Stress-induced Magnetic Anisotropy Research Articles

Three-dimensional stress-induced magnetic anisotropic constitutive model for ferromagnetic material in low intensity magnetic field

Metal magnetic memory (MMM) technique is a promising tool for inspecting early damage in ferromagnetic components due to its high sensitivity to stress in weak geomagnetic field. However, the quantitative analysis methods for the MMM haven’t been sufficiently studied yet for absence of a reasonable constitutive model. A three-dimensional stress-induced magnetic anisotropic constitutive model is proposed in this paper to study magneto-mechanical coupling effect of the MMM. The model is developed in principal stress space and a linear relation between magnetization and magnetic field is employed for low intensity magnetic field. As a result, stress-induced magnetic anisotropy is represented by stress dependence of magnetic permeability in different directions, which is simple and convenient for applications in the MMM technique. Based on the model, the effect of stress on magnetic permeability and surface magnetic field is computed and compared with experimental data for a tensioned ferromagnetic specimen in low intensity magnetic field. The good consistency implies the validity of the proposed model.

Magnetic moment orientation of nano-islands by electrostriction along two directions

This article introduces a new method to realize the 180° magnetic moment reversal of a ferromagnetic and ferroelectric heterostructure through electrostriction-induced magnetic anisotropy. A rectangular magnetic FeAl alloy island with a large magnetostrictive coefficient on a PZN (011) substrate was adopted in our investigation through micromagnetic simulation. Using electrostriction along the [11-1] and [1-11] directions, the magnetic moment was rotated from the long axis of the rectangular island to the direction of the strain and finally reversed to the opposite direction despite the strain sequence. The magnetic moment can be oriented to a certain direction through a certain sequence of strain if a several hundred Oe magnetic field is applied along the short axis of the island. The suitable stress-induced magnetic anisotropy energy and external magnetic field were also investigated. In consideration that a high magnetic field along the short axis leads to small thermal stability of the magnetic moment, the suitable value of stress-induced anisotropy energy is around the critical value where the stress can reverse the magnetic moment without a magnetic field. We compared the stress-induced magnetic reversal processes for same-sized semicircular, elliptical, and rectangular islands and found that the semicircular island can be more easily reversed.

Electric field control of microwave characteristics in composition-graded FeCoTa film grown onto [Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32(011) crystal

The magnetic and microwave properties of a heterostructure composing of a composition-graded FeCoTa film and a [Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32(011) substrate were investigated with respect to a varied applied electric field. For the as-deposited sample in the initial unpoled state, the resonance frequency is 7.2 GHz and it is suddenly increased to 8.4 GHz when the applied electric field reaches 2 kV/cm. Then upon the changing of the electric field from 6 kV/cm to −6 kV/cm, the resonance frequency is varied in the range from 8.4 GHz to 9.2 GHz. The resonance frequency can only be reset back to the lower level with the value of 7.6 GHz through the depolarization process. The results are interpreted in terms of the change in ferroelectric domain structures leading to the variation of the stress-induced magnetic anisotropy, which is experimentally verified by the magnetic and microwave behaviors after depolarization.

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.

Strain-driven fractional spontaneous exchange bias in ferromagnetic/antiferromagnetic thin films with composition-graded ferromagnetic layer

We experimentally demonstrate that the stress-induced magnetic anisotropy in composition-graded ferromagnetic NiFeTa layers can be employed to trigger exchange bias in NiFeTa/IrMn bilayers without using any deposition field or field cooling procedure. In particular, we found that the NiFeTa/IrMn bilayers exhibit double-shifted loops being composed of both negative and positive exchange biases when the deposition angle is low. As the deposition angle is increased, the magnetization curves change into a single-shifted loop with spontaneous exchange bias aligned along negative or positive direction. The results can be explained by the formation of magnetic domain state under the presence of a strong stress-induced magnetic anisotropy and this domain state is pinned upon the deposition of an antiferromagnetic layer. We also studied the dynamic permeability spectra of the films with respect to temperature and discussed the results in relation with the static magnetic properties.

Annealing control of magnetic anisotropy and phase separation in CoFe2O4-BaTiO3 nanocomposite films

Multiferroic heteroepitaxial nanocomposite films of BaTiO3 and CoFe2O4 (CFO) have been grown by pulsed laser deposition employing alternating ablation of two ceramic targets. Films grown at temperatures between 650 °C and 710 °C contain columnar CFO grains about 10–20 nm in diameter embedded in a BaTiO3 matrix. The very strong vertical compression of these grains causes large perpendicular magnetic anisotropy. Post-growth annealing treatments above the growth temperature gradually release the compression. This allows one to tune the stress-induced magnetic anisotropy. Additionally, annealing leads to substantial enhancement of the saturation magnetization MS. Since MS of a pure CFO film remains unchanged by a similar annealing procedure, MS is proposed to depend on the volume fraction of the obtained CFO phase. We suggest that MS can be utilized to monitor the degree of phase separation in nanocomposite films.

Thermal stability of high frequency properties of gradient-composition-sputtered FeCoHf films with and without stripe domains

A systematic study on the thickness dependence of dynamic magnetic properties and their thermal stability behaviors of FeCoHf thin films grown by gradient-composition sputtering technique was carried out. The critical thickness for the formation of stripe domain structures at room temperature was found to be around 120 nm based on the appearance of the multiple resonance peaks and the shape of the magnetization curves. For the films with thicknesses less than 90 nm, the ferromagnetic resonance frequency and in-plane magnetic anisotropy are increased with the increasing of temperature; however, for the films with thicknesses in the range from 90 nm to 120 nm, the ferromagnetic resonance frequency is reduced with temperature and the secondary peak appears as the temperature is raised suggesting an evolution of stripe domains. For the films with stripe domains at room temperature, the ferromagnetic resonance frequency is also decreased with increasing temperature, and in some cases, there is a splitting up of the resonance peaks indicating that there is a change in the stripe domain states when the sample is heated up. All the results are discussed considering the contribution of stress-induced magnetic anisotropy and the increasing of a weak perpendicular magnetic anisotropy.

(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.

Role of deposition magnetic field on magnetic properties and their unusual thermal behaviors of FeCoZr films prepared by gradient composition sputtering

We report our systematic investigation of the temperature-dependent microwave properties of FeCoZr fabricated by gradient-composition sputtering technique with regards to the variation of the Zr deposition power with and without magnetic field applied during deposition. Specifically, we show that the films fabricated by this special method may have a peculiar thermal behavior whereby the magnetic anisotropy is increased with temperature if the induced magnetic anisotropy is sufficiently large. Moreover, our study reveals that the magnetic field applied during deposition process plays a vital role for the increment of the stress-induced magnetic anisotropy, which is useful for enhancing the resonance frequency as well as its thermal stability.

Observation of magnetic anisotropy increment with temperature in composition-graded FeCoZr thin films

Through a systematic investigation, we demonstrate that FeCoZr thin films deposited by gradient composition sputtering technique possess a unique magnetic thermal behavior, namely, the increase in magnetic anisotropy with temperature. Moreover, this gradient composition sputtering technique also offers a viable method to tailor the high-frequency magnetic properties as well as their thermal stability by changing deposition angle and deposition power. The unusual temperature dependence of magnetic anisotropy in such thin films can be interpreted in terms of stress-induced magnetic anisotropy arising from the composition gradient in the films.

Martensitic transformation and magnetic anisotropy in Ni-Mn-Ga/NaCl(001) thin films probed by ferromagnetic resonance

By the ferromagnetic resonance and magnetometry measurements in a broad temperature range, it is found that the 220-fiber textured Ni51.4Mn28.3Ga20.3 (at. %) film of 100 nm thickness deposited onto NaCl(001) exhibits in the martensitic state an easy-plane magnetic anisotropy. This is in a drastic difference with the identical film of the same texture deposited onto Si(001) wafer showing out-of-plane oblique type of anisotropy [Golub et al., J. Appl. Phys. 105, 07A942 (2009)]. The results are discussed in terms of the different martensitic variant selections and stress-induced magnetic anisotropy contributions having opposite signs.

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.

Anomalous Temperature Dependence of Magnetic Anisotropy in Gradient‐Composition Sputterred Thin Films

An abnormal behavior of increasing magnetic anisotropy with temperature in magnetic thin films fabricated by a gradient-composition sputtering technique is observed and consistently confirmed by two independent measurements of static magnetic hysteresis loops and dynamic magnetic permeability spectra. This peculiar behavior is suggested to be due to the physical origin of stress-induced magnetic anisotropy.

Microwave Frequency Performance and High Magnetic Anisotropy of ${\rm Fe}_{70}{\rm Co}_{30}-{\rm B}$ Films Prepared by a Modified Composition Gradient Sputtering

A composition gradient sputtering (CGS) method, in which the doping elements have a gradient distribution from one side to another of the sample, was proposed in our previous work [Li SD, Appl. Phys. Lett., 92 (2008) 092501]. An ultra high magnetic anisotropy field over 500 Oe and ferromagnetic frequency over 7 GHz were obtained in as-deposited FeCoHf films by CGS method due to the stress-induced uniaxial magnetic anisotropy. However, the magnetic properties of the CGS samples are non-uniform, showing a location dependence. In this paper, a modified CGS (MCGS) method was proposed to improve the original CGS method. It is revealed that the MCGS method dramatically improves the uniformity of the high-frequency soft magnetic properties of the as-deposited Fe70Co30-B films. A narrow ferromagnetic resonance frequency (fFMR) range around 5.5 GHz (5.2-5.7 GHz) with a deviation less than 10% and high uniaxial magnetic anisotropy field up to 330 Oe were obtained for as-deposited films with 75 mm in length. As Comparison, the fFMR of the CGS samples is very inhomogeneous and distribute in a broad range from 3.1 to 6.7 GHz with a large deviation as high as 116%. The evident advantages of MCGS samples, such as high UMA and relatively uniform high-frequency characteristics, suggest that the MCGS Fe70Co30-B films are particularly in favor of the integration between magnetic films and RF/microwave components.

Tuning stress-induced magnetic anisotropy and high frequency properties of FeCo films deposited on different curvature substrates

Abstract It is important to control magnetic anisotropy of ferromagnetic materials. In this work, FeCo thin films are deposited on the curving substrates by electrochemical deposition to adjust the stress-induced magnetic anisotropy. The compressive stress is produced in the as-deposited films after the substrates are flattened. A simplified theoretical model of ferromagnetic resonance is utilized to measure the intrinsic magnetic anisotropy field and saturation magnetization. The results show that the stress-induced magnetic anisotropy and the resonance frequency increase with the increase of substrate curvature. The induced easy axis is perpendicular to the compressive stress direction.

Magnetoactive feature of in-situ polymerised polyaniline film developed on the surface of manganese–zinc ferrite

A polyaniline film exhibits magnetoactive properties when deposited on the surface of multidomain particles of manganese–zinc ferrite during in-situ polymerisation of aniline. This is reflected in the increased coercivity and thermomagnetic stability of an in-situ prepared composite compared with bare ferrite and its mixed composite with polyaniline. In addition, the deposition of a polyaniline film results in a shift of the complex-permeability dispersion region towards ultrahigh frequency band. These changes in the magnetic properties of polyaniline-coated ferrite are attributed to the increased value of the inner demagnetisation factor, which results from stress-induced magnetic anisotropy due to the pinning of domain walls appearing on the surface of ferrite. This study is focused on the mechanism of pinning of domain walls and its influence on the magnetic properties of in-situ prepared composites in terms of the molecular mechanism of oxidative polymerisation of aniline. Ferrite stimulates the propagation of polyaniline chains, which start to grow on the domain walls on the ferrite surface. It leads to the pinning of domain walls and restricts their mobility in a magnetic field. The further increase in the coercivity and the resonance frequency of polyaniline-coated ferrite due to film shrinkage after deprotonation of polyaniline makes it obvious that polyaniline coating induces elastic stresses in a ferrite particle that stimulate the growth of the effective magnetic anisotropy. Stress-induced magnetic anisotropy contributes to the reorientation of the magnetisation vectors in domains with respect to the new directions of easy magnetisation, given by magnetoelastic stresses, which leads to complex changes in the magnetic properties of in-situ prepared composites.

Anisotropic exchange coupling and stress-induced uniaxial magnetic anisotropy in Fe/GaAs(001)

The magnetization reversal process within the first two iron layers at the Fe/GaAs(001) interface is found to be different and independent from the Fe thin film bulk as measured by magnetic second-harmonic generation and magneto-optical Kerr effect. The interface magnetization is largely noncollinear from the bulk with an abrupt magnetic boundary and an anisotropic exchange coupling stiffness, weak interlayer coupling but relatively strong intralayer stiffness. In contrast, Fe/GaAs(110) exhibits a rigid coupling between interface and bulk magnetization suggesting that the interfacial bonding structure can dramatically change the nature of the exchange coupling. Moreover, the uniaxial magnetic anisotropy in Fe/GaAs(001) extends from the interface to the first 5 nm in the Fe film and is induced by stress. These results are also relevant to other magnetic/nonmagnetic interfaces with abrupt chemical bond structures.

Stress-induced magnetic anisotropy in Fe-based nanocrystalline alloy with addition of 1–5 at.% Cr

Magnetic properties and thermal stability of the nanocrystalline Fe73.5−xCrxSi13.5B9Nb3Cu1 (x=0, 1, 2, 3 and 5%) ribbons obtained by rapid quenching after thermal- and stress-annealing at 520°C were investigated with the aim to produce materials with new functional possibilities. In this study it is shown that in the alloys with 1–5at.% Cr, just as in Finemet alloy without Cr, a magnetic anisotropy can be induced in the course of stress-annealing and its easy magnetization axis is perpendicular to the direction of tensile stress, i.e. perpendicular to long side of ribbon. The curves of the magnetization reversal measured along the ribbon axis were inclined, indicating a constant value of a magnetic permeability in a wide range of magnetic fields. The results show that substitution of Fe for Cr improves the thermal stability of the alloy. The higher the Cr-content, the slower the process of the induced anisotropy reduction in the course of annealing at 520°C. Cr-containing iron-based nanocrystalline materials can be therefore proposed for the study as MI sensitive elements at enhanced temperatures.

Stress-induced magnetic and structural anisotropy of nanocrystalline Fe-based alloys

The structural anisotropy of Fe–Si–B–Nb–Cu nanocrystalline alloys annealed under tensile stress was studied by x-ray diffraction techniques with transmission geometry. A clear difference was observed in the peak positions of the Fe–Si crystals under two different conditions: with the diffraction vector parallel or perpendicular to the applied stress. The strains calculated from the anisotropy of the peak positions show a linear response to the applied stress, independent of Si content, indicating that the observed structural anisotropy is due to a quenching of the elastic strain, not in the directional ordering of the Fe–Si pair. The induced magnetic anisotropy energy is well explained by the residual strains and their magnetostrictions.

Study on Physical Mechanism of Metal Magnetic Memory Technique

The evaluation of stresses in engineering structures to provide early indications of stress status is a fast growing area in non-destructive testing. Metal magnetic memory technique is the magnetic stress measurement technique for ferromagnetic materials using passive magnetic fields to monitor changes in the magnetic properties of materials. This paper studied the physical formation process of metal magnetic memory effect. This paper studied the physical mechanism between stress and magnetic field in metal magnetic memory effect, through the influence of stress-induced magnetic anisotropy on magnetization process of ferromagnetic crystal.