Uniaxial Magnetic Anisotropy Field Research Articles

Ultrahigh in-plane uniaxial magnetic anisotropy of amorphous FeCoHf composition gradient films

Amorphous FeCoHf films with a Hf composition gradient were prepared at room temperature. The composition gradient sputtering technique was used to control the composition gradient of the doped element Hf by changing the deposition power of Hf. Interestingly, in the as-deposited FeCoHf films, an in-plane uniaxial magnetic anisotropy field of up to 640 Oe was achieved, and the resonance frequency was 6.5 GHz. The large anisotropy field can be attributed to the high sensitivity of the amorphous FeCoHf films to the composition gradient. The ultrahigh anisotropy exhibited by FeCoHf films at room temperature holds significant technological potential for various applications.

The effect of anisotropic field on magnon dispersion of antiferromagnetic metal fluoride materials

This article investigates the dynamics of spin waves in two sublattice antiferromagnetic (AFM) system spins’ interaction and magnon dispersion relation. The analysis is done starting with a standard model that includes a uniaxial magnetic anisotropy field. Quantum field theory is employed in formulating the problem, and double-time temperature-dependent Green function technique is used to obtain magnon dispersion, whereby random phase approximation is considered to decouple and diagonalize the higher order terms. At low temperatures and long wavelength approximation, dispersion of uniaxial symmetric AFM crystal lattice of metallic fluoride materials, such as MnF2, FeF2, and RbMnF3, is analyzed for illustration. Our findings indicate that as the anisotropic field increases, the magnon dispersion vs wave vector k gradually varies, attempts linearity from being curved, and attains a sinusoidal structure when extended further in the first Brillouin zone. Perhaps, these results are useful to understand the feature of magnon dispersion of stable similar AFM materials for practical application.

Magnetocrystalline anisotropy study of Co-substituted M-type strontium hexaferrite single crystals

The study on the magnetocrystalline anisotropy (MA) of La–Co co-substituted strontium hexaferrite (La–Co SrM) shows a joint effect of Fe2+ and Co2+ ions in the enhancement of MA. Since the role of Fe2+ single ion has been studied with La-substituted strontium ferrite, in this work, Co-substituted strontium hexaferrite SrFe12-xCoxO19 (Co-SrM) single crystals were successfully grown for 0 ≤ x ≤ 0.31 by the Na2CO3 flux method to elucidate the anisotropy of Co2+ single ions. Co-substitution in this preparation condition has a limit solubility of 0.31 and enhances uniaxial magnetic anisotropy field HA by 19% for 0.03 = x ≤ 0.11, with a mere loss of 7% of saturation magnetization MS at 5 K. The enhanced HA of Co-SrM is reported for the first time, even higher than that of La–Co SrM, which is suitable to be used as permanent magnets in this concentration range. But with the further substitution of Co, the planar anisotropy of x = 0.31 was observed at 5 K. The potential nonlinear magnetic structure of Co-SrM remains to be discovered for magnetoelectric effects. This work is also of great significance as a complement to the magnetocrystalline anisotropy study of La–Co SrM.

Study of growth and broadband FMR spectroscopy in PLD grown Y3Fe5O12/Gd3Ga5O12 thin films

We report the structural and magnetization dynamics of pulsed laser ablated Y3Fe5O12 (YIG) thin films grown on gadolinium gallium garnet (GGG[110]) substrate. The co-planar waveguide ferromagnetic resonance measurement was performed to study the thickness and inhomogeneity effect on damping constant. We also estimated the effective demagnetization () value which was lower than that of single-crystalline bulk YIG. A detailed line width analysis revealed the significant two-magnon scattering and inhomogeneity contribution to damping which varied for different thickness films. The Gilbert damping constant (α) of the grown film was found to be lowest in the case of 100 nm film (≈3 × 10−4), and the corresponding inhomogeneous broadening (ΔH O) was recorded to be 77 Oe. Further angular measurements on 100 nm thin film revealed the presence of strong uniaxial magnetic anisotropy field of 735 Oe at 10 GHz RF frequency.

Investigation on interfacial effect of CoFeB/GaAs heterostructure

Interfacial effect of amorphous cobalt-iron-boron (Co60Fe20B20) films deposited on GaAs(001) by DC magnetron-sputtering has been precisely studied. In-plane uniaxial magnetic anisotropy (UMA) as a significant magnetic property has been found in Co60Fe20B20/GaAs heterostructure and the UMA field (Hu) of (∼75 Oe) is achieved. Magnetic Schottky barrier contact has been achieved by current-voltage (I–V) characteristic through the interface with a barrier height of 0.72 eV, which is an appropriate for tunneling injection of spin current from ferromagnet to semiconductors in spin-injection devices.

Magnetic Properties of Permalloy Thin Film Edges

The paper presents the results of ferromagnetic resonance (FMR) spectrometry of magnetic properties of nanocrystalline thin films obtained by magnetron sputtering of permalloy targets of various composition (NixFe1–x, x = 0.6–0.85). The behavior of the main magnetic properties of the thin film edges is analyzed. Near the film edges, not only the fluctuation of the uniaxial magnetic anisotropy field is observed, but also a drastic widening of the FMR line and the decrease in the effective saturation magnetization.

Experimental study of the magnetic characteristics of nanocrystalline thin films: the role of edge effects

Magnetic characteristics and their spatial distribution of magnetron sputtered nanocrystalline NiFe thin films of various compositions were investigated by ferromagnetic resonance (FMR) and magneto-optical Kerr effect microscopy. A sharp increase in the FMR linewidth and a strong deviation of the uniaxial magnetic anisotropy field were observed near the film edges. It was shown that the observed magnetic anisotropy behavior can be explained by assuming that besides the field-induced uniaxial magnetic anisotropy an additional source of the uniaxial anisotropy near the film edges exists, with the easy axis parallel to the edges. The possible origins of this additional contribution were discussed.

Annealing influence on magnetic anisotropies of CoFe thin films

Post-annealing effect on the magnetic anisotropies of cubic CoFe films epitaxially grown on MgO (001) substrates are investigated. X-ray diffraction patterns reveal that the crystallization degree gradually improves with the increase of annealing temperature (Ta), which results in obvious enhancement in both the uniaxial (HU) and biaxial magnetic anisotropy fields. Magnetic hysteresis loops of the unannealed sample show two equivalent easy axes along the CoFe [110] and [11¯0] directions, being in accord with the observed fourfold symmetry of angular remanent magnetization (ARM) curve. Nevertheless, with the increase of Ta, the two easy axis loops become inequivalent due to the increased HU along [110] direction, thus giving rise to a two-step switching behavior for the [11¯0] direction loop at Ta>350°C and the ARM curve transformation from fourfold to twofold symmetry. This work provides a deep insight and an effective approach to control the magnetic anisotropies and magnetization states for practical applications.

Influence of Deposition Cycle and Magnetic Annealing on High-Frequency Magnetic Properties of the [Co90Fe10/Ta]<italic>n</italic> Multilayer Thin Films

In this paper, a series of [Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> /Ta] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> multilayer thin films with various deposition cycles n were prepared by magnetron sputtering. The crystal structure, top-surface topography, and static and dynamic magnetic properties of [Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> /Ta] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> multilayer thin films were investigated systematically. The results showed that the deposition cycle n has slight impact on the high-frequency magnetic performance of the multilayer thin films except damping coefficient α and real part of permeability μ'. Moreover, we studied the influence of magnetic annealing temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> ) on high-frequency soft magnetic properties of [Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> /Ta] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> multilayer thin films. It was found that saturation magnetization, coercivity, in-plane uniaxial magnetic anisotropy field, damping coefficient, and real part of permeability were all highly dependent on T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> . When T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> = 250 °C, the [Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> /Ta] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> multilayer thin film exhibited a relatively good comprehensive performance: saturation magnetization 4πM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = 13.06 kG, in-plane uniaxial magnetic anisotropy fields H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> = 42 Oe, easy-axis coercivity H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ce</sub> = 2.8 Oe, ferromagnetic resonance frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 2.25 GHz, and real permeability μ' = 255.

Electric-regulated enhanced in-plane uniaxial anisotropy in FeGa/PMN–PT composite using oblique pulsed laser deposition

The FeGa film with in-plane uniaxial magnetic anisotropy was fabricated onto different oriented single-crystal lead magnesium niobate–lead titanate using oblique pulsed laser deposition. An enhanced in-plane uniaxial magnetic anisotropy field of FeGa film can be adjusted from 18 Oe to 275 Oe by tuning the oblique angle and polarizing voltage. The competitive relationship of shape anisotropy and strain anisotropy has been discussed, which was induced by oblique angle and polarizing voltage, respectively. The (100)-oriented and (110)-oriented PMN–PT show completely different characters on voltage-dependent magnetic properties, which could be attributed to various anisotropy directions depended on different strain directions.

The evolution of in-plane magnetic anisotropy in CoFeB/GaAs(001) films annealed at different temperatures

A considerable in-plane uniaxial magnetic anisotropy (UMA) field (Hu ∼ 300 Oe) could be achieved when the amorphous CoFeB film was deposited on the GaAs(001) wafer by magnetron-sputtering after proper etch-annealed procedure. In order to get deep insights into the mechanism of the UMA, the film was annealed at different temperatures and the evolution of the in-plane magnetic anisotropy was investigated carefully. With increasing the annealing temperature (TA), the UMA could be maintained well when TA reached 250°C, but became very weak at 300°C. However, when TA was elevated to 400°C, another UMA (Hu ∼ 130 Oe) was built accompanied with a fourfold magnetic anisotropy with its strength of about 50 Oe. In terms of the magnetic anisotropy evolution along with TA, the anelastic strain, which is thought to be resulted from the interfacial interaction between CoFeB and GaAs, may play a dominant role in producing the enhanced UMA based on the ‘bond-orientational’ anisotropy (BOA) model.

Annealing effect on elastic, magnetic and magnetoelastic properties of CoFeB thin films on polymer substrate

We have studied the magnetomechanical properties of thin films deposited on polyimide substrate. Particularly, we studied the effect of annealing in the accessible temperature range (0–375 °C) allowed by the polymer substrate. Complementary techniques have been used to characterize the elastic, magnetic and magnetoelastic properties of annealed samples (Brillouin light scattering and tensile tests combined with in situ ferromagnetic resonance). Below 200 °C, no significant evolutions of the properties have been found excepted the magnetic damping parameter. In contrast, above 200 °C, strong variations are observed (+15% for Young’s modulus, for magnetostriction coefficient and +500% for the uniaxial magnetic anisotropy field). This is in correlation with the x-ray diffraction peak sharpening observed in the studied thin films. This is most probably due to exceeding of the glass transition temperature of the thin film. The complete data analysis allowed an estimation of the thermal stability of alloy thin films.

Gilbert damping in CoFeB/GaAs(001) film with enhanced in-plane uniaxial magnetic anisotropy

A 3.5 nm amorphous CoFeB film was sputtered on GaAs (001) wafer substrate without applying magnetic field during deposition, and a significant in-plane uniaxial magnetic anisotropy (UMA) field (Hu) of about 300 Oe could be achieved. To precisely determine the intrinsic Gilbert damping constant (α) of this film, both ferromagnetic resonance (FMR) and time-resolved magneto-optical Kerr effect (TRMOKE) techniques were utilized. With good fitting of the dynamic spectra of FMR and TRMOKE, α is calculated to be 0.010 and 0.013, respectively. Obviously, the latter is 30% larger than the former, which is due to the transient heating effect during the TRMOKE measurement. In comparison with ordinary amorphous CoFeB films with negligible magnetic anisotropies, α is enhanced significantly in the CoFeB/GaAs(001) film, which may be mainly resulted from the enhanced spin-orbit coupling induced by the CoFeB/GaAs interface. However, the significant in-plane UMA plays minor role in the enhancement of α.

Monte-Carlo calculation of the coercive force and phase transitions in ensembles of Stoner-Wohlfarth particles with exchange interactions

A Monte-Carlo (MC) method is used to study the magnetization of an ensemble of Stoner-Wohlfarth particles with interparticle interactions of a ferromagnetic type. A modification of the procedure for the MC calculation is proposed to speed up the calculations. The magnetization of the ensemble is studied at different temperatures and for different ratios of the exchange field of the interparticle interaction and the uniaxial magnetic anisotropy field of the particles. It is shown that Neel relaxation has a significant influence on the coercive properties of the ensemble if the interparticle exchange field does not exceed the anisotropy field of the particles. It is also found that, at low temperatures, the coercive properties of Stoner-Wohlfarth particles with exchange interactions are related to the loss of stability of the orientation of the average magnetic moment vector of the particles. At high temperatures, the coercivity of the particle ensemble is associated with the complete loss of stability of the superferromagnetic state. The critical fields and critical temperatures for an ensemble of Stoner-Wohlfarth particles with exchange interactions are analyzed.

High uniaxial magnetic anisotropy of the Fe1−xSix films synthesized by MBE

The structure and the magnetic anisotropy of the films obtained by simultaneous deposition of iron and silicon on n-Si(111) 7×7 at 130°C are investigated. It is found the uniaxial magnetic anisotropy field for the Fe1−xSix films with x=0.25 (Fe3Si stoichiometric ratio) deposited on Si(111) 7×7 depends on both the surface miscut angle and the oblique sputtering direction and changes from 0.82Oe up to 117.26Oe.

Dynamic magnetic characteristics of obliquely sputtered Co2FeSi film with ultrahigh in-plane uniaxial anisotropy

We performed systematically studies on the magnetostatic and magnetodynamic properties of obliquely deposited Co2FeSi thin films. By varying the oblique deposition angle of Co2FeSi films, we induced a large in-plane uniaxial magnetic anisotropy field with the maximum value of 626.7 Oe at oblique angle of 39°, which significantly enhanced its zero-field ferromagnetic resonance (FMR) frequency up to 10.8 GHz. The magnetodynamic parameters such as Gilbert damping factor and exchange stiffness of Co2FeSi films were determined from the uniform FMR mode and the first perpendicular standing spin-wave, respectively. It is found that the Gilbert damping factor can be easily tuned from 0.006 to 0.013 by changing oblique deposition angle, whereas the exchange stiffness stays almost constant. These Co2FeSi films with tunable magnetic properties might be a good candidate for applications in both conventional and spintronics microwave devices.

Magnetic properties of [FeCoSiN/SiNx]18 multilayer thin films for applications in GHz range

[FeCoSiN/SiNx]18 multilayer thin films with different SiNx layer thickness (t) ranging from 0.75 to 4 nm were fabricated by reactive magnetron co-sputtering without applying an external induced magnetic field. The grain size, morphology, electrical properties, and static and dynamic magnetic properties of [FeCoSiN/SiNx]18 multilayer thin films were investigated systematically. The results indicated that SiNx layer thickness had a profound impact on the physical properties of the multilayer thin films. The in-plane uniaxial magnetic anisotropy field (from 114 ± 21 to 163 ± 14 Oe), ferromagnetic resonance frequency (from 4.09 to 4.64 GHz) and resistivity (from 188 to 333 μΩ cm) could be tailored effectively by adjusting the SiNx layer thickness from 0.75 to 4 nm. Moreover, when the SiNx layer thickness reached 2 nm, the continuous growth of FeCoSiN polycrystalline layers was to be interrupted completely and it would result in a minimum grain size of 4.9 ± 0.7 nm. The root mean square roughness of multilayer thin films also acquired a minimum value of 0.8 nm and the corresponding easy axis coercivity achieved a minimum value of 2.8 ± 0.1 Oe.

Interfacial Dzyaloshinskii-Moriya interaction studied by time-resolved scanning Kerr microscopy

We investigate the influence of the interfacial Dzyaloshinskii-Moriya interaction (DMI) on the propagation of Damon-Eshbach spin waves in micrometer-sized Pt(2 nm)/Co(0.4 nm)/Py(5 nm)/MgO(5 nm) stripes. We use time-resolved scanning Kerr microscopy to image the spin waves excited by a microwave antenna and to directly access their dispersion. The presence of an interfacial DMI manifests itself in an asymmetry in the dispersion for counterpropagating spin waves which reverses sign upon reversal of the direction of the externally applied magnetic field. From this asymmetry we deduce the strength of the interfacial DMI. Micromagnetic simulations confirm that the observed difference in the wave numbers and the signature of the asymmetry are characteristic for the occurrence of an interfacial DMI at the Pt/Co interface and cannot be explained by the uniaxial perpendicular magnetic anisotropy field originating from the same interface.

Film Thickness Gradient-Induced Magnetic Anisotropy and Ferromagnetic Resonance in Fe&lt;sub&gt;56&lt;/sub&gt;Co&lt;sub&gt;24&lt;/sub&gt;B&lt;sub&gt;20&lt;/sub&gt; Amorphous Films Prepared by Pulse Laser Deposition

The ferromagnetic resonance frequency f FMR of soft magnetic films (SMFs) can be expressed by the Kittel equation. Clearly, high 4pM S and H K are needed to achieve a high f FMR in SMFs. Previous research on achieving high f FMR SMFs has mostly been focused on enhancing uniaxial magnetic anisotropy field H K since it is relatively easier to be enhanced by 1–2 orders of magnitude, compared to saturation magnetization that is capped at 24.5 kGs at room temperature1. Magnetron sputtering of SMFs in in-situ magnetic fields and/or subsequent magnetic annealing after deposition have been widely employed for inducing a uniaxial magnetic anisotropy2. However, the induced uniaxial magnetic anisotropy fields are usually in the range of <50 Oe, which leads to limited ferromagnetic resonance frequency of < 3 GHz for most of the metallic magnetic films3. Several different approaches have been investigated for achieving high uniaxial magnetic anisotropy in SMFs, such as composition gradient sputtering4, oblique sputtering5, facing target sputtering6, exchange coupling7, and magnetoelectric coupling8, etc.

Electric field induced natural resonance and magnetic damping in FeCo/ Pb (Mg1/3Nb2/3) O3-PbTiO3 heterostructures

We demonstrated that magnetic damping and natural resonance frequency could be modulated by the electric field in an FeCo layer on Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) heterostructures by the microstrip method with a vector network analyzer. Strain mediated natural resonance increased from 0.8 to 2 GHz with increasing the electric field from 0 to 12.5 kV cm−1. Furthermore, the magnetic damping factor increased from 0.008 to 0.225, which resulted from magnetization precession under a microwave field and interface charge mediated spin current due to the spin screening effect. The results were also validated by the measurements of ferromagnetic resonance, which was also clear from analysis of the intrinsic and extrinsic contributions to the magnetic damping. In addition, in-plane uniaxial static magnetic anisotropy field was also modulated from 8 to 200 Oe with a different electric field.