Strong In-plane Magnetic Anisotropy Research Articles

Enhancement of in-plane magnetic anisotropy in (111)-oriented Co0.8Fe2.2O4 thin film by deposition of PZT top layer

The CoFe2O4 and Co0.8Fe2.2O4 single layer (CFO) as well as PZT/CoFe2O4 and PZT/Co0.8Fe2.2O4 bilayer thin films were grown using the pulsed laser deposition technique on Pt(111)/Si substrates at 600 °C. All films had a perfect (111)-orientation and the degree of orientation of CFO films was improved by the deposition of a PZT top layer. Precision X-ray diffraction analysis (avoiding the shift of peaks due to sample misalignment) revealed that the CFO films on Pt(111)/Si substrate were under an out-of-plane contraction and the deposition of a PZT top layer led to the increase in the out-of-plane contraction. The (111)-oriented CFO single layer films had a strong in-plane magnetic anisotropy as a result of orientation as well as the stress-induced magnetic anisotropy. The magnetic properties of CFO film were altered by the deposition of a PZT top layer leading to the enhancement of in-plane magnetic anisotropy. The enhanced in-plane magnetic anisotropy was more detectable in PZT/Co0.8Fe2.2O4 rather than PZT/CoFe2O4 bilayer film, which could be expected from its higher magnetocrystalline as well as magnetostriction constants.

(111)-Oriented Co0.8Fe2.2O4+δ thin film grown by pulsed laser deposition: structural and magnetic properties

The perfect (111)-oriented Co0.8Fe2.2O4+δ thin films were grown on Pt(111)/Si substrate by pulsed laser deposition technique. Co0.8Fe2.2O4+δ film grown at oxygen pressure of 10 mTorr (optimum condition) has the highest (111)-orientation degree, the lowest surface roughness, uniformly compacted nanosize grain-feature structure (50–80 nm), and the highest magnetization. The Fe K-edge X-ray absorption near edge structure analyses revealed that, in Fe-doped CoFe2O4 film, the Fe also exists as Fe3+ (Co0.8Fe2.2O4+δ), which affects the lattice parameter as well as magnetic properties. The magnetic properties (saturation magnetization, coercivity, and squareness) of Co0.8Fe2.2O4+δ thin film are significantly higher than those of CoFe2O4 film. Moreover, the (111)-oriented Co0.8Fe2.2O4+δ thin film demonstrates strong in-plane magnetic anisotropy, which results from orientation, as well as the stress-induced magnetic anisotropy.

Strong in-plane magnetic anisotropy in (111)-oriented CoFe2O4 thin film

The perfect (111)-oriented CoFe2O4 thin films were grown on Pt(111)/Si substrate by pulsed laser deposition technique at substrate temperature of 600°C. The optimum oxygen pressure was found to be 10mTorr based on structural and magnetic properties. The film grown at 10mTorr has the highest (111)-orientation degree and magnetization. The films are under in-plane tensile stress due to the residual thermal strain which is thickness-dependent. It was found that the (111)-oriented CoFe2O4 thin film demonstrates the strong in-plane magnetic anisotropy which results from orientation as well as the stress-induced magnetic anisotropy.

Detection of Electrically Modulated Inverse Spin Hall Effect in anFe/GaAsMicrodevice

We report the detection of the inverse spin Hall effect (ISHE) in n-gallium arsenide (n-GaAs) combined with electrical injection and modulation of the spin current. We use epitaxial ultrathin-Fe/GaAs injection contacts with strong in-plane magnetic anisotropy. This allows us to simultaneously perform Hanle spin-precession measurements on an Fe detection electrode and ISHE measurements in an applied in-plane hard-axis magnetic field. In this geometry, we can experimentally separate the ordinary from the spin-Hall signals. Electrical spin injection and detection are combined in our microdevice with an applied electrical drift current to modulate the spin distribution and spin current in the channel. The magnitudes and external field dependencies of the signals are quantitatively modeled by solving drift-diffusion and Hall-cross response equations.

Extraordinary Hall effect on Fe-rich amorphous thin films and Fe-rich/Cu multilayers

In this study we investigated the magnetic and transport properties of thin Fe-rich amorphous films and Fe-rich/Cu multilayers. We compared the extraordinary Hall effect in these two types of samples and discussed it in terms of thickness and sample structure. The thicker films exhibited a strong in-plane magnetic anisotropy, and by decreasing film thickness both saturated Hall resistivity and Hall sensitivity increase. A Hall resistivity value of 20μΩcm is observed in 100nm thick Fe-rich films at 12K and a sensitivity of 1.3Ω/T is obtained at room temperature. Electrical conductance increases and Hall resistivity decreases when the films are sandwiched with Cu.

Fabrication and uniaxial magnetic anisotropy of Co nanowires on a Pd(110) surface

We have fabricated Co atomic chains and nanowires on a Pd(110) surface oriented along the [1-10] direction. This is possible due to high diffusion anisotropy of the Co adatom on the Pd(110) surface. The Co nanowires on Pd(110) exhibit a strong uniaxial in-plane magnetic anisotropy, in which the easy axis is along [1-10], i.e., nanowire direction.

Magnetic domains and flux pinning properties of a nanostructured ferromagnet/superconductor bilayer

We have investigated the magnetic and superconducting properties of a nanostructured ferromagnet/superconductor hybrid system, consisting of a Co layer with a square array of rectangular holes (antidots), covered with a thin continuous (nonperforated) superconducting Pb layer. The Co film with an antidot lattice shows a strong in-plane magnetic shape anisotropy determined by the array configuration and the rectangular shape of the antidots. Remanent domain structures in the uncovered Co antidot array are imaged at room temperature by magnetic force microscopy. The superconducting pinning properties of the hybrid ferromagnet/superconductor system are studied for different magnetic states of the Co antidot lattice. We demonstrate that the contribution to the superconducting pinning potential caused by the stray field from the domain walls is stronger than that arising from the periodic modulation due to the underlying antidot lattice.

Step-induced in-plane orbital anisotropy in FeNi films on Cu(111) probed by magnetic circular x-ray dichroism

The effects of nanostructured magnetic ${\mathrm{Fe}}_{65}{\mathrm{Ni}}_{35}$ films deposited on a vicinal Cu(111) single-crystal surface on the magnetic anisotropy have been studied using magnetic circular x-ray dichroism (MCXD) at the Fe ${L}_{2,3}$ edges. In the one-dimensional (1D) limit a large dipolar out-of-plane anisotropy is evidenced with in-plane isotropic magnetic moments. After the 1D coalescence the orbital moment shows a more complex behavior depending on the in-plane direction of saturation. We show that MCXD is strongly sensitive to in-plane orbital anisotropy for the 1D stripes. We demonstrate the importance of the step induced in-plane anisotropy by measuring the orbital magnetic moment dependence as a function of the in-plane azimuth angle. In the submonolayer regime an in-plane magnetic anisotropy is observed related to the step decoration growth mode. In the thickness range of 2--4 equivalent monolayers, 2D coalescence induces a strong in-plane magnetic anisotropy of the magnetic orbital moment. The microscopic origin of the strong in-plane variation of ${M}_{L}$ has been attributed to magnetocrystalline effects. Strained films give rise to an in-plane magnetic anisotropy energy up to 2 meV/at., which is larger than those measured out of the plane (0--1 meV/at.).

Strain-induced magnetic anisotropy in epitaxial Fe3O4/Co3O4 multilayers

Epitaxial multilayers of Fe3O4/Co3O4 were successfully grown on MgO and SrTiO3(001) single crystal substrates using a molecular beam epitaxy apparatus. The multilayers showed a strong in-plane magnetic anisotropy and an increase of coercive field for thin Fe3O4 samples. Multilayered Co3O4 exhibited a significant lattice expansion along the growth direction in order to compensate lattice mismatch at the interface. A small lattice distortion in the Fe3O4 layers might be the origin of the strong anisotropy.

Epitaxial nanomagnets with intrinsic uniaxial in-plane magnetic anisotropy

High quality epitaxial Fe films were grown on GaAs(001) by molecular beam epitaxy and magnetron sputtering. Two-dimensional arrays of circular dots with 200 nm diameter and 500 nm period were made by interferometric lithography and ion beam etching. Large area patterning (about 1 cm2) allows integral magnetic measurements with an alternating gradient magnetometer. The magnetic behavior of thick patterned films is dominated by the demagnetizing field. Ultrathin continuous films and dot arrays of these show a strong uniaxial in-plane magnetic anisotropy with the easy axis in [110] direction which is fully conserved during the patterning process. This means that two stable remanent single domain states exist in ultrathin Fe(001) sub-μm dots on GaAs(001) because (i) the magnetostatic energy is not important due to the small aspect ratio, and (ii) the Fe/GaAs(001) interface creates a strong uniaxial in-plane magnetic anisotropy. Nanomagnets with these properties seem very attractive for high density memory elements.

Magnetic moments and anisotropies in ultrathin epitaxial Fe films on ZnSe(001)

The morphology, atomic magnetic moments, and in-plane magnetic anisotropies of ultrathin bcc Fe(001) films deposited by molecular beam epitaxy on ZnSe epilayers grown on GaAs(001) single crystal are reported. The growth mode and structure have been determined in situ by means of reflection high energy electron diffraction and Auger electron spectroscopy. The magnetic properties were characterized ex situ by an alternating gradient magnetometer, superconducting quantum interference device (SQUID) magnetometry, and conversion electron Mössbauer spectroscopy (CEMS). The Fe growth is epitaxial and occurs by three dimensional nucleation at the beginning. The coalescence of the islands is observed around 7 monolayers (ML). In agreement with SQUID results, CEMS measurements indicate no reduction of the Fe magnetic moment compared to the bulk value even for the first Fe monolayers. Determination of the in-plane anisotropy constants as function of the Fe thickness shows a strong interface-induced uniaxial in-plane magnetic anisotropy, which leads to a continuous evolution from a pure uniaxial anisotropy with easy axis along [110] direction for thickness below 10 ML to the pure bulk cubic Fe anisotropy above 40 ML.

Magnetization of Pt in the Co/Pt(110) system investigated with surface x-ray magnetic diffraction: Evidence for in-plane magnetic anisotropy

Ultrathin films of Co were deposited in situ on a well-prepared Pt(110) single-crystal surface and the induced magnetization of the Pt atoms at the interface was investigated with resonant magnetic surface x-ray-diffraction measurements at the L absorption edges of Pt. The measurements indicate that the magnetization of the Pt atoms extends to three atomic layers below the Co film and that a strong in-plane magnetic anisotropy exists. The easy direction of magnetization in the surface plane is perpendicular to the close-packed atomic rows in the Pt substrate.

Influence of GaAs (001) surface termination on the in-plane magnetic anisotropies of MnSb epitaxial films

We have studied the in-plane magnetic anisotropy of epitaxial MnSb (11̄01) films grown on GaAs (001) by molecular beam epitaxy. The MnSb films were grown on (2×4) and (4×6) reconstructed GaAs surfaces at 250 and 50 °C. At 250 °C, the films showed a strong twofold in-plane magnetic anisotropy independent of the GaAs surface reconstruction. In contrast, at 50 °C, the in-plane anisotropy appeared only on the (2×4) reconstructed surface. The anisotropic crystallographic domain structure of the MnSb films is thought to cause the magnetic anisotropy. The anisotropic domain formation is explained by the different chemisorption of the Mn adatom on the GaAs surface as a function of the termination.

Structural and magnetic properties of Co/Au(001) superlattices

Co/Au(001) superlattices were prepared using an ultra-high-vacuum deposition technique. When the Co layer thickness is above 7 AA or when the Au layer thickness is below 12 AA, a drastic increase is found in the interface roughness parameter, indicating the change from a coherent to an incoherent structure of the interface. From magnetization measurements at 5 K, the magnetic moment for the Co layers in the Co/Au(100) superlattices is found to be 1.7 mu B per atom. The easy magnetization direction lies in the film plane for all the samples. A strong in-plane magnetic anisotropy is observed for the samples with small Co layer thickness and highly ordered interface structure.

Magnetic anisotropies of ultrathin Co films on Cu(001) and Cu(1113) substrates

We have determined the magnetic anisotropies of ultrathin Co layers on Cu(001) and Cu(1113) substrates using Brillouin light scattering and the magneto-optical Kerr effect. Experimental evidence was found that ferromagnetic order at room temperature in ultrathin epitaxial Co(001) layers on Cu(001) is stabilized by in-plane magnetic anisotropies. In the Co/Cu(1113) system we found a strong additional uniaxial in-plane magnetic anisotropy contribution of magnetoelastic origin with the easy axis parallel to the step edges.

Magnetic Anisotropy of Ni Films Prepared by Ion Beam Sputtering

The magnetic anisotropy in Ni films deposited by ion beam sputtering (IBS), triode rf sputtering and diode rf sputtering, was studied in relation to the internal stress in the films. A strong in-plane easy-axis magnetic anisotropy (K u ? -5 × 105 erg/cm3) was observed in IBS Ni films deposited at room temperature under an accelerating voltage exceeding 1 kV. The internal compressive stress was found to be as large as -1.2 × 1010 dyn/cm2, which caused a stress-induced magnetic anisotropy of about -1.2 × 106 erg/cm3 in the IBS Ni films. There is some positive contribution to the magnetic anisotropy, possibly due to the anisotropic internal shape effect (K int ? = 6 × 105 erg/cm3). Both this perpendicular magnetic anisotropy and the stress-induced in-plane anisotropy decreased with increasing substrate temperature during deposition. It is possible to obtain a stress-free, isotropic IBS Ni film at an appropriate substrate temperature (250 to 300°C) and at an appropriate ion beam accelerating voltage (1.1 kV).

イオンビームスパッタＮｉ薄膜の磁気異方性

The magnetic anisotropy in Ni films deposited by ion beam sputtering (IBS), triode rf sputtering and diode rf sputtering, was studied in relation to the internal stress in the films. Strong in-plane easy magnetic anisotropy (Ku∼-5 ×105 erg/cm3) was observed in IBS Ni films deposited at an acceleration voltage above 1 kV at room temperature. The internal compressive stress was found to be as large as -1.2×1010 dyn/cm2, which causes a stress-induced magnetic anisotropy of about -1.2×106 erg/cm3 in the IBS Ni films. There is some positive contribution to the magnetic anisotropy, possibly due to anisotropic internal shape effect (Kint∼6 ×105 erg/cm3). Both this perpendicular magnetic anisotropy and the stress-induced in-plane anisotropy are reduced with increasing substrate temperature during deposition. It is possible to obtain a stress-free isotropic IBS Ni film at an appropriate substrate temperature (250∼300°C) and an acceleration voltage (1.1 kV) of the ion beam

Magnetic anisotropy of IBS Ni films

The magnetic anisotropy in Ni films deposited on Pyrex glass substrates by different sputtering methods, i.e., ion beam sputtering (IBS), triode rf sputtering, and diode rf sputtering, was studied in relation to the internal stress in the films. Strong in-plane easy magnetic anisotropy (Ku=−4.9×105 erg/cm3) was observed in IBS Ni films. The average in-plane stress in the IBS film was estimated from the radius of convex curvature of the disk substrate as large as −1.2×1010 dyn/cm2 (a negative sign implies the compressive stress), which is due to the atomic peening effect by kinetic incident atoms during deposition. The stress-induced magnetic anisotropy is calculated to be about −1.2×106 erg/cm3, which is overwhelming to the observed magnetic anisotropy in the IBS Ni film. Positive Ku and tensile internal stress, one or two order of magnitude smaller in absolute values than that in IBS film, were observed in Ni films prepared by the other sputtering methods.