Average Magnetic Moment Research Articles

Magnetocrystalline anisotropy of small CoPt binary alloy metal clusters: interplay between structure, chemical composition, and spin-orbit coupling

The ground-state magnetic properties of ConPtm binary alloy clusters of size N = n + m ≤ 9 are studied systematically as a function of size, composition, and chemical order in the framework of the generalized gradient approximation (GGA) to density functional theory (DFT). Interestingly, strong cluster-size and chemical-composition dependence exhibiting substantial values (0.4–22 meV/atom) in the magnetic anisotropy energy (MAE) are revealed. Such behavior crucially depends on the Pt moments induced by the proximity to Co, and on the resulting spin-orbit interactions at the Pt atoms. Moreover, we show that the MAEs and direction of magnetization can be tuned to some extent by varying the Pt concentration showing spin reorientations and the easy axis of magnetization is cluster size dependent. A thorough cluster-geometry optimizations together with a collinear and noncollinear magnetic moment arrangement sampling including the spin-orbit coupling are carried out to identify the ground-state and the low-lying structures. The relative directions between Co and Pt magnetic moments induced by spin-orbit interaction show an early tendency to arrange the magnetic moments along with Co and Pt layers in a way resembling the L10 phase with tetragonal crystal lattice which can be appreciated in the clusters having N ≥ 5 atoms. Our results show that planar-like structures are preferred in small cluster sizes (N ≤ 4 atoms) while for N ≥ 5 tend to form three-dimensional core-shell compact structures with a composition around 50/50% ordering maximizing the number of Co-Pt bonds. The average magnetic moment per atom $\bar {\mu }_{T}$ increases approximately linearly with Co content and important enhancement of the local Co moments is observed as a result of Pt doping for n + m ≤ 4. This is mainly a consequence of the increase in the number of Co d holes due to Co to Pt charge transfer. Finally, our results show important spin and orbital moments induced at the Pt atoms as well as significant orbital moments at the Co atoms .

Remarkable Energy Barrier for Magnetization Reversal in 3D and 2D Dysprosium‐Chloranilate‐Based Coordination Polymers

Herein, we report two coordination polymers (CPs)[{Dy(Cl2An)1.5(CH3OH)}.4.5H2O]n(CP1) and [Dy(Cl2An)1.5(DMF)2]n(CP2) (where Cl2An2-= chloroanilate (2,5-dihydroxy-1,4-benzoquinone dianion))exhibiting field inducedsingle molecule magnet behavior with moderate barrier of magnetization reversible.Detailed structural and topological analysis disclose that CP1possesses three dimensional network whereas CP2has a two dimensional layered type structure. In both CPs, the magnetic measurements show weak antiferromagnetic exchange interaction between the dysprosium centers and field induced slow magnetic relaxation with the barrier of 175(9) K (CP1) and 145(7) K (CP2) for CPs1and2, respectively.Notably, thevaluesfor CP1and CP2represent remarkableenergy barrier of magnetization reversalin anymetal-chloranilate based 3D (CP1) and 2D (CP2)coordinationpolymers [Anchor] .The temperature and field dependence of relaxation time indicate the presence of multiple relaxation like direct, QTM, Raman, and Orbach processes in both the CPs. The theoreticalab initiocalculations reinforce the experimentally observed higher energy barrier in CP1as compared to CP2due to the presence of large transverse anisotropy on the ground state in the later compound. The average value of the transition magnetic moment between the computed low-lying spin-orbit states also rationalized the possible relaxation process as Orbach and Raman process through the first excited state. The BS-DFT calculations have been carried out to provide more insight into the exchange interaction.

First-principles study on the thermodynamic, mechanical and magnetic properties of the Fe-N phases

To clear the intermetallic Fe-N phases, how to effect the strength and magnetic features of iron nitrides thin films, the thermodynamic, mechanical and magnetic attributes of the Fe-N phases have been calculated at Perdew, Burke and Enzerhof (PBE) level. The results show that the [Formula: see text] and [Formula: see text] phases are more stable than the other considered Fe-N phases by the formation energies. [Formula: see text] and [Formula: see text] phases are metastable at 0 K, which can be further decomposed into other more stable phases with temperature decreasing, i.e., [Formula: see text] and [Formula: see text]. [Formula: see text] is the only brittle phase, while [Formula: see text] is the most ductile phase. The [Formula: see text] possesses the highest thermal conductivity by Debye temperatures. The [Formula: see text] possesses the highest anisotropic behavior by [Formula: see text], [Formula: see text] and [Formula: see text] values. The [Formula: see text] and FeN phases possess higher average magnetic moments (MM) than their neighbors. The [Formula: see text] has stronger ionic bond by Mülliken population analysis.

Material informatics for layered high-T C superconductors

Superconductors were typically discovered by trial-and-error aided by the knowledge and intuition of individual researchers. In this work, using materials informatics aided by machine learning (ML), we build an ML model of superconductors, which is based on several material descriptors with apparent physical meanings to efficiently predict critical superconducting temperature TC. The descriptors include the average atomic mass of a compound, the average number of electrons in an unfilled shell, the average ground state atomic magnetic moments, the maximum difference of electronegativity, etc. To fully optimize the ML model, we develop a multi-step learning and multi-algorithm cross-verification approach. For known high TC superconductors, our ML model predicts excellent TC values with over 92% confidence. When the ML model is applied to about 2500 layered materials in the inorganic crystal structure database, 25 of them are predicted to be superconductors not known before, including 12 cuprates, 7 iron-based crystals, and 6 others, with TC ranging from ∼32 K to ∼138 K. The findings shed considerable light on the mapping between the material descriptors and TC for layered superconductors. The ML calculates that in our descriptors, the maximum difference of electronegativity is the most important one.

Enhanced Ferromagnetism and Tunable Magnetism in Fe3GeTe2 Monolayer by Strain Engineering.

Recent discovery of intrinsic ferromagnetism in Fe3GeTe2 (FGT) monolayer [Deng, Y.; Nature 2018, 563, 94-99; Fei, Z.; Nat. Mater. 2018, 17, 778-782] not only extended the family of two-dimensional (2D) magnetic materials but also stimulated further interest in the possibility to tune their magnetic properties without changing the chemical composition or introducing defects. By means of density functional theory computations, we explore strain effects on the magnetic properties of the FGT monolayer. We demonstrate that the ferromagnetism can be largely enhanced by the tensile strain in the FGT monolayer due to the competitive effects of direct exchange and superexchange interaction. The average magnetic moments of Fe atoms increase monotonically with an increase in biaxial strain from -5 to 5% in FGT monolayer. The intriguing variation of magnetic moments with strain in the FGT monolayer is related to the charge transfer induced by the changes in the bond lengths. Given the successful fabrication of the FGT monolayer, the strain-tunable ferromagnetism in the FGT monolayer can stimulate the experimental effort in this field. This work also suggests an effective route to control the magnetic properties of the FGT monolayer. The pronounced magnetic response toward the biaxial strain can be used to design the magnetomechanical coupling spintronics devices based on FGT.

Energetics, electronic and magnetic properties of vanadium diselenide Nanoribbons: A first-principles study

Using the first-principles method based on density functional theory, we studied the structural, magnetic and electronic properties of 2H/1T-VSe 2 nanoribbons. The ground states of armchair-edge and zigzag-edge nanoribbons are obtained. With width increasing, the edge stabilities are nearly unchanged in H phase nanoribbons, whereas the edge stabilities of T phase nanoribbons increase. Meanwhile, the average magnetic moment per V atom grows monotonously in the ferromagnetic nanoribbons but fluctuates with the width parity in the antiferromagnetic armchair-edge nanoribbons. Due to strong confinement effects and magnetic coupling, the electronic structures of VSe 2 nanoribbons are sensitive to both the magnetic state and width, resulting in the nanoribbons vary in semiconductor, semi-metal and metal. These findings suggest that VSe 2 nanoribbons are promising candidates for spintronic applications. • 2H and 1T-VSe 2 nanoribbons show distinct width-dependency in stabilities. • The energetic more favorable edge-chirality structure is armchair for 2H and zigzag for 1T nanoribbons. • With width increasing, the average magnetic moment grows monotonously in the ferromagnetic. • Width can tune the electronic properties of VSe 2 nanoribbons change in semiconductors, semi-metals and metals.

Effect of strain on magnetic and orbital ordering of LaSrCrO3/LaSrMnO3 heterostructures

We investigate the effect of strain and film thickness on the orbital and magnetic properties of LaSrCrO$_3$ (LSCO)/LaSrMnO$_3$ (LSMO) heterostructures using bulk magnetometry, soft X-ray magnetic spectroscopy, first-principles density functional theory, high-resolution electron microscopy and X-ray diffraction. We observe an anti-parallel ordering of the magnetic moments between the ferromagnetic LSMO layers and the LSCO spacers leading to a strain-independent ferromagnetic ground state of the LSCO/LSMO heterostructures for LSMO layers as thin as 2 unit cells. As the LSMO thickness is increased, a net ferromagnetic state is maintained, however, the average magnetic moment per Mn is found to be dependent on the magnitude of the substrate-induced strain. The differences in the magnetic responses are related to preferential occupation of the Mn $x^2-y^2$ (in-plane) d-orbitals for tensile strain and $3z^2-r^2$ (out-of-plane) orbitals under compressive strain leading to competing ferromagnetic and anti-ferromagnetic exchange interactions within the LSMO layers. These results underscore the relative contributions of orbital, structural and spin degree of freedom and their tunability in atomically-thin crystalline complex oxide layers.

Magnetization process of the insulating ferromagnetic semiconductor (Al,Fe)Sb

We have studied the magnetization process of the new insulating ferromagnetic semiconductor (Al,Fe)Sb by means of x-ray magnetic circular dichroism. For an optimally doped sample with 10% Fe, a magnetization was found to rapidly increase at low magnetic fields and to saturate at high magnetic fields at room temperature, well above the Curie temperature of 40 K. We attribute this behavior to the existence of nanoscale Fe-rich ferromagnetic domains acting as superparamagnets. By fitting the magnetization curves using the Langevin function representing superparamagnetism plus the paramagnetic linear function, we estimated the average magnetic moment of the nanoscale ferromagnetic domain to be 300-400 $\mu_{B}$, and the fraction of Fe atoms participating in the nano-scale ferromagnetism to be $\sim$50%. Such behavior was also reported for (In,Fe)As:Be and Ge:Fe, and seems to be a universal characteristic of the Fe-doped ferromagnetic semiconductors. Further Fe doping up to 14% led to the weakening of the ferromagnetism probably because antiferromagnetic superexchange interaction between nearest-neighbor Fe-Fe pairs becomes dominant.

Antiferromagnetic Inverse Spinel Oxide LiCoVO4 with Spin-Polarized Channels for Water Oxidation.

Exploring highly efficient catalysts for the oxygen evolution reaction (OER) is essential for water electrolysis. Cost-effective transition-metal oxides with reasonable activity are raising attention. Recently, OER reactants' and products' differing spin configurations have been thought to cause slow reaction kinetics. Catalysts with magnetically polarized channels could selectively remove electrons with opposite magnetic moment and conserve overall spin during OER, enhancing triplet state oxygen molecule evolution. Herein, antiferromagnetic inverse spinel oxide LiCoVO4 is found to contain d7 Co2+ ions that can be stabilized under active octahedral sites, possessing high spin states S = 3/2 (t2g 5 eg 2 ). With high spin configuration, each Co2+ ion has an ideal magnetic moment of 3 µB , allowing the edge-shared Co2+ octahedra in spinel to be magnetically polarized. Density functional theory simulation results show that the layered antiferromagnetic LiCoVO4 studied contains magnetically polarized channels. The average magnetic moment (µave ) per transition-metal atom in the spin conduction channel is around 2.66 µB . Such channels are able to enhance the selective removal of spin-oriented electrons from the reactants during the OER, which facilitates the accumulation of appropriate magnetic moments for triplet oxygen molecule evolution. In addition, the LiCoVO4 reported has been identified as an oxide catalyst with excellent OER activity.

Magnetic properties of selected Fe-based soft magnetic composites interpreted in terms of Jiles-Atherton model parameters

The paper presents the Jiles-Atherton model application to selected Fe-based soft magnetic composites (of different types prepared with the intention of verifying the model), with inner demagnetizing fields consideration implemented. The model fits experimental anhysteretic magnetization curves with very good accuracy, obtaining parameters: the effective domain density, the interdomain coupling and the average magnetic moment of effective domain. The parameters are interpreted in comparison to maximum total and differential permeability, inner demagnetization factor and hysteresis losses. The denser effective domain structure with stronger interdomain coupling is found for the decreasing ferromagnetic filler content and mean particle size, together with higher inner demagnetizing fields, leading to lower number of active magnetic objects, reflected by magnetic properties worsening. The relation of magnetic properties to interdomain coupling strength and effective domain density is specific for each ferromagnetic component of composite. The parameters absolute values are found remarkably different from bulk ferromagnets values in literature, pointing out the specific magnetization reversal of composites.

Influence of the electronic polymorphism of Ni on the classification and design of high entropy alloys

According to a recent Hume-Rothery approach, the electron concentration, e/a, and the average radius can be used to identify the domain of stability of HEAs and to estimate the phases that may occur in the alloy. The present study investigates the influence of the electronic polymorphism of nickel on the efficiency of the classification and on the design of HEAs for magnetic applications. Many different compositions were used, based on 4 to 7 elements out of a total 13 different elements (Co, Cr, Fe, Ni, Al, Cu, Pd, Ti, Mn, V, Nb, Sn, Ru). Phases have been determined by X-ray and neutron diffraction as well as in some cases high energy X-ray diffraction. The e/a for the constituent elements is calculated according to Massalski. The two polymorphic electronic structure of nickel, namely (e/a)Ni = 1 or (e/a)Ni = 2 are considered. The average e/a for the alloy is calculated assuming a solid solution case. The electronic structure [Ar] 3d9 4s1 seems to be more appropriate for the classification of HEAs. Based on a Self-organising Map predictions are made for the average magnetic moment at saturation for this electronic structure of Ni. Non-saturated values and data from the literature are compared with the predictions. The consequences of such results when modelling the structure and properties of Ni containing HEAs are presented, in particular the consideration of the shape and transformation of the Brillouin zone.

The effect of [formula omitted] phase preference on magnetic properties of AlxCrFeCoNi high entropy alloys

AlxFeNiCrCo (0≤x≤1.5) high entropy alloys (HEA) have been studied both experimentally and theoretically, considering the multi-phase character of investigated samples. Magnetic properties of these alloys (ordering temperatures and average magnetic moments) were determined from magnetization measurements (VSM), being found strongly dependent on Al content. Decomposition of this HEA system into phases with different stoichiometries and different crystal structures was analyzed using electronic structure calculations by the KKR and KKR-CPA methods, and discussed in terms of total energy balance. Additional energy lowering was achieved by admitting atoms separation in Al- and Ni-rich bcc-phase within B2-like crystal structure, and in consequence ordering of some elements constituting HEA, has been determined. Accounting for all experimentally detected phases in AlxFeCrNiCo samples, it was found that calculated total and site-decomposed magnetic moments strongly depended on stoichiometries, more particularly on crystal structures. Comparison of KKR calculations based on ordered supercell models and KKR-CPA results performed for fully disordered model of HEA systems, clearly indicates strong influence of local atoms neighborhood on magnetic moments. It is observed that in spite of increase of nominal Al content in AlxFeNiCrCo HEA, the actual concentration of Al in the detected fcc and bcc phases only slightly changes. Hence the strong measured variation of saturated magnetization with x is essentially driven by relative phase contributions. On the whole, much better agreement between measured and theoretical magnetic moments was obtained when averaging computational results obtained for experimentally detected phases and their contributions, than KKR-CPA results achieved for single-phase HEAs with nominal compositions.

Effect of similar element Nb and Ti substitution for Zr in Fe70(ZrNbTi)10B20 bulk metallic glasses

A family of Fe70(ZrNbTi)10B20 bulk metallic glasses (BMGs) were developed through the stepwise substitution of Nb and Ti for non-major solvent element Zr. The glass-forming ability (GFA), magnetic and mechanical properties of Fe70Zr10B20, Fe70Zr6Nb4B20 and Fe70Zr4Nb4Ti2B20 metallic glasses were studied to explore the influence of minor similar solvent element substitution. With the substitution of 4 at.% Nb for Zr, the critical diameter of Fe70Zr6Nb4B20 BMG increases to 1 mm while the saturation magnetization (Ms) decreases slightly. After the further substitution of 2 at.% Ti, the resulting BMG exhibits higher GFA and lower Ms. The enhanced GFA and decreased Ms are attributed to the more solute-solute avoidance and smaller average magnetic moments of the resulting bulk metallic glass, respectively. In addition, the analysis of charge density distribution reveals the origin of high fracture strength and microhardness of Fe70Zr4Nb4Ti2B20 BMG.

A detailed study of magnetic properties and room temperature memory effect in wet chemically prepared [formula omitted][formula omitted] nanostructured alloy

We present the magnetic properties of nanostructured Ni0.2Cu0.8 granular alloy prepared by a chemical reduction process. Zero-field-cooled and field cooled magnetization studies show branching due to the presence of superparamagnetism. The large particle size distribution in our sample is reflected in a broad blocking temperature distribution which on the higher side extends to 390 K. Magnetic field dependence of magnetization shows a superparamagnetic component accompanied with a ferromagnetic part at low temperature with prominent hysteresis loops exhibited at temperatures 2–50 K. The average magnetic moment of nickel (0.5μB) is smaller than its expected ferromagnetic saturation value (0.6μB) indicating that not all Ni atoms contribute to ferromagnetism. The magnetization data are analyzed in terms of an existing core–shell nanoparticle model. The study demonstrates that the overall behavior of the system is that of an assembly of non-interacting superparamagnetic (SPM) particles exhibiting the magnetic memory effect in relaxation dynamics, which has been observed using different experimental protocols, and persists even up to room temperature.

Noncollinear Ordering of the Orbital Magnetic Moments in Magnetite.

The magnitude of the orbital magnetic moment and its role as a trigger of the Verwey transition in the prototypical Mott insulator, magnetite, remain contentious. Using 1s2p resonant inelastic x-ray scattering angle distribution (RIXS-AD), we prove the existence of noncollinear orbital magnetic ordering and infer the presence of dynamical distortion creating a polaronic precursor for the metal to insulator transition. These conclusions are based on a subtle angular shift of the RIXS-AD spectral intensity as a function of the magnetic field orientation. Theoretical simulations show that these results are only consistent with noncollinear magnetic orbital ordering. To further support these claims we perform Fe K-edge x-ray magnetic circular dichroism in order to quantify the Fe average orbital magnetic moment.

Possible Ferromagnetism in YCuO System

polycrystalline CuxYyOz are made through solid state reaction. Ferromagnetism is found in this YCuO system at room temperature. The ferromagnetism quite probably originates from Cu2Y2O5 , the Copper Yttrium Oxide. The average magnetic moment per Cu2+ is estimated to be 0.04μB. Itinerant electron magnetism is a rational explaination for the observed ferromagnetism. The experiment shows that the excessive amount of Cu may lead more defects and further distortion in the lattice and decrease the exchange interaction. This reminds us that the Copper Yttrium Oxide is a substance not only should be avoided in fabricating YBCO superconductors but also should be considered as a potential substance of magnetic semiconductor.

Magnetic Properties of Metastable BCC-Cobalt During Reduction of Cobalt Oxide (Co3O4)

Cobalt Oxide (Co3O4) was reduced to metallic Co using the nut shells of pistachio by heat treatment at temperatures of 1400°C and 1500°C in an argon gas atmosphere. This method for reducing Cobalt Oxide may provide a valuable route for reclaiming nanoparticles of metallic Co from waste material. Rietveld analysis of the x-ray diffraction profiles showed the presence of two phases of Co; FCC (γ-Co), and ΒCC phase of Co in addition to the presence of C in the graphite phase. The samples synthesized by processing at 1400°C showed only the FCC phase of Co whereas mixed phases of FCC and BCC Co were formed for samples heat treated at 1500°C. The magnetic properties were determined using VSM and FMR measurements. A magnetic saturation value of 160 emu/g was determined for the FCC phase which is consistent with the literature value. On the other hand, the magnetic saturation value of BCC Co was measured to be 214 emu/g. Magnetic data suggest the average magnetic moment is consistent with FCC cobalt. This simple method of producing BCC-Co has potential industrial and possible medical applications such as magnetic sensors, electromagnetic shielding, magnetic memory, magnetic fluids, magnetic composites and catalysis.

A giant enhancement of magnetic moment in a ternary three-shell icosahedral cluster: Fe@Mn12@Au20

ABSTRACTThe average magnetic moment per atom of Mn13 cluster is expected to be enhanced by doping or coating with a shell. Several ternary core–shell icosahedral clusters TM@Mn12@Au20 were constructed by combining substituting the central Mn with VIII elements (Fe, Co, Ni, Ru, Rh, Pd and Pt) and coating with a icosahedral Au20 shell, and systematically studied by using the first-principles density functional method. Compared to Mn13, Fe@Mn12@Au20 cluster shows a giant enhancement on total magnetic moment (52 µB) which can be greatly attributed to the ferromagnetic coupling between spin moments of atoms. Coating with Au20 shell enlarged the average distances of TM-Mn and Mn-Mn and is a useful way to change the magnetic coupling style. By analysis of density of states and electron localisation functional, we can conclude that the weak hybridisation between Fe and Mn in Fe@Mn12@Au20 is propitious to maintain their original direction of spin moments of atoms and then form ferromagnetic coupling.

Structures, electronic properties and adsorption mechanisms of the O2Fe3N clusters

The structures, adsorption mechanisms and electronic attributes of the O2Fe3N clusters are calculated at Perdew, Burke and Ernzerhof (PBE) functional. The results show that two O atoms prefer to be located at the Fe–Fe bridge site of Fe–N molecule which form the ground-state O2Fe3N cluster, respectively. It means that O2 molecule is dissociated by Fe3N molecule. Compared to the isomer (3)–(6), it indicates that an O2 molecule is preferentially adsorbed on the top site of Fe atom which is close to N atom of the Fe3N molecule in the vertical direction. The adsorptions of Fe3N with O2 are the exothermic before endothermic reaction. All the O2Fe3N clusters possess higher kinetic activity. The average spin magnetic moments of the O2Fe3N clusters are as follows: isomer (6) [Formula: see text] isomer (1) [Formula: see text] isomer (3) [Formula: see text] isomer (5) [Formula: see text] ground-state [Formula: see text] isomer (2) [Formula: see text] isomer (4). Compared to the external charge transfer of the O2Fe3N clusters, the transfer of electrons between 4s and 3d, 4p orbitals in the same atom is significantly higher.

U-turn trajectories of magnetotactic cocci allow the study of the correlation between their magnetic moment, volume and velocity.

Magnetotactic bacteria are microorganisms that present intracellular chains of magnetic nanoparticles, the magnetosome chain. A challenge in the study of magnetotactic bacteria is the measurement of the magnetic moment associated with the magnetosome chain. Several techniques have been used to estimate the average magnetic moment of a population of magnetotactic bacteria, and others permit the measurement of the magnetic moment of individual bacteria. The U-turn technique allows the measurement of the individual magnetic moment and other parameters associated with the movement and magnetotaxis, such as the velocity and the orientation angle of the trajectory relative to the applied magnetic field. The aim of the present paper is to use the U-turn technique in a population of uncultured magnetotactic cocci to measure the magnetic moment, the volume, orientation angle and velocity for the same individuals. Our results showed that the magnetic moment is distributed in a log-normal distribution, with a mean value of 8.2 × 10-15Am2 and median of 5.4 × 10-15Am2. An estimate of the average magnetic moment using the average value of the orientation cosine produces a value similar to the median of the distribution and to the average magnetic moment obtained using transmission electron microscopy. A strong positive correlation is observed between the magnetic moment and the volume. There is no correlation between the magnetic moment and the orientation cosine and between the magnetic moment and the velocity. Those null correlations can be explained by our current understanding of magnetotaxis.