Magnetic Anisotropy Of Films Research Articles

Contribution from Ising domains overlapping out-of-plane to perpendicular magnetic anisotropy in Mn4N thin films on MgO(001)

Single phase ε-Mn4N thin and ultrathin films are grown on MgO(001) using molecular beam epitaxy. Reflection high-energy electron diffraction and out-of-plane X-ray diffraction measurements are taken for each sample in order to determine the in- and out-of-plane strain for each sample. Vibrating sample magnetometry and superconducting quantum interference device measurements, which are performed on the thin and ultrathin films respectively, are used to plot the magnetization of each sample versus both in- and out-of-planeH→-fields and to determine the magnitude of perpendicular magnetic anisotropy in these films. Three significant components of perpendicular magnetic anisotropy are observed in these films and are attributed to sample strain (1 component) and shape (2 components). Among these components, the most significant component 0.8–4.9Mergcm3 is identified as a second term of shape anisotropy, which possesses a negative linear relationship with sample thickness over the range from 9nm to 310nm. Atomic (magnetic) force microscopy measurements show the presence of a surface localized magnetic polarization (22–82%), which increases with decreasing thickness, when the net magnetizations of the films are zero. The second term of shape anisotropy as well as the surface localized polarization, which each depend on sample thickness, are each regarded as a consequence of Ising domains overlapping out-of-plane in these films.

Magnetic anisotropy of quaternary GaMnAsP ferromagnetic semiconductor

We report a systemeatic investigation of magnetic anisotropy of quaternary GaMnAsP ferromagnetic semiconductor films by magneto-transport. Hall measurements showed a transition of the easy magnetization direction from in-plane to out-of plane with incorporation of the P into the GaMnAs films. Quantitative information on magnetic anisotropy of the films is obtained by fitting the angular dependence of Hall resistance data to magnetic free energy using the coherent rotation model. Values of magnetic anisotropy parameters show that in-plane anisotropy decreases and out-of-plane anisotropy increases with increasing P content in these films. The out-of-plane magnetic anisotropy in GaMnAsP layers is further enhanced by low temperature annealing. By optimizing the growth and annealing conditions, we were able to obtain a Curie temperature of 125 K in such quaternary films, with strong out-of-plane anisotropy. This study showed that the magnetic anisotropy of the GaMnAsP films can be controlled by adjusting the concentration of the P, and by appropriate post-growth annealing.

Growth of Y3Fe5O12/GaN layers by laser molecular-beam epitaxy and characterization of their structural and magnetic properties

Laser molecular-beam epitaxy has been employed to obtain layers of yttrium-iron garnet (YIG) Y3Fe5O12 on gallium nitride substrates. It was found that there exists a polycrystalline YIG phase without admixtures of other structural phases. A magnetic anisotropy of films of the “easy-magnetic plane” type was found. The gyromagnetic ratio and the demagnetizing field 4πMS were calculated.

Analytical theory and method for longitudinal magneto-optical Kerr effect of optically anisotropic magnetic film

The Fresnel equations are solved to analyze the reflection and propagation properties of the ordinary and extraordinary light of the optically anisotropic magnetic film. Using the boundary and propagation matrix, the longitudinal magneto-optical Kerr rotation expression is derived. After that, simulations are performed on optically anisotropic and isotropic Co/SiO2 film. Results show that for Co material in the thin-film limit, the anisotropic Co can provide larger max rotations than the isotropic Co in the visible region. This is because that the refractive index discrepancy of optically anisotropic Co film reduces the Fresnel reflective coefficient rpp, which improves the Kerr rotation. This makes the optically anisotropic Co film more effective in magneto optical sensor design and device fabrication.

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.

Layer-by-Layer Self-Assembly: Toward Magnetic Films with Tunable Anisotropy

Highly anisotropic magnetic films are possible to fabricate by control of the coupling between individual magnetic particles. Selective control over coupling in the horizontal and vertical directions are of both fundamental and practical interest. Here we show such control in the multiple layer-by-layer (LBL) self-assembly of layered double hydroxide (LDH) nanosheets (x = 1, 2, 3 and 4) with thicknesses of 5–15 nm, co-assembled with 3-aminopropyl-trimethoxysilane (APTS) modified spherical Fe3O4 nanoparticles (APTS-Fe3O4 NPs) on quartz substrates. The electrostatic charge density on the LDH sheets, controlled by the Mg/Al composition ratio, affects the NP packing in a single horizontal layer, while the thickness of the LDH sheets controls magnetic coupling between layers. The tunable magnetic properties (coercivity Hc, saturation magnetization Ms, anisotropy, and blocking temperatures) are measured as a function of these parameters. The maximum saturation magnetizations Ms, 36.3 and 25.1 emu·g–1 in the per...

Ultra-high resistive and anisotropic CoPd–CaF2 nanogranular soft magnetic films prepared by tandem-sputtering deposition

Ultra-high resistive and anisotropic soft magnetic films for gigahertz applications are desirable to demonstrate the really practical films. Here we present a study of novel nanogranular films fabricated by tandem-sputtering deposition. Their electromagnetic properties and nanostructure have also been discussed. These films consisted of nanocrystallized CoPd alloy-granules and CaF2 matrix, and a specimen having a composition of (Co0.69Pd0.31)52–(Ca0.31F0.69)48 exhibited distinct in-plane uniaxial anisotropy after uniaxial field annealing with granule growth. Its complex permeability spectra have a ferromagnetic resonance frequency extending to the Super-High-Frequency band due to its higher anisotropy field, and its frequency response was quite well reproduced by a numerical calculation based on the Landau–Lifshitz–Gilbert equation. Furthermore, it was clarified that the CaF2-based nanogranular film exhibits a hundredfold higher electrical resistivity than conventional oxide or nitride-based films. Higher resistivity enables the film thickness to achieve a margin exceeding threefold against eddy current loss. The greater resistivity of nanogranular films is attributed to the wide energy bandgap and superior crystallinity of CaF2 matrix.

磁気コンプトン散乱で調べる化学結合の形とその磁場依存性～垂直磁化膜の起原～

磁気コンプトン散乱で調べる化学結合の形とその磁場依存性～垂直磁化膜の起原～

Magnetization reversal in ferromagnetic thin films induced by spin-orbit interaction with Slonczewski-like spin transfer torque

We theoretically investigate the dynamics of magnetization in ferromagnetic thin films induced by spin-orbit interaction with Slonczewski-like spin transfer torque. We reproduce the experimental results of perpendicular magnetic anisotropy films by micromagnetic simulation. Due to the spin-orbit interaction, the magnetization can be switched by changing the direction of the current with the assistant of magnetic field. By increasing the current amplitude, wider range of switching events can be achieved. Time evolution of magnetization has provided us a clear view of the process, and explained the role of minimum external field. Slonczewski-like spin transfer torque modifies the magnetization when current is present. The magnitude of the minimum external field is determined by the strength of the Slonczewski-like spin transfer torque. The investigations may provide potential applications in magnetic memories.

A surface-chemistry study of barium ferrite nanoplates with DBSa-modified surfaces

Abstract Barium ferrite (BaFe 12 O 19 ) is a ferrimagnetic oxide with a high magnetocrystalline anisotropy that can be exploited in magnetically aligned ceramics or films for self-biased magnetic applications. Magnetic alignment of the films can be achieved by the directed assembly of barium ferrite nanoplates. In this investigation the nanoplates were synthesized hydrothermally and suspended in 1-butanol using dodecylbenzene sulphonic acid (DBSa) as a surfactant. They were then deposited in an electric or magnetic field on flat substrates and exhibited a significant preferential alignment in the plane of the substrate, allowing a differentiation between the analysis of their basal and side planes using scanning photoelectron microscopy with a lateral resolution down to 100 nm. The surface chemistry of the nanoplates was additionally studied with X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. For a comparison, bare barium ferrite nanoplates were also analyzed after decomposing the DBSa at 460 °C. The deviation of the surface chemistry from the stoichiometric composition was observed and the adsorption of the DBSa molecules on the nanoplates was confirmed with all three methods. Different types of bonding (physi- or chemisorption) were possible and considered with respect to the assembly of the barium ferrite nanoplates into anisotropic magnetic films.

Effects of ferroelectric-poling-induced strain on magnetic and transport properties of La0.67Ba0.33MnO3 thin films grown on (111)-oriented ferroelectric substrates

La0.67Ba0.33MnO3 thin films were epitaxially grown on (111)-oriented 0.31Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.34PbTiO3 ferroelectric single-crystal substrates. During ferroelectric poling and polarization rotation, the resistance of La0.67Ba0.33MnO3 films tracks the electric-field-induced in-plane strain of substrates effectively, implying strain-mediated coupling. Upon poling along the [111] direction, ferromagnetism is suppressed for T < 175 K, but enhanced for T > 175 K, which is explained by magnetoelastic coupling that modifies the film's magnetic anisotropy. Our findings also show that the magnetic field has an opposite effect on the strain-tunability of resistance [i.e.,(ΔR/R)strain] above and below the Curie temperature TC, which is interpreted within the framework of phase separation.

TEM studies of microstructure, interfaces, and intermixing of FePt/MgO/FePt/Pt/Cr(Ru) films

We have investigated the microstructure, interfaces, and intermixing in sputter-deposited FePt/MgO/FePt/Pt/Cr(Ru)/SiN/Si magnetic tunnel junctions by high-resolution transmission electron microscopy (HRTEM) and correlated these results to the magnetic properties. Cr90Ru10 is used as a texturing layer for the growth of perpendicular magnetic anisotropy (PMA) films. HRTEM confirmed the formation of the desired [001] texture in cubic Cr90Ru10 as well as in the adjacent L10-FePt layer using our growth methods. A 1.5 nm layer of MgO was deposited as a tunnel barrier for magnetic tunnel junction in an attempt to fabricate fully perpendicular tunnel junctions of these materials. The HRTEM observations, however, show that the MgO layer was partially crystalline but randomly oriented. The top FePt layer was also found to grow as discrete islands with random orientations and is mostly fcc crystal structure reducing the utility of this multilayer in PMA tunnel junction devices. The fine probe energy-dispersive X-ray spectroscopy showed the interdiffusion of Cr to Pt/FePt layers. The magnetic properties show out-of-plane coercivity larger than that of the in-plane values but with a loss of squareness, consistent with the loss of [001] texture and of L10 structure in the top magnetic layer.

Au coated Ni nanowires with tuneable dimensions for biomedical applications.

Due to their shape anisotropy, high aspect ratio magnetic nanoparticles offer many advantages in biomedical applications. For biocompatibility, it is essential to have full control over the dimensions and surface chemistry of the particles. The aim of this study was to synthesize biocompatible nanowires with tuneable dimensions. This was achieved by electrodeposition of Ni in polycarbonate membranes. To ensure biocompatibility, a continuous gold coating was deposited onto the Ni wires by a newly developed electroless deposition method. The coating was analysed using electron microscopy and X-ray diffraction. Magnetic properties, anisotropy and Au film thickness were studied using vibrating sample magnetometry. After biofunctionalization, no significant cytotoxic effects were found in studies involving a diverse range of primary and tumour cells exposed to increasing concentrations of nanowires for up to 7 days. These nanowires may thus be used for in vivo applications such as magnetic drug delivery.

Magnetic domain structure in thin CoPt perpendicular magnetic anisotropy films

The relation between thickness and domain structure of Co80Pt20 perpendicular magnetic anisotropy films was investigated through experiments and micromagnetic simulation. The films with thickness over 10 nm exhibited clear maze domain structure, while for the films thinner than 10 nm the domain structure abruptly changed from maze domain to irregular and large domain as the thickness became thinner. The irregular domain had narrower domain wall width than maze domain.

Deposition of Inclined Magnetic Anisotropy Film by Oblique Incidence Collimated Sputtering

Deposition of Inclined Magnetic Anisotropy Film by Oblique Incidence Collimated Sputtering

Magnetic anisotropy of epitaxial zinc ferrite thin films grown by pulsed laser deposition

Epitaxial zinc ferrite thin films are grown on (001) SrTiO3 substrates by pulsed laser deposition. The magnetic anisotropy of the films is examined by superconducting quantum interference device magnetometry and ferromagnetic resonance, with various in-plane and out-of-plane orientations of the magnetic field. The volume magnetization of the films is found to be around 55kA/m. The existence of a cubic magnetic anisotropy is shown, with the easy axes oriented along the [111] crystallographic directions. The films show ferrimagnetic properties with a Curie temperature higher than 350K. The nature of a strong “easy-plane”-type bimodal anisotropy in the films is discussed.

Optimization of perpendicular magnetic anisotropy tips for high resolution magnetic force microscopy by micromagnetic simulations

Magnetic Force Microscopy (MFM) tip coated with perpendicular magnetic anisotropy film (PMA tip) is one of the choices for high resolution imaging at low scan height (SH), since it has negligible tip–sample interaction related to its stable magnetic state, sharp, and small tip stray field. In this work, detailed micromagnetic studies are carried out to understand the effect of geometrical and magnetic parameters including the cone angle θ of the PMA tip, intergrain exchange constant \(A_{2}^{*}\), saturation magnetization M s and uniaxial crystalline anisotropy constant K 1 of the tip coating on the MFM tip resolution. To evaluate the resolution performance of the optimized PMA tip, MFM images of high-density granular recording media and patterned media are simulated. We find that, for the PMA tip and its coating, a cone angle in a range of 36.9∘ to 53.1∘, a saturation M s of 700 emu/cm3, a large uniaxial crystalline anisotropy constant K 1 (>4.9×106 erg/cm3) and a high intergrain exchange constant \(A_{2}^{*}\) of (0.3–1.0)×10−6 erg/cm are optimized conditions for high resolution imaging. The optimized PMA tip has an excellent performance on imaging of high-density thin film media (bit size of 8×16 nm2) at low SH of 2–8 nm and bit pattern media with a pitch of 50 nm, edge-edge spacing of 5–15 nm at SH of 8–15 nm.

Topological Defects and Misfit Strain in Magnetic Stripe Domains of Lateral Multilayers With Perpendicular Magnetic Anisotropy

Stripe domains are studied in perpendicular magnetic anisotropy films nanostructured with a periodic thickness modulation that induces the lateral modulation of both stripe periods and in-plane magnetization. The resulting system is the 2D equivalent of a strained superlattice with properties controlled by interfacial misfit strain within the magnetic stripe structure and shape anisotropy. This allows us to observe, experimentally for the first time, the continuous structural transformation of a grain boundary in this 2D magnetic crystal in the whole angular range. The magnetization reversal process can be tailored through the effect of misfit strain due to the coupling between disclinations in the magnetic stripe pattern and domain walls in the in-plane magnetization configuration.

Ferromodulation Effect Usage for the Magnetic Film Anisotropy Investigation

The ferromodulation effect response model of an anisotropic soft magnetic film placed in the crossed permanent bias and alternating excitation magnetic fields is built. It was shown theoretically and experimentally how such a field configuration can be used for registering the effects relating to the film magnetic anisotropy properties.

Hysteresis Properties of Magnetic/Non-Magnetic (M/NM) Multilayers: Monte Carlo Investigation

In this work, Monte Carlo simulation was used to model the dynamic hysteresis behavior of magnetic/non-magnetic multilayers in the framework of Heisenberg model using the spin-flip algorithm. The purpose is to investigate the hysteresis properties while varying the direction of external applied magnetic field and temperature taking account interface composition of magnetic/non-magnetic atoms. From the results, with thermal variation and interface composition, the simulated hysteresis loops change significantly due to the competition between magnetic anisotropy in magnetic films and the presence of isolated clusters at the interface.