First-Principle Investigation of Structural,Electronic and Magnetic Properties in Mn<Subscript>2</Subscript>RhZ (Z = Si,Ge, and Sn) Heusler Alloys

Mn ₂-based Heusler compounds exhibit different types of anti-site disorder. The electronic structure and magnetism of Heusler alloys Mn₂RhZ (Z = Si, Ge, and Sn) have been studied by first-principle calculations. Mn₂RhSi and Mn₂RhGe are ordinary half-metallic ferrimagnetic metals at equilibrium lattice constants, with a magnetic spin moments obeys to the Slater-Pauling rule and spin polarization of 100 % at the Fermi energy. The tetragonal phase transformation is studied for Mn₂RhSn. The total magnetic moment of Mn₂RhSn in the tetragonal structure is higher compared to the other materials, which results in a large ΔM between the saturation moments of tetragonal and a cubic. The tetragonal Mn₂RhSn predicted to a high spin polarization ratio of 93 %. These properties of these materials are particularly interesting due to their perpendicular magnetic anisotropy (PMA), which was realized in thin films opening the door for application in STT magnetic random access memories (STT-MRAMs)     

First principles study on the elastic properties and electronic structures of (Fe, Cr)3C

First principles calculations are performed to investigate the elastic properties and electronic structures of Cr doped Fe₃C carbides, the obtained results are compared with Cr₃C and Fe₃C. The calculated bulk modulus of Fe₁₁CrC₄ and Fe₁₀Cr₂C₄ is 260GPa and 270GPa, respectively, larger than Fe₃C. So the hardness of Fe₃C phase can be enhanced by doped with an appropriate amount of Cr, however, the calculated formation enthalpy and defect formation enthalpy of Fe₁₁CrC₄ and Fe₁₀Cr₂C₄ are positive. On the other hand, the electronic calculations reveal that the ground states of Fe₁₁CrC₄ and Fe₁₀Cr₂C₄ are ferromagnetic. The evaluated local magnetic moments of Fe at 4c sites are larger than that of 8d sites, which is analogous to Fe₃C. Milliken population results indicate that the stabilities of Fe₁₁CrC₄ and Fe₁₀Cr₂C₄ are reduced mainly due to the strong repulsive bonds among metal atoms.     

Theoretical Investigation of Structural,Electronic, and Magnetic Properties of V-Doped MgSe and MgTe Semiconductors

In this study, we have explored the structural, electronic, and magnetic properties of V-doped zincblende MgSe and MgTe compounds using density functional calculations. The Wu-Cohen generalized gradient approximation is used for optimizing the structural properties, while the modified Becke and Johnson local (spin) density approximation functional has been employed to compute the electronic and magnetic properties. The spin dependent band structures, electronic density of state, and magnetic moments calculated for V-doped MgSe and MgTe semiconductors exhibit occurrence of 100 % spin polarization at the Fermi level which confirms stable half-metallic ferromagnetism in these materials. The spin-down gaps and the half-metallic gaps are analyzed in terms of V-3d and Se-4p (Te-5 p) hybridization, where it is observed that the V-3dstates play a key role in generating spin polarization and the magnetic moment in these compounds. The exchange constants N ₀ αand N ₀ β have been calculated to demonstrate the effects resulting from exchange splitting process. Furthermore, spin-polarized charge density calculation is presented for elucidating the bonding nature, while pressure dependence of total magnetic moment for three concentrations of V-doped MgSe and MgTe are also discussed.     

Theoretical Study of Structural,Magnetic, Elastic,Phonon, and Thermodynamic Properties of Heusler Alloys Fe<Subscript>2</Subscript>Cr<Emphasis Type="Italic">X</Emphasis> (<Emphasis Type="Italic">X</Emphasis> = Al,Ga)

First-principle calculations based on generalized gradient approximation and quasi-harmonic Debye model were executed to analyze the structural, magnetic, elastic, phonon, and thermodynamic properties of Fe₂CrX (X = Al, Ga) Heusler alloys. The computed lattice parameters concurred well with available experimental and theoretical data. The calculated elastic constants reveal that the Fe₂CrAl is brittle and Fe₂CrGa is ductile. The phonon dispersion relation of Fe₂CrX (X = Al, Ga) are calculated using finite displacement method with a cutoff radius of 5 Å. We likewise explored the thermodynamic properties by utilizing quasi-harmonic Debye model in which bulk modulus, heat capacity, Debye temperature, Grüneisen parameter, and thermal expansion coefficient are resolved at 0–30 Gpa pressure and 0–900 K temperature from the non-equilibrium Gibbs functions.     

Effect of spin polarization on the structural properties and bond hardness of Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>B (<Emphasis Type="Italic">x</Emphasis> = 1, 2, 3) compounds first-principles study

In this paper, spin and non-spin polarization (SP, NSP) are performed to study structural properties and bond hardness of Fe _x B (x = 1, 2, 3) compounds using density functional theory (DFT) within generalized gradient approximation (GGA) to evaluate the effect of spin polarization on these properties. The non-spin-polarization results show that the non-magnetic state (NM) is less stable thermodynamically for Fe _x B compounds than spin-polarization by the calculated cohesive energy and formation enthalpy. Spin-polarization calculations show that ferromagnetic state (FM) is stable for Fe _x B structures and carry magnetic moment of 1.12, 1.83 and 2.03 μB in FeB, Fe₂B and Fe₃B, respectively. The calculated lattice parameters, bulk modulus and magnetic moments agree well with experimental and other theoretical results. Significant differences in volume and in bulk modulus were found between the ferromagnetic and non-magnetic cases, i.e., 6.8, 32.8%, respectively. We predict the critical pressure between ferromagnetic and non-magnetic phases. The model for hardness calculation using Mulliken population coupled to semi-empirical hardness theory proved effective in hardness prediction for the metal borides which agree well with the experimental values. These results would help to gain insight into the spin-polarized effect on the structural and bond hardness.     

New Heusler Compounds Cr2YSb (Y=Fe, Co and Ni): Magnetic and Electronic Properties

The electronic and magnetic properties of the Cr₂YSb (Y=Co, Fe, and Ni) Heusler alloys with both CuHg₂Ti-type and AlCu₂Mn-type structures have been investigated using first-principles calculations based on density functional theory (DFT). Two nearly half-metallic ferrimagnets (HMFs), Cr₂CoSb, and Cr₂FeSb in CuHg₂Ti-type structure, are predicted. The energy gap lies in the minority spin band for both alloys. The calculated total spin magnetic moments are 2μ _B and 1μ _B per unit cell for Cr₂CoSb and Cr₂FeSb alloys, respectively, which are in good agreement with the Slater–Pauling relation. For these alloys, the magnetic moments of Y and Cr(B) are antiparallel to that of Cr(A) and all of these moments increase with increasing lattice constant. It was also found that the half-metallic properties of Cr₂CoSb and Cr₂FeSb are unaffected to the lattice distortion and the half-metallicity can be obtained within the wide range of 5.52–6.07 Å and 5.96–6.16 Å for Cr₂CoSb and Cr₂FeSb alloys, respectively.     

Revealing the role of site occupation in phase stability,magnetic and electronic properties of Ni-Mn-In alloys by ab initio approach

The effects of site occupation on the phase stability,martensitic transformation,and the magnetic and electronic properties of a full series of Ni-Mn-In alloys are theoretically studied by using the ab initio calculations.Results indicate that the excess atoms of the rich component directly take the sublattices of the deficient components of the Ni2Mn1+xIn1-x,Ni2-xMn1+xIn,and Ni2+xMn1-xIn alloys.Nevertheless,the mixed and indirect site occupations may coexist in the Ni2+xMnIn1-x system.The relevant magnetic configurations of the austenite for the four alloy systems have also been determined.The results show that,except for the austenite in the Ni2-xMn1+xIn alloys,which tend to be ferrimagnetic,the other alloys all present ferromagnetic austenite.Thus,the site occupation and associated magnetic states are the crucial influencing factors of the phase stability,martensitic transformation,and the total magnetic moment.The electronic structure of the austenite phase also shows that the covalent bonding plays an important role in the phase stability.The key finding of this work is both Ni2Mn1+xIn1-x and Ni2+xMnIn1-x alloys serve as the potential shape memory alloys.     

FePt Hard Magnets

The FePt alloys have recently attracted considerable attention due to their excellent intrinsic magnetic, chemical and mechanical properties. Their possible usage ranges from permanent magnets for special applications (e.g. in micro‐electro‐mechanical systems, magnetic MEMS, and in aggressive environments) to ultra‐high density magnetic storage media. The article describes general aspects concerning the phase formation and magnetic properties of materials based on the L1₀ FePt phase. Both thin film and bulk approaches are considered. The production of bulk nanocrystalline Fe_100‐xPt_x powders by mechanical alloying and subsequent annealing is described. Various combinations of phases, away from thermodynamic equilibrium, have been obtained using this technique.     

Bi4Ti3O12–(Ni0.5Zn0.5)Fe2O4 dielectric–ferromagnetic ceramic composites synthesized with nanopowders

Bi₄Ti₃O₁₂ and (Ni_0.5Zn_0.5)Fe₂O₄ nanopowders were prepared by co-precipitation and hydrothermal methods, respectively. It was found that ethanolamine is effective as a precipitating agent in the synthesis of Bi₄Ti₃O₁₂ nanopowders via co-precipitation, and it also plays an important role in the synthesis of (Ni_0.5Zn_0.5)Fe₂O₄ nanopowders. Bi₄Ti₃O₁₂–(Ni_0.5Zn_0.5)Fe₂O₄ multiferroic ceramics were obtained by sintering the as-prepared nanopowders. Lower sintering temperatures (800–900 °C) were available when compared with the traditional solid state method and ceramic composites with higher density and limited interfacial reaction were obtained. The ceramics also showed lower dielectric loss and higher magnetic moments. Both the ferroelectric and magnetic phases preserve their individual properties in bulk composite form and thus, these types of composite ceramics appear to be good candidate multiferroic materials.     

Effect of metalloids on crystallization and magnetic behaviour of FeCoSiB based metallic glass

A series of amorphous iron-cobalt alloys with varying metalloid, boron and silicon contents were studied for their thermal stability and magnetic behaviour. The crystallization temperature and thermal stability increased with the silicon content. Good soft magnetic properties were observed for the materials with nominal composition, (Fe_0.79Co_0.21)77Si_12.2B_10.8. The magnetic properties were further improved by annealing.     

Half-Metallic Ferromagnetism in Strontium-Doped III–V: Ab Initio Calculations

First-principle calculations are employed by means of an all-electron full-potential linearized augmented plane wave to investigate the electronic structure and magnetic properties of AlP, AlAs, GaP, GaAs, InP, and InAs-based dilute magnetic semiconductors (DMS) with Sr impurities. It is shown that, in all the cases the ferromagnetic phase is energetically favored with respect to the paramagnetic one. In addition, these alloys are found to be half-metallic ferromagnets with a net total magnetic moment of 1.00 μ _B when they assume the zinc-blende structure at the equilibrium lattice constant. Ferromagnetism is induced by the spin polarization of the p shells of anions; the magnetic moment mainly comes from anion atoms surrounding the dopant atom, which is different from conventional DMS. These theoretical results make these materials interesting candidates for spin injection in spintronic devices.     

Design, structure, and properties of functional metal–ligand inorganic modules

From the standpoint of supramolecular chemistry major advances have been made concerning the functional properties of metal–ligand-based coordination complexes/extended solids/polymers. This paper reviews recent results from our laboratories on two contemporary areas of research: (i) spin-crossover Fe^IIN₆ complexes which are representative examples of molecular bistability and (ii) synthesis of tailor-made transition-metal-based 1D coordination polymers and investigation of their magnetic exchange phenomena from the standpoint of molecule-based magnetic materials. Our primary focus is on the magnetic properties which seem to hold promise for future applications. It has been shown that covalent bond-driven discrete complexes/coordination polymers are further stabilized by association due to multiple weak, noncovalent interactions. In the design of Fe^IIN₆ complexes our laboratories have so far relied on synthesis of discrete molecules. However, they are connected by noncovalent interactions, imparting cooperativity.     

Grain boundary wetting in the NdFeB-based hard magnetic alloys

Since the end of 1980s, NdFeB-based hard magnetic alloys have been the materials with the highest available magnetic performance. NdFeB-based magnets are produced either by liquid-phase sintering or by melt spinning. In the present investigation, NdFeB alloys quenched after annealing in the semi-liquid state are used to study the wetting of Nd₂Fe₁₄B grain boundaries by a Nd-rich liquid phase. It is shown that a transition from partial wetting to complete wetting occurs with increasing temperature. The results are compared with the data in the literature for NdFeB-based alloys processed by liquid-phase sintering. The relation between wetting properties and magnetic performance of these alloys is also discussed.     

Synthesis, characterization and magnetoresistance properties study of magnetite thin films by electroless plating in aqueous solution

Polycrystalline half-metallic Fe₃O₄ films with 1 μm in thickness were synthesized on glass substrates directly by electroless plating in aqueous solution at 90 °C without heat treatment. The films have single pure spinal phase structure and the well-crystallized columnar grains grow perpendicularly to the substrates, as revealed by XRD, XPS and SEM. At room temperature, the films exhibit negative magnetoresistance (MR) ratio of about −5.1%, which is ascribed to intergranular tunneling of spin polarized electrons of Fe₃O₄. The resistivity R of the films with 1 μm in thickness at room temperature is about 5.2 × 10⁻¹ Ω cm. The cation distribution and the arrangement of the magnetic moments of the plated Fe₃O₄ ferrite thin films are different from that of the bulk materials, which is likely to be one of the reasons for the modification of R and MR properties.     

Electronic band structure calculations on thin films of the L21 full Heusler alloys X2YSi (X, Y = Mn, Fe, and Co): Toward spintronic materials

To design half-metallic materials in thin film form for spintronic devices, the electronic structures of full Heusler alloys (Mn₂FeSi, Fe₂MnSi, Fe₂FeSi, Fe₂CoSi, and Co₂FeSi) with an L2₁ structure have been investigated using density functional theory calculations with Gaussian-type functions in a periodic boundary condition. Considering the metal composition, layer thickness, and orbital symmetries, a 5-layered Co₂FeSi thin film, whose surface consists of a Si layer, was found to have stable half-metallic nature with a band gap of ca. 0.6 eV in the minority spin state. Using the group theory, the difference between electronic structures in bulk and thin film conditions was discussed.     

Synthesis,characterization and magnetoresistance properties study of magnetite thin films by electroless plating in aqueous solution

Polycrystalline half-metallic Fe₃O₄ films with 1 μm in thickness were synthesized on glass substrates directly by electroless plating in aqueous solution at 90 °C without heat treatment. The films have single pure spinal phase structure and the well-crystallized columnar grains grow perpendicularly to the substrates, as revealed by XRD, XPS and SEM. At room temperature, the films exhibit negative magnetoresistance (MR) ratio of about −5.1%, which is ascribed to intergranular tunneling of spin polarized electrons of Fe₃O₄. The resistivity R of the films with 1 μm in thickness at room temperature is about 5.2 × 10⁻¹ Ω cm. The cation distribution and the arrangement of the magnetic moments of the plated Fe₃O₄ ferrite thin films are different from that of the bulk materials, which is likely to be one of the reasons for the modification of R and MR properties.     

Self-propagating high temperature synthesis of Ni0.35Zn0.65Fe2O4 ferrite powders

The stoichiometric Ni_0.35Zn_0.65Fe₂O₄ ferrite powders were synthesized by SHS method. In the process of SHS, the effects of the molar ratio Fe/Fe₂O₃ in the starting mixture, oxygen pressure, grain size and relative density of the raw materials on combustion temperature, combustion wave velocity, phase composition and microstructure of the combustion products were investigated. X-ray diffraction, scanning electron microscope, TEM, vibrating sample magnetometry were used to characterize the microstructure and magnetic properties of the products. The results showed that as the molar ratio Fe/Fe₂O₃ increases, the combustion temperature and combustion wave velocity increased. The same results can be observed when the oxygen pressure increased from 0.1 to 0.9 MPa. The increase of grain size and relative density of raw materials resulted in the decrease of combustion temperature and combustion wave velocity. Compared with other methods, SHS process leads to ferrite powders with improved magnetic properties.     

Enhancement of soft magnetic properties of FeCoNbB nanocrystalline alloys with Cu and Ni additions

The magnetic properties of annealed Fe₄₂Co₄₂Nb₇B₈Cu_0.5Ni_0.5, Fe₄₂Co₄₂Nb₆B₈Cu₁Ni₁ and Fe_42.5Co_42.5Nb₆B₈Cu_0.5Ni_0.5 alloys produced by melt spinning have been studied. By simultaneous addition of Cu and Ni elements, the soft magnetic properties of nanocrystalline FeCoNbB alloy with high Curie temperature were greatly improved. The annealed alloys show high Curie temperature of more than 1223 K and excellent soft magnetic properties, i.e., low coercivity of about 30 A/m and high effective permeability of above 5000, and these values are superior to the typical nanocrystalline HITPERM alloys for high temperature applications.     

A facile surfactant-free fabrication of single-crystalline truncated Fe3O4 cubes

Single-crystalline truncated Fe₃O₄ cubes with active basal facets have been successfully fabricated through a facile surfactant-free hydrothermal route. The presented materials were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), dynamic light scattering (DLS), selection area electron diffraction (SAED) and magnetic property measurement system (MPMS). The results showed that all products are Fe₃O₄ with face-center-cubic (FCC) structure. The morphology of Fe₃O₄ depends on the contents of hydroxide ions, hydrazine hydrate and reaction time. The well-defined truncated Fe₃O₄ cubes with active basal facets {1 0 0} were fabricated when the pH value, the hydrazine hydrate content and reaction time are 10, 10 mL and 24 h, respectively. The as-prepared Fe₃O₄ cubes exhibit excellent magnetic properties, which endow the materials with great potential applications in many fields.