Anisotropy Field Hk Research Articles

Regulation of static and dynamic magnetic properties of amorphous FeCoZr composition gradient films by Zr doping

A series of amorphous FeCoZr composition gradient monolayer films with varying Zr contents was prepared on the Si(100) substrate using RF magnetron sputtering. The effects of the Zr sputtering power PZr on the static and dynamic magnetic properties of FeCoZr films were systematically investigated. The results demonstrate that the introduction of the Zr element as a composition gradient into FeCo films not only improves the soft magnetic properties of the films but also enhances their in-plane uniaxial magnetic anisotropy. In particular, the doping of Zr elements leads to the destruction of FeCo lattice, inducing a transformation of the films from polycrystalline to amorphous state, resulting in a significant decrease in coercivity (Hc reduced by 82%) and surface roughness (Ra reduced by 78%). In addition, as PZr increases from 30 to 70 W, the anisotropy fields Hk of the films increase from 128 to 340 Oe, and the resonance frequency fr increases from 4.24 to 5.23 GHz. By fitting the permeability spectrum using the LLG equation, it is found that FeCoZr composition gradient films exhibit a lower damping coefficient α of around 0.011–0.014, indicating the reduction of energy loss during magnetization dynamics. These findings highlight the potential applications of FeCoZr composition gradient films in the field of high-frequency microwaves.

Experimental investigation of the effect of topological insulator on the magnetization dynamics of ferromagnetic metal: and heterostructure

We have studied the spin-pumping phenomenon in ferromagnetic metal (FM) ()/topological insulator (TI) () bilayer system to understand magnetization dynamics of FM in contact with a TI. TIs embody a spin–momentum-locked surface state that spans the bulk band gap. Due to this special spin texture of the topological surface state, the spin-charge interconversion efficiency of TI is even higher than that of heavy metals. We evaluated the parameters like effective damping coefficient (), spin-mixing conductance () and spin current density () to demonstrate an efficient spin transfer in heterostructure. To probe the effect of the topological surface state, a systematic low-temperature study is crucial as the surface state of TI dominates at lower temperatures. The exponential increase of for all different thickness combinations of FM/TI bilayers and the enhancement of effective damping coefficient () with lowering temperature confirms that the spin chemical potential bias generated from spin-pumping induces spin current into the TI surface state. Furthermore, low-temperature measurements of effective magnetization () and magnetic anisotropy field (Hk ) showed anomaly around the same temperature region where the resistivity of TI starts showing metallic behavior due to the dominance of conducting TI surface state. The anomaly in Hk can result from the emerging exchange coupling between the TI surface state and the local moments of the FM layer at the interface without any long-range ferromagnetic order in TI at the interface.

Enhanced sensitivity and thermal tolerance in tunnel magnetoresistance sensor using Ta-doped CoFeSiB soft magnetic layer

We developed a tunnel magnetoresistance (TMR) sensor consisting of a CoFeB/MgO/CoFeB magnetic tunnel junction (MTJ) and a CoFeSiB amorphous soft magnetic layer. This multilayer structure is promising for a high-sensitivity sensor because a giant TMR ratio of the MTJ and a small anisotropy field Hk of the free layer can be obtained simultaneously. However, the soft magnetic properties of the CoFeSiB layer disappear when it is annealed at above the crystallization temperature (around 300 °C), which determines the thermal tolerance of the TMR sensor and limits improvements to the sensor's sensitivity and applications. In this study, we doped the CoFeSiB layer with various amounts of Ta to raise its crystallization temperature. TMR sensors using the Ta-doped CoFeSiB layers showed thermal tolerance to annealing temperatures above 425 °C, whereas the sensor with the undoped CoFeSiB layer was tolerant to annealing temperatures up to 325 °C. As well, the Ta doping effectively reduced Hk of the CoFeSiB layer, which resulted in a sensitivity of 50%/Oe, over three times higher than the sensor with the undoped CoFeSiB layer. These results pave the way toward next-generation TMR sensors having higher sensitivity and wider applicability.

Magnetic Properties and Microstructure of FePt(BN, X, C) (X = Ag, Re) Films.

A sputtered FePt(BN, Re, C) film, here boron nitride (BN), was compared to a reference sample FePt(BN, Ag, C). Intrinsically, these films illustrate a high anisotropy field (Hk) and perpendicular magnetocrystalline anisotropy (Ku),although the reference sample shows a higher value (Hk = 69.5 kOe, Ku = 1.74 × 107 erg/cm3) than the FePt(BN, Re, C) film (Hk = 66.9 kOe, Ku = 1.46 × 107 erg/cm3). However, the small difference in the anisotropy constant (K2/K1) ratio presents a close tendency in the angular dependence of the switching field. Extrinsically, the out-of-plane coercivity for the reference sample is 32 kOe, which is also higher than the FePt(BN, Re, C) film (Hc = 27 kOe), and both films present lower remanence (Mr(parallel)/Mr(perpendicular) = 0.08~0.12), that is, the index for perpendicular magnetic anisotropy. The higher perpendicular magnetization for both films was due to highly (001) textured FePt films, which was also evidenced by the tight rocking width of 4.1°/3.0° for (001)/(002) X-ray diffraction peaks, respectively, and high-enough ordering degree. The reference sample was measured to have a higher ordering degree (S = 0.84) than FePt(BN, Re, C) (S = 0.63). As a result, the Ag segregant shows stronger ability to promote the ordering of the FePt film; however, the FePt(BN, Re, C) film still has comparable magnetic properties without Ag doping. From the surface and elemental composition analysis, the metallic Re atoms found in the FePt lattice result in a strong spin-orbital coupling between transition metal Fe (3d electron) and heavy metals (Re, Pt) (5d electron) and we conducted high magnetocrystalline anisotropy (Ku). Above is the explanation that the lower-ordered FePt(BN, Re, C) film still has high-enough Ku and out-of-plane Hc. Regarding the microstructure, both the reference sample and FePt(BN, Re, C) show granular structure and columnar grains, and the respective average grain size and distributions are 6.60 nm (12.5%) and 11.2 nm (15.9%). The average widths of the grain boundaries and the aspect ratio of the columnar grain height are 2.05 nm, 1.00 nm, 2.35 nm, and 1.70 nm, respectively.

New Manufacturing Process for Granular Texture Management in Polycrystalline BaM Hexaferrites through the Goethite Crystallite Laths Aspect Ratio, and a Specialized Law of Approach to the Magnetic Saturation for Partly Polarized Uniaxial Materials

This study is aimed at the manufacture and the magnetic properties of polycrystalline M-type hexaferrites BaFe12O19 (barium ferrite, or BaM) materials of different magnetic texturing grades, going from a random distribution of the BaM crystallites to their almost complete stacking. Our target is to optimize the value of reduced-remanence magnetization MR/MS, which is among the most significant features of the self-polarized materials. In this study, we focus on the role played by the precursors hematite (isotropic spherical shape) and goethite (anisotropic lath shape). Therefore, 11 samples with a flat cylinder shape are fabricated, with an increasing hematite to goethite ratio. We demonstrate that this ratio drives the texturization of the samples by producing self-polarized materials with different MR/MS from the simple green compaction of the precursors, followed by a heat treatment. Most importantly, our study reveals the orientation of BaM particles after compaction; therefore, MR/MS, is strongly influenced by the aspect ratio of the lath-shaped goethite crystallites. Additionally, we show that finer goethite crystallites yield higher-value MR/MS. We optimize the aspect ratio of the goethite crystallites for an improved BaM texture. The optimization of the morphology of the goethite crystallites leads to an increase in the BaM particles’ orientation and stacking. The salient outcome of this work, which distinguishes it significantly from recent works, is that the particles stacking increases with the value of the shape factor η (defined as the ratio of the diameter of the laths to their length) of the goethite, evidenced by XRD results. The Rietveld refinements of powder diffractograms and the measured magnetic properties reveal a particle-stacking enhancement caused by not only the ratio of hematite: goethite but mainly by an optimal aspect ratio of the goethite crystallites. Based on this study, the BaM materials are further manufactured with a controlled magnetic texture; thus, they are partly self-polarized. They show reduced-remanence magnetization MR/MS varying from 0.5 and 0.81, while the angular dispersion of the BaM particles’ easy axis of magnetization varies from 60° to 10°. The magnetic properties of the samples are further studied in microwave experiments, from which the value of the magnetocrystalline anisotropy field HK = 16.6 kOe is deduced. The first magnetization curves of each sample are obtained using a VSM. A law of approach to the saturation suitable for the case of the uniaxial polycrystalline materials, and for which the particle stacking is only partial, is proposed for the fitting of the magnetization process. It is suggested that by using the proposed law with a known magnetocrystalline anisotropy constant K1, the angular grain-dispersion can be found.

Microstructure, magnetic domains and magnetic properties of Ti/Fe/Ni81Fe19/Fe/Ti multilayer films by obliquely deposition

The metallic magnetic thin films are widely used in high-frequency magnetic devices, the reliability of which greatly depends on the saturation magnetization (Ms) and resonance frequency (fr) of the films. However, increasing the operating frequency of the magnetic thin film is extremely challenging. This study investigates the microstructure, magnetic domains and magnetic properties of obliquely deposited Ti/Fe/Ni81Fe19/Fe/Ti multilayer films. The coercivity distribution of the deposited films is investigated by first order reversal curve (FORC) measurements. The result of static magnetic properties revealed the in-plane uniaxial anisotropy with a high anisotropy field (Hk) up to 495 Oe. A magneto-optical Kerr microscope image displayed the multi-step magnetization reversal processes at different oblique angles. Complex permeability spectra indicated that the resonance frequency increases from 1.27 to 4.71 GHz as the deposition angle is increased from 0° to 25°. Thus, Ti/Fe/Ni81Fe19/Fe/Ti multilayer film with tunable magnetic performances is one of the good candidate materials for microwave devices.

Substrate orientation dependent characteristics of half-metallic and metallic superlattices [La0.7Sr0.3MnO3/LaNiO3]10

We report a detailed study on the orientation dependent growth characteristics, electronic structure, transport, magnetic, and vibrational excitations in atomically flat interfaces of [La0.7Sr0.3MnO3/LaNiO3]10 superlattices (SLs) coherently grown on (001/011/111)-SrTiO3 substrates by the pulsed laser deposition technique. X-ray reflectometry confirms the periodic superlattice stacks from the Kiessig interference fringes and well-defined even interfaces between the nickelate and manganite layers. A complex local atomic environment across the interfaces was noticed, yet trivalent La, divalent Sr, and mixed valent Ni2+/3+ and Mn3+/4+ electronic states prevail at the core level with enhanced relative intensity ratio of the Mn ions in the superlattices grown on (111) oriented SrTiO3 substrates as compared to those grown on (001) and (011) oriented SrTiO3. The temperature (5≤T≤300K) dependence of electrical resistivity ρ(T) analysis reveals 3D variable range hopping model [ρ(T)=ρ0exp⁡(T0/T)(1/4)] with large magnitude of hopping energies (≥40 meV) for the SL-111 system associated with the high energy gap developed by the accumulation of disorderness in the individual constituents of polar layers. Moreover, all SL systems exhibit reduced ferromagnetic ordering temperatures (67≤TC≤110K) with a low-temperature anomaly (11.4≤T∗≤22K) and a substantial enhancement in the effective exchange interaction (Jeff∼3.52meV) having altered ground state-spin configuration S∼1/2 different from S=3/2 of La0.75Sr0.25MnO3. Nevertheless, the SL-011 system exhibits large anisotropy field HK∼18kOe and cubic anisotropy constant K1∼9.3×103J/m3 in comparison to the other two orientations. The second order two-phonon interaction driven by the local polaronic distortion causes significant changes in the vibrational excitations of the investigated system. Nonetheless, most of the Raman modes follow the substrate-induced, highly oriented epitaxial growth pattern except for two modes ν4 (326cm−1) and ν8 (728cm−1), which slightly differ in the case of SL-111 superlattices.

Tailoring Magnetic and Transport Anisotropies in Co100−x–Cux Thin Films through Obliquely Grown Nano-Sheets

The magnetic and transport properties of pulsed laser-deposited Co100−x–Cux thin films were tailored through their nano-morphology and composition by controlling for the deposition geometry, namely normal or oblique deposition, and their Cu content. All films were composed of an amorphous Co matrix and a textured growth of Cu nanocrystals, whose presence and size d increased as x increased. For x = 50, all films were superparamagnetic, regardless of deposition geometry. The normally deposited films showed no in-plane magnetic anisotropy. On the contrary, controllable in-plane uniaxial magnetic anisotropy in both direction and magnitude was generated in the obliquely deposited films. The magnetic anisotropy field Hk remained constant for x = 0, 5 and 10, Hk ≈ 35 kAm−1, and decreased to 28 and 26 kAm−1 for x = 20 and 30, respectively. This anisotropy had a magnetostatic origin due to a tilted nano-sheet morphology. In the normally deposited films, the coercive field Hc increased when x increased, from 200 (x = 0) to 1100 Am−1 (x = 30). In contrast, in obliquely deposited films, Hc decreased from 1500 (x = 0) to 100 Am−1 (x = 30) as x increased. Activation energy spectra corresponding to structural relaxation phenomena in obliquely deposited films were obtained from transport property measurements. They revealed two peaks, which also depended on their nano-morphology and composition.

Self-biased optical mode ferromagnetic resonance beyond 22 GHz in artificial exchange coupled trilayers

The ferromagnetic resonance frequency (fr) determines the maximum operating frequency of magnetic devices, nevertheless, it is very difficult to increase the fr(H=0) above 10 GHz by simply increasing the magnetic anisotropy field HK. In this study, a series of FeCoB/Ru/FeCoB sandwich trilayers with strong antiferromagnetic coupling were prepared by a compositional gradient sputtering method. As a result, the fr(0) increases from 13.69 to 22.68 GHz with the increase of B content, which can be attributed to the strong interlayer exchange coupling. In addition, a dramatic frequency shift over 16 GHz along easy-axis direction can be achieved simply via transition of magnetic configuration using a small magnetic field of the order of 100 Oe. This study provides an effective fabrication method to prepare self-biased soft magnetic films with ultrahigh resonance frequency for today’s microwave integrated circuits.

Heusler compound [formula omitted]FeGa nanoarchitectures

Heusler type one-dimensional nanogeometries Ni2FeGa have been fabricated in the nanopores of 150 nm AAO (Anodic Aluminium Oxide) templates using simple and low-cost electrodeposition technique at room temperature. The structure of prepared nanoarchitectures is face centered cubic (fcc) with a secondary γ phase. Magnetic properties have been studied at room temperature as well as at low temperatures. It has been found that saturation magnetization MS decreases as temperature rise up. The nanowires have maintained ferromagnetic behavior from 5 K to 350 K. The Ni2FeGa nanowires (NWs) and nanotubes (NTs) have the same saturation magnetization, the difference of the resonance field Hr is mainly attributed to the difference of the anisotropy field Hk under the fixed microwave frequency. Hr for the NT sample is smaller than that for the NW sample.

Characterisation of magnetisation ripple using Lorentz microscopy: Effect of ultra-thin Ni79Fe21 seed layers on magnetic properties of Ni45Fe55

Ni45Fe55 has long been a high moment alternative for Ni80Fe20, which is commonly used in hard disk drive (HDD) read-write head design. In this paper we investigate the effect of ultra thin Ni79Fe21 seed layers on controlling the physical and magnetic behaviour of Ni45Fe55. Transmission electron microscopy (TEM) was used to observe grain size variation. Introducing a seed layer of 0.5 nm thickness reduced the average grain size diameter by over 80% to 2 nm. Diffraction analysis shows texture exists along the [010] direction for the unseeded and 0.25 nm seed layer films. The addition of the Ni79Fe21 seed layer reduces film texture. Bulk magnetic measurements showed seed layers improved uniaxial anisotropy, with decreasing easy axis coercivity HC, and an increase in the anisotropy field HK. The Fresnel mode of Lorentz microscopy was used to image micromagnetic behaviour during in situ magnetising experiments. The nano-scale visualisation of the magnetic structure allows for not only the mapping of hysteresis behaviour, but quantitative characterisation of the material in the form of magnetisation ripple. This was characterised in two ways; the ripple dispersion and wavelength. The addition of Ni79Fe21 seed layers acted to significantly reduce ripple wavelength and dispersion angle. The dramatic effect of seed layer addition suggests that the ultra-thin film is a good candidate for controlling both the physical and magnetic properties of Ni45Fe55 films, whilst maintaining a high magnetic moment density.

Properties of assembly of superparamagnetic nanoparticles in viscous liquid

Detailed calculations of the specific absorption rate (SAR) of a dilute assembly of iron oxide nanoparticles with effective uniaxial anisotropy dispersed in a liquid are performed depending on the particle diameters, the alternating (ac) magnetic field amplitude H0 and the liquid viscosity. For small and moderate H0 values with respect to particle anisotropy field Hk the SAR of the assembly as a function of the particle diameter passes through a characteristic maximum and then reaches a plateau, whereas for sufficiently large amplitudes, H0 ~ Hk, the SAR increases monotonically as a function of diameter. The realization of viscous and magnetic oscillation modes for particle unit magnetization vector and director for moderate and sufficiently large H0 values, respectively, explains this behavior. It is found that the SAR of the assembly changes inversely with the viscosity only in a viscous mode, for nanoparticles of sufficiently large diameters. In the magnetic mode the SAR of the assembly is practically independent of the viscosity, since in this case the nanoparticle director only weakly oscillates around the ac magnetic field direction. The conditions for the validity of the linear response theory have been clarified by comparison with the numerical simulation data.

Electronic structure and magnetic exchange interactions in Zn diluted CuFe2O4 magneto-ceramics

We report a detailed study on the electronic structure and temperature (1.9K≤T≤900K) dependence of magnetization in Zn diluted cuprospinel [Cu1−xZnxFe2O4 (0≤x≤0.6)]. The electronic structure determined from the x-ray photoelectron spectroscopy and Rietveld analysis of the x-ray diffraction patterns reveals the structure to be (Cu(1−x)/5ZnxFe4(1−x)/5)A [Cu4(1−x)/5Fe2−4(1−x)/5]BO4. Beyond a specific dilution limit (0.05≤xp≤0.1), a sudden phase-change from tetragonal (I41/amd) to cubic (Fd3m) is noticed with an alteration in the A–O–A (3.29%) bond angle and A–O bond length (0.67%). Our analysis shows that all these compounds order ferrimagnetically below the Néel temperature (TFN) due to dissimilar site-specific magnitudes of spins, yet, they undergo a second transition at low temperatures T1∼66K with asymptotic Curie temperature TA(=C/χ0) as high as −547.2K for the undoped case. Dilution with Zn cause quadratic decay (b2x2+b1x+yo) of the ferrimagnetic ordering temperature from 743 K to 370.5 K for x=0 and 0.6, respectively. On the contrary, a significant increase in the saturation magnetization (MS) was observed with increasing x until the critical composition xc∼0.4 beyond which MS decreases continuously (MS=1.64μB and 4.73μB for x=0 and 0.4, respectively). From the temperature dependence of inverse paramagnetic susceptibility [χ−1(T>TFN)] data and Néel’s expression for ferrimagnets, we evaluated the molecular field constants and exchange interactions (J) between the tetrahedral A- and octahedral B-sites. A systematic compositional dependence of this analysis yields that JAB (∼25kB for x=0) is the dominant exchange interaction in comparison to JBB and JAA; however, JAB decreases significantly with increasing the composition (JAB∼−5.5kB for x=0.6). The isothermal magnetization data and law of approach to saturation analysis reveals that the investigated system possesses very high anisotropy field HK ≥5.5kOe with cubic anisotropy constant K1≥1.6×106erg/cc at xc.

Structural, magnetic and electrical investigations of Fe1─XMnX (0 ≤ x ≤ 0.39) alloy nanowires via electrodeposition in AAO templates

The Fe1─XMnX (0 ≤ x ≤ 0.39) nanowire (NW) arrays were synthesized through anodic aluminum oxide (AAO) template-based electrodeposition method. The elemental composition of the NWs was varied by changing the Mn-ions concentration in the electrochemical bath during electrodeposition. Energy Dispersive X-rays Spectroscopy (EDX) spectrums confirmed the Mn contents, that was increased in the NWs from 0 to 39 with respect to increase in Mn-ion concentration in the electrolyte. The X-ray diffraction (XRD) patterns exhibited the NWs were crystallized into the body-centered cubic (bcc) structure. Furthermore, the lattice parameter of NWs decreased as Mn content increased in the NWs whereas the increasing trend in grain size was observed. The magnetic properties of NWs were determined by recording MH-loops at room temperature with applied magnetic field in parallel (∥) and perpendicular (⊥) direction to the long-axis of NWs. The MH-loops revealed the existence of strong magnetic anisotropy and anisotropy field (Hk) that was determined by the Anisotropy Field Distribution (AFD) method. A decreasing trend in the coercivity (Hc), saturation magnetization (Ms) and anisotropy field (Hk) was observed as a function of Mn contents in FeMn NWs. The ZFC-FC curves were also recorded with 1kOe applied magnetic field, which demonstrated the ferromagnetic behavior and exhibited the blocking temperature was increased (Fe NWs ~ 300 K, Fe0.82Mn0.18 NWs ~ 330 K, and Fe0.61Mn0.39 NWs > 350 K) with the increase of Mn content. Moreover, the conductivity and mobility of the NWs were also decreased that were analyzed through four-probe Hall techniques.

Microstructure and magnetoimpedance studies of NiFe films electrodeposited on ITO substrate: Experiments and simulations

Structure and magnetoimpedance (MI) properties of Permalloy films electrodeposited on Indium Tin Oxide (ITO) coated on glass substrate have been investigated. Microstructure and magnetic measurements confirm the composition and formation of single phase films with varying thickness. The MI values increased from 2.8% to 50%, while the frequency at which maximum MI is observed shifted to lower frequency when thickness of the NiFe film is increased. Present results show that MI is not only weak but also exhibits a sign change in the lower frequency range. It is shown that the magnetoinductive component is dominant at lower frequencies. Thickness and frequency dependence of MI values are compared with numerically calculated results on the basis of Maxwell’s and Landau- Lifshitz equations. It is found that the thickness and effective conductivity of the film play a significant role in variation of MI values. We have attempted to extract the relative magnetic permeability (μr), the damping factor (α), the angle between the equilibrium state of magnetization and easy axis (θ) and the magnetic anisotropy field (Hk) by fitting the experimental MI data to the standard equations. Experimental results are consistent with the physical parameters obtained from the phenomenological model. The relative permeability values extracted from the MI data corroborate well with magnetic measurements of literature.

Tunable high-frequency magnetic properties of NiFe films on triangular wave-like surface of Al2O3 substrate

To tune high-frequency properties, NiFe films are fabricated on triangular wave-like surface of Al2O3 substrate by magnetron sputtering. Faceting, the transformation of a planar surface into two or more surfaces, can be observed on m-plane Al2O3 substrate via annealing process and further format the continuous periodic triangular wave-like structure. The wavelength and oscillation can be adjusted by annealing temperature and time. The magnetic anisotropy field (Hk) of the magnetic film is increased to 320 Oe and the resonance frequency (fr) also has a big improvement to 5.4 GHz. These changes are mainly attributed to the dipolar interaction between surface magnetic charges in the studied system. We prove that high-frequency properties of the soft magnetic film can be controlled by designing a nanoscale periodic triangular wave-like morphology on film surface.

Effect of Mn (12 at%) substitution on magnetic anisotropy and magnetization reversal of equiatomic FeCo alloy nanorod arrays

The effect of manganese (Mn) substitution on magnetic properties of equiatomic FeCo (1:1) alloy nanorod arrays was investigated by comparatively analyzing Fe50Co50 and Fe45Co43Mn12 nanorod arrays having diameter and length about 50 nm and 250 nm respectively. The Fe45Co43Mn12 nanorod arrays were also annealed under vacuum at 400 °C, 500 °C, and 600 °C to further improve their properties. The Fe50Co50 and Fe45Co43Mn12 nanorod arrays showed body-centered cubic (bcc) structure while after annealing at 600 °C a hexagonal close pack (hcp) Co phase was also induced in Fe45Co43Mn12 nanorod arrays. The effective anisotropy field (Hk) was determined through anisotropy field distribution method and magnetization reversal was examined by angular dependence of coercivity (Hc). The angular dependence of Hc demonstrated that the magnetization reversal in Fe50Co50 nanorods occurred via coherent rotational mode while magnetization reversal in Fe45Co43Mn12 nanorods occurred by the combination of both coherent rotational and curling mode.

Improvement of high-frequency properties of Co2FeSi Heusler films by ultrathin Ru underlayer**Project supported by the National Natural Science Foundation of China (Grant Nos. 11674187 and 51871127) and the Fund from the Technology on Electronic Test & Measurement Laboratory (Grant No. 6142001180103).

Heusler Co2FeSi films with a uniaxial magnetic anisotropy and high ferromagnetic resonance frequency fr were deposited by an oblique sputtering technique on Ru underlayers with various thicknesses tRu from 0 nm to 5 nm. It is revealed that the Ru underlayers reduce the grain size of Co2FeSi, dramatically enhance the magnetic anisotropy field HK induced by the internal stress from 242 Oe (1 Oe = 79.5775 A⋅m−1) to 582 Oe with an increment ratio of 2.4, while a low damping coefficient remains. The result of damping implies that the continuous interface between Ru and Co2FeSi induces a large in-plane anisotropic field without introducing additional external damping. As a result, excellent high-frequency soft magnetic properties with fr up to 6.69 GHz are achieved.

Tailoring the magnetization linearity of Finemet type nanocrystalline cores by stress induced anisotropies

In this paper a theoretical and experimental investigation will be presented on the linearity of the flat hysteresis loop obtained by continuous stress annealing of Finemet type nanocrystalline ribbon. The stability of the effective permeability versus the magnetizing field depend on the residual random distribution of local magnetization and can be characterized by i) the coefficient a in the expression of magnetization approaching the saturation: M/Ms = 1 − a/H, valid in a restricted region, for Hlin < H < Hsat, where Hlin is the limit of linearity and by ii) the distribution of the anisotropy field ΔHK. The theoretical upper limit of linearity is given by the anisotropy field HK = Bs/µo.µeff. The linearity limit, Hlin, can be expressed as a difference between the value HK and the half width of the anisotropy field distribution, ΔHK. The linearity will be measured by the ratio R = Hlin/HK. The parameter R is almost constant (around 0.72) for large applied stresses and carefully selected annealing parameters (furnace geometry, temperature distribution along the furnace and pulling velocity). For small applied stresses (i.e. for effective permeability’s above 4000) however this linearity parameter is reduced to zero and a potbellied loop appears. A possible explanation will be given for the stress dependence of linearity parameter based on the back stress model of stress annealing.

Efficient excitation of exchange dominated spin waves in oblique deposited CoFeB thin films

Spin waves play a vital role as potential data carriers in low power wave-like computing and high-frequency spintronic devices, which stimulate intensive studies on the efficient excitation of spin waves in magnetic thin films. Here, we suggest a controllable approach for the efficient excitation of perpendicular standing spin waves (PSSWs) in a series of CoFeB/Si thin films by the oblique angle deposition technique. It is experimentally demonstrated that the intensity of the PSSW mode can be enhanced significantly with increased oblique angle, and a comparable intensity of spin wave to that of uniform FMR mode is achieved at an oblique angle of 39°. Moreover, the dependence of in-plane anisotropy field Hk, exchange constant A, as well as intrinsic Gilbert damping α on oblique deposition angle are also investigated.