Half-metallic properties of the CuHg2Ti-type Mn2ZnSi full-Heusler compound

The half-metallic properties of novel CuHg₂Ti-type Mn₂ZnSi full-Heusler compound were examined by density functional theory (DFT) calculations. The electronic band structures and density of states of the Mn₂ZnSi compound show that spin-up electrons are metallic, but the spin-down bands are semiconductor with a gap of 0.48 eV, and the spin-flip gap is of 0.28 eV. The Mn₂ZnSi Heusler compound has a magnetic moment of 2 μ_B at the equilibrium lattice constant a = 5.80 Å. The Mn₂ZnSi full-Heusler compound is ferrimagnetic and maintains the half-metallic character having 100% polarization for lattice constants ranging between 5.62 and 6.91 Å.     

Half-metallic ferrimagnetism in the Ti2CoAl Heusler compound

Density functional calculations performed on the Ti₂CoAl Heusler compound confirm it to be a half-metallic ferrimagnet with the spin-down energy gap of 0.49 eV. The Ti₂CoAl Heusler compound has a magnetic moment of 2 μ_B at the equilibrium lattice constant a=6.14 Å. The Ti₂CoAl Heusler compound is ferrimagnetic and maintains the half-metallic character having 100% polarization for lattice constants ranging between 5.85 and 6.44 Å.     

Non-collinear magnetic moments of seven-atom Cr, Mn and Fe clusters

The non-collinearity of magnetic moments of pentagonal bipyramid Cr₇, Mn₇ and Fe₇ clusters is discussed. The magnetic moments are calculated by the discrete variational non-collinear spin-density functional method. For the Cr₇ cluster, a coplanar magnetic arrangement appears at the large interatomic distance. With decreasing the interatomic distance, the coplanar arrangement changes to the parallel arrangement with a small absolute magnetic moment. For the Mn₇ cluster, the magnetic arrangement changes from coplanar to antiparallel with decreasing the interatomic distance. Also for the Fe₇ cluster, some coplanar magnetic moments appear at the interatomic distance of 2.23 ?. In these coplanar magnetic arrangements, the magnetic moment at the basal site of the pentagon rotates with a step of 144 degrees for the Cr₇ clusters and 72 degrees for the Mn₇ and Fe₇ clusters. Received 30 November 2000     

First-principle calculations of structural,electronic and magnetic investigations of Mn2RuGe1-xSnx quaternary Heusler alloys

First-principles calculations were used to calculate the structural, electronic and half-metallic ferromagnetism of Mn₂RuGe_1-xSn_x (x?=?0, 0.25, 0.50, 0.75, 1) Heusler alloys. The Hg₂CuTi-type structure is found to be energetic more than Cu₂MnAl-type structure for both Mn₂RuGe and Mn₂RuSn compounds. The calculated lattice constants for Mn₂RuGe and Mn₂RuSn are 5.91?Å and 6.17?Å, respectively. The electronic band structures and density of states of Mn₂RuGe show a half metallic character with total magnetic moments, 2 μ_B per formula unit that are in good agreement with Slater-Pauling rule with indirect band gap, 0.31?eV along the direction Γ –X. It is observed that the total magnetic moment per cell increases as Sn concentration increases in the Heusler alloys.     

亚铁磁Heusler合金Mn2CoGa和Mn2CoAl掺杂Cr,Fe和Co的局域铁磁结构

通过实验和计算的方法研究了Mn₂CoM_xGa_1-x 和Mn₂CoM_xAl_1-x (M=Cr, Fe, Co)掺杂系列合金样品. 研究发现, 在共价作用的影响下, Fe和Co原子占A位, 使被取代的MnA (-2.1 μ_B)变成MnD (3.2 μ_B), 在最近邻的强交换作用下亚铁磁基体中形成了MnB-CoC-MnD局域铁磁性结构, 使分子磁矩的增量最高可达6.18 μ_B. Fe, Co 掺杂后建立同样的局域铁磁结构, 居里温度的变化趋势却不同. 实验观察到Mn₂Co_1+xAl_1-x中掺杂容忍度高达x=0.64, 远高于在Mn₂CoGa中(x=0.36)的结果; 以及随着Al的减少, 合金由B2有序向A2混乱转变等现象, 为共价作用对合金结构稳定的影响提供了证据. 磁测量中发现Cr掺杂后磁矩增量高达3.65 μ_B以及居里温度快速上升的反常现象, 意味着对占位规则的违背.     

A first-principles study on the lower-valence coexisting Cr2TiX (X=Al, Ga, Si, Ge, Sn, Sb) Heusler alloys

The electronic, magnetic, and bonding properties of the Cr₂TiX (X=Al, Ga, Si, Ge, Sn, Sb) Heusler alloys have been investigated using first-principles calculations. The results show that Cr₂TiSb exhibits a half-metallic nature and Cr₂TiGa and Cr₂TiSn exhibit a nearly half-metallic nature. From analysis of the density of states and the electron density difference along the Ga→Sn→Sb series for sp atoms, we found that the Cr-Ti bond demonstrates covalent character with more or less the ionic and metallic nature. In addition, the Cr-Ti bonding strength increases along this series. All the compounds have a negative total magnetic moment, most of which are confined to the Cr atoms. There exists a 1.0μ_B increasing trend of the total moment along the III→IV→V main group for sp atoms, and only the total moment of Cr₂TiSb coincides well with the Slater-Pauling behavior.     

First-principles study on the electronic structure, magnetic properties and phase stability of alloyed cementite with Cr or Mn

Using the first-principles technique, the electronic structures, magnetic properties and phase stability of alloyed cementite with Cr or Mn were investigated. The calculations show that the chemical and mechanical stability of alloyed cementite can be strengthened by the use of Cr/Mn-doped method. The Magnetic Moments (Ms) of Mn₁Fe₂C, Mn₂Fe₁C, Cr₁Fe₂C and Cr₂Fe₁C are 5.274, 0.941, 1.864 and 0.736 μ_B/f.u, respectively. The Ms of Cr in Fe₂CrC (−1.374 μ_B) and Cr₂FeC (−0.032 μ_B) are different due to replacing different sites Fe atoms. The magnetic behaviors of Mn are different from Cr in alloyed cementite. The Ms of Mn in Fe₂MnC and Mn₂FeC are 2.300 μ_B and −0.147 μ_B, respectively.     

Magnetism in the new full-Heusler compound,Zr2CoAl: A first-principles study

The electronic structure and magnetic properties of Zr₂CoAl bulk material were investigated within the Density Functional Theory (DFT) framework. The material, basically a complete spin polarized half-metallic ferromagnet in the ground state, crystallizes in the ordered full-Heusler inverse structure (Hg₂CuTi-type structure). The energy band gap, localized in minority spin channel is 0.48 eV at equilibrium lattice parameter, 6.54 Å. The total magnetic moment calculated, equal to 2 μ_B/f.u., is an integral, in agreement with the Slater-Pauling curve for full-Heusler alloys.     

Magnetism of alloyed models of Cr(Mn) V and Mn Cr overlayers on V (001) substrates

The magnetism is calculated for substitutional alloyed of Cr_x(Mn_x)V_1-x monolayers (MLs) and Cr_xMn_1-x on V (001) surface with a variety of concentrations (x = 0.25, 0.50 and 0.75). The substitutional surface alloys were treated by an artificial super cell construction. Parallel magnetic ordering is obtained for all the considered structures. The surface net magnetization increases in terms of Cr (Mn) concentration in Cr_x(Mn_x)V_1-x/V (001) system, while no serious variations occur in Cr_xMn_1-x/V (001). Vanadium atoms at the interfacial layers acquire appreciable magnetic moments antiferromagneticlly (AF) coupled with the surface moments. Received 25 February 2002 / Received in final form 13 May 2002 Published online 14 October 2002 RID="a" ID="a"e-mail: jkalifa@sci.ju.edu.jo     

Half-metallic properties of Ti2FeSi full-Heusler compound

In this study, the electronic structure and magnetic properties of novel half-metallic Ti₂FeSi full-Heusler compound with CuHg₂Ti-type structure were examined by density functional theory (DFT) calculations. The electronic band structures and density of states of the Ti₂FeSi compound show the spin-up electrons are metallic, but the spin-down bands are semiconductor with a gap of 0.45 eV, and the spin-flip gap is of 0.43 eV. Fe atom shows only a small magnetic moment and its magnetic moment is antiparallel to that of Ti atoms, which is indicative of ferrimagnetism in Ti₂FeSi compound. The Ti₂FeSi Heusler compound has a magnetic moment of 2 μ_B at the equilibrium lattice constant a=5.997 Å.     

Magnetic properties of Co–Si alloy clusters

We have investigated the electronic structure and the magnetic properties of Co–Si alloy clusters using ab initio spin-polarized density functional calculations. The possible CoSi₂, CoSi, and Co₂Si phase clusters with oblique hexagon prism, icosahedron, and cuboctahedron structures are introduced. The CoSi phase cluster with icosahedron structure has the largest binding energy and amount of charge transfer. We found that HOMO-LUMO gap, magnetic moment, and spin polarization for the Co–Si alloy clusters with icosahedron structure increase with Co concentration. The Si atoms in the CoSi phase with icosahedron structure have negative magnetic moment.     

Low-temperature electronic and magnetic transitions in the antiferromagnetic semiconductor Cr0.5Mn0.5S

Experimental-theoretical studies were carried out of the electrical and magnetic properties of the antiferromagnetic semiconductor Cr_0.5Mn_0.5S in the temperature range 4.2–300 K. A magnetic antiferromagnetic-ferrimagnetic phase transition was observed along with a semimetalsemiconductor electronic transition. Monte Carlo calculations indicate that the changes in the type of magnetic ordering and conductivity are due to the cooperative Jahn-Teller effect caused by the Cr₂₊ ions. Fiz. Tverd. Tela (St. Petersburg) 41, 1660–1664 (September 1999)     

First-principles calculations to investigate half-metallic ferromagnetism in Zn0.50Ti0.50S alloy by using DFT + U calculations

ABSTRACT

The spin-polarized structural, electronic and magnetic properties of the Ti-doped zincblende ZnS compound at x?=?0.50 (Zn_0.50Ti_0.50S alloy) have been investigated by employing the first-principles full-potential linearised augmented plane wave with local orbitals (FP-L/APW?+?lo) method within the frame-work of spin-polarized density functional theory (spin-DFT). For the treating of the structural properties, the electronic exchange and correlation (XC) functional was defined by generalised gradient approximation (GGA), whereas both GGA and GGA?+?U approximations are applied to treat and to compare the electronic and magnetic properties (U is the Coulomb repulsion energy). It has been confirmed that the ferromagnetic (FM) state of this alloy is found the most stable phase; however, all the equilibrium lattice parameters such as; lattice constant (a₀), bulk modulus (B₀), and its first-pressure derivative (B′) are computed in all paramagnetic, ferromagnetic and anti-ferromagnetic phases. The calculations of electronic properties unveil the perfect half-metallic character in the tetragonal Zn_0.50Ti_0.50S system. The computed magnetic properties reveal that the total magnetic moment is mainly originated from the transition element (TM) of Ti. Moreover, we have found that the p-d hybridisation is the paramount responsible for the reduction of the magnetic moment of TM from its free space charge value and for the production of minor magnetic moments on the nonmagnetic Zn and S sites.     

Electronic structure and magnetism of disordered bcc Fe alloys

We study the electronic structure and magnetic properties of disordered bcc Co_xFe_1-x, Cr_xFe_1-x and Mn_xFe_1-x alloys in their ferromagnetic phases using the Augmented Space Recursion (ASR) technique coupled with the tight-binding linearized muffin tin orbital (TB-LMTO) method. We calculate the density of states and magnetic moment of these alloys to show the variation upon alloying Fe with the other neighbouring 3d transition metals using arguments based on charge transfer, exchange splitting and hybridization effects. Received 10 April 2001 and Received in final form 15 August 2001     

Ferromagnetism,half-metallicity and spin-polarised electronic structures characterisation insights in Ca1−xTixO

ABSTRACT

In this study, we have computed the structural, electronic and half-metallic ferromagnetic properties of Ca_1?xTi_xO compounds at concentrations x?=?0.125, 0.25, 0.5 and 0.75 by employing the first-principle approaches of density functional theory. The generalised gradient approximation of Wu and Cohen (GGA-WC) is used to calculate the structural parameters, whereas the electronic structures and magnetic properties are characterised by the accurate Tran–Blaha-modi?ed Becke–Johnson potential (TB-mBJ). The lattice constant, bulk modulus and indirect gap of CaO are in good agreement with other theoretical and experimental results. The Ca_0.25Ti_0.75O at x?=?0.75 has metallic ferromagnetic nature. The Ca_0.875Ti_0.125O, Ca_0.75Ti_0.25O and Ca_0.50Ti_0.50O compounds have total magnetic moments of 2?μ_B per Ti atom with a half-metallic character, a spin polarisation of 100% and a large half-metallic gap of 1.345?eV for x?=?0.125. Therefore, the Ca_1?xTi_xO material with a low concentration of Ti is a true half-metallic ferromagnet and seems to be a promising candidate for semiconductor spintronics.     

Possible Topological Hall Effect in a Spin Gapless Semiconducting Mn2CoAl Heusler Compound

Topological Hall effect (THE), induced by the interaction of charge carriers with mesoscopic or microscopic noncoplanar spin structures, holds promising applications in the field of spintronics. In the present study, a giant THE of about 2 μΩ cm at room temperature is reported in a bulk spin gapless semiconducting Mn₂CoAl cubic Heusler compound. Temperature-dependent investigation of magneto-transport data reveals that the Mn₂CoAl has the large THE over a wide temperature range of 2–300 K. The alternating current (AC) susceptibility as a function of magnetic field exhibits a smooth and continuous response rather than any kink or anomaly, suggests that the observed THE in the Mn₂CoAl compound results from the interaction of charge carriers with the microscopic noncoplanar spin texture. The observed THE as a function of temperature follows the same behavior as the magnetocrystalline anisotropy (MCA) of the cubic Mn₂CoAl, indicating the competition of the MCA with ferromagnetic and antiferromagnetic exchange interactions as the origin of the noncoplanar spin texture and hence THE. Micromagnetic simulations further support the emergence of noncoplanar spin structure as a result of the competition between different energies.     

Half-metallic ferrimagnetism in Mn2CuGe

We study magnetism properties and the electronic structure of a new Mn-based Heusler alloys Mn₂CuGe using ab initio electronic structure calculations. We take into account both possible L 2₁ structures (CuHg₂Ti and AlCu₂Mn types). The CuHg₂Ti-type structure is found to be energetically more favorable than the AlCu₂Mn-type structure and exhibits half-metallic ferrimagnetism. Calculations show that their total spin moment is for a wide range of equilibrium lattice constants and magnetic moment mainly comes from the two Mn atoms, while the Cu atom is almost nonmagnetic. The small total moment comes from the antiparallel configurations of the Mn partial moments. And the CuHg₂Ti-type Mn₂CuGe alloy keeps a 100% of spin polarization at the Fermi level. Thus, the Mn₂CuGe is the compound of choice for further experimental investigations.     

Magnetic properties of Cr-rich crystals of Rb2Cr1−xMxCl4(M = Mn,Cd)

Magnetic data for Rb₂Cr_1?xCd_xCl₄ and Rb₂Cr_1?xMn_xCl₄ are reported. Curie temperatures can be determined quite accurately in these systems with the help of magnetometers if small fields are applied. The magnetic moment per mol Cr(II) is independent of x for small concentrations of cadmium. A roughly linear decrease of that moment is observed in the case of an admixture of manganese. This gives evidence for an antiferromagnetic interaction between Cr(2+) and Mn(2+) in the mixed crystal system Rb₂Cr_1?xMn_xCl₄.     

Exchange mechanism of half-metallic ferromagnetism of TiO2 doped with double impurities: A first-principles ASW study

The electronic structure and ferromagnetic properties of rutile TiO₂ doped with double-impurities Ti_1−2xCr_xMn_xO₂ has been investigated using first-principles calculations within the density-functional theory (DFT) and the local density approximation (LDA), functional for treating the effects of exchange and correlation. They were performed using the scalar-relativistic implementation of the augmented spherical wave (ASW). The advantages of doping TiO₂ with double impurities instead of single impurities are the increase of the total moment of the system and the exhibition of the half-metallic ferromagnetic nature in Cr- and Mn-doped TiO₂ rutile. These behaviors are due to the hybridization of Cr 3d states and nearest-neighboring O 2p states. The spin-spin interaction between magnetic impurities examined by the total energy between parallel and antiparallel aligned states indicated that the Cr and Mn impurities are energetically favorable to be parallel coupled, which mean that the ferromagnetic state is more stable than the ferrimagnetic one. We proposed a bond magnetic polarons (BMP) model, based on localized carriers, to explain the mechanism of ferromagnetism in these systems.     

Titanium atoms dimerization phenomenon and magnetic properties of titanium-antisite (TiO) and chromium doped rutile TiO2, ab-initio calculation

The ab-initio calculations based on the Korringa Kohn Rostoker approximation approach combined with coherent potential approximation (KKR-CPA), were used to study the magnetic properties of the titanium anti-site (Ti_O) and chromium (Cr) doped TiO₂. In the considered systems, we used different concentrations for Ti_O defect and Cr doping. In TiO_2(0.98)(Ti_O)_0.02, the obtained results indicate that Ti_O is a donor having half-metal behavior. Ti_O[3d] band is located at the Fermi level, although isn’t 100% polarized, the ferromagnetic (FM) state is verified as being more stable than disordered local moment (DLM) state. For Ti_0.98Cr_0.02O₂ the Cr doping introduced new states which give the material half-metallic feature. The majority spin of Cr impurities are located at the Fermi level and the conduction electrons around the Fermi level are 100% spin polarized. This indicates the stability of (FM) state. Moreover, in Ti_0.98Cr_0.02O_2(0.98)(Ti_O)_0.02, the top of the valence band is shifted to lower energy compared to pure TiO₂, and the n-type of TiO₂ is verified. The majority spin of Cr[3d] are located at 0.025 Ry close to the Fermi level. The predicted Curie temperatures (Tc) were calculated using the mean field approximation (MFA) and we predicted that Ti_O defect in Cr doped TiO₂ makes Tc higher. This kind of defect makes the material useful for spinotronics's applications and devices.