Anisotropy Constant Decreases Research Articles

ANALYSIS OF STUDYING THE STRUCTURE OF EPITAXIAL IRON FILMS ON GALLIUM ARSENIDE Fe/GaAs

The anisotropy in thin films coincides with the crystallographic direction of an increase in the thickness of the iron layer. The value of the cubic anisotropy constant decreases. In this case, the value of the uniaxial anisotropy constant, on the contrary, increases. The dilution of the semiconductor matrix with iron atoms is also noted, and the formation of Fe-Ga or Fe-As compounds is assumed. An analysis of the surface sensitivity of the spectra of As and Ga shows that As is more easily mixed with Fe than with Ga.

Temperature-dependent magnetic properties of the room-temperature ferromagnetic Janus monolayer Fe2XY (X, Y = I, Br, Cl; X ≠ Y).

Excellent magnetic properties at room temperature are crucial for the application of ferromagnets in spintronic and topological quantum devices. Using first-principles calculations and atomistic spin model simulations, we investigate the temperature-dependent magnetic properties of the Janus monolayer Fe2XY (X, Y = I, Br, Cl; X ≠ Y), as well as the effects of different magnetic interactions within the next-nearest-neighbor shell on the Curie temperature (TC). A large isotropic exchange interaction between one Fe atom and its next-nearest-neighbor counterparts can significantly increase the TC, while an antisymmetric exchange interaction decreases it. More importantly, we employ the temperature rescaling method, which can obtain temperature-dependent magnetic properties quantitatively consistent with experimental values, and find that the effective uniaxial anisotropy constant and coercive field decrease with increasing temperature. Moreover, at room temperature, Fe2IY is a rectangular-loop magnetic material with a giant coercive field up to ∼8 T, demonstrating its potential for application in room-temperature memory devices. Our findings can advance the application of these Janus monolayers in room-temperature spintronic devices and through heat-assisted techniques.

Composition and property optimization of rare-earth-free Mn-Al-C magnet by phase stability and magnetic behavior analysis

Mn-Al-C system offers a possibility of rare-earth-free permanent magnets with the reduced temperature-dependent deterioration of magnetic properties. The Mn-Al-C alloy composition and magnetic properties have been optimized via calculations of electronic structures and phase stability of L 1 0 -ordered ferromagnetic τ-phase (Mn 0 . 5 Al 0 . 5 ) 100−x C x . The WIEN2k program package, Vienna Ab-initio simulation package (VASP), and Alloy Theoretic Automated Toolkit (ATAT) were used to calculate and identify the optimal carbon content for the most stable τ-phase of the L 1 0 -structured Mn-Al-C. We used the Brillouin function and Callen-Callen semiempirical relation to obtain the saturation magnetization and magnetocrystalline anisotropy constant at elevated temperatures. It was found that a carbon content of 2.33 at% gives the most stable τ-phase L 1 0 (Mn 0 . 5 Al 0 . 5 ) 100−x C x that has the lowest formation energy and highest saturation magnetization among the studied carbon contents (x = 0–3.03 at %). The magnetocrystalline anisotropy constant at 0 K increases with increasing the carbon content. Therefore, the carbon-doped Mn-Al becomes magnetically harder than the pure Mn 50 Al 50 . However, the anisotropy constant decreases at 300 K as the carbon content increases. The Curie temperature decreases to 590 K at x = 2.33 from 685 K at x = 0.0. The estimated saturation magnetization was approximately 130 emu/g at 300 K, leading to 18 MGOe under B s = B r and H ci > B r /2. Therefo r e, it is highly probable that Mn-Al-C potentially fills the gap between 10 and 30 MGOe magnets. The results in this study quantify and explain the reason for widely studying the approximately 2 at% carbon-doped Mn-Al systems. • A rare-earth-free, ferromagnetic L10 τ-phase (Mn0.5Al0.5)100-xCx was designed by first-principle calculations. • The calculated carbon content of 2.33 at% gives the lowest formation energy. • Theoretically optimized carbon content was in good agreement with experimental results. • The results explain the reason for widely studying the approximately 2 at% carbon-doped Mn-Al systems. • Rare-earth-free Mn-Al-C potentially fill the gap between 10 and 30 MGOe magnets.

Effects of carbon implantation on the low temperature magnetism behavior in amorphous Fe93Zr7 films

We present a detailed investigation on the effects of C-implantation on low temperature magnetic behavior in Fe93Zr7 amorphous films using spin wave theory, law of approach to saturation, and Alben and Becker's theory. Significant increase in Curie temperature with a decrease in coercivity were observed upon C-implantation. Bloch's law was used to analyze the temperature dependence of magnetization, and several important parameters were extracted such as the stiffness constant of the spin wave, and the exchange constant. The local random anisotropy constant decreases from 0.35 to 0.19 MJ/m3 with increasing carbon concentration from 0 to 11%. The ferromagnetic correlation length for which the anisotropy directions are assumed to be arbitrarily oriented increases significantly with increasing carbon content. By the use of the theory of Alben and Becker, we also extracted the local anisotropy from coercivity, and reasonable agreement was found with random magnetic anisotropy approach.

Investigation of structural, magnetic and electrical properties of aluminum substituted Co-Mg ferrite

The effect of nonmagnetic Al3+ substitution on the structural, morphological, magnetic, and dielectric characteristics of Co0.5Mg0.5AlxFe2−x04 ferrite nanoparticles synthesized using the co-precipitation method was investigated. All samples were found to have a single-phase cubic spinel by X-ray diffraction. The decrease in crystallite size from 55 to 29 nm with Al3+ substitution validated the materials nano-crystalline formation. The infrared spectrum exhibits two distinct absorption bands matching to the spinel structure as well as two extra absorption bands and a shoulder between 360 and 265 cm−1. The DSC exothermic peaks around 440 °C may be attributed to the phase shift of the prepared samples from amorphous to the crystalline state. The TEM results were used to investigate the sample shape and quantify particle size demonstrating that increasing the Al3+ content induces a decrease in particle size. The VSM technique revealed a decrease in magnetic properties which was attributable to an increase in nonmagnetic Al3+ ions. The magnetic permeability is found to rise with increasing Al3+ content as the anisotropy constant decreases. Dielectric characteristics were investigated at room temperature in the frequency range of 0.1 Hz–20 MHz. The presence of polaron type conduction in the prepared samples was confirmed by the ac conductivity. These produced nanoparticles dielectric characteristics demonstrate their utility in high-frequency device development applications and electronic device production.

Nanoscale-driven single-domain structure in nickel substituted superparamagnetic cobalt ferrites

In this letter, we reported nickel substituted cobalt nano-ferrites of ∼ 5 nm particle size synthesized with forced hydrolysis methods. The magnitude of the anisotropy constant decreases from 6.06×105 to 2.45×104 erg/cm3 due to the Ni2+ doping. Whereas the gradual increment of Ni2+ ions decreases the blocking temperature from ∼182 k to ∼52 K. The single-domain superparamagnetic behaviour observed here above the blocking temperature. This behaviour could help the material be a promising candidate in quantum technologies as a bit for storage devices.

Spin dynamics study and experimental realization of tunable single-ion anisotropy in multiferroic Ba2CoGe2O7 under external magnetic fields

We report a spin-wave study on multiferroic ${\mathrm{Ba}}_{2}{\mathrm{CoGe}}_{2}{\mathrm{O}}_{7}$ under magnetic fields up to 12 T using low-energy inelastic neutron scattering. In-plane transverse $({T}_{1})$ spin-wave modes are highly dispersive along $(h00)$ and rather flat but strong in intensity along $(30l)$. In addition, two dispersive electromagnon modes have been observed around 3.5 meV. Dispersion of the out-of-plane transverse modes $({T}_{2})$ under fields reveals that the single-ion anisotropy constant decreases with increasing magnetic field, which is consistent with the linear spin-wave theory. Our results imply that the field-dependent single-ion anisotropy plays a crucial role in determining the characteristics of ${T}_{2}$ and electromagnon modes in the three-dimensional anisotropic spin-wave spectrum.

Random magnetic anisotropy approach in amorphous Fe88.4Zr11.6 films: Effects of hydrogen implantation

The effects of hydrogen implantation on the magnetic properties in amorphous Fe88.4Zr11.6Hx films with different hydrogen contents (0≤ x≤16) were investigated. The Curie temperature increases with increasing hydrogen content while the coercivity presents an important decrease upon H implantation. Based on the analysis of the approach to saturation in magnetization, the local random anisotropy constant KL was extracted. The local random anisotropy constant decreases from 1.468 MJ/m3 to 0.667 MJ/m3 when the concentration of H increases from 0 to 16%. The ferromagnetic correlation length was found to significantly increase with increasing hydrogen content. The local anisotropy was also extracted from the coercivity based on the Alben and Becker theory, which fits reasonably with that obtained using random magnetic anisotropy approach.

Physical properties of liquid crystals doped with CsPbBr3 quantum dots

ABSTRACT CsPbBr3/SiO2 perovskite quantum dots (PQDs), which exhibit good stability in water, air, and light, are synthesised using the water-trigger method. Due to the interaction between the long alkyl ligands of the PQDs and the liquid crystal, the liquid-crystal molecules prefer to align perpendicular to the surface of the PQDs, which disturbs the liquid crystal order and decreases its clearing point. The effect of CsPbBr3/SiO2 PQDs on the electro-optical properties and physical parameters of a nematic liquid crystal are investigated. The dielectric anisotropy (Δε) and splay elastic constant (K11) decrease substantially with increasing concentration of PQDs. PQDs, which are doped into the liquid crystal, can effectively reduce the threshold voltage (V th), which opens possibilities to reduce energy consumption in many optoelectronic devices.

Temperature dependent first order magnetocrystalline anisotropy constant model for ferromagnetic metals

In this work, a temperature dependent first order magnetocrystalline anisotropy constant model without any fitting parameters for ferromagnetic metals is developed, based on the equivalent relation between magnetocrystalline anisotropy energy and heat energy. The model establishes the quantitative relationship between temperature dependent first order magnetocrystalline anisotropy constant, heat capacity and volume expansion coefficient, providing a new idea of studying the intrinsic relationship between magnetocrystalline anisotropy constant and temperature. The available first order magnetocrystalline anisotropy constants, including dysprosium, terbium, holmium, iron and cobalt, are predicted at different temperatures, and the predictions are all in good agreement with the reported experimental results. Compared with existing models, our model offers a more convenient and simple method for pure metals to predict the first order magnetocrystalline anisotropy constants at different temperatures. More importantly, this study helps to obtain the temperature where the first order magnetocrystalline anisotropy constant decreases to zero.

Structural and magnetic properties of lead doped nickel ferrite nanoparticles using co-precipitation method

Lead doped nickel ferrite Ni1-xPbxFe2O4 (x = 0.0 to 1.0) nanoparticles have been successfully prepared via co-precipitation method. The structural and magnetic properties investigated by XRD, FTIR, TEM, and VSM. XRD confirmed the formation of cubic spinel structure. Particle size evaluated using Debye Scherrer formula was found to be in the range 30–50 nm. In FTIR spectra, two fundamental absorption bands at around 620 cm−1 and 500 cm−1 observed whereas the characteristic of M-O vibrations. TEM image shows that the particles are agglomerated and spherical shape. Magnetic parameters of coercivity, remenence, squareness ratio, and anisotropy constant values decrease.

Structure and magnetic properties of Ni0.5Zn0.5Mn0.5-xMoxFe1.5O4 ferrites prepared by sol-gel auto-combustion method

A series of Mo doped Ni-Mn-Zn ferrites compounds with the formula Ni0.5Zn0.5Mn0.5-xMoxFe1.5O4 (x = 0, 0.025, 0.05, 0.075 and 0.1) were first synthesized by sol-gel auto-combustion method. The X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM) analysis were carried out to characterize the microstructural and magnetic properties of ferrites. Rietveld refinement of X-ray diffraction data confirmed the formation of cubic spinel structure and the emergence of FeMoO4 phase with the substitution of Mo6+ contents. The grain size increased remarkably due to the formation of the liquid phase. The saturation magnetization (Ms) increased while the coercivity (Hc) decreased from 67.3 to 12.1 Oe due to the decrease of magneto-crystalline anisotropy constant. The initial permeability (μi) increased significantly from 34 (x = 0) to 114 (x = 0.075) and later decreased for x = 0.1. In our experiment, Ni0.5Zn0.5Mn0.425Mo0.075Fe1.5O4 ferrite presented the best microstructure and soft magnetic properties.

Macro- and Nanoscale Magnetic Anisotropy of FeNi(P) Micropillars in Polycarbonate Membrane

Macroscopic and local magnetic anisotropy of the FeNi(P) pillars deposited using electroless plating in the pores of the nuclear track-etched polycarbonate membrane has been studied. The alloy fills the pores and forms a nail-shaped pillar. The macroscopic easy magnetization axis was found to be perpendicular to the membrane plane due to magnetic shape anisotropy. The macroscopic magnetic anisotropy constant decreases with decreasing pillar diameter from 0.4 to 0.1 μm supposedly due to increase of the pillar cap contribution. Approach to magnetic saturation analysis indicates that the order in local easy magnetization axis is localized on a nanoscale. The correlation length of the local easy axis and the local magnetic anisotropy field in (Fe100−xNix)98P2 pillars of different compositions with diameter of 0.4 μm are studied.

The tunable magnetic properties and microstructures of Co–Ni double-substituted M-type Casrla hexaferrites

M-type hexaferrites with Co2+ and Ni2+ions substituting for Fe3+ ions (Ca0.30Sr0.35La0.35Fe12.0−x(Co0.5Ni0.5)xO19, 0.0 ≤ x ≤ 1.0) were prepared by the traditional solid state method. X-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), physical property measurement system-vibrating sample magnetometer (PPMS-VSM) have been employed to study the microstructures and magnetic properties of hexaferrites. XRD patterns showed that the single magnetoplumbite phase is obtained if Co–Ni content (x) ≤ 0.4 and impurity phases are observed in the structure when Co–Ni content (x) ≥ 0.4. FE-SEM micrographs showed that the hexaferrites with hexagonal platelet-like grains is obtained. The saturation magnetization (Ms), remanent magnetization (Mr), Mr/Ms ratio, magneton number (nB), coercivity (Hc), magnetic anisotropy field (Ha) and first anisotropy constant (K1) decrease with increasing Co–Ni content (x) from 0.0 to 1.0. And our reported results with tunable Hc and Mr can be used for recording applications.

Tunable ferromagnetic resonance linewidth of cobalt-substituted NiCuZn ferrites

Polycrystalline ferrites Ni0.5-xCu0.12Zn0.4CoxFe1.98O4-δ with different cobalt-substituted contents (x = 0, 0.003, 0.006, 0.009, 0.012, 0.015) are synthetized via the solid-state reaction method. The magnetocrystalline anisotropy constant is calculated based on the law of approach to saturation. As the amount of cobalt substitution increases, the absolute value of the magnetocrystalline anisotropy constant first decreases and then rises due to the positive compensation by the Co2+ ions. The value of the magnetocrystalline anisotropy constant tends to be zero for the samples with cobalt substitution contents in the range of 0.003–0.006. Meanwhile, when the cobalt substitution content is 0.003, the NiCuZn ferrite shows minimum ferromagnetic resonance linewidth (9.87 kA/m) and low dielectric loss tangent (tgδε, 1.1 × 10−4) at 9.4 GHz as well as a high magnetization (Ms, 406 kA/m) and high squareness ratio (Br/Bs, 0.83). Furthermore, the linewidth contribution is identified by the anisotropy and porosity linewidth broadening model based on the spin-wave approach, and the results show that porosity linewidth broadening is the predominant effect.

Influence of Sn-Mg co-substitution on the microstructural and magnetic characteristics of M-type SrCaLa hexagonal ferrites

Sn-Mg co-substituted M-type SrCaLa hexaferrites Sr0.5Ca0.2La0.3Fe12.0−2x(SnMg)xO19 (0.0 ≤ x ≤ 0.5) have been synthesized by ball milling and calcining. The results of X-ray diffraction show that a single magnetoplumbite phase is exhibited in all the samples and no impurity phase is observed in the structure. Lattice constants (c and a) increase with increasing Sn-Mg content (x) from 0.0 to 0.5. Platelet like structure exhibited by FE-SEM micrographs confirms the hexagonal structure of the synthesized samples. The saturation magnetization (Ms) first increases with increasing SnMg content (x) from 0.0 to 0.1, and then decreases when Sn-Mg content (x) ≥ 0.1. The remanent magnetization (Mr), Mr/Ms ratio, coercivity (Hc), magnetic anisotropy field (Ha) and first anisotropy constant (K1) decrease with increasing Sn-Mg content (x) from 0.0 to 0.5.

Competition between the impact of cation distribution and crystallite size on properties of MnxFe3−xO4 nanoparticles synthesized at room temperature

Abstract In the present study, the effect of Mn doping on the structural, morphological and magnetic properties of MnxFe3−xO4 (0≤x≤1) samples has been investigated. The obtained X-ray diffraction patterns indicate that the crystallite size depends on the cation distribution in the samples. The Rietveld full-pattern fitting by MAUD software determines the cation distribution, ion coordination, ion occupancy, crystallite size, microstrain and unit cell parameter. The magnetic hysteresis measurements show that the saturation magnetization and effective anisotropy constant decrease by increasing the Mn content up to x=0.2, while they increase by further Mn doping. Structural and magnetic properties have been completely described on the basis of the competition between the effects of cation distribution and crystallite size. The obtained results show an increase in the crystallite size and consequently, increase in magnetization for the 0.2

Temperature-Dependent Magnetic Damping Constant of Fe2Co Films Doped by Rare-Earth Yb

The temperature-dependent magnetic properties are investigated in amorphous (Fe2Co)[Formula: see text]Ybx ([Formula: see text], 0.64) thin films with in-plane uniaxial anisotropy. The decreases of saturation magnetization and easy axis coercivity with increasing temperature were observed and quite well explained by the Bloch’s law of [Formula: see text] dependence based on three-dimensional (3D) spin wave excitations and the thermally activated domain wall motion model of [Formula: see text] dependence, respectively. The decrease of in-plane uniaxial anisotropy constant is also observed and can be quite well fitted at temperature below 300[Formula: see text]K. The magnetic damping constant, which was deduced from the angular dependent ferromagnetic resonance spectra, shows a minima over the temperature range 100–435[Formula: see text]K, just like the previous results from 3D-transition metals based on Kamberský’s torque-correlation model. However, a positive correlation between damping and the in-plane uniaxial anisotropy constant was obtained with a clear deviation from the linear relationship. This deviation indicates that temperature-dependent damping and anisotropy may have different origins instead of the common source of the temperature-dependent spin-orbital coupling strength.

Coercivity, microstructure and magnetization reversal mechanism in TiNi-doped L10 FePt thin films

Controlling coercivity and understanding how it is affected by the microstructure are of essential importance for practical application of FePt thin films as a recording media. In this study, the small size of ordered domain, lower coercivity and weak intergranular exchange coupling interaction in TiNi-doped L10 FePt thin films are obtained. The TiNi additions maybe diffuse out of the FePt lattice into FePt grain boundaries, which separate FePt grains. The doping in grain boundary provides the nucleation center of reversed domain, which leads both nucleation-type and pinning-type mechanism to coexist in magnetization reversal processes for TiNi-doped FePt thin films. The decrease of anisotropy constant and nucleation field of reversed domain provides an explanation for the coercivity reduction of FePt thin films after TiNi doping.

Structural, Morphological, Optical and Magnetic Properties of Al-Doped CoFe2 O 4 Nanoparticles Prepared by Sol–Gel Auto-Combustion Method

CoFe2−xAlxO4 (x = 0.0,0.5,1.0, and 1.5) ferrite nanoparticles have been synthesized by the sol–gel auto-combustion method. The effect of non-magnetic Al content on their structural, morphological, optical, and magnetic properties was also investigated. X-ray diffraction (XRD) diffraction analysis was applied and indicated that the synthesized nanopowders of samples with x<1.5 and calcined at 800 ∘C have single-phase spinel structure. It has shown also by increasing Al content, the particle size, lattice parameter, unit cell volume, coercivity, anisotropy constant, and magnetization decrease, while the energy band gap increases. The size of particles was measured by TEM being in the range of 65–75 nm (for x = 0.0) and 9–10 nm (for x = 1.0). For sample with x = 1.5, the minimum calcination temperature for obtaining a single-phase spinel structure was 1000 ∘C. By increasing the calcination temperature from 1000 to 1100 ∘C, the mean crystallite size and crystallinity increase, while the lattice parameter, coercivity, anisotropy constant, and magnetization decrease. The average grain size evaluated by SEM analysis was found to be \(\tilde 91\) and 166 nm for samples calcined at 1000 and 1100 ∘C, respectively.