Magnetic Anisotropy Of Co Research Articles

Tuning the Magnetic Anisotropy of Co–N‐Doped Graphene

Large magnetic anisotropy energy and out‐of‐plane easy magnetization direction are beneficial for the application of 2D ferromagnetism. Although the robust room‐temperature ferromagnetism is reported in Co–N‐doped graphene [Nat. Commun. 2021, 12, 1854], its magnetic anisotropy and easy axis of magnetization are still unclear. Herein, the magnetic anisotropy of CoN4–graphene and CoN3–graphene is systematically studied. The CoN4–graphene has an in‐plane easy magnetization direction, while the easy magnetization direction of CoN3–graphene is out‐of‐plane. The magnetic anisotropy energy can be tuned by injecting charge or applying strain. Especially, for CoN3–graphene, both charge injection and tensile strain can tune the easy magnetization direction from out‐of‐plane to in‐plane. The tunable magnetic anisotropy may promote the application of Co–N‐doped graphene in spintronic devices.

Field-Free Magnetoplasmon-Induced Ultraviolet Circular Dichroism Switching in Premagnetized Magnetic Nanowires.

Broadband modulation of magnetic circular dichroism (MCD) using a relatively low magnetic field or by producing a field-free magnetoplasmonic effect in the remnant magnetic state was achieved by the integration of the noble metals (NMs) Au and Ag and the perpendicular magnetic anisotropy of Co with ZnO nanowires (NWs) used as the template. The samples containing NMs revealed MCD sign reversals and enhancements when compared with the original Co/ZnO NWs. The magnetoplasmonic effect of Au close to the visible light spectrum could induce the CD change in the visible region. Notably, the ultraviolet (UV) CD in Ag/Co/ZnO NWs is 12.5 times larger under a magnetic field (∼0.2 T) and 10 times greater in the remnant state (field-free) than those of the original Co/ZnO NWs because of the magnetoplasmonic effect of Ag in the UV spectrum. These results are attributable to the coupling of the remnant magnetic state of Co magnetization, the magnetoplasmons of the NMs, and the excitons of the ZnO NWs. The findings are potentially applicable in magneto-optical recording, biosensing, and energy contexts involving magnetoplasmonic functionalization.

Large magnetic anisotropy in Co–Fe–Ni–N ordered structures: a first-principles study

Material design of promising rare-earth free permanent magnet requires tailoring and controlling the intrinsic magnetic properties namely large saturation magnetization μ 0 M s, giant uniaxial magnetic anisotropy K u, and high Curie temperature T C. Based on first-principles electronic structure calculations, we present a detailed analysis for the intrinsic magnetic properties of Co x Fe1−x Ni and Co x Fe1−x NiN0.25 ordered structures. We predict an enhanced structural stability with improved K u ranging from 1.53–2.29 MJ m−3 for Co x Fe1−x NiN0.25 ordered structures, with the exception of CoNiN0.25 having planar anisotropy. Detailed analysis of the predicted large K u, based on perturbation theory and electronic structure calculations, is attributed to the cumulative effect of contribution from the increased tetragonal distortion and induced orbital distortion from the simultaneous Co substitution and interstitial N-doping. By tailoring the K u, we may create efficient and affordable PMs, bridging the gap between commonly used ferrite and high-performance Nd–Fe–B magnets.

Cis and Trans Isomers of Fe(II) and Co(II) Complexes with Oxadiazole Derivatives ‐ Structural and Magnetic Properties

AbstractFour complexes with bidentate N,N‐donors 2‐(furan‐2‐yl)‐5‐(pyridin‐2‐yl)‐1,3,4‐oxadiazole (fpo) and 2‐(pyridin‐2‐yl)‐5‐(thiophen‐2‐yl)‐1,3,4‐oxadiazole (pto) with general formula [M(L)2(NCS)2] (M=Co(II), L=fpo for (1); M=Co(II), L=pto for (2); M=Fe(II), L=fpo (3); M=Fe(II), L=pto (4)) are reported. Analysis and characterization of the samples was performed using standard physico‐chemical techniques – elemental analysis, nuclear magnetic resonance, Fourier transform infrared spectroscopy, single‐crystal X‐ray diffraction. Magnetic properties for 1–4 revealed large magnetic anisotropy of Co(II) complexes, and AC susceptibility measurements confirmed their single‐molecule magnetic behaviour. Furthermore, the theoretical calculations at DFT and CASSCF/NEVPT2 level of theory were exploited to better understand magnetism of these compounds.

Interfacial Dzyaloshinskii-Moriya interaction and perpendicular magnetic anisotropy at cobalt/diamond interfaces

The interfacial Dzyaloshinskii-Moriya interaction (DMI) plays a key role in the formation of exotic chiral magnetic textures. Here, the interfacial DMI and magnetic anisotropy of Co(0001)/diamond(111) interfaces are investigated by first-principles calculations. The significant DMI with clockwise chirality can be generated at Co/diamond interface. The DMI strength of Co film decreases on boron doped diamond (B-Dia), while DMI chirality turns into anticlockwise on nitrogen doped diamond (N-Dia). Large perpendicular magnetic anisotropy (PMA) appears at both Co/Dia and Co/B-Dia interfaces, which is weakended at the Co/N-Dia interface. The DMI can be ascribed to the occupied (dz2, dxz) orbitals of interfacial Co atomic layers, while magnetic anisotropy energy is determined by (dx2-y2, dxy) and (dz2, dyz) orbitals. These results provide a promising route to tailor the interfacial DMI and PMA of ferromagnetic films and hence to modulated topological magnetic textures.

Ab initio calculations of magnetic anisotropy of Co and Fe films on Cu and Pt surfaces

In this work, the results of numerical first-principles calculations of the magnetic characteristics for Co and Fe monolayer films on Cu(100) and Pt(100) slabs by using the VASP software package are presented. The values of the difference in the total energy of antiferromagnetic and ferromagnetic configurations depending on the parameters of convergence and thickness of non-magnetic material are calculated. Favorable magnetic anisotropy energy and values of the magnetic moment of atoms in the Co/Cu/Co, Co/Pt/Co, and Pt/Co/Cu/Co/Pt structures are determined. The phenomenon of reorientation in the Co/Cu(100)/Co structure, when the in-plane anisotropy of the cobalt films changes to an out-of-plane anisotropy due to the incorporation of an ultrathin platinum film into the structure is confirmed.

Magnetic properties and the interfacial Dzyaloshinskii-Moriya interaction in exchange biased Pt/Co/NixOy films

We show that a trilayer magnetic structure, consisting of a heavy metal (Platinum) as a buffer, an ultrathin ferromagnet (Cobalt) as a functional layer, and an antiferromagnetic insulator (Nickel oxide, NixOy) as a capping, is a host of intriguing physical phenomena desirable for spintronics. X-ray photoelectron spectroscopy revealed changes in the ratio of NixOy phases with different stoichiometry. Due to strong spin–orbit coupling, the Pt layer induces perpendicular magnetic anisotropy in Co, breaks its structural inversion symmetry, and causes an additive effect of Pt/Co and Co/NixOy interfaces to the effective interfacial Dzyaloshinskii-Moriya interaction (Deff). Manipulation the magnetic anisotropy can be realized by the ferromagnetic layer thickness variation and modification of the Co/NixOy interface. The NixOy capping layer induces the exchange bias in Co, which effective field |Beb| can be controlled in the range from 0 to 24 mT. The magnitude and direction of Beb does not affect Deff. The increase of Ar pressure leads to structural transformation of the Co/NixOy interface and, consequently, to decrease of the surface Dzyaloshinskii-Moriya interaction (Ds), the source of which is the NiO phase. We demonstrate that the studied Pt/Co/NixOy system has a number of functional properties useful for future logic and memory applications.

Anomalous Behavior of Magnetic Anisotropy of Amorphous Co40Fe43B17 Thin Film Sandwiched Between Mo Layers

Anomalous behavior of magnetic anisotropy in Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">43</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sub> film sandwiched between Mo layers has been observed as a function of thermal annealing at different temperatures. The as-deposited amorphous film exhibits a uniaxial magnetic anisotropy, the origin of which can be traced to quenched-in stresses. With thermal annealing up to 300 °C, anisotropy remains unchanged. We observe an anomalous magnetic reversal near the hard axis (HA) in the samples annealed at 350 °C and above. The anomaly of the occurrence of nonuniform magnetization near HA can be explained in terms of distribution of easy magnetization direction, as evidenced by the ripple domain structure in Kerr microscopy images.

Strain-promoted perpendicular magnetic anisotropy in Co–Rh alloys

We report on a comprehensive experimental, numerical, and computational investigation on the concentration dependence of the structural/magnetic properties of Co–Rh alloy films. A sizable perpendicular magnetic anisotropy is achieved by controlling the lattice strain via the Co content. Within the 30–40% range of Co concentrations, an experimental effective magnetic anisotropy on the order of 100 kJ/m3 and a computational uniaxial magnetic anisotropy energy of 567 μeV/atom have been observed. First-principles calculations revealed that the lattice strain promotes a strong d-orbital degeneracy near the Fermi level for 40% of Co concentration, leading to an enhanced magnetic anisotropy energy.

Large effect of metal substrate on magnetic anisotropy of Co on hexagonal boron nitride

We combine x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD) and x-ray magnetic linear dichroism (XMLD) data with first principles density functional theory (DFT) calculations and a multiorbital many-body Hamiltonian approach to understand the electronic and magnetic properties of Co atoms adsorbed on h-BN/Ru(0001) and h-BN/Ir(111). The XAS line shape reveals, for both substrates, an electronic configuration close to 3d8, corresponding to a spin S = 1. Magnetic field dependent XMCD data show large (14 meV) out-of-plane anisotropy on h-BN/Ru(0001), while it is almost isotropic (tens of μeV) on h-BN/Ir(111). XMLD data together with both DFT calculations and the results of the multiorbital Hubbard model suggest that the dissimilar magnetic anisotropy originates from different Co adsorption sites, namely atop N on h-BN/Ru(0001) and 6-fold hollow on h-BN/Ir(111).

Tunability of magnetic anisotropy of Co on two-dimensional materials by tetrahedral bonding

Pairing of $\pi$ electronic state structures with functional or metallic atoms makes them possible to engineer physical and chemical properties. Herein, we predict the reorientation of magnetization of Co on hexagonal BN (h-BN) and graphene multilayers. The driving mechanism is the formation of the tetrahedral bonding between sp$^3$ and d orbitals at the interface. More specifically, the intrinsic $\pi$-bonding of h-BN and graphene is transformed to sp$^3$ as a result of strong hybridization with metallic $d_{z^2}$ orbital. The different features of these two tetrahedral bondings, sp$^2$ and sp$^3$, are well manifested in charge density and density of states in the vicinity of the interface, along with associated band structure near the $\bar{K}$ valley. Our findings provide a novel approach to tailoring magnetism by means of degree of the interlayer hybrid bonds in 2D layered materials.

Tuning magnetic anisotropy in Co-BaZrO3 vertically aligned nanocomposites for memory device integration.

Ferromagnetic nanostructures with strong anisotropic properties are highly desired for their potential integration into spintronic devices. Several anisotropic candidates, such as CoFeB and Fe–Pt, have been previously proposed, but many of them have limitations such as patterning issues or thickness restrictions. In this work, Co–BaZrO3 (Co–BZO) vertically aligned nanocomposite (VAN) films with tunable magnetic anisotropy and coercive field strength have been demonstrated to address this need. Such tunable magnetic properties are achieved through tuning the thickness of the Co–BZO VAN structures and the aspect ratio of the Co nanostructures, which can be easily integrated into spintronic devices. As a demonstration, we have integrated the Co–BZO VAN nanostructure into tunnel junction devices, which demonstrated resistive switching alluding to Co–BZO's immense potential for future spintronic devices.

Unveiling the role of Co-O-Mg bond in magnetic anisotropy of Pt/Co/MgO using atomically controlled deposition and in situ electrical measurement

Despite the crucial role of interfacial perpendicular magnetic anisotropy in Co(Fe)/MgO based magnetic tunnel junction, the underlying mechanism is still being debated. Here, we report an anatomical study of oxygen and Mg effect on Pt/Co bilayers through repeated in-situ anomalous Hall effect measurements, controlled oxygen exposure and Mg deposition in an ultrahigh vacuum system. We found that chemisorbed oxygen not only quenches the effective magnetic moment of the Co surface layer, but also softens its magnetic anisotropy. However, a subsequent Mg dusting on the oxygen pre-exposed Pt/Co surface can recover the magnetic anisotropy. The ab initio calculations on the exchange splitting and orbital hybridization near the Fermi level give a clear physical explanation of the experimental observations. Our results suggest that Co(Fe)-O-M bond plays a more important role than the widely perceived Co(Fe)-O bond does in realizing interfacial perpendicular magnetic anisotropy in Co(Fe)/MgO heterostructures.

First-principles investigation of magnetocrystalline anisotropy at theL21fullHeusler|MgOinterfaces and tunnel junctions

Magnetocrystalline anisotropy at Heusler alloy$|$MgO interfaces have been studied using first principles calculations. It is found that Co terminated Co$_{2}$FeAl$|$MgO interfaces show perpendicular magnetic anisotropy up to 1.31 mJ/m$^2$, while those with FeAl termination exhibit in-plane magnetic anisotropy. Atomic layer resolved analysis indicates that the origin of perpendicular magnetic anisotropy in Co$_{2}$FeAl$|$MgO interfaces can be attributed to the out-of-plane orbital contributions of interfacial Co atoms. At the same time, Co$_{2}$MnGe and Co$_{2}$MnSi interfaced with MgO tend to favor in-plane magnetic anisotropy for all terminations.

The role of electron confinement in Pd films for the oscillatory magnetic anisotropy in an adjacent Co layer

We demonstrate the interplay between quantum well states in Pd and the magnetic anisotropy in Pd/Co/Cu (0 0 1) by combined scanning tunneling spectroscopy (STS) and magneto optical Kerr effect (MOKE) measurements. Low temperature scanning tunneling spectroscopy reveals occupied and unoccupied quantum well states (QWS) in atomically flat Pd films on Co/Cu (0 0 1). These states give rise to sharp peaks in the differential conductance spectra. A quantitative analysis of the spectra reveals the electronic dispersion of the Pd (0 0 1) d-band (-type) along the -X direction. In situ MOKE experiments on Pd/Co/Cu (1, 1, 13) uncover a periodic variation of the in-plane uniaxial magnetic anisotropy as a function of Pd thickness with a period of 6 atomic layers Pd. STS shows that QWS in Pd cross the Fermi level with the same periodicity of 6 atomic layers. Backed by previous theoretical work we ascribe the variation of the magnetic anisotropy in Co to QWS in the Pd overlayer. Our results suggest a novel venue towards tailoring uniaxial magnetic anisotropy of ferromagnetic films by exploiting QWS in an adjacent material with large spin–orbit coupling.

A synthetic strategy for switching the single ion anisotropy in tetrahedral Co(II) complexes.

Four novel mononuclear tetrahedral cobalt(II) complexes containing exocyclic mesoionic ligands of molecular formulae [Co(II)(L1)(X)2(MeCN)] X = Cl (1) or Br (2) and [Co(II)(L2)(X)2(MeCN)], X = Cl (3) or Br (4) have been reported. It is found that simple substitution of L1 (O donor in 1 and 2) by L2 (S donor in 3 and 4) results in switching of the single ion magnetic anisotropy parameter (D) from positive to negative, with a significant change in magnitude.

Spatial modulation of in-plane magnetic anisotropy in epitaxial Co(111) films grown on macrostep-bunched Si(111)

We compared magnetic properties of epitaxial Co(111) films grown on microstep- and macrostep-bunched vicinal Si(111) substrates. A surface of the microstep-bunched Si(111) substrate represents regular array of step-bunches with height of 1.7 nm divided from each other by flat microterraces with a width of 34 nm. A surface of the macrostep-bunched Si(111) substrate is constituted by macrostep bunches with a height of 75–85 nm divided by atomically flat macroterraces. The average sum width of a macrostep bunch and a macroterrace is 2.3 μm. While in-plane magnetic anisotropy was spatially uniform in Co(111) films grown on the microstep-bunched Si(111), periodic macromodulation of the topography of the Si(111) substrate induced spatial modulation of in-plane magnetic anisotropy in Co(111) film grown on the macrostep-bunched Si(111) surface. The energy of uniaxial magnetic anisotropy in the areas of the Co(111) film deposited on the Si(111) macrosteps was higher more than by the order of magnitude than the energy of the magnetic anisotropy in the areas grown on macroterraces. Magnetization reversal in the areas with different energy of the magnetic anisotropy occurred in different magnetic fields. We showed the possibility of obtaining high density of domain walls in Co(111) film grown on the macrostep-bunched Si(111) by tuning the spatial step density of the Si(111) substrate.

Magnetoelastic coupling induced magnetic anisotropy in Co2(Fe/Mn)Si thin films

The influence of epitaxial strain on uniaxial magnetic anisotropy of Co$_{2}$FeSi (CFS) and Co$_{2}$MnSi (CMS) Heusler alloy thin films grown on (001) SrTiO$_3$ (STO) and MgO is reported. The in-plane biaxial strain is susceptible to tune by varying the thickness of the films on STO, while on MgO the films show in-plane easy axis for magnetization (\overrightarrow{M}) irrespective of their thickness. A variational analysis of magnetic free energy functional within the Stoner-Wohlfarth coherent rotation model with out-of-plane uniaxial anisotropy for the films on STO showed the presence of magnetoelastic anisotropy with magnetostriction constant $\approx$ (12.22$\pm$0.07)$\times 10^{-6}$ and (2.02$\pm$0.06)$\times 10^{-6}$, in addition to intrinsic magnetocrystalline anisotropy $\approx$ -1.72$\times 10^{6}$ erg/cm$^{3}$ and -3.94$\times 10^{6}$ erg/cm$^{3}$ for CFS and CMS, respectively. The single-domain phase diagram reveals a gradual transition from in-plane to out-of-plane orientation of magnetization with the decreasing film thickness. A maximum canting angle of 41.5$^{\circ}$ with respect to film plane is predicted for the magnetization of the thinnest (12 nm) CFS film on STO. The distinct behaviour of \overrightarrow{M} in the films with lower thickness on STO is attributed to strain-induced tetragonal distortion.

Giant magnetoimpedance in thin amorphous wires: From manipulation of magnetic field dependence to industrial applications

Abstract We present the results on tailoring of soft magnetic properties and GMI effect in thin microwires paying special attention on achievement of low hysteretic high GMI effect in the extended frequency range (up to 4 GHz). We observed considerable dependence of the GMI ratio and magnetic anisotropy field, Hk, of Co-rich amorphous microwires with vanishing magnetostriction constant on the internal and applied stresses. For low magnetostrictive Co-rich composition we obtained microwires low coercivity values (generally below 10 A/m). Field dependence of the off-diagonal voltage response measured in pulsed regime (pulsed GMI) exhibits anti-symmetrical shape. The magnetic anisotropy of Co and Fe-rich microwires can be tailored by stress or magnetic field annealing. Particularly stress annealed Fe-rich microwires exhibit stress-sensitive GMI effect and hysteretic properties. Varying the time and the temperature of such stress annealing we are able to tailor both magnetic properties and GMI. Additionally, magnetic response of linear microwires arrays and GMI effect of the system containing few microwires can be tailored through the magnetostatic interaction between the microwires. We found, that if the surface anisotropy is not circumferential, then the MI curve Z(H) presents hysteresis. This hysteresis can be suppressed by application of sufficiently high DC bias current IB that creates a circumferential bias field HB.

Tuning the magnetic anisotropy of Co–Ni nanowires: comparison between single nanowires and nanowire arrays in hard-anodic aluminum oxide membranes

CoxNi1−x alloy nanowires with varying Co content (0 ≤ x ≤ 0.95), having a diameter of 130 nm and length of around 20 μm, are synthesized by template-assisted electrodeposition into the nanopores of SiO2 conformal coated hard-anodic aluminum oxide membranes. The magneto-structural properties of both single isolated nanowires and hexagonally ordered nanowire arrays of Co–Ni alloys are systematically studied by means of magneto-optical Kerr effect magnetometry and vibrating sample magnetometry, respectively, allowing us to compare different alloy compositions and to distinguish between the magnetostatic and magnetocrystalline contributions to the effective magnetic anisotropy for each system. The excellent tunable soft magnetic properties and magnetic bistability exhibited by low Co content Co–Ni nanowires indicate that they might become the material of choice for the development of nanostructured magnetic systems and devices as an alternative to Fe–Ni alloy based systems, being chemically more robust. Furthermore, Co contents higher than 51 at.% allow us to modify the magnetic behavior of Co-rich nanowires by developing well controlled magnetocrystalline anisotropy, which is desirable for data storage applications.