Evolution Of Magnetic Properties Research Articles

Microstructure, phase compositions, and coercivity evolution in micron-thick SmCo-based permanent magnetic films

Permanent magnetic thick films are increasingly used in Micro-Electro-Mechanical Systems (MEMS) devices, but the interplay between magnetic properties, microstructure, and film thickness remains underexplored. We deposited SmCo-based films with thicknesses ranging from 350 nm to 1300 nm using magnetron sputtering at room temperature, followed by in-situ annealing. Our study examined the evolution of microstructure, phase composition, magnetic properties, and domain structures as thickness increases. The films displayed dense, fibrous structures typical of the zone T-type region, with 3D morphologies forming a network structure and an arc-shaped surface that expands with thickness. At thinner levels (around 350 nm), an amorphous SmCo phase predominates, prone to oxidation, while at greater thicknesses, the SmCo5 phase dominates but maintains a grain size of 12–15 nm. Coercivity decreases significantly from 33 kOe to 8 kOe as thickness increases from 630 to 1300 nm due to the diminishing pinning effect and dominance of the reversal domain nucleation mechanism. Analysis using magnetic force microscopy and micromagnetic simulations indicates that this reduction in coercivity is mainly due to the decomposition of the SmCo5 phase and a reduction in magnetic domain size.

A zero-carbon emission approach for the reduction of refractory iron ores: Mineral phase, magnetic property and surface transformation in hydrogen system

In this study, a feasible strategy, named hydrogen mineral phase transformation (HMPT) technology, is proposed and employed to achieve efficient and clean recovery of Hainan Shilu refractory iron ore (HSRIO). The influences of HMPT roasting temperature, roasting time, and H2 concentration on the separation index of HSRIO are investigated. Under the optimal experimental conditions, the iron concentrate grade increases from 62.5% to 67.9%, and the iron recovery increases from 65.0% to 94.7% compared with the original beneficiation process. In addition, the evolution of mineral phases, magnetic properties, and mineral microstructures is analyzed using XRD, VSM, SEM, and high-temperature hot-stage microscopy. It is revealed that the transformation of hematite to magnetite occurs during the HMPT process, with the newly formed magnetite exhibiting a loose and porous reticulation structure. This study is of guiding significance for the development of Hainan Shilu refractory iron ore with high efficiency and zero-carbon emission.

Thermodynamic stabilities of NdFe3Al2, Nd5Fe17 and μ compounds and evolutions of microstructures and magnetic properties of Nd-Fe-Al alloys with nanocrystallites

In the Nd-Fe-Al ternary system, thermodynamic stabilities of three compounds, NdFe3Al2, Nd5Fe17 and μ, were determined by the equilibrated alloys, indicating that both NdFe3Al2 and μ ternary compounds are metastable phases, while Nd5Fe17 compound is a stable phase. Meantime, the microstructures of five representative as-cast alloy buttons are illustrated, which are consisted of crystalline phases and the complex of nanocrystallites + amorphous matrix (NCAM). The crystalline phases including Nd, Nd3Al, Nd2Fe17-xAlx and Nd6Fe13-xAl1+x as well as the nanocrystallites such as dhcp-Nd, fcc-Nd and Nd6Fe13-xAl1+x embedded in the amorphous matrix were observed. Particularly, it is concluded that the fcc-Nd nanocrystallites may be transformed from the fcc dense packing clusters of the amorphous matrix and/or dhcp-Nd nanocrystallites. The hard magnetic properties of these as-cast alloys can be attributed to NCAM and present a non-strict proportionate effect. The alloy composed of Nd + NCAM, with curie temperature (Tc) 515 K, displays the highest intrinsic coercivity Hci 305 kA/m and remanent magnetization Br 10.8 emu/g. Its good glass-forming ability is presented by the high ratio (Tx/Tm) 0.88 and the small interval (Tm-Tx) 105 K of the crystallization temperature (Tx) with the melting temperature (Tm). Since the present investigation focuses on phase stabilities, microstructural characterizations, magnetic properties and glass-forming ability of the Nd-Fe-Al alloys, the obtained results can provide a better understanding for advancing the design of the Nd-Fe-Al based hard magnets and amorphous materials.

Evolution of static and dynamic magnetic properties of Re/Co/Pt and Pt/Co/Re trilayers with enhanced Dzyaloshinskii-Moriya interaction

The influence of Re layer insertion either at the bottom or top interface of epitaxially grown Pt/Co/Pt heterostructures on their static and dynamic magnetic properties is discussed in terms of their crystalline structure. Magnetic properties were studied as a function of both Re and Co layer thicknesses (dRe and dCo, respectively) in the matrix-like samples with a double-wedge structure, in which the layer thickness gradients were oriented orthogonally. The comprehensive investigations of the changes in coercivity, perpendicular magnetic anisotropy, spin reorientation transition, interfacial Dzyaloshinskii-Moriya interaction (iDMI) and spin wave damping are reported. Two different magnetic phases depending on the Co layer thickness with volume anisotropies (determined without demagnetization term) of KV∼0.25 (low) and KV∼0.75 MJ/m3 (high) were observed. The relation between these phases depends on the stack sequence and thickness of Re inserted layer. For dRe = 0.2 ÷ 0.7 nm deposited as the bottom interface, dCo induced transition at dtr ∼ 2 nm from low to high volume anisotropy phases was observed. Low and high volume anisotropy phases are associated to Co fcc and hcp structural phases. The insertion of half atomic layer of Re had no influence on surface anisotropy but significantly enhanced iDMI above 1 pJ/m and reduced spin wave damping.

Deciphering the evolution of electronic and magnetic properties in alkali doped nickel oxide: An In-silico approach

In this study, we employed the DFT+U method to systematically explore the electronic, and magnetic properties of nickel oxide doped with alkali metal atoms (Li, Na, K). The Hubbard potential-U was judiciously applied to all doped compound resulting from alkali doping, and were found to exhibited half-metallic properties. A noteworthy observation was the half-metallic band gap in the spin-down channel, which exhibited a linear variation with the increasing value of the Hubbard potential. Furthermore, the total magnetic moment was discernible in the supercells, with all supercells demonstrating 100% spin polarization at the Fermi level. Consequently, the findings from this study hold significant potential for applications in spintronics, thereby paving the way for future research in this domain.

Evolution of Magnetic Properties with Structure and Morphology of Co/Alq3 Bilayer: A Thickness Dependent Study

Evolution of Magnetic Properties with Structure and Morphology of Co/Alq3 Bilayer: A Thickness Dependent Study

Evolution of Structure, Morphology, and Magnetic Properties of YFeO3 Under Co-Doping of Nd and Ni

Evolution of Structure, Morphology, and Magnetic Properties of YFeO3 Under Co-Doping of Nd and Ni

The delicate coupling between magnetism and magneto-transport in Fermi-energy-adjusted MnBi2Te4 crystals

We explored the coupling between magnetic and magneto-transport properties in MnBi2Te4 crystals with Fermi energy EF ranging from 10 to 100 meV in the conduction band. Electrical, magnetic, and magneto-transport measurements reveal distinct behaviors depending on EF. At lower EF values (10 meV), MnBi2Te4 exhibits degenerate-semiconductor-like electrical transport and ferrimagnetism, with weak coupling between magneto-resistance and ferrimagnetism. In contrast, MnBi2Te4 displays metallic transport and antiferromagnetism (AFM) at higher Fermi energies, with magneto-resistance strongly coupled to antiferromagnetism and canted antiferromagnetism under a large external magnetic field. Remarkably, Hall measurements demonstrate a pronounced anomalous Hall resistivity (AHR) when the EF of MnBi2Te4 is 10 meV, larger than that reported for other bulk MnBi2Te4 crystals in the literature. Significant AHR is attributed to the Berry-phase effect in electronic-band structure based on first-principles calculation. The evolution of magnetic and magneto-transport properties in EF shifted MnBi2Te4 can be semi-quantitatively explained by the Ruderman–Kittel–Kasuya–Yosida interaction between neighboring MnTe layers. Our work suggests that the strongly Fermi-energy-sensitive magneto-transport properties observed in MnBi2Te4 may be useful in developing magnetic sensors/detectors.

Evolution of structure, magnetism, and electronic/thermal-transports of Ti(Cr)-substituted Fe2CrV all-d-metal Heusler ferromagnets

All-d-metal full-Heusler alloys possess superior mechanical properties and high spin polarization, which would play an important role in spintronic applications. Despite this, their electrical and thermal transport properties have not been comprehensively investigated till now. In this work, we present an analysis on the evolution of structural, magnetic and transport properties of Cr- and Ti-substituted Fe2CrV all-d-metal Heusler alloys by combining theoretical calculations and experiments. Both series of alloys crystallize in Hg2CuTi-type structure. With increasing Ti doping, the calculated total magnetic moments of Fe50Cr25V25-xTix decrease linearly. The experimental saturation magnetization is highly consistent with theoretical calculations and Slater-Pauling rule when x < 4, indicating the highly ordered atomic occupation. The magnetization and Curie temperature can be significantly tuned by altering spin polarizations and exchange interactions. The introduction of the foreign atom, Ti, results in a linear increase in residual resistivity, while electron-phonon scattering keeps relatively constant. The maximum values for electrical and thermal transport properties are observed in the stoichiometric Fe2CrV composition.

Novel mechanism of the grain boundary diffusion process with Tb based on the discovery of TbFe2 phase

The grain boundary diffusion process (GBDP) has proven to be an effective method for enhancing the coercivity of sintered Nd-Fe-B magnets. However, the limited diffusion depth and thicker shell structure have impeded the further development of magnetic properties. Currently, the primary debates regarding the mechanism of GBDP with Tb revolve around the dissolution-solidification mechanism and the atomic substitution mechanism. To clarify this mechanism, the microstructure evolution of sintered Nd-Fe-B magnets during the heating process of GBDP has been systematically studied by quenching at different temperatures. In this study, it was found that the formation of TbFe2 phase is related to the dissolution of Nd2Fe14B grains during GBDP with Tb. The theory of mixing heat and phase separation further confirms that the Nd2Fe14B phase dissolves to form a mixed phase of Nd and TbFe2, which then solidifies into the (Nd, Tb)2Fe14B phase. Based on the discovery of the TbFe2 phase, the dissolution-solidification mechanism is considered the primary mechanism for GBDP. This is supported by the elemental content of the two typical core-shell structures observed.

Relationship between disorder, magnetism and band topology in Mn(Sb1–x Bi x )2Te4 single crystals

We investigate the evolution of magnetic properties as well as the content and distribution of Mn for Mn(Sb1−x Bi x )2Te4 single crystals grown by large-temperature-gradient chemical vapor transport method. It is found that the ferromagnetic MnSb2Te4 changes to antiferromagnetism with Bi doping when x ≥ 0.25. Further analysis implies that the occupations of Mn ions at Sb/Bi site MnSb/Bi and Mn site MnMn have a strong influence on the magnetic ground states of these systems. With the decrease of MnMn and increase of MnSb/Bi, the system will favor the ferromagnetic ground state. In addition, the rapid decrease of T C/N with increasing Bi content when x ≤ 0.25 and the insensitivity of T N to x when x > 0.25 suggest that the main magnetic interaction may change from the Ruderman–Kittel–Kasuya–Yosida type at low Bi doping region to the van-Vleck type in high Bi doped samples.

The magnetic and electric transport properties in erbium-doped layered perovskite iridate Sr2–xErxIrO4

The 5d oxide Sr2IrO4 with a layered perovskite structure has been investigated due to its peculiar Jeff = 1/2 insulating ground state. In this research, we investigate the evolution of magnetic and electric transport properties of Er-doped polycrystalline perovskite iridates Sr2–xErxIrO4 (0 ≤ x ≤ 0.06). Er3+ is magnetic and can thus provide magnetic interactions with Ir. Also, Er3+ doping introduces a carrier-doping effect. We find that substituting Sr2+ with Er3+ still preserves the I41/acd crystal structure, while it causes the rotation of IrO6 octahedra φ to decrease. In this case, the Ir–O1–Ir bond angle increases and the tetragonal distortion c/a decreases. The magnetic properties present a suppressed transition temperature, a decreased Curie–Weiss temperature, and an increased effective magnetic moment. The electrical resistivity of the doped samples decreases with doping, which originates from the crystal distortion and electron doping. Theoretical calculations represent an increase in band filling and an improvement in the conduction property with doping.

Effect of aging on temperature dependence of FeCuSiNbB nanocrystalline materials

Nowadays, increasing energy efficiency in the automotive industry is promoted by employing compact electrical systems. This reduction in the mass and volume of electrical systems exposes magnetic components to high temperatures for extended periods. The present paper investigates the magnetic behavior of FeCuSiNbB nanocrystalline materials across various temperature ranges. Subsequently, the temperature dependency is reevaluated after exposing the magnetic cores to aging at 200 °C. The entire study is founded on monitoring the evolution of macroscopic magnetic properties and analyzing anisotropic energies.

Influence of forming Fe-Al phase on coercivity in Pr-Fe-B thin films on glass substrate

Pr-Fe-B thin films were fabricated on the AlN underlayer and glass substrates using the sputtering technique. Underlayers of various thicknesses in the range of 2 to 100 nm were inserted. The influence of the AlN underlayer on the orientation of thin films along the c-axis and the development of magnetic properties was systematically investigated. Grain sizes ranged from 40 to 100 nm, and the surface roughness measured between 1.77 nm and 4.44 nm. The obtained coercivities were in the range of 0.2–4.0 kOe. The thin film exhibited better magnetic properties at a 20 nm underlayer thickness. The formation of the Fe-Al (110) phase at the Pr-Fe-B/AlN interface supported the growth of Pr-Fe-B thin films.

Evolution of microstructure, magnetic and microwave properties of sputter deposited polycrystalline YIG thin films

Evolution of microstructure, magnetic and microwave properties of sputter deposited polycrystalline YIG thin films

The effect of In-doping on the evolution of microstructure, magnetic properties, and corrosion resistance of NdFeB magnet

Abstract The grain boundary phase affects the magnetic properties and corrosion resistance of sintered NdFeB magnets. In this work, a small amount of Indium (In) was added to the NdFeB magnet by induction melting to systematically investigate its effect on the evolution of the microstructure, magnetic properties, and corrosion resistance of the NdFeB magnet. The microstructural analysis illustrated that minor In-addition generated more grain boundary phases and an abundant amorphous phase at the triple junction grain boundary. While the addition of In element failed to enhance the magnetic isolation effect between adjacent matrix grains, fortuitously, its incorporation elevated the electrochemical potential of the In-containing magnets. Besides, during corrosion, an In-rich precipitate phase formed, hindering the ingress of the corrosive medium into the magnet. Consequently, this significantly bolstered the corrosion resistance of sintered NdFeB magnets. The phase formation, magnetic properties, and corrosion resistance of In-doped NdFeB magnets are detailed in this work, which provides a new prospect for the preparation of high-performance sintered NdFeB magnets.

Comparison of Magnetic Deflection among Neutral Sodium-Doped Clusters: Na(H2O)n, Na(NH3)n, Na(MeOH)n, and Na(DME)n.

Using a pulsed Stern-Gerlach deflection experiment, we present the results of a comparative study on the magnetic properties of neutral sodium-doped solvent clusters Na(Sol)n with n = 1-4 (Sol: H2O, NH3, CH3OH, CH3OCH3). Experimental deflection ratios are compared with values calculated from molecular dynamics simulations. NaNH3 and NaH2O are deflected as a spin 1/2 system, consistent with spin transitions occurring on a time scale significantly longer than 100 μs. For all other clusters, reduced deflection is observed. The observed magnetic deflection behavior is correlated to the number of thermally populated rotational states in the clusters. We discuss that spin-rotational couplings allow for avoided crossings and a reduction in the effective magnetic moment of the cluster. This work attempts to understand the evolution of magnetic properties in isolated weakly bound clusters and is relevant to diamagnetic and paramagnetic species expected to exist in solvated electron systems.

Microstructure and magnetic properties of binary Mn54-Al46 alloy particulates obtained by severe plastic deformation processing via end-milling and annealing

We utilize the plastic deformation process associated with the machining operation of end-milling for the preparation of ε-phase Mn-Al particulates with micron scale external dimensions and self-similar shapes from binary as-cast feedstock with composition 54 at.% Mn and 46 at.% Al. The structural evolution and development of magnetic properties in response to the single-pass plastic deformation processing by the end-milling and subsequent thermal annealing have been studied. Effects of end-milling process parameter combinations, primarily the rotational speed of the cutting tool, have been identified to permit genesis of morphological self-similar particulates of ε-phase characterized by cold-worked and sub-micron to nanometer scale refined microstructures. The end-milling derived particulates were suitable for preparation of τ-phase based MnAl particulates with enhanced permanent magnet properties via isothermal annealing. Discernibly higher rates for the exothermic ε-phase decomposition reactions in the end-milling derived particulates have been observed for isothermal annealing at temperatures in the range of 673 K ≤ T ≤ 723 K. The enhanced decomposition reaction kinetics have been attributed to reduced effective nucleation barriers for the respective product phases stemming primarily from reduced grain size. Large saturation magnetization and coercivity in combination with reasonable squareness ratios of the magnetization curves resulted in a (BH)max = 4.2 MGOe for the end-milling derived binary Mn54Al46 particulates obtained for the highest rotational tool speed of 4200 RPM used here after annealing for 20 min at 673 K. The ε-phase Mn-Al particulates derived by end-milling have potential as precursors for the fabrication of τ-phase Mn-Al based PM materials.

Characterization of long-term magnetic stability in sintered MnBi: Influence of exposing time and storage conditions

This study investigated the evolution of magnetic properties in low-temperature vacuum-sintered MnBi samples over an 18-month period at room temperature. Two sample conditions were examined: one exposed to ambient air in powder form and the other softly compressed within a sealed tube. Over time, both samples demonstrated an enhanced remanence ratio, resulting in a significant increase of over 60% in the energy product (BH)max. The compressed sample in the tube exhibited greater magnetic alignment and slightly higher values of (BH)max. Distinct evolution patterns of the M-H curves were observed in the two samples. Oxides were detected in the as-prepared samples, showing a slight increase during the exposure period. Furthermore, the particle size experienced a substantial growth from approximately 10 µm to 30 µm. These changes in magnetic properties were attributed to the continuous formation of MnBi, governed by the diffusion mechanism, and the creation of new complex oxides. The magnetic and phase stabilities of MnBi could benefit from its Mn/MnBi/Bi core/double-shell structure. The diffusion mechanism was proposed as the primary factor contributing to the long-term enhancement of (BH)max in the preserved MnBi samples. To describe the increase in (BH)max, a relation between (BH)max and diffusion length was established.

Temperature evolution of pseudo magnetic properties and vortex state in Fe71Ga29 thin films

We report on the temperature evolution of pseudo magnetic properties and vortex state in Fe71Ga29 thin films at different substrate temperatures (RT-25 °C, 50 °C, 75 °C, and 150 °C) using minor loop analysis and first-order reversal curves respectively. Phase purity of Fe71Ga29 thin films confirmed with grazing incidence X–ray diffraction, which confirms the A2-type disordered phase. The minor loop parameters such as energy loss coefficient WF0 (362 kOe.emu/cc to 278 kOe.emu/cc) and trough depth coefficient WR0 (67.30 kOe.emu/cc to 50.23 kOe.emu/cc) values drop as grain size increases due to a reduction in defects as a result of an increase in substrate temperature. First-order reversal curves allow us to estimate the coercivity variation and switching field distribution that allow us to get information about magnetic interactions between the domains. Additionally, the contour plots of FORC and MFM phase images infer the coexistence of multidomain and Vortex State (VS) in all the Fe71Ga29 thin films deposited at different substrate temperatures.