in disordered Mn<Subscript>2</Subscript>CoSn and Mn<Subscript>2</Subscript>NiSn Heusler alloys

Heusler alloys, Mn₂CoSn and Mn₂NiSn, were prepared and characterized by X-ray studies. Mössbauer studies using Sn-119 were carried out to investigate the hyperfine fields present at the Sn site in these alloys. The hyperfine field distribution in these alloys as well as X-ray studies point to the chemical disorder present in both alloys. Co-existence of a paramagnetic portion along with the magnetic hyperfine part was observed in Mn₂CoSn even at low temperatures, while this was not found in Mn₂NiSn spectra. Hyperfine fields at Sn site were calculated using Blandin and Campbell model and compared with the experimental results.     

Magnetic Properties,Possible Martensitic Transformation,and Elastic Properties of Heusler Alloy Fe<Subscript>2</Subscript>NiSb from First-Principles Calculations

The first-principles plane-wave pseudopotential method has been used to investigate the structural, magnetic, electronic and elastic properties of the Heusler alloy Fe₂NiSb. It is found that the tetragonal phase of Fe₂NiSb is more stable compared with the cubic phase from the energetic point of view. The martensitic transformation from a cubic to a tetragonal structure may happen with decreasing temperature. This phase transition is nearly volume-conserving, suggesting that this alloy is predicted to be a superior shape memory alloy. Fe₂NiSb is found to be a ferromagnet. The saturation magnetization is 5.08 and 4.88 μB/f.u. in the cubic and tetragonal phases, respectively. It is confirmed that Fe₂NiSb displays an excellent ductile behavior by analyzing the ratio of bulk modulus to shear modulus. The calculated densities of states show that the peak splitting at the Fermi level decreases the total energy and is related to the stabilization of the tetragonal phase.     

First-Principles Study on Half-Metallic Full-Heusler Compound Mn2ZnSi

By first-principle calculation, the electronic structure and magnetic properties of the Mn₂ZnSi full-Heusler alloy with CuHg₂Ti-type structure are investigated. Calculations show that Mn₂ZnSi compound presents half-metallic ferrimagnetic properties under the equilibrium lattice constant. The influence of spin-orbit interaction for the magnetic moments is investigated. The result shows spin-orbit interaction has little influence on magnetic moment. The bulk modulus of Mn₂ZnSi obtained by a fit of the Murnaghan equation of state is 134.3 GPa, which is more compressible than some other Heusler alloys. At the pressure range of 0 to 17.7 GPa, Mn₂ZnSi presents half-metallic character. Mn₂ZnSi would be a promising material for future spintronic applications.     

Electronic and Magnetic Properties of SnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Spinel Ferrites

In this work, the electronic and magnetic properties of SnFe₂O₄ spinel ferrite with various cation distributions (mixed, normal and inverse spinel phases) were studied. The calculations were performed by Korringa–Kohn–Rostoker (KKR)-coherent potential approximation (CPA) method with generalized gradient (GGA) approximation for the exchange and correlation functional. Our spin-polarized calculations give a half-metallic character for SnFe₂O₄ inverse spinel phase and near half-metallic character for SnFe₂O₄ mixed spinel phase and metal character for SnFe₂O₄ normal spinel phase. These results, which contribute to understanding the effect of the cation distribution in SnFe₂O₄ ferrite with spinel structure in the existence of gap states occupied by majority and minority spin electrons, the spin magnetic moments, the magnetization and the half-metallic behaviour.     

Half-Metallic and Antiferromagnetism Property of Mn2CdMg Under Pressure

The electronic and magnetic properties of Mn₂CdMg were investigated using ab initio electronic structure calculations. The CuHg₂Ti-type structure is energetically more preferable compared with the AlCu₂Mn-type structure in antiferromagnetism state and presents half-metallic property. Calculations exhibit that the CuHg₂Ti-type Mn₂CdMg alloy keeps 100?% spin polarization of states at the Fermi level. The total spin magnetic moment in the unit cell (M _t ) follows the rule M _t =Z _t ?28, where Z _t represents the number of the valence electrons. The magnetic moments of Mn₂CdMg change nearly linear with pressure from 0 to 809.03 GPa. Meanwhile, the alloy keeps half-metallic property from 0 to 421.57 GPa, and a magnetic phase transition appears at the pressure of 809.03 GPa. Mn₂CdMg may be a promising material for future spintronic device applications.     

First-Principle Study of Half-Metallic Ferrimagnet Behavior in Titanium-Based Heusler Alloys Ti<Subscript>2</Subscript>FeZ (Z = Al,Ga, and In)

Using density functional theory with the full-potential linearized augmented plane-wave method (FP-LAPW), we have study the structural, electronic, and magnetic properties of Ti₂FeZ (Z = Al, Ga, and In) alloys with Hg₂CuTi-type structure. The magnetic stabilities reveal that all our compounds exhibit ferrimagnetic (FiM) behaviors. The electronic structure report the existence of a gap energy equal to 0.56, 0.60, and 0.64 eV for Ti₂FeAl, Ti₂FeGa, and Ti₂FeIn, respectively, in the spin-down state and divulge metallic intersections at the Fermi level for the spin-up state. These results indicate that our compounds have a half-metallic (HM) nature. In addition to this, the total magnetic moments are in agreement with the obtained one by the Slater-Pauling rule (M _tot = Z _tot ? 18), which indicates the 100% spin polarization for these compounds.     

Engineering Co2MnAlxSi1−x Heusler Compounds as a Model System to Correlate Spin Polarization,Intrinsic Gilbert Damping,and Ultrafast Demagnetization

Engineering of magnetic materials for developing better spintronic applications relies on the control of two key parameters: the spin polarization and the Gilbert damping, responsible for the spin angular momentum dissipation. Both of them are expected to affect the ultrafast magnetization dynamics occurring on the femtosecond timescale. Here, engineered Co₂MnAl_xSi_1-x Heusler compounds are used to adjust the degree of spin polarization at the Fermi energy, P, from 60% to 100% and to investigate how they correlate with the damping. It is experimentally demonstrated that the damping decreases when increasing the spin polarization from 1.1 × 10⁻³ for Co₂MnAl with 63% spin polarization to an ultralow value of 4.6 × 10⁻⁴ for the half-metallic ferromagnet Co₂MnSi. This allows the investigation of the relation between these two parameters and the ultrafast demagnetization time characterizing the loss of magnetization occurring after femtosecond laser pulse excitation. The demagnetization time is observed to be inversely proportional to 1 – P and, as a consequence, to the magnetic damping, which can be attributed to the similarity of the spin angular momentum dissipation processes responsible for these two effects. Altogether, the high-quality Heusler compounds allow control over the band structure and therefore the channel for spin angular momentum dissipation.     

Magnetic properties of CuGa<Subscript>0.94</Subscript>Mn<Subscript>0.06</Subscript>Te<Subscript>2</Subscript>

As part of a search for new spintronic materials, we have studied the magnetic properties of the CuGa_0.94Mn_0.06Te₂ chalcopyrite solid solution in the range 2–400 K in weak and strong magnetic fields. Magnetization isotherms, σ(H), were obtained in magnetic fields of up to 3980 kA/m. σ(T) data were collected in two ways: the sample was cooled in a magnetic field or in zero field. The experimental data were analyzed by fitting to the Langevin function. The data are adequately represented by this relation in the case when the magnetic moment of the clusters is μ_cl = 23.4μ_B and the concentrations of magnetic clusters and noninteracting Mn²⁺ ions are n _cl = 2.4 × 10²⁵ m^?3 and n _pm = 5.7 × 10²⁵ m^?3, respectively. The calculated average cluster size is d _cl = 33 Å, the number of Mn²⁺ ions per cluster is z = 21 atoms per cluster, and the magnetic moment per Mn²⁺ ion in the clusters is μ_Mn = 1.1μ_B. This μ_Mn value is far below the theoretical magnetic moment of the Mn²⁺ ion in the electronic configuration d ⁵(5.9μ_B), suggesting antiferromagnetic exchange interaction.     

First-Principles Prediction of Structural,Magnetic, Electronic,and Elastic Properties of Full-Heusler Compounds Co<Subscript>2</Subscript>YIn (Y = Ti,V)

Density functional theory based on the full-potential linearized augmented plane wave (FP-LAPW) method is used to investigate the structural, magnetic, electronic, and elastic properties of Heusler alloys Co₂YIn (Y = Ti, V). It is shown that the calculated spin magnetic moments using the local spin-density approximation (LSDA), generalized gradient approximation (GGA), LSDA + U, and Tran–Blaha (TB)-modified Becke–Johnson (mBJ)-local density approximations (LDA) are in good agreement with the Slater–Pauling rule. The obtained results with LSDA, GGA-PBE, and LSDA + U of the density of states illustrate that both compounds have a metal behavior; however, mBJ-LDA predicts Co₂VIn alloy to be a half metal. The band structure obtained with mBJ-LDA has an indirect band gap along the Γ–X symmetry with energy of 0.4 eV for Co₂VIn, and E _F lies in the middle of the gap; the electrons at the Fermi level are fully spin-polarized. The calculation of elastic properties indicates the stability of these compounds, and they have a ductile behavior. The 3D dependences of Young’s modulus exhibit a strong anisotropic character. The high values of the elastic constant C ₁₁ reflect the strength of the bonding Ti (V)–In.     

Phase separation of Mn<Subscript>2</Subscript>Sb at high pressures and temperatures

The intermetallic compound Mn₂Sb (tetragonal structure, Cu₂Sb type) was exposed to high pressures (4 to 8 GPa) and temperatures (up to 2300 K) for 10 min and was shown to phase-separate to Mn₃Sb and Mn_1.5Sb at certain processing temperatures, pressures, and durations.     

Magnetic,Optoelectronic, and Thermodynamic Properties of Sr<Subscript>2</Subscript>Cr<Emphasis Type="Italic">X</Emphasis>O<Subscript>6</Subscript> (<Emphasis Type="Italic">X</Emphasis> = La and Y): Half-Metallic and Ferromagnetic Behavior

The effects of spin polarization on the structure, magnetic, and optoelectronic properties of Cr-based series of double perovskites Sr₂CrXO₆ (X = La and Y) have been studied by using the full-potential linearized augmented plane-wave method (FP-LAPW), based on the density functional theory (DFT) as implemented in the Wien2k code, within the generalized gradient approximation (GGA), GGA + U, and GGA plus Trans-Blaha-modified Becke–Johnson (TB-mBJ) as the exchange correlation. Our results show a similar half-metallic ferromagnetic ground state for both materials. From the electronic properties, it is found that Sr₂CrYO₆ has a direct band gap at (Γ-Γ) direction and Sr₂CrLaO₆ has an indirect band gap at (Γ-W) direction. Furthermore, we have computed the optic and thermodynamic properties which are investigated for the first time. Consequently, the magnetic, optoelectronic, and thermodynamic properties show these compounds are promising for high technological applications, namely spintronic materials.     

Synthesis and physical properties of new oxide AgMnO<Subscript>2</Subscript>

A novel oxide AgMnO₂ was prepared from LiMnO₂ via Ag⁺ → Li⁺ exchange in the eutectic melt AgNO₃-KNO₃. It crystallizes in a monoclinically distorted unit cell (SG C2/m) caused by the Jahn-Teller (J-T) ion Mn³⁺ (3d ⁴). The structure was refined by isotypy with the crednerite CuMnO₂. There are two long axial Mn–O of 264.2(0) pm and four equatorial bonds of 192.7(3) pm and Mn–O–Mn adjoining (83.07°) are bent below the ideal angle. The thermal variation of the magnetic susceptibility (χ/T ⁻¹) obeys a Curie-Weiss law with manganese in a trivalent, high spin (HS) state accommodated in elongated MnO₆ octahedra (14.8%). Direct coupling between Mn³⁺ involves negative exchange interactions through long-range antiparallel moments with a temperature θ _p = −436 K and a magnetic moment of 5.26 μ_B/Mn³⁺ slightly larger than the spin only moment. The title oxide is stable in air up to ∼680 °C before it decomposes into metal silver. It displays a semi-conducting behavior with an activation energy of ∼0.45 eV, characteristic of a conduction by low mobility polarons between Ag^+/2+ where nearly all polarons are bonded. The photoelectrochemical properties of AgMnO₂ have been investigated by photocurrent technique in 1 M KOH. The cathodic photocurrent J _ph provides unambiguous evidence of p-type character attributed to oxygen insertion (0.025 oxygen by formula unit) as required by the charge compensating mechanism. The valence band is made up of Ag−4d wave functions positioned at ∼5.14 eV below vacuum. A comparison with CuMnO₂ was also reported.     

Microstructure and phase transformations in a Ni<Subscript>50</Subscript>Mn<Subscript>29</Subscript>Ga<Subscript>16</Subscript>Gd<Subscript>5</Subscript> alloy with a high transformation temperature

A Heusler Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy with a high transformation temperature has been obtained by substituting 5 at% Gd for Ga in a ternary Ni₅₀Mn₂₉Ga₂₁ ferromagnetic shape memory alloy. The microstructure and phase transformations in the Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy have been investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and differential scanning calorimetry. It is shown that the microstructure of the Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy consists of matrix and hexagonal Gd (Ni,Mn)₄Ga phase, which indicates a eutectic structure composed of these two phases. One-step thermoelastic martensitic transformation occurs in this quaternary alloy. Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy exhibits a martensite transformation start temperature up to 524 K, approximately 200 K higher than that of Ni₅₀Mn₂₉Ga₂₁ alloy. At room temperature, non-modulated martensite with twin substructure is observed in Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy.