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Ab Initio Study of the Electronic Structure, Elastic Properties, Magnetic Feature and Thermodynamic Properties of the Ba{sub 2}NiMoO{sub 6} Material
We report first-principles calculations of the elastic properties, electronic structure and magnetic behavior performed over the Ba{sub 2}NiMoO{sub 6} double perovskite. Calculations are carried out through the full-potential linear augmented plane-wave method within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient and Local Density Approximations, including spin polarization. The elastic properties calculated are bulk modulus (B), the elastic constants (C{sub 11}, C{sub 12} and C{sub 44}), the Zener anisotropy factor (A), the isotropic shear modulus (G), the Young modulus (Y) and the Poisson ratio (υ). Structural parameters, total energies and cohesive properties of the perovskite are studied by means of minimization of internal parameters with the Murnaghan equation, where the structural parameters are in good agreement with experimental data. Furthermore, we have explored different antiferromagnetic configurations in order to describe the magnetic ground state of this compound. The pressure and temperature dependence of specific heat, thermal expansion coefficient, Debye temperature and Grüneisen parameter were calculated by DFT from the state equation using the quasi-harmonic model of Debye. A specific heat behavior C{sub V} ≈ C{sub P} was found at temperatures below T = 400 K, with Dulong–Petit limit values, which is higher than those, reported for simple perovskites.
Magnetic properties of Fe-Mn-Pt for heat assisted magnetic recording applications
We calculate the electronic structures of FePt and Fe{sub 0.5}Mn{sub 0.5}Pt using first-principles calculations based on density functional theory within the local-spin-density approximation. The Curie temperature (T{sub c}) was calculated by mean field approximation. Composition dependence of the Cure temperature (T{sub c}(x)) of Fe{sub 1−x}Mn{sub x}Pt was used to identify a composition to meet the desired T{sub c} in the range of 600–650 K. The identified composition (0.0294 ≤ x ≤ 0.0713) gives saturation magnetization (M{sub s}) in the range of 1041–919 emu/cm{sup 3} and magnetocrystalline anisotropy constant (K) in the range of 9.96–8.36 × 10{sup 6 }J/m{sup 3} at 0 K. Temperature dependent M(T) and K(T) of Fe{sub 1−x}Mn{sub x}Pt (0.0294 ≤ x ≤ 0.0713) were calculated using the Brillouin function and Callen-Callen experimental relation, respectively. Fe{sub 1−x}Mn{sub x}Pt (0.0294 ≤ x ≤ 0.0713) shows 930–800 emu/cm{sup 3} of M{sub s} and 7.18–5.61 × 10{sup 6 }J/m{sup 3} of K at 300 K, thereby satisfying desired magnetic properties for heat-assisted magnetic recording media to achieve 4 Tb/in.{sup 2} areal density.
Annealing Effects on Microstructure and Magnetic Properties of (NdPr){sub 9.5}(FeNbCoCu){sub 79.5}(BC){sub 11} Nanocomposite Magnets
Annealing effects on microstructure and magnetic properties of (NdPr){sub 9.5}(FeNbCo){sub 79.5}(BC){sub 11} ribbons were investigated. It was observed that Nd{sub 2}Fe{sub 14}B and Fe{sub 3}B phases were directly formed at low spinning speed. Then, the alloys transformed to an amorphous state at a speed of 20 m/s. Annealed at 700 {sup ∘}C for 10 min, the amorphous alloys as-quenched at 20 m/s crystallized into a nanocomposite composed of Nd{sub 2}Fe{sub 14}B and α-Fe phases. The formation of Fe{sub 3}B phases was inhibited. The magnetic properties firstly increased and then decreased with the increasing of annealing time. The optimum magnetic properties were achieved in the alloys annealed at 700 {sup ∘}C for 10 min. The corresponding coercivity, remanence, and the maximum energy product was 427.5 kA/m, 0.94 T, and 101.2 kJ/m{sup 3}, respectively. In addition, fine and uniform grains were formed. The average grain size was 10 nm.
Magnetic properties and transformation of crystal structure in the ErFe{sub 2}-ErAl{sub 2} system
The modification of structural properties and magnetic behaviour of the ErFe{sub 2−x}Al{sub x} Laves phase intermetallic compounds have been studied while changing the Al content in the range 0.36 ≤ x ≤ 1.5. Powder X-ray diffraction study at room temperature showed the formation of the cubic C15 structure, in the samples with Al content of 0.36 ≤ x < 0.75 and 1.4 ≤ x ≤ 2.0. For the intermediate compositions with 0.75 ≤ x ≤ 1.4, the hexagonal C14 structure is observed. Magnetic and magnetocaloric properties of polycrystalline ErFe{sub 2−x}Al{sub x} intermetallic compounds were investigated experimentally using magnetic and heat capacity measurements. The Curie temperature T{sub C} decreases from 275 to 28 K as the Al content increases from x = 0.36 to x = 1.5, respectively. Magnetization measurements in strong magnetic fields showed the complex mechanism of magnetic saturation in the studied compounds. Under an external field change from 0 to 2 T, the maximum entropy change is 6 J/kg K at T = 28 K for the composition with x = 1.5. The minimum in the concentration dependence of the magnetic entropy change is observed in the vicinity of x equal to 1.25. Regularities of variations of magnetocaloric properties of ErFe{sub 2−x}Al{sub x} intermetallic compounds with increasing Al content are discussed from the point of view of their both structural and magnetic states.
Preliminary Stress-Annealing Process and its Effect on Magnetic Properties of Fe-based Soft Magnetic Alloys
Stress-annealing (SA) is a novel secondary processing technique capable of significantly increasing magnetic anisotropy and controlling magnetic permeability in planar-cast amorphous precursor ribbons. In this technical memorandum, measures taken to improve the mechanical handling of brittle Fe-based ribbons are described for a custom SA system. This system was then used to process a series of Fe-based alloys (Fe-2Nb-2Mo-1Cu-15.5Si-7B at.%, Fe-5Co-3Ta-1Cu-16Si-6.5B at.%, and Fe-5Co-3Ta-1Cu-16.5Si-6B at.%) and the resulting magnetic properties were determined. The Fe-5Co-3Ta-1Cu-16.5Si-6B at.% alloy was found to be the most promising composition of the three in terms of surviving an optimized spool-to-spool continuous SA process under 90 MPa of tensile stress at 650 °C using a feed rate of 75.5 in/min, which equated to approximately 10 second anneal time. These optimally annealed ribbons exhibited flat hysteresis loops with a saturation magnetization of nearly 1.2 T, low magnetic coercivity (≈ 2 A m-1), and relative permeability of approximately 500.
Fe and Co nanostructures embedded into the Cu(100) surface: Self-Organization and magnetic properties
The self-organization and magnetic properties of small iron and cobalt nanostructures embedded into the first layer of a Cu(100) surface are investigated using the self-learning kinetic Monte Carlo method and density functional theory. The similarities and differences between the Fe/Cu(100) and the Co/Cu(100) are underlined. The time evolution of magnetic properties of a copper monolayer with embedded magnetic atoms at 380 K is discussed.
Effects of La Doping and Zn or O Vacancy on the Magnetic Property of ZnO
Research on the magnetic origin and mechanism of La-doped ZnO system has been controversial. To solve this problem, we studied the effects of La doping and Zn or O vacancy on the magnetic property of ZnO using geometry optimization and energy calculation on the basis of first-principle generalized gradient approximation method of density functional theory. The electronic structures and magnetic properties of undoped ZnO, La-doped ZnO system, and systems with coexisting La doping and Zn or O vacancies were calculated. Results showed that the systems of La-doped ZnO and the coexistence of La doping and O vacancy are nonmagnetic. In addition, the system of La replacing Zn and one Zn vacancy exhibits long-range orderly ferromagnetism, and the Curie temperature of the doping system can achieve room temperature. The magnetism source of the systems with La doping and Zn vacancy coexisting in ZnO demonstrates strong hybrid coupling electron exchange effects existing among Zn-4s, Zn-3p, O-2p, and La-5s orbits that are nearest to the Zn vacancy. The next nearest distance between doping and Zn vacancy leads to the lowest formation energy and highest stability under the same doping condition.
Effects of wear on structure-sensitive magnetic properties of ceramic ferrite in contact with magnetic tape
Wear experiments and electron microscopy and diffraction studies were conducted to examine the wear and deformed layers in single-crystal Mn-Zn (ceramic) ferrite magnetic head material in contact with magnetic tape and the effects of that contact on magnetic properties. The crystalline state of the single-crystal magnetic head was changed drastically during the sliding process. A nearly amorphous structure was produced on its wear surface. Deformation in the surficial layer of the magnetic head was a critical factor in readback signal loss above 2.5 dB. The signal output level was reduced as applied normal load was increased. Considerable plastic flow occurred on the magnetic tape surface with sliding, and the signal loss due to the tape wear was approximately 1 dB.
Heptacopper(II) and dicopper(II)-adenine complexes: synthesis, structural characterization, and magnetic properties
The syntheses, crystal structures, and magnetic properties of two new copper(II) complexes with molecular formulas [Cu 7 (μ 2 -OH 2 ) 6 (μ 3 -O) 6 (adenine) 6 (NO 3 ) 2 6H 2 O (1) and [Cu 2 (μ 2 -H 2 O) 2 (adenine) 2 (H 2 O) 4 ](NO 3 ) 4 2H 2 O (2) are reported. We composed the heptanuclear compound of a central octahedral CuO 6 core sharing edges with six adjacent copper octahedra. In 2, the copper octahedra shares one equatorial edge. In both compounds, these basic copper cluster units are further linked by water bridges and bridging adenine ligands through N3 and N9 donors. All copper(II) centers exhibit Jahn-Teller distorted octahedral coordination characteristic of a d 9 center. Our study of the magnetic properties of the heptacopper complex revealed a dominant ferromagnetic intra-cluster interaction, while the dicopper complex exhibits antiferromagnetic intra-dimer interactions with weakly ferromagnetic inter-dimer interaction.
Co thickness dependence of structural and magnetic properties in spin quantum cross devices utilizing stray magnetic fields
We investigate the Co thickness dependence of the structural and magnetic properties of Co thin-film electrodes sandwiched between borate glasses in spin quantum cross (SQC) devices that utilize stray magnetic fields. We also calculate the Co thickness dependence of the stray field between the two edges of Co thin-film electrodes in SQC devices using micromagnetic simulation. The surface roughness of Co thin films with a thickness of less than 20 nm on borate glasses is shown to be as small as 0.18 nm, at the same scanning scale as the Co film thickness, and the squareness of the hysteresis loop is shown to be as large as 0.96–1.0. As a result of the establishment of polishing techniques for Co thin-film electrodes sandwiched between borate glasses, we successfully demonstrate the formation of smooth Co edges and the generation of stray magnetic fields from Co edges. Theoretical calculation reveals that a strong stray field beyond 6 kOe is generated when the Co thickness is greater than 10 nm at a junction gap distance of 5 nm. From these experimental and calculation results, it can be concluded that SQC devices with a Co thickness of 10–20 nm can be expected to function as spin-filter devices.
A facile route to synthesize core/shell structured carbon/magnetic nanoparticles hybrid and their magnetic properties
Graphical abstract: Controllable synthesis of core/shell structured carbon/magnetic nanoparticles hybrid and their tunable magnetic properties. - Highlights: • The paper reports a simple route for core/shell structured carbon/magnetic nanoparticles hybrid. • By controlling the temperature, Fe{sub 3}O{sub 4}@CNCs, Fe@HCNTs and Fe@LCNTs were produced selectively. • The magnetic properties of the obtained core/shell structured hybrid could be tuned effectively. - Abstract: By controlling the pyrolysis temperature, core/shell structured Fe{sub 3}O{sub 4}/carbon nanocages, Fe/helical carbon nanotubes and Fe/low helicity of carbon nanotubes could be synthesized selectively over Fe{sub 2}O{sub 3} nanotubes generated by a hydrothermal method. The transmission electron microscopic and scanning electron microscopic investigations revealed that the efficiency of generating core/shell structured hybrid was high, exceeding 90%. Because of the magnetic nanoparticles tightly wrapped in graphitic layers, the obtained core/shell structured hybrids showed high stability and good magnetic properties. And the magnetic properties of the obtained core/shell structured hybrid could be tuned by the decomposition temperature and time. Therefore, a simple, inexpensive and environment-benign route was proposed to produce magnetism-tunable core/shell structured hybrid in large quantities.
Design guidance for ferrites: Insights from density functional theory on magnetic properties
A grand challenge in materials research is identifying the relationship between composition and performance. Herein, we explore this relationship for magnetic properties, specifically magnetic saturation (M s ) and magnetocrystalline anisotropy energy (K) of ferrites. Ferrites are materials derived from magnetite (chemical formula = Fe 3 O 4 ) that comprise metallic elements such as Fe, Mn, Ni, Co, Cu and Zn. Experimentally, synthesizing and characterizing ferrites is time consuming. Further, selection of compositions to achieve particular magnetic properties currently relies on intuition. To address this, in this work, density functional theory (DFT) is used to predict M s and K for 571 ferrite structures. These structures are primarily double-substituted non-stoichiometric ferrites with formulae M1 x M2 y Fe 3–x–y O 4 , where M1 and M2 can be Mn, Ni, Co, Cu and/or Zn and 0 ≤ x ≤ 1 and y = 1–x. Calculated magnetic properties for the structures in this study vary from 0.04 × 10 5 to 9.6 × 10 5 A m −1 for M s and from 0.02 × 10 5 to 14.08 × 10 5 J m −3 for K. All structures are made publicly available in a FAIR database.
The effect of boron doping on crystal structure, magnetic properties and magnetocaloric effect of DyCo 2
In this study, the magnetic properties and magnetic entropy changes of DyCo 2 B x (x=0, 0.05, 0.1, and 0.2) alloys were investigated. The Curie temperature (TC) increases with increasing B concentration. The frequency dependence of ac magnetic susceptibility of DyCo 2 caused by the narrow domain wall pinning effect is depressed by B doping, but the coercivity and the magnetic viscosity are prominently increased in the B doped alloys. The magnetic transition nature of DyCo 2 B x changes from the first-order to the second-order with increasing x, which leads to the decrease of the maximum magnetic entropy change. However, the relative cooling power (RCP) of DyCo 2 and the B doped alloys remains nearly constant.
Optimization of permanent magnetic properties in melt spun Co{sub 82−x}Hf{sub 12+x}B{sub 6} (x = 0–4) nanocomposites
Magnetic properties of melt spun Co{sub 82−x}Hf{sub 12+x}B{sub 6} ribbons made with various wheel speeds have been studied. The ribbons with x = 0–1 are not easy to crystallize and thus display soft magnetic behavior even at wheel speed of 10 m/s. In contrast, the ribbons with x = 1.5–4 at optimized wheel speed exhibit good permanent magnetic properties of B{sub r} = 0.41–0.59 T, {sub i}H{sub c} = 120–400 kA/m, and (BH){sub max} = 10.6–48.1 kJ/m{sup 3}. The optimal magnetic properties of B{sub r} = 0.59 T, {sub i}H{sub c} = 384 kA/m, and (BH){sub max} = 48.1 kJ/m{sup 3} are achieved for Co{sub 80}Hf{sub 14}B{sub 6} ribbons at wheel speed of 30 m/s. X-ray diffraction, thermo-magnetic analysis, and transmission electron microscopy results show that good hard magnetic properties of Co{sub 82−x}Hf{sub 12+x}B{sub 6} ribbons (x = 2–4) are originated from the Co{sub 11}Hf{sub 2} phase well coupled with the Co phase. The change of magnetic properties for Co{sub 82−x}Hf{sub 12+x}B{sub 6} ribbons spun at various wheel speeds is correlated to microstructure and phase constitution. The strong exchange-coupling effect between magnetic grains for the ribbons with x = 2–3 at wheel speed = 30 m/s leads to remarkable permanent magnetic properties. The presented results suggest that the optimized Co{sub 82−x}Hf{sub 12+x}B{sub 6} (x = 2–3) ribbons are much suitable than others (x = 0–1.5 and 4) for making rare earth and Pt-free magnets.
Tuning the magnetic properties of the CrMnFeCoNi Cantor alloy
Magnetic properties of more than 20 Cantor alloy samples of varying composition were investigated over a temperature range of 5 K to 300 K and in fields of up to 70 kOe using magnetometry and muon spin relaxation. Two transitions are identified: a spin-glass-like transition that appears between 55K and 190K, depending on composition, and a ferrimagnetic transition that occurs at approximately 43K in multiple samples with widely varying compositions. The magnetic signatures at 43K are remarkably insensitive to chemical composition. A modified Curie-Weiss model was used to fit the susceptibility data and to extract the net effective magnetic moment for each sample. The resulting values for the net effective moment were either diminished with increasing Cr or Mn concentrations or enhanced with decreasing Fe, Co, or Ni concentrations. Beyond a sufficiently large effective moment, the magnetic ground state transitions from ferrimagnetism to ferromagnetism. The effective magnetic moments, together with the corresponding compositions, are used in a global linear regression analysis to extract element-specific effective magnetic moments, which are compared to the values obtained by ab initio based density functional theory calculations. Finally, these moments provide the information necessary to controllably tune the magnetic properties of Cantor alloy variants.
The Crystal Structure, Raman Spectra, and Magnetic Properties of HoCrO{sub 3} Annealed in Different Atmospheres
The crystal structure, phonon Raman scattering, and magnetic properties of HoCrO{sub 3} were studied in a way of impacting the oxygen site by annealing treatment in argon and oxygen atmospheres. Although there are no dramatic changes in magnetic properties, a negative magnetization phenomenon below T{sub N} was observed in all prepared HoCrO{sub 3} samples and a certain of lattice distortion was affected due to the variation of Ho–O bond length and Cr–O–Cr bond angle and bond lengths. The Raman spectra exhibit an obvious shift of mode-related Ho ion instead of modes involved with Cr, which unconsciously leads to the variation of effective paramagnetic moments. The magnetic properties were systematically analyzed by Curie-Weiss and modified Curie-Weiss laws. The effective magnetic moment and symmetric and antisymmetric exchange interactions of J{sub e} and D were discussed. The reduced effective magnetic moments in HoCrO{sub 3} and annealed ones demonstrate possible vacancies of Ho and Cr, which was verified by elemental composition tested by energy-dispersive X-ray spectroscopy.
Cationic distribution assisted tuning of magnetic properties of Li{sub 0.5-x/2}Zn{sub x}Fe{sub 2.5-x/2}O{sub 4}
Zn addition induced modification of cationic distribution for tuning magnetic properties of Li{sub 0.5-x/2}Zn{sub x}Fe{sub 2.5-x/2}O{sub 4} (x = 0, 0.1, 0.25, 0.3, 0.5, 0.7, 0.9, 1.0) powders is studied by x-ray diffraction (XRD) and magnetic measurements. XRD shows the formation of cubic spinel structure, with Scherrer’s grain diameter ranging between 26.7 to 37.8 nm. With Zn addition, oxygen anions are displaced in such a way that the A-B interaction weakens, whereas A-A and B-B interaction strengthens; furthermore it also pushes Fe{sup 3+} and Li{sup 1+} ions to B site, leading to changes in magnetic properties. Highest saturation magnetization (M{sub s}) of 64.6 A m{sup 2} / kg was obtained for sample with x = 0.25 and lowest coercivity (H{sub c}) of 4949.9 A/m was obtained for the sample with x = 0.7. Calculated values of experimental magnetic moment ‘n{sub B}’ and Neel magnetic moment ‘n{sub N}’, display similar trend as that of M{sub s}. Present results very clearly show a strong correlation between Zn-addition induced changes in cation distribution and magnetic properties, which can be utilized effectively for tuning magnetic properties.