Stress-induced Magnetic Anisotropy Research Articles

Mesostructural origin of stress-induced magnetic anisotropy in Fe-based nanocrystalline ribbons

The cross-sectional mesostructure of a stress-annealed Fe-based (Fe73.5Cu1Nb3Si13.5B9) ribbon (SAR) has been investigated by atomic force microscopy. The magnetic anisotropy field was measured via the curves of the giant magnetoimpedence effect in SAR. The stress-induced magnetic anisotropy field (ΔHk) showed a linear correlation with the transverse congregating vector Kv of the agglomerated grains. This indicated that the ΔHk originated from the directional congregation of the agglomerated grains formed in SAR. A model for this directional congregation has been established. The previous diverse viewpoints on the mechanism of stress-induced magnetic anisotropy have been unified in this model.

Local stress engineering of magnetic anisotropy in soft magnetic thin films

The magnetic anisotropy of amorphous thin films was modified laterally by masked ion irradiation without alteration of the intrinsic magnetic properties. The changes were introduced by local ion implantation in a protection layer, causing additional stress-induced magnetic anisotropy in the magnetostrictive layer. The underlying local variation in magnetic anisotropy was modeled and confirmed experimentally. The described method, relying purely on magnetoelastics, introduces a new path to the alteration of magnetic properties subsequent to magnetic film preparation. With the use of the resulting artificial magnetization patterns, it is possible to tailor the ferromagnetic thin film structure used in magnetoelectronic applications.

Magnetization behaviors for FeRh single crystal thin films

The structural and magnetic phase transition in FeRh thin films are investigated. The (001) oriented single crystal FeRh thin films fabricated onto MgO (100) substrate possess lattice parameter a smaller than c, because of the compressive stress along the a axis from MgO substrate. With increasing annealing temperature, paramagnetic FeRh thin films transform into ferromagnetic and then antiferromagnetic-ferromagnetic (AF-FM) stages. The transition temperature of AF-FM increases with annealing temperature, while the thermal hysteresis width decreases. The M-H loops of the film annealed at 700°C show an opening at high magnetic fields during the transition state. Note that the opening in M-H loops disappears when AF phase has transformed into FM phase. The origin of the opening is not known but possibly due to the combination of hysteresis loops of FM and AF phases, where FM phase is soft magnetic and the AF phase FeRh shows a hysteresis behavior with coercivity due to the reduction of magnetic anisotropy at high temperatures. The abrupt change of coercivity along the perpendicular direction during the AF-FM transition suggests that a stress-induced magnetic anisotropy exists in FeRh thin films due to the volume expansion in the phase transition process.

The influence of anisotropic fields on stress-impedance effect in amorphous alloys

The theory of stress-impedance effect in amorphous alloys was established by introducing stress-induced anisotropy and magnetic anisotropy and solving Maxwell's equations and Landau-Lifshitz equation with the Gilbert term. The established theory can be used to explain the stress-impedance effect, and the calculation results were in good agreement with the experimental results. We calculated the stress-impedance change with different anisotropy parameters, and reached important conclusions both in theory and for applications.

Magnetization Reversal Technique of DyTbFeCo Films at Magnetic Field as Low as 1/6 of Coercivity Using a Stress-Induced Magnetic Anisotropy

A method to cause magnetization reversal in rare earth-transition metal (RE-TM) films at low magnetic field for perpendicular magnetic random access memory (MRAM) was demonstrated. The magnetic anisotropy was changed from perpendicular to in-plane in DyFeCo and TbDyFeCo films while the mechanical tensile stress is applied to the films. It is succeeded to cause magnetization reversal at low magnetic field as low as 1/6 of original coercivity of the film

Finite-Element Analysis of Stress Induced Magnetic Anisotropy in Perpendicular Writers

This paper presents finite-element analysis of the stress-induced magnetic anisotropy in perpendicular magnetic recording (PMR) heads developed during fabrication. The intrinsic stresses of various thin films used in the heads were measured using wafer curvature, while the stress in the yoke region was measured using X-ray diffraction. The measured stresses are provided. The initial strains due to the intrinsic stresses in the films were modeled using equivalent thermal strains and the calculations were verified by correlations with the stress measurements. Finite-element simulations were performed for calculating the stresses in full PMR heads. Detailed simulation procedures are described. Computed results are presented on how sensitive the magnetic anisotropy in the write pole are to the pole tip length and the slider lapping and the compressive stress in overcoat as well as the ambient temperature

On the mechanism of hysteresis in conductance of point contacts to single ferromagnetic films

Single nonmagnetic/ferromagnetic interfaces can exhibit magnetic excitations and hysteretic switching, provided that the current density traversing the interface is sufficiently high (≳108A∕cm2) and the flow regime is diffusive. We measure hysteretic switching in conductance induced by nominally unpolarized electron currents in nanocontacts to thin Co films and successfully model the effect for ∼20nm scale point contacts using micromagnetic simulations, which take into account an out of plane stress-induced magnetic anisotropy in the point contact region.

Stress-induced anisotropy, magnetic domain structure and spin-reorientation transition in R(FeCo)11Ti single crystals (R = Dy, Tb)

Abstract The magnetic domain structure on (1 0 0), (1 1 0), (0 0 1) and arbitrary oriented planes of the R(FeCo) 11 Ti single crystals (R = Dy, Tb) is investigated. The role of the stress-induced magnetic anisotropy in the DS formation and the spin-reorientation transitions is analyzed. It is shown that the magnetoelastic contribution to the anisotropy in these compounds is large and can cause changes of the spin-reorientation temperatures and special domain patterns formation.

Stress-induced magnetic anisotropy of CoFe 2O 4 thin films using pulsed laser deposition

Cobalt ferrite (CoFe 2O 4) thin films (≈70 nm) were epitaxially grown on TiO 2-terminated (0 0 1) SrTiO 3 substrates by pulsed laser deposition (PLD). Films with very smooth surface, which follow the terrace of the substrate, were obtained at temperatures below 600 °C. The magnetic properties of CoFe 2O 4 can be controlled by changing the deposition parameters. The in-plane magnetic anisotropy can be explained as induced by the compressive stress in films growing at low temperature and low oxygen pressure. Tuneable magnetic properties by PLD make CoFe 2O 4 more attractive for practical application, especially to create multi-functional devices in combination with perovskite ferroelectric films.

On annealing-induced amorphization and anisotropy in a ferromagnetic Fe-based film: A magnetic and property study

Magnetic and property characteristics of sputtered Fe65Ti13Co8Ni7B6Nb1 film in as-deposited and annealed conditions are examined. The film is transformed into various nanoscale and amorphous structures during annealing. Fully amorphous structure is obtained at 773–823K, whereas nanocrystalline γ-fcc FeNi, cubic Fe(Ni) and FeNi phases evolve sequentially at various temperatures. Amorphization and nanocrystallization yield alterations in electrical, hardness and magnetic properties with good soft magnetic properties obtained at 898K. Magnetic force images reveal stripe magnetic domain structures at 923–973K, indicating the presence of the strong stress-induced perpendicular magnetic anisotropy due to the combined effect of the positive magnetostriction and the compressive stress.

Stress-induced magnetic anisotropy in Xe-ion-irradiated Ni thin films

Samples consisting of 75nm Ni films deposited on Si substrates were bent mechanically and irradiated with 200keV Xe-ions at a dose of 4×1014ions/cm2. Magneto-optical Kerr effect, Rutherford backscattering spectrometry and X-ray diffraction were used to investigate the changes in the magnetic and microstructural properties. Perfect uniaxial magnetic anisotropy was found in the Ni films after irradiation and removal of the samples from the target holder. The magnetic behavior is shown to be very sensitive to the external stress produced in the films. With increasing curvature of the bent samples (≈2m−1), the easy axis of the magnetic anisotropy rotated in the direction perpendicular to the bending axis, indicating a compressive stress in the films after irradiation and relaxation.

Effect of Stress-induced Magnetic Anisotropy on the Properties of Giant Magnetostrictive Single Layer and Multilayer Thin Films

ABSTRACTGiant magnetostrictive thin films deposited on nonmagnetic substrates can constitute effective sensors and actuators for microdevices. In this work, we investigated the effects of a stress-induced anisotropy on the magnetic properties of Tb0.4Fe0.6, Fe0.5Co0.5 single layer films and [Tb0.4Fe0.6/Fe0.5Co0.5]n multilayers deposited on Si substrates. The magnetostrictive thin films were fabricated by means of RF sputtering and were subjected to a post-deposition annealing treatment. The uniaxial magnetic anisotropy was induced by bending the substrate before deposition and then allowing it to resume its original flat shape after depositing the film. The heat treatment was performed in a vacuum system with a vacuum of 10−6 Torr. The magnetic properties of the fabricated specimens were measured using a SQUID. SEM and XRD analyses were performed to ensure that the thermal treatment would relax the internal stresses induced during the deposition process without crystallizing the film. The thickness of the single layer thin films studied was between 300 and 800 nm while multilayer samples consisted of 6 layers with each layer thickness ranged from about 20 to 40 nm. Compared to single layer samples, multilayer samples with stress anneal growth exhibited an improvement in magnetic saturation by a factor of two while maintaining a low coercive field. Manipulations of the magnitude and direction of magnetic anisotropy was observed by introducing various values of tensile and compressive stress into the film.

Direct evidence for structural origin of stress-induced magnetic anisotropy in Fe–Si–B–Nb–Cu nanocrystalline alloys

The structural origin of magnetic anisotropy in Fe–Si–B–Nb–Cu alloys annealed under a tensile stress of 200 MPa is studied by transmission x-ray diffraction. The diffraction peak of the (310) plane, whose normal vector is parallel to the tensile direction (ribbon direction), appears at a lower angle than the one perpendicular to it by about 0.1°. This indicates that the spacing of the (310) plane normal to the tensile direction is about 0.2% larger than the one parallel to it. This is direct evidence for the structural origin of the stress-induced magnetic anisotropy of nanocrystalline soft magnetic alloys.

Stress-induced magnetic anisotropy in nanocrystalline alloys

Stress-annealing experiments were extended to both nanocrystalline alloy families, Finemet and Nanoperm (Hitperm), and, for comparison, to amorphous Fe 62Nb 8B 30 alloy. For both Finemet and bulk amorphous, stress-annealing results in a strong induced transversal anisotropy (flattening of hysteresis loop) but yields longitudinal induced anisotropy (square hysteresis loop) in Nanoperm and Hitperm. These results are interpreted in terms of back-stress theory.

Properties of amorphous magnetic materials by magnetic force microscopy

The aim of this work has been to show and analyze the domain structure of different amorphous magnetic materials by means of magnetic force microscopy (MFM). The following samples are successfully imaged: amorphous and devitrified melt-spun ribbons, amorphous electrodeposited microtubes which have a giant magneto-impedance effect, and sputtered films with a modulated stress-induced magnetic anisotropy. A correlation between the MFM images and the magnetic characteristics obtained from hysteresis loop measurements has been found.

Magnetoelastic effects in ultrathin epitaxial Ni films: an ab initio study

The effect of the nonlinear magnetoelastic coupling on the magnetostrictive stress and the magnetic anisotropy of epitaxially grown ultrathin Ni films with large epitaxial strain is investigated by the ab initio density functional electron theory. The nonlinear coupling has a considerable influence on the magnetostrictive stress, in agreement with the experimental results from the optical bending beam technique, but a weaker influence on the stress-induced magnetic anisotropy. Estimates are given for the nonlinear magnetoelastic coupling coefficients m 1 γ,2 and m 2 γ,2 . The results are compared with those for Fe.

Field- and Stress-Induced Magnetic Anisotropy in Nanocrystalline Fe-Based and Amorphous Co-Based Alloys

For nanocrystalline alloy Fe73.5Cu1Nb3Si13.5B9 thermomechanical treatment was carried out simultaneously with nanocrystallizing annealing (1) or after it (2). It was shown that a change in magnetic properties for the case 1 is essentially greater than for the case 2. Complex effect of thermomagnetic and thermomechanical treatments on magnetic properties was studied in the above-mentioned nanocrystalline alloy as well as in the amorphous alloy Fe5Co70.6Si15B9.4., During the annealings both field and stress were aligned with the long side of the specimens. It was shown that the magnetic field, AC or DC, decreases an effect of loading. Moreover, the magnetic field, AC or DC, applied after stress-annealing can destroy the magnetic anisotropy already induced under load.

Stress-induced magnetic anisotropy in thick oriented NiZn–ferrite films on (100) MgO substrates

Thick films (10–12 μm) of NiZn–ferrite (Ni0.6Zn0.4Fe2O4) were grown on single-crystal (100) magnesium oxide substrates using pulsed laser deposition (PLD). The morphology, phase, orientation, strain, and magnetic properties of the as-deposited films were investigated as a function of substrate temperature (400–700 °C) and O2 background pressure (50–200 mTorr). Compositional analysis shows that the PLD NiZn–ferrite films are about 45% Zn deficient when grown using a standard polycrystalline single phase Ni0.4Zn0.6Fe2O4 target regardless of substrate temperature or O2 pressure. However, Zn-rich targets were successfully used to compensate for the Zn deficiency in the NiZn–ferrite films. PLD NiZn–ferrite films grown at 700 °C exhibit the highest degree of crystalline quality and nearly bulk saturation magnetization values (i.e., 5000 G). At low O2 pressures (<75 mTorr) the films, which were grown at 700 °C, are under a significant compressive stress. The stress decreases when the PLD NiZn–ferrite films are grown in higher O2 pressures but the crystalline quality and surface morphology deteriorate. The compressive stress produces a planar anisotropy field of about 1000–3500 Oe depending on the O2 pressure, which is consistent with the stress results from x-ray diffraction measurements on the NiZn–ferrite films. It is hypothesized that the film stress is largely the result of oxygen loss from the films during deposition.

Contribution of stress-induced magnetic anisotropy to perpendicular magnetic anisotropy for Co/Pd and Co/Pt multilayers

The stress-induced magnetic anisotropy of Co/Pd and Co/Pt multilayers has been estimated by measuring the average internal stress 〈σCo〉 and the magnetostriction constant (λ111co) in the Co layers. For the Co/Pd multilayers, the stress-induced magnetic anisotropy in the Co layers contributes greatly to the perpendicular magnetic anisotropy. Conversely, for the Co/P1 multilayers, the stress-induced magnetic anisotropy does not contribute to the perpendicular magnetic anisotropy.

Uniaxial magnetic anisotropy in Co/Pd multilayers estimated by an in situ stress measurement and a computer simulation

The stress-induced magnetic anisotropy is thought to be one of the origins of the perpendicular magnetic anisotropy, K u, for Co/Pd multilayer films. The stress is evaluated by measuring the substrate bending during fabrication. To know the distribution of the stress in the film, computer simulations were performed by employing the pair-potentials from the microscopic point of view. It is clarified that K u corresponds well to the average stress in each Co layer.