Low Magnetic Moment Research Articles

Tailoring structural, morphological, and magnetic properties of Sr0.54Ca0.46Fe6.5-xNixAl5.5O19 hexaferrites via Ni substitution

Sr0.54Ca0,46Fe6.5-xNixAl5.5O19 (0 ≤ x ≤ 0.3) hexaferrite powders were prepared by the sol-gel auto combustion method and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Magnetic measurements were performed with physical properties measurement system (PPMS). The lattice parameters, volume, and lattice strain were calculated. XRD analyses revealed a reduction in crystallite size with increasing Ni content. Interestingly, the magnetic analysis indicated that nickel, with its low magnetic moment, significantly enhanced the magnetization of Sr0.54Ca0.46Fe6.5-xNixAl5.5O19 (0.0 ≤ x ≤ 0.3) and reduced the coercive field. Furthermore, the Law of Approach to Saturation (LAS) theory was employed to extract the first anisotropy constant, the anisotropy field, and several essential magnetic parameters, providing valuable insights into the magnetic behavior of samples.

Slow Magnetic Relaxation in a Californium Complex.

We report the synthesis and characterization of the macrocyclic californium derivative Na[Cf(H2O)(DOTA)] (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate), 1-Cf, which was studied in comparison to its dysprosium counterpart, Na[Dy(H2O)(DOTA)], 1-Dy. Divergent spectroscopic and magnetic behaviors were observed between 1-Cf and 1-Dy. Based upon spectroscopic measurements, we propose that accessible 5f → 6d transitions (potentially operating in tandem with charge-transfer transitions) are the major contributors to the observed broadband photoluminescence in 1-Cf. Dc magnetic susceptibility data for 1-Cf revealed lower magnetic moments than those previously observed for 1-Dy and expected for an f9 free ion, which calculations suggest is the result of greater ligand field effects. Notably, 1-Cf displays slow magnetic relaxation on the time scale of ac susceptibility measurements, making it the first example of a californium-based single-molecule magnet. A side-by-side comparison of the ac susceptibility data reveals magnetic relaxation properties that widely differ between 1-Cf and 1-Dy. This divergent relaxation behavior is attributed mainly to the inherent difference in spin-orbit coupling between Dy3+ and Cf3+.

Mechanochemical oxidative complexation of copper(I) chloride with acetic acid, benzoic acid, their chloro derivatives and l-histidine affording anhydrous copper(II) complexes

This work reports solvent-free synthesis of copper(II)-carboxylates by grinding the reactants in solid state (the mechanochemical method). Here we used copper(I) salt to synthesize copper(II) complexes to demonstrate the potential of oxidative synthesis of the mechanochemical technique. The complexes were synthesized by grinding copper(I) chloride with a carboxylic acid together in 1:2 molar ratio in mortar and pestle. The carboxylic acids used were acetic acid, benzoic acid, 2-chloroacetic acid, 2-chlorobenzoic acid and l-histidine. The oxidative complexation occurred in the solid state producing anhydrous dimeric copper(II)-carboxylates (except that of l-histidine) in quantitative yield (>96 %) having 1:2 metal to ligand ratio. The first evidence to oxidation of copper(I) to copper(II) ion was a change in color (pale to greenish blue) and a change in magnetic susceptibility from diamagnetic to paramagnetic value. The complexes were also characterized by elemental analysis, electronic absorption spectroscopy, FT-IR spectra, mass spectrometry, powder X-ray diffraction and thermal analysis. The electronic absorption, magnetic susceptibility, ESR and X-ray diffraction data supported a distorted square-planer geometry. This study provided for a distinct test in the form of magnetic susceptibility for the formation of copper(II)-complexes from a copper(I) salt. The dimeric nature of the complexes, except that of bis(histidinato)copper(II), was confirmed by the lower magnetic-moments (1.40–1.50 BM) than the spin only value (1.73 BM).

Magnetic coupling through flux branching of adjacent type-I and -II superconductors in a neutron star

ABSTRACT The inner and outer cores of neutron stars are believed to contain type-I and -II proton superconductors, respectively. The type-I superconductor exists in an intermediate state, comprising macroscopic flux-free and flux-containing regions, while the type-II superconductor is flux-free, except for microscopic, quantized flux tubes. Here, we show that the inner and outer cores are coupled magnetically, when the macroscopic flux tubes subdivide dendritically into quantized flux tubes, a phenomenon called flux branching. An important implication is that up to ${\sim} 10^{12} (r_1/10^6 \, {\rm cm}) \, {\rm erg}$ of energy are required to separate a quantized flux tube from its progenitor macroscopic flux tube, where $r_1$ is the length of the macroscopic flux tube. Approximating the normal-superconducting boundary as sharp, we calculate the magnetic coupling energy between a quantized and macroscopic flux tube due to flux branching as a function of, $f_1$, the radius of the type-I inner core divided by the radius of the type-II outer core. Strong coupling delays magnetic field decay in the type-II superconductor. For an idealized inner core containing only a type-I proton superconductor and poloidal flux, and in the absence of ambipolar diffusion and diamagnetic screening, the low magnetic moments (${\lesssim} 10^{27} \, {\rm G \, cm^3}$) of recycled pulsars imply $f_1 \lesssim 10^{-1.5}$.

Photocatalytic degradation of the remazol red ultra RGB dye using SrFe12O19-Fe3O4 magnetic oxides dispersed in silica: Effect of reduction temperature

Dyes are the most frequently discarded industrial wastes in aquatic ecosystems, among which Remazol Red ultra RGB stands out. In this context, magnetic iron-based catalyst dispersed in silica were prepared by Pechini route as an alternative for the photodegradation of Remazol Red Ultra RGB. The XRD and Mössbauer spectroscopy results indicated the formation of a magnetic material that, after reduction treatment with H2, forms a magnetite phase combined with Sr hexaferrite dispersed in amorphous silica. The TPR-H2 profiles indicated the reduction of Fe3+ to Fe2+ within the considered temperature range, the amount of Fe2+ increased with rising temperature. The SEM images showed sponge-like morphology for the samples. The EDS spectra and mapping confirmed a high uniformity in the distribution of active iron species in the silica. The magnetic measurements showed a lower magnetic signal for the sample reduced at 600 °C, due to the lower magnetic moment of Fe2+ formed after the reduction. The diffuse reflectance spectra showed a main absorption region between 500 and 200 nm and the estimated band-gap values were of 1.4 and 1.9 eV for the reduced sample and the fresh oxide, respectively. The surface charge was obtained via zeta potential, demonstrating good stability under pH changes and reaching a negative potential in the pH range from 2 to 6. The photocatalytic tests showed that the samples with higher content of Fe2+ demonstrated a greater photocatalytic degradation of the Remazol Red Ultra RGB dye, reaching 100 % degradation in 1 h for the solid reduced at 600 °C. A plausible mechanism for the photodegradation of Remazol Red Ultra RGB was proposed, considering the different elementary steps involving the participation of iron sites and the formation of oxidant radicals.

Boundary-induced phase in epitaxial iron layers

We report on the discovery of a boundary-induced body-centered tetragonal iron phase in thin films deposited on MgAl2O4 (001) substrates. We present evidence for this phase using detailed x-ray analysis and density functional theory calculations. A lower magnetic moment and a rotation of the easy magnetization direction are observed, as compared with body-centered cubic iron. Our findings expand the range of known crystal and magnetic phases of iron, providing valuable insights for the development of heterostructure devices using ultrathin iron layers. Published by the American Physical Society 2024

Effect of Deformation on the Magnetic Properties of CrMnFeCoNi and CrMnFeCoNi-CN High-Entropy Alloys

The magnetic behavior of two high-entropy alloys, CrMnFeCoNi and CrMnFeCoNi-CN, was investigated under varying degrees of deformation through uniaxial tensile tests. Microstructural, morphological, and crystalline structural analyses using XRD and SEM revealed a uniform and stable austenitic structure in all samples, with no presence of α’-martensite or ε-martensite phases. The main deformation mechanisms identified were twinning and slip dislocation for the CrMnFeCoNi-CN alloy, and slip dislocation for the CrMnFeCoNi alloy at room temperature. The alloys exhibited low magnetic moments attributed to magnetically frustrated configurations. At temperatures below 70 K, distinct magnetic states were observed ranging from paramagnetic to ferrimagnetic and spin-glass-like behavior. Antiferromagnetic interactions were confirmed by a negative paramagnetic Curie temperature for both alloys. The magnetization of the CrMnFeCoNi alloy increased with deformation, reflected in effective magnetic moments varying from 1.81 (0 pct) to 2.60 (20 pct) μB, while for the CrMnFeCoNi-CN alloy remained stable around 2.39 to 2.48 μB. The magnetization of the CrMnFeCoNi-CN alloy was found to be higher than that of the CrMnFeCoNi alloy, suggesting that the presence of C and N as alloying elements can enhance magnetization to some extent.

Assessment of micro-structural and magnetic properties of M0.5Cu0.4Zn0.1Fe2O4 (M = Ni, Co) nanocrystalline ferrites

The micro-structural and magnetic properties are significantly modified with substitution of different elements in ferrite nanocrystalline materials. The preliminary structural analysis indicates for the synthesized M0.5Cu0.4Zn0.1Fe2O4 (M = Ni, Co) nanocrystalline ferrites that only the diffraction peaks due to the spinel ferrite phase are present and it has been crystallized in Fd 3 ¯ m space group with cubic symmetry. The SEM micrographs indicate that the particles in the sample have a strong tendency to form agglomerates, which is a typical feature of magnetic nano-materials. Two metal-oxygen bands are clearly observed for both the prepared compounds. The peak to peak line width increases with the increase in nickel nanocrystalline ferrite than cobalt nanocrystalline ferrite. Finally, when Co is substituted, Ms rises because the low magnetic moment Cu2+/Zn2+ ions in sites B are replaced by the high magnetic moment Co2+ ions.

Ferrimagnetic half-metal Mn[formula omitted]RhSi inverse Heusler for spintronic applications

Using DFT and Monte Carlo simulation, we studied the physical properties of the ferrimagnetic half-metal Mn2RhSi Heusler alloy. Our calculations reveal a stable face-centered cubic structure without any possibility of martensitic transition. The electronic structure shows half-metallic behavior with a band gap in spin-down of 0.49eV calculated using PBE and 0.85eV using the r2SCAN functional, and antiferromagnetic–ferromagnetic coupling with a Curie temperature of 460K. The elastic constants and moduli decrease with temperature due to thermal expansion, but Mn2RhSi retains its mechanical stability. The dominance of metallic bonds, large band gap, high Curie temperature, low magnetic moment, and good mechanical properties make Mn2RhSi a promising candidate for spintronic applications at room temperature.

Magnetic interactions in epitaxial films of Mn[formula omitted](Ge[formula omitted]Si[formula omitted])[formula omitted]/Ge(111) : 55Mn NMR study

55Mn NMR experiments have been performed at 4.2 K on a series of Mn5(Ge1−xSix)3 epitaxial films (0⩽x⩽0.55) to investigate changes introduced by silicon when it replaces germanium in a hexagonal Mn5Ge3 crystal lattice. The Si/Ge substitution was found to reduce the magnetic moment on manganese located in the 6(g) sublattice creating a new population of manganese atoms with distinctly lower magnetic moment. This effect is attributed to the orbital overlay due to a lattice distortion introduced by Si. Interestingly, these modified Mn sites retain the orbital moment practically unaltered. The amount of new manganese environments in the 6(g) sublattice coincides with a probability of Mn having two Si neighbors as first neighbors. Mn atoms located in the 4(d) sublattice are not significantly affected by the Si substitution in the studied concentration range.

DFT investigations of structural, electronic, magnetic, and optical properties of CeO2-X (X=Mo/Cr) and Mo-Cr co-doped CeO2 for optoelectronic applications

Current research elucidate investigations on calculating the structural, electronic, magnetic, and optical properties of Mo/Cr doped CeO2 and Mo-Cr co-doped CeO2 using the Wien2k code. The exchange-correlation functional is approximated using the PBE-GGA approximation. Spin-polarized DOS present the magnetic character of proposed materials. A higher magnetic moment (3.749 μB) is noticed for Mo-Cr@CeO2 while lower magnetic moment (2.247 μB) is observed for Mo@CeO2 material. The Ce 4f-, O 2p-, Mo 3d-, and Cr 3d-states appreciably tune electronic properties. Absorption spectra of Mo@CeO2 and Mo-Cr@CeO2 materials exhibit blueshift, while Cr@CeO2 material shows redshift. Curie temperature indicates spintronic applications of these materials. Enhanced conductivity, improved dielectric response, and decreased reflectivity of proposed materials in the UV region implicate their uses in high-frequency UV optoelectronics, photovoltaics, spintronics, photonics and capacitive devices.

Navigating the magnetic contribution of the commonly used single-crystal substrates SrTiO3 (100) and LaAlO3 (100) in weak magnetic thin films

In recent years, thin films of weak ferromagnetic materials have been in huge demand; however, probing their magnetic characteristics has been difficult due to contributions from underlying substrates. In the present study, we have analyzed the magnetic properties of the commonly used single-crystal SrTiO3 (100) and LaAlO3 (100) substrates and performed a time-dependent annealing protocol in vacuum and ambient oxygen pressure to mitigate the intrinsic weak ferromagnetic contributions from these substrates arising due to the presence of disorder or defects such as vacancies in the pristine substrates. It is shown that after proper air annealing, the substrate magnetic background becomes diamagnetic. When such air-annealed diamagnetic substrates are used for the deposition of low-thickness films carrying low magnetic moments such as SrRuO3 and SrMnO3 thin films, their magnetic transitions are explicitly observed. The proposed annealing protocols help to improve the signal from weak magnetic samples. This allows us to analyze the film’s magnetic properties without worrying about the contribution from the substrate.

Mitigating magnetic frustration to improve single-crystalline nonstoichiometric Li1.06Ni0.90Mn0.04O2 for lithium-ion batteries

A molten salt-assisted synthesis and Li-refeeding strategy is applied to prepare single-crystalline slightly Li-rich Li1.06Ni0.90Mn0.04O2 with low magnetic moment and mitigated Li+/Ni2+ cation mixing, which enhances cycling performance.

From Feast to Famine: A Systematic Study of Accretion onto Oblique Pulsars with 3D GRMHD Simulations

Disk-fed accretion onto neutron stars can power a wide range of astrophysical sources ranging from X-ray binaries, to accretion-powered millisecond pulsars, ultraluminous X-ray sources, and gamma-ray bursts. A crucial parameter controlling the gas–magnetosphere interaction is the strength of the stellar dipole. In addition, coherent X-ray pulsations in many neutron star systems indicate that the star's dipole moment is oblique relative to its rotation axis. Therefore, it is critical to systematically explore the 2D parameter space of the star's magnetic field strength and obliquity, which is what this work does, for the first time, in the framework of 3D general-relativistic magnetohydrodynamics. If the accretion disk carries its own vertical magnetic field, this introduces an additional factor: the relative polarity of the disk and stellar magnetic fields. We find that depending on the strength of the stellar dipole and the star–disk relative polarity, the neutron star's jet power can either increase or decrease with increasing obliquity. For weak dipole strength (equivalently, high accretion rate), the parallel polarity results in a positive correlation between jet power and obliquity, whereas the antiparallel orientation displays the opposite trend. For stronger dipoles, the relative-polarity effect disappears, and jet power always decreases with increasing obliquity. The influence of the relative polarity gradually disappears as obliquity increases. Highly oblique pulsars tend to have an increased magnetospheric radius, a lower mass accretion rate, and enter the propeller regime at lower magnetic moments than aligned stars.

Introducing gradient Er ions and oxygen defects into SrCoO3 for regulating structural, electrical and magnetic transport properties.

The SrCoO3-δ system has broad application potential due to its diverse crystal structures, oxidation stoichiometric ratio, and significant electrical and magnetic properties. However, it faces the challenges of a complex crystal structure and oxygen defect control in this material system. Herein, we introduce oxygen defects into SrCoO3-δvia Er doping to regulate the structural, electrical and magnetic transport properties. Sr1-xErxCoO3-δ (x = 0-0.25) undergoes an evolution of structure and oxygen content (measured using the iodometric method) from hexagonal SrCoO2.626 (H + Co3O4) to cubic perovskite Sr0.9Er0.1CoO2.689 (CP) and finally to ordered tetragonal Sr0.8Er0.2CoO2.635 (OT). Among the three phases, Sr0.9Er0.1CoO2.689 (CP) exhibits the lowest resistivity, only 4.06 mΩ cm at room temperature, which is attributed to its high three-dimensional symmetry, overlap of O 2p and Co 3d orbitals at high oxygen ion concentration. Further introduction of Er ions and oxygen defects promotes the transformation from low spin Co4+ (LS, t52ge0g, S = 1/2) to high spin Co3+ (HS, t42ge2g, S = 2), and from the CoO6 octahedron (low magnetic moment transformation) to the CoO4.25 tetrahedron (high magnetic moment). The oxygen-deficient CoO4.25 layer appears, which can enhance the ordering of A sites and oxygen vacancies, and the CP phase transforms into room-temperature ferromagnetic Sr0.8Er0.2CoO2.635 (OT, TC∼330 K). Er ions provide unpaired electrons in the 2f orbital, which results in a strong magnetization of Sr0.8Er0.2CoO2.635 (OT, 4.66 μB/Co) at low temperatures.

Investigations of the structure and tunable magnetic properties of Cu doped cobalt chromite nanoparticles

This article reports the synthesis, microstructural, magnetic and optical properties of copper ions substituted cobalt chromite nanoparticles. We have prepared four nanosized chromite samples with a general composition of CuxCo1-xCr2O4 (x = 0.0, 0.1, 0.2 and 0.3) using conventional wet chemical co-precipitation method. The x-ray diffraction profiles verified the presence of pure spinel crystal structure of the samples. Using the Williamson-Hall (W-H) method, the average crystallite size of all the samples were calculated to be between 11 nm and 16 nm. A tensile microstrain in all the samples was noticed. Surface morphology and average particle size of doped cobalt chromite nanocrystals was examined using HRTEM images. A moderate increment in the optical band gap was detected with increasing Cu ions in cobalt chromite nanoparticles which is attributed to the nanosize effect of the samples. The presence of all five distinctive Raman active modes in the chromite samples ensured phase purity and a decrease in crystal symmetry was also observed as the amount of Cu dopants was increased. Due to low magnetic moment of Cu2+ ions when compared with Co2+ ions, incorporation of copper ions reduces the coercive field of the host chromite system. With increasing Cu percentage in chromite especially for 30 % Cu doped sample, the spin-spiral transition TS vanishes which indicates TS is affected by the dopant concentrations.

Magnetic properties and identification of Griffiths-like phase in Mn2FeSi Heusler antiferromagnet

Materials having low magnetic moments with high spin polarization are promising for spintronic applications. Among these materials, Mn-based Heusler alloys are attractive candidates due to the antiferromagnetic alignment of Mn atoms. Theoretical calculations predict Mn2FeSi to have an inverse Heusler (XA) structure with a magnetic moment of 2 μB/f.u. However, no experimental reports exist on a phase-pure composition of this material. In this study, our first principle calculations demonstrate the effect of various types of disorder on the electronic and magnetic properties of Mn2FeSi. The B2-type disorder seems responsible for forming secondary phases in stoichiometric Mn2FeSi. We verify this by conducting theoretical calculations for different configurations of the atomic disorders permissible in a Heusler phase. We substantiate our theoretical investigation with an experimental study wherein we first stabilize the phase-pure Mn2FeSi in an inverse Heusler structure by substituting Al at the Si site. Amongst the prepared Mn2FeSi1−xAlx (x = 0, 0.1, 0.15), the compositions with x = 0 and 0.15 show a clear presence of a secondary phase, identified as the β − Mn phase with a lattice constant of 6.24 Å. Analysis of the back-scattered electron spectroscopy images and X-ray diffraction patterns confirm the formation of a pure Heusler phase in x = 0.1 composition. Magnetization measurements reveal an antiferromagnetic behavior in all compositions, with a N é el temperature of ∼ 50 K. However, deviation from Curie-Weiss law was observed for x = 0.1, suggesting competing magnetic interactions. Further investigation into the magnetic properties of this composition displays signatures of Griffiths phase, possibly caused by antisite disorder in the compound.

Atomic order, magnetic and transport phenomena in half-Heusler CoMnSb0.9Z0.1 alloys (Z = Si, Al, Sn, and Bi)

In this study, we investigate the effects of doping with ∼10 at% of Si, Al, Sn, and Bi on the atomic order, microstructure, and magnetic properties of CoMnSb samples prepared using the arc-melting method. X-ray diffraction, scanning electron microscopy, and magnetometry techniques were employed to derive the structural and magnetic parameters. The samples demonstrate a superstructure with an Fm-3m space group. They exhibit a saturation moment of 3.71–4.71 μB per formula unit at 5 K and a Curie temperature ranging from 474 to 507 K. Rietveld refinement performed on the XRD data revealed a possible occupation of magnetic atoms in the vacant 32f (x’, x’, x’) sites and atomic swapping, both of which may affect the magnitudes of the magnetic moment and Curie temperature. The electrical measurement results show that the grain boundaries and voids govern the conductivity of the samples. The spin polarization of the Si-doped sample was determined based on the grain-boundary magnetoresistance effect, which showed that this sample has a high degree of atomic order, consistent with the low magnetic moment, Curie temperature, and lattice constant.

Magnetocrystalline anisotropy of interstitially and substitutionally Sn-doped MnBi for high temperature permanent magnet applications

First-principles calculations were performed to calculate the electronic structures of low temperature phase (LTP) MnBi (Mn50Bi50) and substitutionally and interstitially Sn-doped MnBi [Mn50Bi25Sn25, (Mn0.5Bi0.5)66.7Sn33.3]. Brillouin function predicts the temperature dependence of saturation magnetization M(T). Sn substitution for Bi in MnBi (Mn50Bi25Sn25) changes the magnetocrystalline anisotropy constant (Ku) from −0.202 MJ/m3 (the in-plane magnetization) for LTP MnBi to 1.711 MJ/m3 (the out-of-plane magnetization). In comparison, the Ku remains negative but slightly decreases to −0.043 MJ/m3 when Sn is interstitially doped in MnBi [(Mn0.5Bi0.5)66.7Sn33.3]. The Curie temperature (TC) decreases from 716 K for LTP Mn50Bi50 to 445 K for Mn50Bi25Sn25 and 285 K for (Mn0.5Bi0.5)66.7Sn33.3. Mn50Bi25Sn25 has a lower magnetic moment of 5.034 μB/f.u. but a higher saturation magnetization of 64.2 emu/g than (Mn0.5Bi0.5)66.7Sn33.3 with a magnetic moment of 6.609 μB/f.u. and a saturation magnetization of 48.2 emu/g because the weight and volume of the substitutionally Sn-doped MnBi are smaller than the interstitially Sn-doped MnBi. The low Curie temperature and magnetization for Sn-doped MnBi are attributed to the high concentration of Sn. Thus, future study needs to focus on low Sn-concentrated MnBi.

Microstructural and Magnetic Property Investigations into Antiferromagnetic Mn2FeSi Heusler Alloy for Spintronics Applications

Magnetic materials, possessing low magnetic moment and high spin-polarization capability, are much in demand for spintronics applications these days. In this work, a ternary Mn2FeSi Heusler alloy was prepared by vacuum arc remelting technique followed by annealing it in vacuum at 773 K for 120 h. The crystal structure, chemical composition, and magnetic properties of the alloy annealed at optimum conditions were studied and proved using relevant experimental techniques. The X-ray diffraction analysis revealed the formation of the Heusler phase with a simple cubic structure with a = 5.63 Å in the alloy. This value matches well with that theoretically predicted. The chemical composition analysis of the sample shows that it is highly homogeneous and being closer to nominal. The Curie-Weiss equation was used to fit the thermomagnetic data and the paramagnetic Curie temperature (θ P) calculated, point to the occurrence in the alloy of the antiferromagnetic ordering of spins at low temperature. The magnetic measurements of the alloy showed its antiferromagnetic transformation (TN) at 64.5 K. This study demonstrates that Mn2FeSi Heusler phase may be explored as a low magnetic moment material for spintronics applications.