Origin Of Magnetic Anisotropy Research Articles

On the origin of magnetic anisotropy in 4f-free ferromagnets based on the CaCu5 structure*

Using first-principles calculations, we investigate the origin of magnetocrystalline anisotropy in a series of
4f -electron-free intermetallics with CaCu5-based structures: YCo5, YCo4B, and Y3Co13B2. The electronic
structure of these compounds is characterized by a set of narrow 3d-bands near the Fermi level. In YCo5
the easy-axis anisotropy originates primarily in the spin-orbit coupling-induced mixing of the electronic states
with Co dx2-y2 and dxy character. The analysis of k-resolved anisotropy shows that positive contributions
accumulate from the entire Brillouin zone but are particularly large near the kz = 0 plane.
The analysis of the single-site and two-site terms reveals a large positive single-site contribution to the mag-
netocrystalline anisotropy from the Co atoms on the honeycomb sublattice, along with two-site contributions
from both honeycomb and kagome sublattices.

Magnetic anisotropy driven by ligand in 4d transition-metal oxide SrRuO3

The origin of magnetic anisotropy in magnetic compounds is a longstanding issue in materials science, and nonmagnetic ligand ions are considered to contribute little to magnetic anisotropy. Here, we introduce the concept of ligand-driven magnetic anisotropy in a complex transition-metal oxide. We conducted x-ray magnetic circular dichroism spectroscopies at the Ru and O edges in the 4d ferromagnetic metal SrRuO3. Systematic variation of the sample thickness in the range of ≤10 nm allowed us to control the localization of Ru 4d t2g states, which affects the magnetic coupling between the Ru and O ions. We observe that the orbital magnetic moment of the ligand O 2p orbitals induced through the charge transfer to the Ru 4d t2g states becomes anisotropic first, and the anisotropic magnetic moment of Ru and, therefore, the entire system is induced via magnetic coupling between Ru 4d and O 2p orbitals.

Origin of Magnetic Anisotropy in Nickelocene Molecular Magnet and Resilience of Its Magnetic Behavior

The robustness of nickelocene’s (NiCp2, Cp = cyclopentadienyl) magnetic anisotropy and addressability of its spin states make this molecular magnet attractive as a spin sensor. However, microscopic understanding of its magnetic anisotropy is still lacking, especially when NiCp2 is deposited on a surface to make quantum sensing devices. Quantum chemical calculations of such molecule/solid-state systems are limited to density functional theory (DFT) or DFT+U (Hubbard correction to DFT). We investigate the magnetic behavior of NiCp2 using the spin-flip variant of the equation-of-motion coupled-cluster (EOM-SF-CC) method and use the EOM-SF-CC results to benchmark SF-TD-DFT. Our first-principle calculations agree well with experimentally derived magnetic anisotropy and susceptibility values. The calculations show that magnetic anisotropy in NiCp2 originates from a large spin–orbit coupling (SOC) between the triplet ground state and the third singlet state, whereas the coupling with lower singlet excited states is negligible. We also considered a set of six ring-substituted NiCp2 derivatives and a model system of the NiCp2/MgO(001) adsorption complex, for which we used SF-TD-DFT method. To gain insight into the electronic structure of these systems, we analyze spinless transition density matrices and their natural transition orbitals (NTOs). The NTO analysis of SOCs explains how spin states and magnetic properties are retained upon modification of the NiCp2 coordination environment and upon its adsorption on a surface. Such resilience of the NiCp2 magnetic behavior supports using NiCp2 as a spin-probe molecule by functionalization of the tip of a scanning tunneling microscope.

Magnetism of Atomically Precise Gold and Doped Nanoclusters: Delocalized Spin and Interparticle Coupling

The magnetic properties of Au nanoparticles (NPs) have long been an intriguing topic in fundamental research. In the quantum size regime (1–3 nm), Au NPs indeed exhibit distinct magnetism in contrast to diamagnetic gold in bulk or relatively large plasmonic NPs. However, previous studies often give controversial results due to imprecise NPs used in magnetic studies, making it difficult to understand the origin of magnetism in Au NPs. Recent progress has led to atomically precise Au nanoclusters (NCs for differentiation with regular NPs), which can serve as a unique model for studying the delocalized spin in isolated NCs and the spin–spin exchange interaction between NCs in assembled solids. Moreover, such mechanisms are correlated to the atomic structures of the magnetic NCs. The precise formulas of the NCs serve as a clear indicator for magnetism. So far, the Au-thiolate NCs reported to be magnetic, including the doped ones, all contain icosahedral kernel structures, which are facile compared to other structures in adding or removing one electron for endowing magnetism to the NCs. Heteroatom doping in the NCs is an effective method to probe the magnetic mechanism in NCs, such as the origin of magnetic anisotropy, and the counterion tailoring for those charged NCs can also impart magnetism to the initially diamagnetic NCs via stabilizing a particular charge state of the NCs. While only a few cases of NCs have been reported with magnetism thus far, future research on metal NCs (especially in the critical regime between molecular and metallic state) will reveal more fundamentals of magnetism, and the control of spin–spin exchange coupling in nanocluster-assembled solids is particularly promising for tailoring the magnetic functionality of NCs and ultimately finding versatile applications.

Magnetization relaxation dynamics of a rare coordinatively unsaturated Co(II) complex: experimental and theoretical insights.

A robust and unusual three coordinate Co(ii) complex [Li(DME)3][Co(L)3] (1, where L = Lithium (2,6-diisopropylphenyl) amide and DME = Dimethoxyethane) shows easy plane magnetic anisotropy (D) which is validated by variable temperature X-band EPR studies. 1 also registered with the largest anisotropic barrier (51.1 K, τ0 = 1.98 × 10-8 s; Hdc ≠ 0) to the magnetization reversal among the three coordinate Co(ii) complexes. The role of its geometry on the SH parameters and the experimental observations are rationalized by theoretical calculations including the origin of magnetic anisotropy.

Insights into the origin of magnetic anisotropy in linear iron complexes from the experimental electron density

Insights into the origin of magnetic anisotropy in linear iron complexes from the experimental electron density

Controlling the supermagnetic response of tetragonal α-FeSi2 nanoislands

We used solid phase (SPE) and reactive deposition (RDE) epitaxy to grow crystallographically identical – but morphologically different – islands. Tetragonal α-FeSi2 islands crystallized pseudomorphically in the α-FeSi2(1 1 2)〈1 1 0〉||Si(1 1 1)〈1 1 0〉 and α-FeSi2(1 1 0)〈1 1 1〉||Si(2 2 0)〈1 1 2〉 orientation relations, with flat (2 × 2)-reconstructed top facets. The SPE-grown islands self-ordered in the form of 1D chains decorating the vicinal Si(1 1 1) step bunch edges along a specific 11¯0 direction. The RDE-grown islands elongated along three equivalent 112¯ directions, and were typically shorter, narrower, and thinner than the SPE-grown ones. In both cases, vast majority of the islands evolved sufficiently close to one another to enable dipolar interactions. Analyzing response to applied magnetic field, we identified areas of the island perimeter rims as the source of uncompensated magnetic moments creating the superspins, lateral island shape anisotropy as the origin of magnetic anisotropy, and periodic 1D ordering of interacting SPE-islands as the origin of superferromagnetic order. In contrast, three-fold orientational domains of the smaller RDE islands showed behavior more consistent with a superspin glass state. The above comparison emphasizes importance of the number of atoms at the island perimeter rims, and the role of dipolar interactions between the islands, for the magnetic behavior of the system.

Tailoring of in-plane magnetic anisotropy in polycrystalline cobalt thin films by external stress

Polycrystalline Co films of nominal thickness ~180Å were deposited on intentionally curved Si substrates. Tensile and compressive stresses of 100MPa and 150MPa were induced in the films by relieving the curvature. It has been found that, within the elastic limit, presence of stress leads to an in-plane magnetic anisotropy in the film and its strength increases with increasing stress. Easy axis of magnetization in the films is found to be parallel/ transverse to the compressive /tensile stresses respectively. The origin of magnetic anisotropy in the stressed films is understood in terms of magneto- elastic coupling, where the stress try to align the magnetic moments in order to minimize the magneto-elastic as well as anisotropy energy. Tensile stress is also found to be responsible for the surface smoothening of the films, which is attributed to the movement of the atoms associated with the applied stress. The present work provides a possible way to tailor the magnetic anisotropy and its direction in polycrystalline and amorphous films using external stress.

Origin of magnetic anisotropy in ZnO/CoFe2O4 and CoO/CoFe2O4 core/shell nanoparticle systems

ZnO-core/CoFe2O4-shell nanoparticles of 7.4 nm average size have been synthesized and their magnetic properties have been compared to those of CoO-core/CoFe2O4-shell nanoparticles with similar morphology. The coercive field values are much lower than those for CoO/CoFe2O4 nanoparticles (e.g., at 5 K: Hc = 7.8 kOe for ZnO/CoFe2O4; Hc = 27.8 kOe for CoO/CoFe2O4). The nature of the coercive field values is explained by a phenomenological model for the free energy of a non-magnetic core, or an antiferromagnetic core, encapsulated by a hard ferrimagnetic shell.

Single-Molecule-Magnet Behavior in a Fe12Sm4 Cluster

Through the combination of Sm(III) spin carriers with a Fe(III) system, the largest Fe-Ln cluster so far has been synthesized. To our knowledge, the new complex, Fe(12)Sm(4), is the first Sm(III) single-molecule magnet. Furthermore, Fe(12)La(4) and Fe(12)Gd(4) have also been synthesized to help understand the magnetic exchange interactions and origin of magnetic anisotropy in Fe(12)Sm(4).

Slow Magnetic Relaxation from Hard‐Axis Metal Ions in Tetranuclear Single‐Molecule Magnets

We report the synthesis of the novel heterometallic complex [Fe(3)Cr(L)(2)(dpm)(6)]⋅Et(2)O (Fe(3)CrPh) (Hdpm=dipivaloylmethane, H(3)L=2-hydroxymethyl-2-phenylpropane-1,3-diol), obtained by replacing the central iron(III) atom by a chromium(III) ion in an Fe(4) propeller-like single-molecule magnet (SMM). Structural and analytical data, high-frequency EPR (HF-EPR) and magnetic studies indicate that the compound is a solid solution of chromium-centred Fe(3)Cr (S=6) and Fe(4) (S=5) species in an 84:16 ratio. Although SMM behaviour is retained, the |D| parameter is considerably reduced as compared with the corresponding tetra-iron(III) propeller (D=-0.179 vs. -0.418 cm(-1)), and results in a lower energy barrier for magnetisation reversal (U(eff)/k(B)=7.0 vs. 15.6 K). The origin of magnetic anisotropy in Fe(3)CrPh has been fully elucidated by preparing its Cr- and Fe-doped Ga(4) analogues, which contain chromium(III) in the central position (c) and iron(III) in two magnetically distinct peripheral sites (p1 and p2). According to HF-EPR spectra, the Cr and Fe dopants have hard-axis anisotropies with D(c)=0.470(5) cm(-1), E(c)=0.029(1) cm(-1), D(p1)=0.710(5) cm(-1), E(p1)=0.077(3) cm(-1), D(p2)=0.602(5) cm(-1), and E(p2)=0.101(3) cm(-1). Inspection of projection coefficients shows that contributions from dipolar interactions and from the central chromium(III) ion cancel out almost exactly. As a consequence, the easy-axis anisotropy of Fe(3)CrPh is entirely due to the peripheral, hard-axis-type iron(III) ions, the anisotropy tensors of which are necessarily orthogonal to the threefold molecular axis. A similar contribution from peripheral ions is expected to rule the magnetic anisotropy in the tetra-iron(III) complexes currently under investigation in the field of molecular spintronics.

Experimental Observation of the1/3Magnetization Plateau in the Diamond-Chain CompoundCu3(CO3)2(OH)2

The magnetic susceptibility, high field magnetization, and specific heat measurements of Cu3(CO3)2(OH)2, which is a model substance for the frustrating diamond spin chain model, have been performed using single crystals. Two broad peaks are observed at around 20 and 5 K in both magnetic susceptibility and specific heat results. The magnetization curve has a clear plateau at one third of the saturation magnetization. The experimental results are examined in terms of theoretical expectations based on exact diagonalization and density matrix renormalization group methods. An origin of magnetic anisotropy is also discussed.

Electronic structure and ferromagnetic effect in Ni2MnGa alloy

By using the first-principles discrete variational method (DVM), we have investigated the magnetic contribution to the binding energy, the Fermi energy level, the interatomic energy, the bond order (BO), the total density of states (DOS), and the charge density distribution for varying c/a in Ni2MnGa alloy. The binding energy curves for the ferromagnetic (FM) phase for varying c/a are more complicated than those in the nonferromagnetic (NM) phase whose energy difference displays the magnetic contribution to the binding of the crystal. The interactions between the central atom Mn and the surrounding atoms, including the interatomic energies and the BOs, are different from each other, which leads to crystal anisotropy. The finding suggests that the interatomic energy difference between the FM and NM phases will be the origin of magnetic anisotropy. The difference in electron density on the different distortions for the FM and NM phases varying with c/a shows the different redistribution of the magnetization for the Mn and Ni in the [110] plane.

Origin of magnetic anisotropy in thin films deposited on step-bunched substrates

Ferromagnetic thin films of cobalt and permalloy have been grown on a non-planar Si(1 1 1) substrate presenting the step-bunching phenomenon. Room temperature hysteresis loop measurements show a strong uniaxial magnetic anisotropy, which decreases as the magnetic layer thickness increases. In the case of permalloy, the measured anisotropy is of magnetostatic origin and results from the non-planar nature of the substrate. The effective demagnetising field induced by the substrate is determined using a simple model based on the surface magnetic-charge density. The obtained values of the demagnetising field are then used to show that in the cobalt layers, the effective anisotropy is given by the substrate-induced shape anisotropy and an additional magneto-elastic contribution, which scales as the inverse of the thickness, consistent with the transition from FCC to HCP cobalt above a critical thickness close to 20 Å.

Electrical resistivity and magnetism of Fe/Si multilayers prepared by oblique incidence evaporation

We discussed the origin of the uniaxial magnetic anisotropy of the Fe/Si multilayered films prepared by varying oblique evaporation angle from the view of electric resistance. The tendency in the incidence angle dependence of the uniaxial magnetic anisotropy is in agreement with that of the angle dependence of the electric resistance ratio. The origin of the magnetic anisotropy seems to be due to anisotropic arrangement of atoms in the film.

Microstructural and magnetic properties of metallic thin films obliquely sputtered on polymer

Co and Co–Ni films have been obliquely sputtered on polymer substrate. Depending on the incidence angle, a large in-plane magnetic anisotropy can be induced. The origin of magnetic anisotropy is mainly related to the columnar structure because of the low magnetocrystalline anisotropy in the films (FCC Co). The rotational hysteresis analysis suggests that the magnetization reverse by incoherent rotation in films with a large in-plane anisotropy.

Magnetism of Cobalt Base Artificial Lattice Films

ABSTRACTThe Co/Pd and Co/Pd artificial lattice films have attracted much interest by their special magnetization properties. We discussed the effect of the Pt, Pd layer thickness on the magnetic anisotropy, and we showed the effect of the hydrogen ion implantation on the magnetic properties of multi-layered films. The Co/Pt and Co/Pd multi-layered films were formed on Si(111) substrates with molecular beam epitaxy. We did structure analysis, magnetic domain analysis and magnetic properties evaluation with XRD, MFM and VSM, respectively. Among the series of films of 0.4nm Co layer, XRD showed that the film of 1.0nm Pt layer had a highest periodicity and that they had (111) plane orientation completely. The magnetic domain size reduced with the increase of the thickness of Pt layer. We found out that the coercivity decreased linearly as a function of the length of magnetic domain wall in the unit area. The result of VSM showed that the multi-layered films of Pt thickness of less than 2.8nm had perpendicular magnetic anisotropy. The perpendicular anisotropy energy changed by the nonmagnetic layer thickness and had a maximum value for 0.4nm Co 0.4nm/ nonmagnetic metal 1.0nm multi-layered film. After hydrogen implantation into the films, XRD showed that the lattice spacing was swelled with hydrogen dose. Also, MFM observed that the magnetic domain size reduced with the increase of the hydrogen dose. The easy axis of magnetization changed from perpendicular to parallel in the plane with the increase of the hydrogen dose. After evacuation of hydrogen at 473K, perpendicular anisotropy was partially recovered. This phenomenon suggested that the origin of magnetic anisotropy was mainly the lattice mismatch and distortion in the layer interface. But Co/Pd film was not recovered by this thermal treatment. This means that Pd made stable hydride and did not evacuate hydrogen at this temperature.

Correlation of stress and magnetic anisotropy in CoCrPt/Cr films grown on textured substrates

Stress in Cr and CoCrPt/Cr films grown on smooth and lithographically textured silicon substrates were studied to investigate the origins of magnetic anisotropy in grooved longitudinal magnetic recording media. Crystallographic texture changes from Cr(110) to Cr(200) orientations are correlated with large stress changes. Magnetostrictive effects due to stress anisotropy in grooved samples are explored.

Zr site determination and origin of magnetic anisotropy in HDDR processed Nd2Fe14B-based magnets.

Zr site determination and origin of magnetic anisotropy in HDDR processed Nd2Fe14B-based magnets.

Determination of the magnetic axes of cobalt(II) and nickel(II) azurins from 1H NMR data: influence of the metal and axial ligands on the origin of magnetic anisotropy in blue copper proteins.

The orientation and the axial, Deltachiax, and rhombic, Deltachirh, components of the magnetic susceptibility tensor anisotropy for the cobalt(II) and nickel(II) derivatives of azurin from Pseudomonas aeruginosa have been determined from 1H NMR data. For both derivatives, the axial geometry of the system determines the orientation of the chi-tensor, whose z-axis forms an angle of 18.6 and 20.1 degrees with the Cu-OGly45 axial bond in the cobalt(II) and nickel(II) derivatives, respectively. For protons close to this axis, large negative pseudocontact shifts are observed, while those close to the NNS plane of the equatorial ligands experience lower and positive pseudocontact shifts for the same distance. Dipolar shifts are larger in the cobalt derivative, not only because of the larger spin number but also due to its intrinsically higher anisotropy. The contact contribution to the hyperfine shifts for the coordinated residues has been evaluated and analyzed in terms of unpaired spin delocalization mechanisms and geometry considerations. The results are extended to other blue copper proteins whose cobalt derivatives have been studied by 1H NMR. The electronic structure and its implications in the redox properties of the native copper proteins are also commented.