Journal ArticleDOI

# Magnetic anisotropy and anisotropic ballistic conductance of thin magnetic wires

01 May 2006--Vol. 300, Iss: 1, pp 136-139

AbstractThe magnetocrystalline anisotropy of thin magnetic wires of iron and cobalt is quite different from the bulk phases. The spin moment of monatomic Fe wire may be as high as 3.4  μ B , while the orbital moment as high as 0.5  μ B . The magnetocrystalline anisotropy energy (MAE) was calculated for wires up to 0.6 nm in diameter starting from monatomic wire and adding consecutive shells for thicker wires. I observe that Fe wires exhibit the change sign with the stress applied along the wire. It means that easy axis may change from the direction along the wire to perpendicular to the wire. We find that ballistic conductance of the wire depends on the direction of the applied magnetic field, i.e. shows anisotropic ballistic magnetoresistance. This effect occurs due to the symmetry dependence of the splitting of degenerate bands in the applied field which changes the number of bands crossing the Fermi level. We find that the ballistic conductance changes with applied stress. Even for thicker wires the ballistic conductance changes by factor 2 on moderate tensile stain in our 5×4 model wire. Thus, the ballistic conductance of magnetic wires changes in the applied field due to the magnetostriction. This effect can be observed as large anisotropic BMR in the experiment.

Topics: , Magnetic anisotropy (60%), Ballistic conduction (57%), Magnetoresistance (54%)

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Journal ArticleDOI
Abstract: Ab initio simulations are used to investigate the magnetic and electronic properties of freestanding Fe(1−x)M x (M = Co/Ni) nanowires. The stability of the nanowires increases with Co (Ni) addition, as seen from the increase in cohesive energy. With the addition of Co (Ni), the average magnetic moment shows a monotonic decrease, in contrast to the Slater–Pauling behavior observed in bulk Fe–Co/Ni alloys. The magnetic anisotropy energy of the nanowire is observed to change sign, from a parallel alignment of spins along the wire axis, to a perpendicular alignment with the increase of Co and Ni content. The magnetic anisotropy energy variation is seen to be correlated with the orbital moment anisotropy. The coercivity, as calculated using the Jacobs–Bean model is observed to decrease with Co (Ni) addition to the nanowire.

12 citations

B. Lazarovits
01 Mar 2003
Abstract: We present first-principles calculations of the magnetic moments and magnetic anisotropy energies of finite monoatomic ${\mathrm{Co}}_{n}$ $(1l~nl~10)$ chains deposited along the (110) direction on top of a fcc Pt(111) surface. The calculations were performed fully relativistically using the embedded-cluster technique within the Korringa-Kohn-Rostoker method. The magnetic anisotropy energy was evaluated by means of the magnetic force theorem. As a direct consequence of the reduced coordination number of the Co atoms, we found enhanced spin and orbital moments as well as enhanced anisotropy energies in the Co chains as compared to a Co overlayer on Pt(111). For the Pt atoms adjacent to the Co atoms, however, we obtained induced magnetic moments smaller than in the case of a Co monolayer on Pt(111). The moments and the contributions of the individual atoms to the magnetic anisotropy energy depend characteristically on the position within the chains, i.e., on the local environment of the individual atoms. Independent of the length of the chains we found that the easy axis is perpendicular to the surface. The size of the calculated magnetic anisotropy energy and of the anisotropy of the orbital moment fits very well to available experimental values for monoatomic Co chains deposited on a Pt(997) surface.

3 citations

01 Aug 2007
Abstract: Stony Brook University Libraries SBU Graduate School in physics Lawrence Martin (Dean of Graduate School), Chi-Chang Kao - Advisor Professor, Department of Physics and Astronomy Senior Scientist, Brookhaven National Laboratory, Christopher Jacobsen - Chairperon Professor, Department of Physics and Astronomy, Philip Allen Professor, Department of Physics and Astronomy, Kenneth Evans-Lutterodt Senior Scientist, Physics, Brookhaven National Laboratory

2 citations

### Cites background from "Magnetic anisotropy and anisotropic..."

• ...Tetragonal strain and changes in nearest-neighbor distance on the order of a percent have been theoretically predicted to have a significant impact on both spin and orbital magnetic moments [20,23]....

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• ...3 Å along a theoretical unit-cell wide wire [20]....

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##### References
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Journal ArticleDOI
Pietro Gambardella
16 May 2003-Science
TL;DR: The isotropic magnetic moment of a free atom is shown to develop giant magnetic anisotropy energy due to symmetry reduction at an atomically ordered surface and the results confirm theoretical predictions and are of fundamental value to understanding how magnetic an isotropy develops in finite-sized magnetic particles.
Abstract: The isotropic magnetic moment of a free atom is shown to develop giant magnetic anisotropy energy due to symmetry reduction at an atomically ordered surface. Single cobalt atoms deposited onto platinum (111) are found to have a magnetic anisotropy energy of 9 millielectron volts per atom arising from the combination of unquenched orbital moments (1.1 Bohr magnetons) and strong spin-orbit coupling induced by the platinum substrate. By assembling cobalt nanoparticles containing up to 40 atoms, the magnetic anisotropy energy is further shown to be dependent on single-atom coordination changes. These results confirm theoretical predictions and are of fundamental value to understanding how magnetic anisotropy develops in finite-sized magnetic particles.

827 citations

Journal ArticleDOI

TL;DR: Three-dimensional switching field measurements performed on a 3 nm cobalt cluster embedded in a niobium matrix are reported, able to separate the different magnetic anisotropy contributions and evidence the dominating role of the cluster surface.
Abstract: Using a new micro-SQUID setup, we investigate magnetic anisotropy in a single 1000-atom cobalt cluster. This system opens new fields in the characterization and understanding of the origin of magnetic anisotropy in such nanoparticles. For this purpose, we report three-dimensional switching field measurements performed on a 3 nm cobalt cluster embedded in a niobium matrix. We are able to separate the different magnetic anisotropy contributions and evidence the dominating role of the cluster surface.

371 citations

Journal ArticleDOI
Abstract: We present magnetoresistance experiments in magnetic Ni nanocontacts in the ballistic transport regime at room temperature. It is shown that the magnetoresistance for a few-atom contact reaches values of $280%$ at room temperature and for applied magnetic fields of 100 Oe. Results are presented for over 50 samples showing the trend that the smaller the contact the larger the magnetoresistance response. This indicates that the effect arises just at the nanocontact.

353 citations

Journal ArticleDOI

TL;DR: One-dimensional Co atomic wires grown on Pt(997) have been investigated by x-ray magnetic circular dichroism and the easy axis of magnetization, the magnetic anisotropy energy, and the coercive field oscillate as a function of the transverse width of the wires, in agreement with theoretical predictions for 1D metal systems.
Abstract: One-dimensional Co atomic wires grown on Pt(997) have been investigated by x-ray magnetic circular dichroism. Strong changes of the magnetic properties are observed as the system evolves from 1D- to 2D-like. The easy axis of magnetization, the magnetic anisotropy energy, and the coercive field oscillate as a function of the transverse width of the wires, in agreement with theoretical predictions for 1D metal systems.

125 citations

Journal ArticleDOI
TL;DR: The magnetoresistance is strongly enhanced for the narrow PC and oscillates with the conductance and the sequence of quantized conductances depends on the relative orientation of magnetizations between left and right electrodes.
Abstract: We theoretically study the electron transport through a magnetic point contact (PC) with special attention given to the effect of an atomic scale domain wall (DW). The spin precession of a conduction electron is forbidden in such an atomic scale DW and the sequence of quantized conductances depends on the relative orientation of magnetizations between left and right electrodes. The magnetoresistance is strongly enhanced for the narrow PC and oscillates with the conductance.

108 citations