Average Magnetic Moment Research Articles

Machine learning-based prediction of FeNi nanoparticle magnetization

This work proposes a computationally efficient approach for estimating the magnetization of Fe0.7Ni0.3 body-centered cubic (bcc) nanoparticles (NPs) at room temperature using machine-learning algorithms, in terms of the average magnetic moment per atom, ⟨μ⟩. The magnetization data of isolated NPs were generated using atomistic spin dynamics (ASD) simulations for various nanoparticle shapes (cubes, spheres, octahedra, cones, cylinders, ellipsoids, flakes, and pyramids, with or without nanovoids) and FeNi distributions (random, core-shell, onion, sandwich, and Janus with different boundary planes). More than 1600 NPs were created and split into training and testing sets (70%-30% split), with features including the number of Ni/Fe surface and core atoms, potential energy distributions, pair correlation functions, and coordination distributions. Several machine-learning algorithms, including Random Forest (RF), Elastic Net, Support Vector Regression (SVR), and Gradient Boosting Regression (CatBoost), were applied to predict the average magnetic moment per atom of these NPs. The best-performing models, CatBoost and RF, achieved R2 scores of up to 0.86, demonstrating their accuracy in predicting NP magnetization. Feature analysis highlighted the significance of the interface between Fe and Ni clusters, Fe-Fe interactions, and the presence of Fe on the surface as critical contributors to overall magnetization. Random alloy spherical NPs without porosity exhibited the highest ⟨μ⟩ ∼ 1.6μB due to reduced Ni-Ni interactions. Applying machine-learning methods significantly reduces computational time and memory requirements compared to traditional ASD simulations. This allows for rapid prediction of NPs with desired magnetic properties, making them suitable for various technological applications.

Effects of transition metals (V, Cr, Mn, Fe and Ni) doping on magnetic properties of Co-based amorphous alloys

Amorphous alloys exhibit numerous interesting and abundant magnetic properties due to their disordered structural traits and have been extensively studied by researchers. In this work, the effects of a small amount of transition metals doping on the magnetic properties of Co80-xMxB20 (x = 0, 2, 4, 6, 8, 10; M = V, Cr, Mn, Fe, Ni) amorphous alloys were systematically investigated by utilizing first-principles molecular dynamics. The trend of the magnetic moment change in the simulated calculation conforms well to the experimental results. The doping of V atoms leads to the fastest rate of decrease in the magnetic moment of the surrounding Co atoms, and there is only an antiferromagnetic interaction between the V and Co atoms. When doped with Cr and Mn atoms, there is mutual competition between ferromagnetic and antiferromagnetic coupling in the amorphous alloy, Cr reduces the magnetic moment of the surrounding Co atoms, while the change in the magnetic moment of the Co atoms around Mn is small. The doping of Fe and Ni causes an increase in the magnetic moment of the surrounding Co atoms. The reason may be due to the charge transfer between atoms. The doping of Fe and Ni has a small effect on the average magnetic moment of the Co atoms in the amorphous alloy. The results provide necessary theoretical support for the development of the Co-based amorphous alloys with excellent magnetic characteristics.

Band Structure Calculations, Magnetic Properties and Magnetocaloric Effect of GdCo1.8M0.2 Compounds with M = Fe, Mn, Cu, Al

The magnetic properties, band structure results, and magnetocaloric effect of GdCo1.8M0.2 with M = Fe, Mn, Cu, and Al are reported. The band structure calculations demonstrate that all the samples have a ferrimagnetically ordered ground state, in perfect agreement with the magnetic measurements. Calculated magnetic moments and variation with the alloy composition are strongly influenced by hybridisation mechanisms as sustained by an analysis of the orbital projected local density of states. The XPS measurements reveal no significant shift in the binding energy of the investigated Co core levels with a change in the dopant element. The Co 3s core-level spectra gave us direct evidence of the local magnetic moments on Co sites and an average magnetic moment of 1.3 µB /atom was found, being in good agreement with the theoretical estimation and magnetic measurements. From the Mn 3s core-level spectra, a value of 2.1 µB/Mn was obtained. The symmetric shapes of magnetic entropy changes, the Arrott plots, and the temperature dependence of Landau coefficients clearly indicate a second-order phase transition. The relative cooling power, RCP(S), normalized relative cooling power, RCP(∆S)/∆B, and temperature-averaged entropy change values indicate that these compounds could be promising candidates for applications in magnetic refrigeration devices.

Indirect effect of Si on the ferromagnetic transformation of Mn in FeCoMnAlSi high-entropy soft magnetic alloy

In this study, we examined the indirect impact of Si on the ferromagnetic transformation of Mn in (Fe0.8Co0.2)80-xMn10Al10Six (x = 0, 1, 2, 3, 4, & 5 at%) high-entropy soft magnetic alloys. Our findings indicate strong correlation between Si and the ferromagnetic transformation, substantiated by simulation calculations. With Si content increasing the saturation magnetization of the system exhibits a distinctive trend of an initial increase followed by a subsequent decrease. Notably, the coercivity consistently decreases with x increases. Remarkably, when x equals 3, the soft magnetic properties of the system reach an optimal state, characterized by a saturation magnetization of 186.5 emu·g−1 and a coercivity of 1.6 Oe. The density of states and magnetic moment of the system are obtained by simulation calculation. Notably, the average atomic magnetic moment of Mn (1.642 μB) surpasses that of Co (1.434 μB), suggesting the excellent soft magnetic properties inherent in the system.

Mössbauer and magnetization measurements of multicomponent iron garnets

Four Gd-containing iron garnets were investigated using Mössbauer spectroscopy and Vibrating Sample Magnetometry over a wide temperature range, from 4K to ∼600K. The magnetic ordering temperature and hyperfine parameters determined on the basis of Mössbauer spectra for all samples were found to be surprisingly similar, differences were only noted for the average magnetic moments, which turned out to be strongly correlated with the magnetic moments of rare earth elements present in the structure. Further differences between the systems were also highlighted in measurements in the external 9T magnetic field, especially around the compensation temperature. Changes in the nature of the Mössbauer spectra were interpreted based on the crystal field approximation confirming the correctness of the interpretation of the temperature dependence of magnetization for these samples.

Probing temperature-dependent magnetism in cobalt and zinc ferrites: A study through bulk and atomic-level magnetic measurements for spintronics

Spinel ferrites (MFe2O4) are integral to various industries, particularly spintronics, which utilizes the intrinsic spin of electrons as well as the electronic charge to develop devices that dictate spin-based transport, advancing new memory, logic applications, and improving magnetic storage technologies. These materials are valued for their exceptional optical, magnetic and electrical properties, and their easily tunable shape and size. This flexibility of spinel ferrites and their connection to the material’s magnetic behavior can be investigated by studying a range of spinel ferrite structures. In this study, the magnetic behaviors of cobalt ferrite (CFO) and zinc ferrite (ZFO) nanoparticles were examined using a vibrating sample magnetometer (VSM, bulk magnetometry) and X-ray Magnetic Circular Dichroism (XMCD, atomic magnetometry). The Rietveld refinement of XRD data supported single phase spinel structure, while X-ray Absorption Spectroscopy (XAS), particularly through the Co L-edge XANES analysis, detected both Co2+ and Co3+ ions in CFO, suggesting significant ferromagnetic behavior due to octahedral site occupation. In contrast, ZFO exhibited antiferromagnetic character, with Zn2+ ions in tetrahedral sites, and canted antiferromagnetism manifesting as a hysteresis loop below 300 K, potentially related to lattice distortions or strain. At the atomic scale, XMCD analysis, along with sum rules, estimated the average magnetic moments for cobalt and zinc ferrites to be 3.045 ± 0.1 (1.448 ± 0.1) and 0.657 ± 0.1 (2.12 ± 0.1) μB at temperatures of 300 K (90 K), respectively. However, VSM-based bulk measurements indicated magnetic moments of 2.566 (2.288) and 0.281 × 10−3 (0.6503 × 10−3) μB for CFO and ZFO, respectively, at the same temperatures. The observed variation between bulk and atomic-scale magnetic moments points to complex interstitial interactions within the spinel ferrite’s sublattices. This discrepancy between the atomic-scale and bulk magnetic moments suggests intricate interstitial interactions within the spinel ferrite’s sublattices. These insights into the structural and magnetic intricacies of spinel ferrite nanoparticles enhance our understanding, facilitating the design of cutting-edge spintronic devices.

Unraveling the effect of 600 keV carbon ion irradiation on the structural and magnetic properties of ZnO thin film

600 keV 12C+ carbon ions have been irradiated upon 800 nm thin ZnO film. The thin ZnO films have been grown by pulsed laser deposition technique upon SiO2/Si substrate. The glancing incidence X-ray diffraction study exhibits the hexagonal wurtzite crystal structure of ZnO, having space group P63mc. Systematic X-ray diffraction analysis of both unirradiated and irradiated samples, reveals that the strain decreases in the sample post irradiation. Room temperature magnetization studies have been performed using SQUID-VSM. As the 600 keV carbon ion fluence is varied, an onset of ferromagnetic ordering in the ZnO thin film is observed. The maximum average magnetic moment induced by each carbon ion is found to be about 6.71 μB. X-ray photoelectron spectroscopy has been utilized to analyze the oxidation state of the C/O/Zn, which also rules out the presence of any transition metal elements in carbon ions irradiated ZnO thin film samples. The chemical and structural analysis of the samples have been examined by Raman spectroscopy. It reveals a red shift in A1 (LO) mode, which confirms the presence of tensile strain in the sample post irradiation. These experimental results, clearly indicate that oxygen vacancies and strain in the film trigger the onset of ferromagnetism in the ZnO thin film system.

Separating the contributions of the magnetic subsystems in antiferromagnetic ferrihydrite nanoparticles by analyzing the magnetization in fields of up to 250 kOe

Contributions of different magnetic subsystems formed in the systems of synthetic ferrihydrite nanoparticles (characterized previously) with an average size of < d>≈2.7 nm coated with polysaccharide arabinogalactan in different degrees have been separated by measuring the dependences of their magnetization M on magnetic field H of up to 250kOe on vibrating sample and pulsed magnetometers. The use of a wide measuring magnetic field range has been dictated by the ambiguity in identifying a linear M(H) portion for such antiferromagnetic nanoparticle systems within the conventional field range of 60–90 kOe. The thorough analysis of the magnetization curves in the temperature range of 100–250 K has allowed the verification of the contributions of (i) uncompensated magnetic moments µun in the superparamagnetic subsystem, (ii) the subsystem of surface spins with the paramagnetic behavior, and (iii) the antiferromagnetic susceptibility of the antiferromagnetically ordered ferrihydrite particle core. As a result, a model of the magnetic state of ferrihydrite nanoparticles has been proposed and the numbers of spins corresponding to magnetic subsystems (i)–(iii) have been estimated. An average magnetic moment μunof ∼ 145μB (μB is the Bohr magneton) per particle corresponds approximately to 30 decompensated spins of iron atoms in a particle (about 3 % of all iron atoms), which, according to the Néel’s hypothesis μun∼<d>3/2, are localized both on the surface and in the bulk of an antiferromagnetically ordered particle. The fraction of free (paramagnetic) spins is minimal in the sample without arabinogalactan coating of the nanoparticle surface (7 %) and is attained 20 % of all iron atoms in the sample with the highest degree of spatial separation of particles. According to this estimation, paramagnetic spins are located mainly on the edges and protruding areas of particles. Most magnetic moments of iron atoms are ordered antiferromagnetically and the corresponding magnetic susceptibility of this subsystem behaves as in an antiferromagnet with the randomly distributed crystallographic axes, i.e., increases with temperature.

Tuning the magnetic properties of van der Waals Fe3GaTe2 crystals by Co doping.

Tuning the magnetic properties of two-dimensional van der Waals ferromagnets has special importance for their practical applications. Using first-principles calculations, we investigate the magnetic properties of Co-doped Fe3GaTe2 with different Co concentrations and different Co atomic sites. Calculation results show that Fe or Co atoms with relatively lower atomic concentrations preferentially occupy Fe1 sites with interlayer coupling, which is more energetically favorable. As the doping concentration of Co atoms increases, the total magnetic moment of the doped system decreases, while the average atomic magnetic moments of Fe1 and Fe2 increase and decrease, respectively, with Fe1 reaching ∼2.08μB. The spin polarization of the doped model 2Co-2 near the Fermi energy level is significantly reduced, while 4Co-3 exhibits an enhanced trend. At some doping level, a phase change from ferromagnetism to antiferromagnetism appears at high Co concentration. These results provide a theoretical basis for experimental studies and valuable information for the development of Fe3GaTe2-based spintronic devices.

Exploring phase formation and magnetic transitions in Sm(Fe1−xMnx)14B by Mössbauer spectroscopy

The Sm2(Fe1−xMnx)14B (0 ≤ x ≤ 0.3) rare earth alloy was prepared by a reduction-diffusion method, and a corresponding reduction-diffusion model was established. The crystal structure, microscopic morphology, and magnetic properties were systematically characterized to investigate the effect of Mn doping. The results show that the diffusion of Sm into FeB proceeded with the formation of the Sm2Fe14B phase from the very beginning of the reaction. Sm2(Fe1−xMnx)14B alloy undergoes a transition from the ferromagnetic phase (x = 0) to the paramagnetic phase (x = 0.2), and the average magnetic moment of Fe decreases from 2.066 to 0.719 µB as observed by 57Fe Mössbauer spectroscopy. In addition, the Curie temperature decreases rapidly from 620 to 230 K. In other words, a wide temperature-regulation of TC can be achieved by adjusting the Mn content, which is attributed to the fact that Mn doping greatly weakens the atomic exchange interactions. These results provide value for potential applications of Re–Fe-based alloys in room temperature magnetic refrigeration.

Magnetic properties and structural phase transition in ultrathin fcc Fe(111) and bcc Fe(111) films: First-principles study

The aim of this work is to investigate the structural and magnetic characteristics of Fe thin films with a triangular (hexagonal) lattice surfaces (fcc (111) and bcc (111)). The properties of these structures have been calculated using density functional theory (DFT) implemented in the full-potential local-orbital (FPLO) code. The results indicate a structural phase transition from fcc to bcc structure when the film thickness exceeds 23 Fe atomic monolayers. The considered fcc films prefer the low-spin ferromagnetic state with an average magnetic moment of about 1.0 μB per atom. This moment decreases with increasing film thickness until the critical thickness, where, after the structural transition to the bcc phase, it reaches a value close to that of bulk bcc Fe. Moreover, the values of the magnetic anisotropy energy are positive (perpendicular magnetic anisotropy) for the entire thickness range of films with fcc structure (in ferromagnetic low-spin state) and systematically decrease with increasing film thickness. The presented computational results explain the experimentally observed structural transition and may help to select appropriate substrates with suitable lattice parameters for the deposition of ultrathin Fe(111) films.

Surface Stability and Exfoliability of Non-van der Waals Magnetic Chromium Tellurides.

Exfoliation of two-dimensional (2D) magnetic materials from non-van der Waals (non-vdW) materials has attracted increasing attention because it provides a great platform for the construction of 2D magnetic materials. For non-vdW magnetic chromium tellurides with high Curie temperatures, their few-layer samples show promising applications in the field of spintronics. However, there is still no consensus on whether the surface structures of few-layer chromium tellurides should be terminated by Cr or Te atoms. By calculating the surface and exfoliation energy, we find that which structure is more stable depends greatly on the value of the chemical potential of Te atoms, and the few-layer sample with a Cr-terminated surface is easier to exfoliate than that with both Te-terminated surfaces. Finally, we propose that different exfoliated structures can be identified by using the atomic number ratio of Cr to Te and the average magnetic moment of Cr atoms in few-layer samples.

2D Materials by Design: Intercalation of Cr or Mn between two VSe2 van der Waals Layers.

Insertion of metal layers between layered transition-metal dichalcogenides (TMDs) enables the design of new pseudo-2D nanomaterials. The general premise is that various metal atoms may adopt energetically favorable intercalation sites between two TMD sheets. These covalently bound metals arrange in metastable configurations and thus enable the controlled synthesis of nanomaterials in a bottom-up approach. Here, this method is demonstrated by the insertion of Cr or Mn between VSe2 layers. Vacuum-deposited transition metals diffuse between VSe2 layers with increasing concentration, arranging in ordered phases. The Cr3+ or Mn2+ ions are in octahedral coordination and thus in a high-spin state. Measured and computed magnetic moments are high for dilute Cr atoms, but with increasing Cr concentration the average magnetic moment decreases, suggesting antiferromagnetic ordering between Cr ions. The many possible combinations of transition metals with TMDs form a library for exploring quantum phenomena in these nanomaterials.

First-principles study on the magnetic properties in non-metallic co-doped cubic LaNiO3

Using the first principles spin polarized calculations, the electronic structures and magnetic properties of two C atoms and two S atoms doped LaNiO3 (LNO) are investigated. For the double C-doped LNO (C-LNO), C–O–C chain exhibits the ferromagnetic (FM) order arrangement. The introduction of C atoms increases the average magnetic moment of each Ni atom by 0.23 μB/cell and enhances the hybridization between Ni-3d and O-2p states. The C atom generates a weak magnetic moment of 0.07 μB/atom due to the magnetization in the FM ground state. For the case of double S-doped LNO (S-LNO), S–O–S chain exhibits the antiferromagnetic (AFM) order. In the ferromagnetic configuration of S-LNO, each S atom generates a magnetic moment of 0.18 μB/atom due to the Ni–O hybridization. In addition, the interesting phenomenon of magnetic moment reversal of S atoms is observed in both the FM and AFM structures of S-LNO.

Magnetic properties of the FCC and BCC phases of (MnFeCoNi)80Cu[formula omitted] ([formula omitted]: Al, Ga) high-entropy alloys

In this work, the FCC-BCC phase transition in (MnFeCoNi)80Cu20−xZx (Z: Al, Ga) high entropy alloys were investigated on the basis of structural, magnetic, hardness and thermal expansion properties. It is found that the equiatomic MnFeCoNiCu alloy is FCC and exhibits mixed ferromagnetic/anti-ferromagnetic interactions with a Curie temperature, Tc, close to room temperature. However, the BCC structure emerges with increasing amount of Al (10 at%) and Ga (15 at%) with additional ferromagnetic interactions and associated Tcs. It is evidenced that in terms of the valence electron concentration and the average magnetic moment values, the investigated HEAs obey the Slater-Pauling rule in a region close to the Heusler alloys. Additionally, they may exhibit similar physical properties like Invar property with low thermal expansion coefficient with the 3d-transition metal-alloys having same valence electron concentration.

Charge invertible nanowires [Ni5Bi5.6]x (x = 1+, 0, 1−): Infinite columns [Ni5Bi5.6]− in a novel quasi-one-dimensional compound KNi5Bi5.6

A novel quasi-one-dimensional (Q1D) compound KNi5Bi5.6 has been synthesized and its crystal structure has been determined by X-ray crystallography. The structure contains double-walled anionic nanowires [Ni5Bi5.6]− separated by potassium cations. KNi5Bi5.6 forms a new series of compounds together with previously reported Bi5.6Ni5I and Bi28Ni25 featuring [Ni5Bi5.6]x (x = 1+, 0, 1−) nanowires for which the charge can be cationic, neutral or anionic without appreciably affecting the structure and composition. This unique characteristic provides a new platform to investigate charge invertible Q1D transition metal systems. Resistivity measurement of KNi5Bi5.6 reveals a metallic type of conductivity. Magnetic susceptibility obeys a modified Curie-Weiss behavior with a small average effective magnetic moment of Ni and shows a weak magnetic anisotropy.

Origin of the improved Bs for Fe-Si-B-Mn microalloyed amorphous alloys

In this study, the saturation magnetic flux density (Bs) and the local structure of Fe80Si9-xB11Mnx (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1.0 at.%) amorphous alloys are investigated. The optimum addition of 0.3 at.% Mn on Bs results from the strengthening of ferromagnetism with larger interatomic distance of Fe. However, excess Mn addition will result in the antiferromagnetic coupling between Mn and Fe atoms, which in turn leads to the decrease of Bs. A model has been proposed to evaluate the optimum doping content of Mn for the highest Bs by calculating the fraction of amorphous pure Fe with average magnetic moment of 0.40 μB and the coordination number of one Mn solute. The present work is promising to provide a guideline for choosing the content of the minor alloying on improving Bs of Fe-Si-B amorphous system.

Study of structural, magnetic and electronic properties of a new off-stoichiometric series of full-Heusler alloy Co2Nb1+xZ1−x (Z = Sn, In, Ga): Ab initio approach

Using ab initio calculation, we investigate systematically the structural, electronic and magnetic properties of Co2Nb1+xZ1−x (x = 0, 0.25, 0.50). Here, Plane-Wave self-consistent field (PWscf) program implemented in open-source Quantum Espresso software package within generalized gradient approximation (GGA) - Perdew-Burke-Ernzerhof (PBE) for the exchange-correlation functional has been used. Equilibrium lattice parameters in cubic austenitic phase of Co2Nb1+xZ1−x (x = 0, 0.25, 0.50) have been inquired. It has been found out that except Co2NbSn, all the compositions do not show martensitic structural transition. The microscopic origin for this has been associated with Jahn-Teller distortion of Co 3deg orbitals in close proximity of the Fermi level. The density of states for both tetragonal and 4 O orthorhombic structure in martensitic phase of Co2NbSn have been investigated. Moreover, from the density of states plots we have recognized the metallic character of Co2NbSn. However, Co2NbGa & Co2NbIn and all of the off-stoichiometric alloys have been anticipated to possess partial half-metallic character. Furthermore, we have examined the total magnetic moment and average atomic magnetic moments in off-stoichiometric Co2Nb1+xZ1−x in the cubic phase to understand the effect of Nb doping in stoichiometric compounds. Nb doping increases the total magnetic moment due to increased Nb-Co hybridization of d orbitals.

Magnetic properties and muon localization in Cr2S3

We investigate the magnetic ground state of rhombohedral chromium sulphide Cr2S3 by density functional theory. We identify the muon implantation sites, their hyperfine couplings and the role of charge states in this compound. Our calculations show that we can obtain a compensated ferrimagnetic ground state. We find that strong electronic correlations are required to correctly obtain the semiconducting band behaviour of Cr2S3 in agreement with experiment. Relying on earlier µSR measurements, our calculations suggest that the two muon local fields in Cr2S3 are due to distinct charge states for two very close but distinct muon sites bonded between two sulphur atoms. Further analysis of the static field at the muon allows to determine by µSR the average Cr magnetic moment in good agreement with experiment.

Structure and magnetism of rhodium particles as a size effect

The magnetic properties of Rh clusters with face-centered-cubic (FCC) and hexagonal-closed-packed (HCP) structures were studied by first-principles calculations. The results show that both the structure and magnetic properties have size effects. Bulk Rh exists as a FCC structure. However, as the size of Rh particles shrinks, the FCC and HCP structures have comparable energies, consistent with the coexistence of the two structures experimentally observed previously. Although the bulk Rh is nonmagnetic, the nanoparticles or clusters of Rh in both the FCC and HCP structures are magnetic. The average magnetic moment gradually increases as the clusters shrink. The origin of the magnetism of Rh clusters can be attributed to the reduction of coordination number, other than the lattice expansion. The findings provide insights for understanding the magnetic properties of noble metal clusters.