Magnetic Moment Of Co Research Articles

Electronic, magnetic and structural properties of CoFeVAl and CoFeV0.5Mn0.5Al

In this study, we present results of a comprehensive computational and experimental study of CoFeVAl and CoFeV0.5Mn0.5Al Heusler alloys. It is shown that while CoFeVAl exhibits a fairly large degree of spin polarization, this material is not half-metallic due to the presence of the vanadium spin-down states at the Fermi level. However, replacing 50% of vanadium with manganese results in a nearly half-metallic transition, largely due to the shift of the Fermi level towards occupied states. Moreover, the half-metallicity of CoFeV0.5Mn0.5Al is rather robust in a wide range of considered mechanical strain and under experimentally observed B2-type atomic disorder, thus making this alloy potentially suitable for practical spintronic applications. Both considered alloys exhibit ferromagnetic alignment at larger lattice constants, aside from a relatively small magnetic moment of vanadium which is anti-aligned with the magnetic moments of Co, Fe and Mn. We have synthesized both CoFeVAl and CoFeV0.5Mn0.5Al alloys in cubic structure with some structural disorder using arc melting and annealing. The structural and magnetic properties of the synthesized CoFeV0.5Mn0.5Al alloy are in good agreement with the theoretical calculations but vary slightly from the parent compound.

Effect of Cobalt on the Microstructure of Fe-B-Sn Amorphous Metallic Alloys

Fe78B15Sn7 and (Fe3Co1)78B15Sn7 amorphous metallic alloys were prepared using the method of planar flow casting. The amorphous nature of ribbons containing 7 at. % Sn was verified by X-ray diffraction. The resulting chemical composition was checked by flame atomic absorption spectroscopy and by mass spectrometry with inductively coupled plasma. The microstructure of the as-quenched metallic glasses was investigated by 57-Fe and 119-Sn Mössbauer spectrometry. The experiments were performed with transmission geometry at 300 K, 100 K, and 4.2 K, and in an external magnetic field of 6 T. The replacement of a quarter of the Fe by Co did not cause significant modifications of the hyperfine interactions in the 57-Fe nuclei. The observed minor variations in the local magnetic microstructure were attributed to alterations in the topological short-range order. However, the in-field 57-Fe Mössbauer spectra indicated a misalignment of the partial magnetic moments. On the other hand, the presence of Co considerably affected the local magnetic microstructure of the 119-Sn nuclei. This was probably due to the higher magnetic moment of Co, which induces transfer fields and polarization effects on the diamagnetic Sn atoms.

Atomic-Scale Description of the Magnetic TiN|FeCo Multilayers.

Motivated by the experimental findings of Wolff et al., we investigated the TiN|FeCo multilayers at the atomic scale. Four different models were employed to investigate the interface, considering both Fe and Co surface terminations of the FeCo compounds. The interface formation energy formalism was employed to study the thermodynamic stability of these models. The results show that an interface mediated by Co atoms is most likely to appear in the experiment. Also, the Fe surface termination is more viable than a Co surface termination. The magnetic moments of Co at the interface are 1.48 μB/atom, which denotes a decay compared to bulk (1.76 μB/atom). Besides, Ti acquires a very small induced magnetization of -0.05 μB/atom. Our proposed atomistic model of the TiN|FeCo multilayer system fits perfectly with the structure obtained in experiments, and it is a step forward in the theoretical-experimental design of wear-resistant coatings with outstanding magnetic and mechanical properties.

Magnetic properties and magnetocaloric effect of DyCo9Si4

Polycrystalline samples of DyCo9Si4 with the tetragonal LaFe9Si4-type structure have been synthesized by arc melting and high-temperature annealing. Results of the magnetization M and specific heat Cp measurements show the existence of two magnetic anomalies at TC = 40 K and Tm = 20 K. The transition at TC = 40 K is attributed to the ferromagnetic transition of the Co sublattice. The magnetic moments of Dy3+ appear to align gradually below TC, and almost fixed below Tm, at which a broad maximum in Cp has been observed. Field-dependent M at T = 2 K up to H = 7 T suggested that the magnetic moment of Dy3+ is coupled antiferromagnetically with those of Co, forming a ferrimagnetic structure. Magnetization measurements up to 50 T at low temperatures using a pulse magnet demonstrated a spin-flip transition around H = 20 T, above which the magnetic moments of Co and Dy are in parallel. The spin-flip transition becomes broad with increasing temperature but still remains at TC = 40 K, indicating a strong antiparallel coupling between Co and Dy moments even in the paramagnetic state. The magnetocaloric effect was evaluated from Cp and M, and also from the sample-temperature variation in the quasi-adiabatic process with the pulsed magnetic field. The maximum entropy change for the field change from 5 to 0 T was observed at around T = Tm with the value ΔS = 5 J/kg K. The maximum temperature of ΔS shifts to higher temperatures in high magnetic fields, resulting in the large value of ΔS = 24 J/kg K at T ∼ TC by the field change from 50 to 0 T. The present results demonstrate that the pulsed-field measurement is a powerful method to evaluate the magnetocaloric effect of materials.

Valence electron structures and thermal and magnetic properties of RCo5 (R=light rare earth) intermetallic compounds with medium- and high-entropy design at R site

RCo5-type (R=light rare earth) medium- and high-entropy intermetallic compounds, which are designed by random occupation of equiatomic multiple rare earth elements at the rare earth site, are prepared by arc melting and vacuum heat-treatment technologies, and their crystal structures and magnetic properties are studied by X-ray diffraction and magnetic measurements. The empirical electron theory of solids and molecules is used to investigate their valence electron structures, thermal and magnetic properties. The theoretical bond lengths and magnetic moments match the experimental ones well. The study reveals that the thermal and magnetic properties are strongly related to the valence electron structures modulated by medium- and high-entropy design at rare earth. The medium and high entropized designs induce the increase of the covalence electron numbers nc. It is helpful for stabilizing the crystal structure. The number of covalence electron pair of the strongest R-CoI bond affects the melting point. The magnetic moments of RCo5-type medium- and high-entropy intermetallic compounds, which mainly originate from the 3d magnetic electrons of Co atoms, are modulated by medium and high entropized rare earth due to their exchange interactions. The magnetic moment of Co at the 2c site is larger than that of Co at the 3g site, which is due to the electron transformations from magnetic to covalence electron for bonding with the rare earth at the 3g site. Curie temperatures raise with the increasing 3d magnetic electron numbers of Co atom.

Effect of Co substitution on ferrimagnetic Heusler compound Mn3Ga

Effect of Co substitution on Mn3Ga is investigated using first-principles study for structural and magnetic properties. Without Co, ferrimagnetic Heusler compound Mn3Ga is in tetragonal phase. With Co substitution, depending on Co concentration (x), Mn3Ga prefers tetragonal (cubic) phase when x≤0.5 (x≥0.5). Ferrimagnetism is robust regardless of x in both phases. While magnetic moments of two Mn do not vary significantly with x, magnetic moments of Co in two phases exhibit different behaviors, leading to distinct features in absolute value of total magnetic moment (|Mtot|). When x≤0.5, in tetragonal phase, magnetic moment of Co is vanishingly small, resulting in a decrease of |Mtot| with x. In contrast, when x≥0.5, in cubic phase, magnetic moment of Co is roughly 1 μB, which is responsible for the increase of |Mtot|. Electronic structure is analyzed with partial density of states for various x. To elucidate the counterintuitively small Co moment, the magnetic exchange interaction is investigated, where exchange coefficient between Co and Mn(II) in x≤0.5 is much smaller than that in x≥0.5.

Temperature Variation of Gilbert Damping Constant in 3d Transition Metals from First Principles

A theoretical investigation of temperature-dependent Gilbert damping is presented. We evaluate the Gilbert damping constant α (and the corresponding Landau frequency λ) at a finite temperature for hcp-Co, fcc-Ni, and Cu-doped fcc-Ni from first principles by combining the torque correlation model and the disordered local moment scheme, in which the finite-temperature effect is included as the transverse spin fluctuation. The calculated λ has, from the viewpoint of the material dependence, well reproduced the experimental results, but quantitatively, these values are more underestimated than the experimental values. A comparison with the lifetime approximation results reveals that a change in the electronic structure due to the spin fluctuation affects λ for Co and Ni but not for Fe. On the basis of the variation of the local magnetic moment of Co and Ni at finite temperature, we conclude that these differences in λ are due to the difference in the degree of itinerancy of spins.

Magnetic optimization and regulation mechanism of La2CoMnO6 double-perovskite ceramics by Ti-doping at Mn-site

This work focuses on the magnetic optimization of La2CoMnO6 (LCMO) double-perovskite ceramics by Ti-doping at Mn-site. LCMO ceramics with different Ti-doping contents (LCMTxO, x = 0.1–0.4) were prepared by plasma activated sintering, and the effect of Ti-doping on the structural and magnetic properties of the ceramics is studied systematically. All the ceramics exhibit dense structure and small grain size, with a monoclinic P21/n crystalline structure. With the increasing of Ti-doping content, the proportions of Co2+ and Mn4+ in the LCMTxO ceramics change accordingly, reaching the highest values at x = 0.1. Since the Co2+-O-Mn4+ ferromagnetic super-exchange is the dominant factor affecting the magnetic properties of the LCMTxO ceramics, it is reasonable that a high saturation magnetization (Ms = 4.58μB/f.u) is obtained for the LCMT0.1O ceramic. The effect of Ti-doping on the orbital structure and magnetic regulation of the LCMTxO double-perovskite ceramics is further investigated by the first-principle calculation. It is found that the magnetic moments of Co and Mn ions will increase by the appropriate addition of Ti, which makes most Co ions exist in the form of Co2+, underpinning the La2Co2+Mn4+O6 ferromagnetic state and improving the magnetic properties.

The internal magnetic field in a ferromagnetic compound Y2Co12P7

The internal magnetic field in a ferromagnetic compound, Y2Co12P7 with T C = 150 K, was studied with µ +SR using a powder sample down to 2 K. The wTF-µ +SR measurements revealed the presence of a sharp magnetic transition at T C = 151 K, and the ZF-µ +SR measurements clarified the formation of static magnetic order below T C. The presence of two muon spin precession signals in the ZF-µ +SR spectrum below T C indicates the existence of the two different muon sites in the lattice. By considering the muon sites and local spin densities at the muon sites predicted with DFT calculations, the ordered magnetic moments of Co were successfully determined.

Half-metallic ferromagnetism in new quaternary Heusler alloys CoX’YP (X’ = Cr and Fe)

ABSTRACT In this study, we investigated the structural, electronic and magnetic properties of new quaternary Heusler alloys CoX'YP (X’ = Cr and Fe) using the accurate full-potential linearised augmented plane waves with local orbitals (FP-LAPW + lo) under the framework of the density functional theory (DFT) and the WIEN2k package. The generalised gradient approximation (GGA) is chosen to treat the exchange–correlation (XC) energy. The structural properties of the presented alloys are investigated in order to determine their structural parameters at equilibrium, such as: the lattice constant (a0 ), the bulk modulus (B0 ) and its first pressure derivative (B’). The structural stability of the CoCrYP and CoFeYP alloys is found in Y-type (I) structure, while their magnetic stability is reported in ferromagnetic phase. The electronic properties of the studied materials show the complete half-metallic character. The magnetic properties reveal that the total magnetic moment of the two alloys is found in integer value, obeying the Slater-Pauling rule. Furthermore, the calculated local magnetic moments of Co and X’ atoms are found with opposite signs, confirming the ferrimagnetic coupling within these compounds. According to the electronic and magnetic results found in this approach, we conclude that the compounds CoCrYP and CoFeYP are full half-metallic ferromagnetic materials.

First-principles study to probe the effect of substitution at X and Z sites on the electronic, magnetic and transport properties of Co2X(V, Nb, Ta)Z(Al, Ga, In, Si, Ge, Sn) Heusler alloys

In the present work, we have used density functional theory based electronic structure calculations to probe the role of isovalent substitution at X@(0.5, 0.5, 0.5) and Z@(0, 0, 0) site of Co2X(= Ta, Nb, V)Z(= Al, Ga, In). Further, we probed the role of electron-rich substitution at Z site on the electronic, magnetic and transport properties of half-metallic(HM) Co2TaZ( = Al,Ga,In) full Heusler alloys(FHA). One of our main aims is to study the effect of electron-rich substitution at Z site on the total and partial moments of X and Z sites. We have used the modified Becke–Johnson(mBJ) exchange–correlation term to calculate the HM band-gap. We observe that, isovalent substitution at X and Z sites provides a way to tune the lattice constant in range of ∼5.75 Å to ∼6.16 Å with sustained HM character. Further, it is noticed that the HM band-gap decreases with isovalent substitution (with low atomic number) at X site with maximum and minimum values of 1.09 eV and 0.5 eV, respectively. Isovalent substitution does not affect the total magnetic moment, however, it affects the atomic magnetic moment values. Further, we observe that 25% of substitution of tetravalent atoms (Si, Ge, Sn) at atomic site Z (having Al, Ga, In) enhances the total magnetic moment with a small decrease in the minority band-gap. However, 75 to 100 % of substitutions destroy the half-metallicity, showing an enhancement in the magnetic moment. Temperature dependent spin Seebeck coefficients corresponding to the 25% and 75% of substitution of tetravalent element at Z site exhibit values close to 150 μV/K and 25–75 μV/K, respectively, for temperatures above 400 K. Interestingly, electron rich substitution at Z cite, changes the orientation of the magnetic moment corresponding to the X (Ta) site element. In order to understand in detail the impact of substitution on the local magnetic moment of Co and X site atoms (V, Nb, Ta), we have performed calculations of respective X-ray magnetic circular dichroism(XMCD) spectra and analyzed the results in terms of unoccupied density of states. XMCD spectra of L2,3 edges of Co atom show only small deviation (in the intensity) with the changes in the X and Z sites. Unlike the case of Co atom, we find that the XMCD spectra of M2,3 edges of Ta atom exhibit substantial changes when tetravalent atoms replace the trivalent atoms at the Z site.

Effects of surface polarity on the structure and magnetic properties of Co implanted polar ZnO wafers

Microstructural and magnetic properties of ion implantation method prepared Co doped Zn polar and O polar ZnO wafers are investigated by a combined experimental and theoretical approach. Substantial intrinsic ferromagnetism is observed in all the doped ZnO wafers. The ferromagnetism of Co implanted oxygen polar ZnO wafer is found to be larger than that of zinc polar ZnO. First principle calculations reveal that the magnetic moments mainly come from the Co-3d and O-2p states. The O-2p state has a stronger hybridization with the Co-3d state in oxygen polar ZnO, resulting in higher magnetic moments of Co implanted oxygen polar ZnO. These results not only benefit to a better understanding of the origin of surface-polarity dependent ferromagnetism in ZnO diluted magnetic semiconductors but also may open up the possibility to employ these polar ZnO in spintronic devices.

Electronic structure, magnetic properties and magnetocaloric effect of GdCo2-xNix

The electronic structure, magnetic properties, and magnetocaloric effect of GdCo2-xNix with x = 0.2, 0.25, and 0.3 were investigated. X-ray diffraction measurements showed that all studied samples are single phase with the cubic MgCu2 - Laves type structure. In agreement with experiments, the band structure calculations explain the following issues: the antiferromagnetic ground state of the system, the coupling between Gd and the transition metals (TM) mediated by the 5d electrons of Gd hybridized with the 3d electrons of the TM (Co, Ni), the reduction of the spin magnetic moment of Co when substituting with Ni due to Co-Ni hybridization. XPS measurements showed no significant shift in the binding energy of the investigated Co core levels with the change of Ni concentration. For all investigated samples the exchange splitting estimated to about 3.2 eV between the high spin final state and the low spin final state of the Co 3 s core level gives direct evidence of the local magnetic moments on Co sites. The measured increase of the saturation magnetizations when substituting cobalt by nickel confirms the ferrimagnetic-type ordering. The decrease of the Co magnetic moments is related to Co-Ni hybridization and filling of bands with the extra-electrons provided by Ni with respect to Co. Moreover, the Arrott plots, the temperature dependence of Landau coefficients and the shapes of magnetic entropy changes confirm the presence of a second order magnetic phase transition. The RCP(∆S)/∆B values decreases slowly when the Ni concentration increases and could be attributed to the narrowing of the │ΔSm│peaks.

Methane gas adsorption and detection using the metal-decorated blue phosphorene

Previous studies showed that the performances of two-dimensional materials as gas sensor can be effectively improved through the assistance of metal atoms. We study the adsorption energies, charge transfers and electronic structures of the blue phosphorene (BP) adsorbing metal atoms (Au, Ag, Cu, Co, Fe and Mn) and then adsorbing methane (CH4) gas molecule. The metal-decorated BP can be used as an excellent CH4 gas adsorption material, and the adsorption capacity is not easily disturbed by the magnetic field. The transfer charges between metal atoms and BP will induce the new energy bands to modulate the band structure of BP effectively. In the absence of a magnetic field, CH4 adsorption hardly change the band structures of BP decorated by six metal atoms. However, the CH4 adsorption can modulate the spin-polarizedbandgaps and magnetic moments of Co, Fe and Mn decorated BP obviously in the present of a magnetic field. In particular, the spin-down band gap of Fe-decorated BP would be reduced by two-third and the corresponding magnetic moment of Fe-decorated BP also decreases from 2.455 µB to 2.229 µB after CH4 adsorption. So, Fe-decorated BP is expected to be used as a material for high sensitivity CH4 gas detection.

Effects of Surface Polarity on the Structure and Magnetic Properties of Co Implanted and Co-Sm Co-Implanted Polar ZnO Films.

We present a comprehensive experimental and theoretical study of the effects of surface polarity on the structure and ferromagnetic properties of Co implanted and Co-Sm co-implanted polar ZnO films deposited on sapphire substrates by molecular beam epitaxy. Substantial intrinsic ferromagnetism (FM) is found for all the implanted polar ZnO films. The magnetization of O-polar ZnO is observed to be higher than that of Zn-polar ZnO under the same implantation conditions, and the magnetization is enhanced for Co-Sm co-implanted ZnO in contrast with unimplanted and Co implanted films. First-principles calculations reveal that the Sm 4f and Co 3d states have strong hybridization with the O 2p state in O-polar ZnO, leading to larger magnetic moments for Co and Co-Sm substituting Zn atoms on the O-polar surface. Meanwhile, X-ray photoelectron spectroscopy results confirm that more oxygen vacancies are introduced into O-polar films by implantation and annealing. We consider that the stronger ferromagnetism in O-polar ZnO is associated with the combined influence of more oxygen vacancies and larger local moments related to Co and Sm doping. These results not only contribute to understanding the origin of FM in diluted magnetic semiconductors but also highlight the feasibility of developing polar spintronic devices for future polar thin film systems.

Tuning isolated zero-field skyrmions and spin spirals at room-temperature in synthetic ferrimagnetic multilayers

We demonstrate the observation of spin spirals and individual skyrmions in synthetic Pt/CoGd/Pt ferrimagnetic multilayers at room-temperature without the assistance of an external magnetic field. The magnetic coupling between the magnetic moments of Co and Gd, was investigated across various CoGd thicknesses by element specific X-ray magnetic circular dichroism (XMCD) performed around the Co L2,3 and Gd M4,5 edges. It shows an uncompensated ferrimagnetic orientation between the Co and Gd atoms preserved at ambient conditions, even for sub-nanometer thick layers. In addition, with the tunable enhanced perpendicular magnetic anisotropy Ku and remnant magnetization MR found for thinner CoGd ≤ (0.9 nm) isolated zero-field skyrmions were imaged by magnetic force microscopy (MFM) as the magnetic ground state, replacing the spin spirals observed for thicker CoGd layers ≥ (1.2 nm). Such stable skyrmions in perpendicularly magnetized materials with antiparallel exchange-coupling are potential candidates for energy-efficient data storage and processing in future antiferromagnetic-based devices.

Phase pure rhombohedral R3¯m$R\bar{3}m$ AgCoO2 delafossite: Rietveld, selected area electron diffraction, X‐ray photoemission spectroscopy, and magnetic studies

AbstractA p‐type rhombohedral AgCoO2 (S.G. ) reported to form only at pressures greater than 300 MPa at 773 K, is stabilized in pure phase at 0.2 MPa oxygen pressure. Analysis of powder X‐ray diffraction pattern by Rietveld and selected area electron diffraction patterns confirms the purity of rhombohedral phase. Core‐shell X‐ray photoemission spectroscopy studies show that Ag ions are in +1 oxidation state with Co ions largely in +3 state. AgCoO2 is paramagnetic undergoing super‐paramagnetic transition at 44 K. The magnetic moment of Co is 0.001 μB which corresponds to low spin (LS) Co3+ along with a small fraction of LS Co4+ ions.

Structural phase transition in cobalt oxyfluoride Co3Sb4O6F6 observed by high-resolution synchrotron and neutron diffraction

A structural transition was observed in non-centrosymmetric oxyfluoride Co3Sb4O6F6 at TS ∼180 K from a cubic phase (I4‾3m) to a c > a tetragonal phase (I4‾), through high-resolution neutron and synchrotron powder diffraction. In addition, specific heat, magnetization, and dielectric measurements were performed to investigate this phase transition. Although the specific heat and dielectric constant showed anomalies at TS, no transition to a ferroelectric phase was observed in the polarization hysteresis loop down to 30 K. Moreover, a magnetic structure analysis using neutron powder diffraction data revealed a transition from a paramagnetic phase to a G-type antiferromagnetic phase at TN ∼67 K, at which a peak was also observed in the specific heat measurements. The magnetic moments of Co2+ were aligned along the tetragonal c-axis with a Co2+ moment of 2.80(1) μB at 13 K. The rotation and deformation of the CoO2F4 octahedron due to the large displacement of F atoms were observed at TS from the structural analysis, which play an important role in the structural phase transition in Co3Sb4O6F6.

The effect of ferromagnetism on the CO activation over FCC crystal phase transition metal catalysts: Insights from DFT calculations

In order to understand the relationship between the ferromagnetism and catalytic performance, three pathways of CO activation over transition metal catalysts (Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au) have been studied by using density functional theory (DFT) calculations. It is shown that Co and Ni metal catalysts have better catalytic performance for CO activation than others. The density of states (DOS) and spin density plots reveal that Co and Ni metal possess ferromagnetism. So it is concluded that the catalytic activity connects with the metal ferromagnetism. To further confirm this deduction, the magnetic moments and Bader charge have been calculated when small molecules (CO, CHO, and COH) adsorbed on the Co and Ni metal surface, and the results shows that the electron transfer between the small molecules and metal catalysts happens on the unpaired d-orbital electrons (nd) of the metal, which changes the magnetic moments of Co and Ni metal. Meanwhile, electron transfer also changes the catalytic performance of Co and Ni metal catalysts. Compared with the CO, the electron transfer of CHO and COH is more, the magnetic moments of metal changes greatly, and the carbon-oxygen bonds of CHO and COH are easier to break. So the magnetic moments of metal catalysts can be used as an indicator to select different metal catalysts.

Structure and magnetism in metastable bcc Co[formula omitted]Mn[formula omitted] epitaxial films

Co-rich Co1−xMnx alloys have hcp or fcc disordered phase and those ferromagnetic orderings are significantly deteriorated with increasing Mn concentration x in bulk. On the other hand, those metastable bcc phases show properties attractive to magnetics and spintronics, as studied recently. Here, we report systematic study of structure and magnetism for epitaxial thin films. The single phase bcc Co1−xMnx(001) films were pseudomorphically grown on Cr(001) for 0.14<x<0.50 with a sputtering technique. The saturation magnetization was larger than that of pure Co for the films with x= 0.14 and 0.25 and smaller for the x= 0.34 films, disappearing completely for the x= 0.5 films. X-ray magnetic circular dichroism unveiled that this behavior stemmed from the composition dependence of elemental magnetic moments. Slight enhancement of magnetic moment of Co was observed in bcc alloy films. We also found that magnetic moments of Mn exceeded 2 μB at the maximum and were not as high as theoretical values, approximately 3 μB, obtained from ab-initio calculation with coherent potential approximation. This difference is qualitatively understood in terms of microscopic Mn atom pairing with antiferromagnetic coupling, being suggested from the ab-initio band structure calculations based on special quasi-random structure of bcc Co1−xMnx.