Magnetoelastic Anisotropy Energy Research Articles

Structural and magnetic asymmetry at the interfaces of MgO/FeCoB/MgO trilayer: Precise study under x-ray standing wave conditions

Magnetic tunnel junctions based on FeCoB as a magnetic electrode and MgO as a tunneling barrier gained much attention because of their applications in random access memories and magnetic sensors in disk drives. In this work, the structural and magnetic properties of the MgO/FeCoB/MgO trilayer have been studied precisely under x-ray standing wave (XSW) conditions, where XSW is generated through a high-density (Pt) waveguide structure. The combined x-ray scattering and fluorescence data obtained under XSW conditions revealed the formation of a high-density FeCoB layer at the MgO/FeCoB interface (FeCoB-on-MgO) in the as-deposited trilayer. Diffusion of B from the FeCoB layer into MgO is attributed to the formation of Fe- and Co-rich high-density layer (B-deficient FeCoB layer) at the interface. Angular-dependent magnetism of the trilayer structure revealed the presence of in-plane magnetic anisotropy (IMA), which disappeared with thermal annealing at a temperature of 450 °C. Stress in B-deficient FeCoB layer at the interface is attributed to the origin of IMA through magneto-elastic anisotropy energy minimization. The disappearance of anisotropy after annealing is mainly due to the removal of long-range stress and the formation of crystalline bcc-FeCo phase.

Thin film rare earth iron garnets with perpendicular magnetic anisotropy for spintronic applications

Perpendicular magnetic anisotropy (PMA) in garnet thin films is important for achieving numerous spintronic applications including spin-orbit switching. In this study, we computationally investigated how to control PMA by tuning substrate strain in Holmium Iron Garnet (HoIG) films grown on five different (111) single crystal garnet substrates of Gadolinium Gallium Garnet (GGG, Gd3Ga5O12), Yttrium Aluminum Garnet (YAG, Y3Al5O12), Terbium Gallium Garnet (TGG, Tb3Ga5O12), Substituted Gadolinium Gallium Garnet (sGGG, Gd3Sc2Ga3O12), and Neodymium Gallium Garnet (NGG, Nd3Ga5O12). The negative sign of effective anisotropy energy density, Keff < 0, and anisotropy field, Ha < 0, determines the easy magnetization axis of the film to be perpendicular to the film surface. Here, we show that magnetoelastic anisotropy energy density determines the sign of the total anisotropy and it can be manipulated by altering the lattice parameter mismatch of the film and its substrate. Based on this study, HoIG is predicted to have PMA when grown on GGG, TGG and YAG among all five substrates mentioned. Moreover, the saturation field magnitude is calculated as an order of several hundreds of Oersteds, which is feasible in practical applications to saturate rare earth iron garnets with perpendicular magnetic anisotropy.

Stress induced magnetic-domain evolution in magnetoelectric composites

Local observation of the stress mediated magnetoelectric (ME) effect in composites has gained a great deal of interest over the last decades. However, there is an apparent lack of rigorous methods for a quantitative characterization of the ME effect at the local scale, especially in polycrystalline microstructures. In the present work, we address this issue by locally probing the surface magnetic state of barium titante–hexagonal barium ferrite (BaTiO3–BaFe12O19) ceramic composites using magnetic force microscopy (MFM). The effect of the piezoelectrically induced local stress on the magnetostrictive component (BaFe12O19, BaM) was observed in the form of the evolution of the magnetic domains. The local piezoelectric stress was induced by applying a voltage to the neighboring BaTiO3 grains, using a conductive atomic force microscopy tip. The resulting stochastic evolution of magnetic domains was studied in the context of the induced magnetoelastic anisotropy. In order to overcome the ambiguity in the domain changes observed by MFM, certain generalizations about the observed MFM contrast are put forward, followed by application of an algorithm for extracting the average micromagnetic changes. An average change in domain wall thickness of 50 nm was extracted, giving a lower limit on the corresponding induced magnetoelastic anisotropy energy. Furthermore, we demonstrate that this induced magnetomechanical energy is approximately equal to the K1 magnetocrystalline anisotropy constant of BaM, and compare it with a modeled value of applied elastic energy density. The comparison allowed us to judge the quality of the interfaces in the composite system, by roughly gauging the energy conversion ratio.

Effect of non-magnetic ions substitution on the structure and magnetic properties of Y3−xSrxFe5−xZrxO12 nanoparticles

In this work, Y3−xSrxZrxFe5O12 (0.0 ≤ x ≤ 0.7) were synthesized by citrate precursor method at 1050 °C. The structural and magnetic properties of Y3−xSrxFe5−xZrxO12 were studied by using the X-ray diffraction technique, scanning electron microscopy, transmission electron microscopy, the Fourier transform infrared spectroscopy and vibrating sample magnetometer. XRD analysis using X’Pert package show a pure garnet phase with cubic structure (space group Ia-3d) and the impurity phase SrZrO3 is observed when the range of x value is exceeded from 0.6. Rietveld refinement using Fullprof program shows the lattice volume expansion with increasing the degree of Sr/Zr substitution. The crystallite sizes remain constant in the range of x = 0.0 − 0.5 and then increase. The different morphology observed in SEM micrographs of the samples can be related to different values of the microstrain in the samples. The hysteresis loops of the samples reveal a superparamagnetic behaviour. Also, the drop in coercivity with increasing of the substitution is mainly originated from a reduction in the magneto-elastic anisotropy energy. The values of the saturation magnetization (MS) indicate a non-monotonically variant with increasing the Sr/Zr substitution and reach a maximum 26.14 emu/g for the sample x = 0.1 and a minimum 17.64 emu/g for x = 0.0 and x = 0.2. The variation of MS, in these samples results from a superposition of three factors; reduction of Fe3+ in a-site, change in angle FeT-O-FeO, and magnetic core size.

Controlling the competing magnetic anisotropy energies in FineMET amorphous thin films with ultra-soft magnetic properties

Thickness dependent competing magnetic anisotropy energies were investigated to explore the global magnetic behaviours of FineMET amorphous thin films. A dominant perpendicular magnetization component in the as-deposited state of thinner films was observed due to high magnetoelastic anisotropy energy which arises from stresses induced at the substrate-film interface. This perpendicular magnetization component decreases with increasing film thickness. Thermal annealing at elevated temperature revealed a significant influence on the magnetization state of the FineMET thin films and controlled annealing steps leads to ultra-soft magnetic properties, making these thin films alloys ideal for a wide range of applications.

Study of mechanical-magnetic and electromagnetic properties of PZT/Ni film systems by a novel bulge technique

A novel multiple functional bulge apparatus was designed to study the mechanical-electronic-magnetic characteristics of electromagnetic materials. The elastic modulus difference effect of Ni thin film was observed and it was about 22.16% in the demagnetized and magnetization saturated states. The mechanical-magnetic behaviors of Ni and lead-titanate zirconate (PZT)/Ni films were in-situ measured by using the new bulge systems, respectively. The evolutions of three key material properties in hysteresis loop including saturation magnetization, remanent magnetization and coercive field were discussed in detail, respectively. The mechanisms of mechanical-magnetic coupled behaviors of Ni and PZT/Ni films were analyzed with the aid of the competitive relationship of stress and magnetization. Similarly, the electronic-magnetic characteristics of PZT/Ni films were in-situ measured by using this experimental system. The evolution of saturated magnetization, remanent magnetization and coercive field Kerr signals were discussed with the magneto-elastic anisotropy energy point. In this paper, a suitable mechanical-electronic-magnetic bulge measurement system was established, which would provide a good choice for further understanding the multi field coupling characteristics of electromagnetic film materials.

Converse magnetoelectric effect in NiFe2O4/BaTiO3 heterostructure by electric field induced inter-ferroelectric phase transition

Converse magnetoelectric effect was experimentally demonstrated in NiFe2O4/BaTiO3 (NFO/BT) heterostructure. Electric field induced inter-ferroelectric phase transition in BT substrate and its impact on magnetization of NFO was studied for the first time. Presence of meta-stable orthorhombic phase (Amm2) along with tetragonal (P4mm) BT was revealed from Rietveld refinement in unpoled state itself. Negative lattice mismatch between NFO film and BT substrate induces compressive stress along in-plane direction of NFO and reduces magnetoelastic anisotropy energy. Hence, large magnetization was obtained along in-plane direction compared to that of out of plane. Poling stabilizes orthorhombic phase that enhances compressive stress further along in-plane direction. Consequently, increase and decrease of magnetization was observed along in and out-of plane respectively. Observations from the present work revealed that magnetization in such heterostructures can be controlled via strain-mediated coupling by voltage which provides an opportunity in spintronic devices for low power consumption.

Thickness Dependent Magnetic Properties of Polycrystalline Nickel Thin Films

Magnetization directions of ferromagnetic ultra-thin lms can be altered by increasing the thickness. The transition between in-plane and out-of-plane axes is induced by the competition among the magnetostatic, magnetocrystalline and magnetoelastic anisotropy energies. Such an e ect has attracted more interest recently, due to the applications in magneto-optical recording technologies. In this study, we have investigated by magneto-optical Kerr e ect the magnetization properties of magnetron sputtered nickel thin lms.

Modeling of Nd-Oxide Grain Boundary Phases in Nd-Fe-B Sintered Magnets

We use atomistic and micromagnetic simulations combined with atomic-scale, aberration-corrected transmission electron microscopy to study the anisotropy profile of the interface between a Nd2O3-hP5 and a Nd2Fe14B phase. It is shown that a hybrid Morse-Buckingham potential approach can be used to study mixed-metallic and oxide-rich systems and to calculate surface-energy-induced large strains and potentially large relaxation effects on the adjacent grains. These are used to derive a magnetoelastic anisotropy energy from a first-order perturbation of the magnetoelastic Hamiltonian and are used to evaluate its effect on coercivity. It is shown that the change in coercivity originates from these distortions in the Nd2Fe14B crystal lattice close to the grain boundary, and the coercivity can be evaluated using such a multiscale modeling approach.

Interplay of the magnetoelastic and shape anisotropy on the evolution of magnetic domain structure of amorphous Nd–Fe–B films

Amorphous Re–Fe–B (Re rare-earth) films are prepared on thermally oxidized Si substrates with Nb buffer layers by dc magnetron sputtering. We observed the evolution of magnetic domain structure in these films under the external magnetic field parallel to the film plane and discussed its origin. The magnetoelastic anisotropy and shape anisotropy can be adjusted by changing the deposition temperature and the thickness of the film. The results showed that the magnetic domain structure for a film with lower sputtering temperature (150°C) and thinner thickness (200nm) has changed significantly with the applied magnetic field and form stripe domains arranged along the direction of the field. However, for the film with higher sputtering temperature (300°C) and thicker thickness (600nm), magnetic domain structure is hardly varied with applied field. We suggest the evolution of magnetic domain structure is determined by the interplay of the magnetoelastic anisotropy and shape anisotropy energy, which will lead to the easy magnetization direction of amorphous Re–Fe–B films inclined to the normal direction instead of perpendicular to the film plane.

Effect of deposition temperature on morphology and magnetic properties of Co 50Fe 50 thin films produced by femtosecond pulsed laser deposition

Deposition temperature effect on morphological, topological and magnetic characteristics of nanoparticle-assembled Co 50Fe 50 films produced by femtosecond pulsed laser deposition (fs-PLD) on Kapton substrate was investigated. For substrate temperature T s ≥ 550 K, a decrement of the nanoparticle's aggregates and an increment of the nanoparticle's density were observed with respect to room temperature deposition; this in association with a strong increase of the magnetoelastic anisotropy energy lead to a reduction of the remanence ratio, a significant rise of the saturation and coercive fields and an enhancement of the saturation magnetization. The results are discussed focusing on: i) the correlation between films structure and their magnetic behavior; ii) the role of the different anisotropy energies in determining the harder in-plane magnetic behavior for T s ≥ 550 K. The thermal strain of Kapton substrate holds an important role in generating morphological and topological characteristics of the fs-PLD films and corresponding magnetic properties.

Cylindrical magnetization model for glass-coated microwires with circular anisotropy: Statics

The static magnetization profile of glass-coated microwires with effective circular anisotropy is investigated using micromagnetics. In this family of microwires, the ferromagnetic nucleus with an amorphous character presents a magnetic structure composed of an inner region with axial domains and an outer region with circular domains, due to magnetoelastic anisotropy. A one-dimensional micromagnetic model is developed, taking into account both the exchange and magnetoelastic anisotropy energies, and solved quasi analytically. The total energy, magnetization profiles and magnetization curves are investigated as a function of radius and anisotropy constant of the nucleus. This work represents a fundamental study of the magnetization process in these amorphous microwires and provides guidelines for the production of microwires with tailored magnetic properties. En passant, the nucleation problem in an infinite cylinder, introduced by W.F. Brown, is revisited.

Study on impedance change of strain sensor using magnetostrictive film

The strain sensor using inverse magnetostriction effect has very high sensitivity with strain. In oreder to improve the sensitivity, the study on the energy behavior of the strain sensor is very important. Therefore we fabricated the sensor with magnetostrictive film and tried to examine the relationships between magnetoelastic energy and anisotropy energy in this study. In particular, we focused on the magnetic domain change by magnetoelastic energy and Zeeman energy. Moreover, we examined impedance property of the strain sensor applied strain and magnetic property with strain. As a result, using magnetic domain change observation, we could observe the anisotropy energy change by applied magnetoelastic energy and discuss the relationships between magnetoelastic energy and anisotropy energy.

Depth-dependent fct to fcc strain relaxation in Co xNi 1− x/Cu 3Au(1 0 0) alloy films

Co x Ni 1− x /Cu 3Au(1 0 0) with x ⩽ 11% was prepared at room temperature to study the strain relaxation and their correlation with the spin-reorientation transition. The vertical interlayer distance relaxed from 1.66 Å (fct) to 1.76 Å (fcc) while the thickness increased from 8 ML to 18 ML. Such rapid strain relaxation with thickness was attributed to the larger lattice mismatch between Co x Ni 1− x and Cu 3Au(1 0 0) ( η ∼ −6.5%). The smooth change for crystalline structure was observed during strain relaxation process in which the crystalline structure seems irrespective of the alloy composition. To explain the strain relaxation, a phenomenological model was proposed. We provide a physical picture that the deeper layers may not relax while the surface layer start to relax. This assumption is based on the several experimental studies. Using the strain averaged from all layers of thin film as the volume strain of magneto-elastic anisotropy energy, the interrelation between strain relaxation and spin reorientation transition can be well described in a Néel type magneto-elastic model.

Quantitative model for anisotropy and reorientation thickness of the magnetic moment in thin epitaxially strained metal films

A quantitative mathematical model for the critical thickness of strained epitaxial metal films is presented, at which the magnetic moment experiences a reorientation from in-plane to perpendicular magnetic anisotropy. The model is based on the minimum of the magnetic anisotropy energy with respect to the orientation of the magnetic moment of the film. Magnetic anisotropy energies are taken as the sum of shape anisotropy, magnetocrystalline anisotropy and magnetoelastic anisotropy, the two latter ones being present as constant surface and variable volume contributions. Other than anisotropy materials constants, readily available from literature, only information about the strain in the films for the determination of the magnetoelastic anisotropy energy is required. Application of the epitaxial Bain path allows to express the strain in the film in terms of substrate lattice constant and film lattice parameter, and thus to obtain an approximate closed expression for the reorientation thickness in terms of lattice mismatch. The model can predict the critical spin reorientation transition thickness with surprising accuracy.

The Magnetic Anisotropy of Thin Epitaxial CrO[sub 2] Films Studied by Ferromagnetic Resonance

The magnetic anisotropy of thin epitaxial films of chromium dioxide (CrO2) has been studied as a function of the film thickness by the ferromagnetic resonance (FMR) technique. CrO2 films with various thicknesses in the range from 27 to 535 nm have been grown on (100)-oriented TiO2 substrates by chemical vapor deposition using CrO3 as a solid precursor. In a series of CrO2 films grown on the substrates cleaned by etching in a hydrofluoric acid solution, the FMR signal exhibits anisotropy and is strongly dependent on the film thickness. The magnetic properties of CrO2 films are determined by a competition between the magnetocrystalline and magnetoelastic anisotropy energies, the latter being related to elastic tensile stresses caused by the lattice mismatch between the film and the substrate. In the films of minimum thickness (27 nm), this strain-induced anisotropy is predominant and the easy magnetization axis switches from the [ 001] crystallographic direction (characteristic of the bulk magnet) to the [ 010] direction.

Ｃｏ／Ｐｔ超格子薄膜の弾性定数のひずみ依存性と磁気異方性

In this paper, the contribution of magnetoelastic-anisotropy effect on perpendicular-magnetic anisotropy of Co/Pt superlattice thin films is studied considering the strain-dependent elastic constants. We measured the effective-magnetic-anisotropy energy changing the Pt-layer thickness (2 to 20 A) keeping the Co-layer thickness unchanged (4 A). The effective-magnetic-anisotropy energy changed depending on the Pt-layer thickness and showed a maximum near dPt=12 A. This result is explained by calculating the magnetoelastic-anisotropy energy considering the change of the elastic constants caused by the lattice misfit. We measured anisotropic elastic constants of Co/Pt superlattice thin films by resonance-ultrasound-spectroscopy method coupled with laser-Doppler interferometry and the picosecond laser-ultrasound method. The measured elastic constants showed elastic anisotropy between the in-plane and out-of-plane directions. They agreed with those predicted from the strain-dependent elastic-constant model. The elastic constants show correlations with the perpendicular-magnetic anisotropy.

Magnetic anisotropy of epitaxial Cu/Ni/Cu nanolines

Continuous nickel films grown pseudoepitaxially between copper layers have been shown to have strong perpendicular magnetic anisotropy due to large magnetoelastic and interface magnetocrystalline anisotropy energies. These Cu/Ni/Cu films with tNi=6.9 nm have been patterned into lines approximately 200 nm wide using interferometric lithography and ion milling. Torque magnetometer measurements show the anisotropy of the nanolines to be significantly different from that of the continuous films. The magnetoelastic anisotropy (favoring perpendicular magnetization) decreases in the patterned films due to strain relaxation at the line edges. Although the anisotropy change for this line width is most likely due to shape anisotropy, we anticipate observation of magnetoelastic anisotropy due to strain relief at the edges of the lines at narrower line widths in future work.

Influence of magnetoelastic effects on the coercivity of ultrasoft nanocrystalline alloys

The density of magnetoelastic anisotropy energy in soft nanocrystalline alloys is estimated from stress due to coexistence of the amorphous and crystal phases. The predictions of the model are compared with data from a set of samples with a broad range of crystal fractions.

Stress level in Finemet materials studied by impedanciometry

In this work, a study of the stress relief in Finemet ribbons, Fe73.5Cu1Nb3Si16.5B6, as a function of the annealing temperature is presented. The as melt-spun samples are amorphous and become partially crystallized after annealing at appropriate temperatures. For temperatures TA⩾480 °C the samples are nanocrystalline, with a microstructure composed by α-Fe1−xSix (x∼0.2) crystallites (10 nm average diameter) embedded in an amorphous matrix. Nanocrystallization, associated with stress relief effects, improves the soft magnetic properties of this kind of material. The stress level was quantified using magnetorestriction (measured by SAMR), magnetoelastic anisotropy, and domain wall energy data obtained from impedance spectra measurements. A reduction of the internal stress from 15 to 0.2 MPa was verified when comparing the as-cast to the sample annealed at 580 °C. Improvement of the magnetic softness of the samples was also followed by the increase of the domain wall and magnetization rotation contributions to the overall effective permeability.