FeCo Thin Film Research Articles

Enhanced Soft Magnetic Properties in N-Doped Amorphous FeCo Thin Film

Enhanced Soft Magnetic Properties in N-Doped Amorphous FeCo Thin Film

The Preparation of High Saturation Magnetization and Low Coercivity Feco Soft Magnetic Thin Films via Controlling the Thickness and Deposition Temperature.

FeCo thin films with high saturation magnetization (4 πMs) can be applied in high-frequency electronic devices such as thin film inductors and microwave noise suppressors. However, due to its large magnetocrystalline anisotropy constant and magnetostrictive coefficient of FeCo, the coercivity (Hc) of FeCo films is generally high, which is detrimental to the soft magnetic properties. Meanwhile, the thickness and deposition temperature have significant effects on the coercivity and saturation magnetization of FeCo films. In this paper, FeCo thin films with different thicknesses were prepared by magnetron sputtering at different temperatures. The effects of thickness and deposition temperature on the microstructure and magnetic properties of FeCo thin films were systematically studied. When the film thickness increases from 50 nm to 800 nm, the coercivity would decrease from 309 Oe to 160 Oe. However, the saturation magnetization decreases from 22.1 kG to 15.3 kG. After that, we try to further increase the deposition temperature from room temperature (RT) to 475 °C. It is intriguing to find that the coercivity greatly decreased from 160 Oe to 3 Oe (decreased by 98%), and the saturation magnetization increased from 15.3 kG to 23.5 kG (increased by 53%) for the film with thickness of 800 nm. For the film with thickness of 50 nm, the coercivity also greatly decreased from 309 Oe to 10 Oe (decreased by 96%), but the saturation magnetization did not change significantly. It is contributed to the increase of deposition temperature, which will lead to the increase of grain size and the decrease of the number of grain boundaries. And the coercivity decreases as the number of grain boundaries decreases. Meanwhile, for the thicker films, when increasing the deposition temperature the thermal stress increases, which changes the appearance of (200) texture, and the saturation magnetization increases. Whereas, it has a negligible effect on the orientation of thin films with small thickness (50 nm). This indicates that high-temperature deposition is beneficial to the soft magnetic properties of FeCo thin films, particularly for the films with larger thickness. This FeCo thin film with high saturation magnetization and low coercivity could be an ideal candidate for high-frequency electronic devices.

TEM-based study of oxidation of FeCo high moment alloy at elevated temperatures

FeCo (60%-70% Fe, 30%-40% Co at.%) alloys have been used as write transducer materials due to their large saturation magnetization at room temperature (μ0M = 2.45 T). In this research, we investigate the influence of oxidation on the magnetic moment of a Fe70Co30 material at elevated temperatures in the application of heat assisted magnetic recording. We find that the moment of Fe70Co30 decreases after oxidation for all temperatures explored and that Co does not take part in the oxidation process. The moment loss is mainly due to the formation of ferrimagnetic Fe3O4 or γ-Fe2O3 as well as the change of the Fe/Co ratio in the FeCo alloy. A 2 nm Cr underlayer has been employed to change the FeCo texture from (110) to (002). This also increases the grain size of the FeCo thin film. In the case of the (002) textured sample, voids form between the FeCo film and the oxide layer, which could be the direct result of Fe cations diffusion.

Fatigue Characteristics of Magnetostrictive Thin-Film Coated Surface Acoustic Wave Devices for Sensing Magnetic Field

Magnetostrictive thin-film coated Surface Acoustic Wave (SAW) devices were promising for sensing magnetic field owing to their superior features as micro-size, fast response, and high sensitivity originated from the magnetostrictive effect. However, the magnetostriction nature in magnetostrictive thin-film causes significantly mechanical fatigue in service, deteriorating the sensor performances. In this work, the fatigue phenomenon in magnetostrictive coating was underlined by characterizing the prepared FeCo thin-film coated magnetic device cyclically. Obvious shedding was observed in FeCo coating after cyclic testing and the magnetic-sensitivity decreases significantly. One of the reasons is the weak adhesion of FeCo thin-film towards the substrate. As an available way allowing enhancement of adhesion, a Cr thin-film was employed as the transition-layer to weaken the mechanical fatigue. However, it accompanied by the issue of the reduced magnetostrictive coefficient and the obstruction in magnetostrain-tranfer to piezoelectric substrate. As a result, the slump in sensitivity was observed. To address such issues, a design of dotted-pattern with Cr transition layer was employed to build the SAW based magnetic-device. High magnetic-sensitivity and excellent long-term stability were achieved because of the release of coercive force in FeCo dots and enhancement of the FeCo adhesion to the substrate.

Effect of Pt doping on the preferred orientation enhancement in FeCo/SiO2 nanocomposite films

We prepared FeCoPt/SiO2 thin films by sol-gel spin-coating technique. As-prepared composite films were reduced in hydrogen to induce texture growth. Structural, magnetic property and surface morphology of the films were characterized by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and scanning electron microscope (SEM). These experimental data indicate that integrated intensity ratio I(200)/I(110) of diffraction peaks (200) and (110) of FeCo firstly increases and then decreases, while the coercivity first decreases and then increases with increasing Pt doping content. The specimen with less Pt doping content has a large I(200)/I(110) value and small coervicity value, which is closely related with strong (200) texture in FeCo thin film. These results indicate that fcc-Pt is also in favor of promoting (200) FeCo texture like Al or Cu elements, and this similar trends of Pt and Al originate from their similar atomic radius and crystal cell volume.

Synthesis and characterization of magnetically exchange coupled Zr2Co11/MgO/FeCo thin films with MgO as diffusion barrier

Zr2Co11 thin films were deposited by sputtering. MgO thin film was deposited on the top of Zr2Co11, followed by FeCo thin film deposition and post-annealing, to have magnetic exchange coupling between Zr2Co11 and FeCo. MgO thin film worked as a diffusion barrier between Zr2Co11 and FeCo during post-annealing. The thickness of FeCo layer was controlled as 4, 8 and 12 nm, respectively. The results showed that when the FeCo thickness was 8 nm, the Zr2Co11/MgO/FeCo showed the optimum magnetic properties, with 58% increased of (BH)max over Zr2Co11, which could be attributed to the effective exchange coupling between Zr2Co11 and FeCo. The exchange coupling between Zr2Co11 and FeCo thin film was investigated by Henkel plots.

Magnetostrictive effect in micro-dotted FeCo film coated surface acoustic wave devices

The magnetostrictive effect in micro-dotted FeCo film coated surface acoustic wave (SAW) devices was demonstrated by solving coupling equations using the specific coupling of modes parameters extracted by FEM analysis. Dotted-pattern on FeCo thin-film proposed in this work contributes well to suppression in hysteresis effect by fully releasing the internal coericivity of the magnetistrictive FeCo thin-film. The theoretical demonstration was confirmed well by characterizing the constructed SAW magnetic devices with FeCo dots depositing along the SAW propagation path. Significantly improvements on suppression of hysteresis phenomenon were observed by characterizing the prepared FeCo dots coated SAW magnetic devices, higher magneto-sensitivity of 21.17 kHz mT−1, and lower hysteresis error of 0.82% were achieved successfully.

Grating-patterned FeCo coated surface acoustic wave device for sensing magnetic field

This study addresses the theoretical and experimental investigations of grating-patterned magnetostrictive FeCo coated surface acoustic wave (SAW) device for sensing magnetic field. The proposed sensor is composed of a configuration of differential dual-delay-line oscillators, and a magnetostrictive FeCo grating array deposited along the SAW propagation path of the sensing device, which suppresses effectively the hysteresis effect by releasing the internal binding force in FeCo. The magnetostrictive strain and ΔE effect from the FeCo coating modulates the SAW propagation characteristic, and the corresponding shift in differential oscillation frequency was utilized to evaluate the measurant. A theoretical model is performed to investigate the wave propagation in layered structure of FeCo/LiNbO3 in the effect of magnetostrictive, and allowing determining the optimal structure. The experimental results indicate that higher sensitivity, excellent linearity, and lower hysteresis error over the typical FeCo thin-film coated sensor were achieved from the grating-patterned FeCo coated sensor successfully.

Nanometer-resolution depth-resolved measurement of florescence-yield soft x-ray absorption spectroscopy for FeCo thin film.

We develop a fluorescence-yield depth-resolved soft x-ray absorption spectroscopy (XAS) technique, which is based on the principle that the probing depth is changed by the emission angle of the fluorescence soft x rays. Compared with the electron-yield depth-resolved XAS technique, which has been established in this decade, we can observe wider range in-depth XAS distribution up to several tens of nm. Applying this technique to a 30 ML (∼4.3 nm) FeCo thin film, we observe Fe L-edge XAS spectra at the probing depth of 0.3-6 nm and find that the film has 22 ML (∼3.1 nm) surface oxide layer while its inner layer shows metallic state. We thus successfully obtain nanometer-resolution depth-resolved XAS spectra and further expect that operando measurement under the electric and/or magnetic fields is possible.

Preparation and high-frequency soft magnetic property of FeCo-based thin films

A series of FeCo-based thin films were prepared by magnetron sputtering without applying an induced magnetic field. The microstructure, electrical properties, magnetic properties and thermal stability of FeCo, FeCoSiN monolayer thin film and [FeCoSiN/SiN x ] n multilayer thin film were investigated systematically. When FeCo thin film was doped with Si and N, the resistivity and soft magnetic properties of the obtained FeCoSiN thin film can be improved effectively. The coercivity (H c), resistivity (ρ) and ferromagnetic resonance frequency (f r) can be further optimized for the [FeCoSiN/SiN x ] n multilayer thin film. When the thickness of FeCoSiN layer and SiN x layer is maintained at 7 and 2 nm, the H c, ρ and f r for [FeCoSiN/SiN x ] n multilayer thin film are 225 A·m−1 392 µΩ·cm−1 and 4.29 GHz, respectively. In addition, the low coercivity of easy axis (H ce ≈ 506 A·m−1) of [FeCoSiN/SiN x ] n multilayer thin film can be maintained after annealing at 300 °C in air for 2 h.

Thermal Annealing Effect on Real Time Atomic Relocation of Iron-Cobalt Alloys Prepared by Electro-Deposition

Atomic structures of fabricated Fe-Co alloys were investigated real time by time resolved x-ray absorption spectroscopy (TRXAS) at annealing temperature of 400° C. The various compositions of Fe-Co alloy thin films were prepared by electro-deposition on indium-tin oxide glass substrate with iron sulfate and cobalt chloride electrolyte solutions. The current density of 80 A/m2was used to deposit Fe-Co thin film with varying the ratio of Fe and Co ion concentrations. The Fe-Co alloys with boron nitride powders were mixed, grinded and pressed in the pallet form in order to insert into environmental controlled sample holder for TRXAS measurement. The samples were annealed under 20% oxygen and 80% nitrogen atmospheric by increasing the temperature up to 400° C and then remaining for an hour. The influence of annealing temperature can modify the atomic structures of Fe-Co alloys as indicated in the variation of extended x-ray absorption fine structure (EXAFS) peaks. Most of the EXAFS peaks followed the temperature profile i.e. increasing or decreasing during the temperature rising and then maintaining about constant values during holding the temperature at 400° C. By transforming the EXAFS peaks into scattering radius space, the modification of relative scattering amplitude from each nearest neighbor position indicated the atomic relocation during annealing the samples. Some of scattering patterns from Fe and Co oxides can be found and their amounts changed during rising the annealing temperature. In addition, the atomic relocations extracted from the Co absorption edge was very much smaller than those of Fe edge probably due to relative more stable of Co atomic positions for this range of annealing temperature.

Growth Method to Improve the Resonant Frequency and Magnetic Permeability of FeCo Thin Films

Fabrication of a Fe-Co thin film with both high magnetic resonant frequency and large permeability for high-frequency device applications is a challenge despite Fe-Co's high magnetization. Limitations are usually due to relatively high coercivity or low anisotropy. Here, we demonstrate a method for fabrication of Fe-Co films with both ultrahigh resonant frequency and large permeability, obtained by slightly tuning their nanostructures and reducing their crystal defects during electrodeposition. With a change from a single direct current density to two well-controlled alternating current densities during deposition, the as-synthesized films (200-600 nm in thickness) have significantly lower coercivity (down to 8 Oe) and improved anisotropy (up to 96 Oe) and magnetic polarization (up to 2.4 T), which lead to an ultrahigh resonant frequency up to 5.1 GHz. Further reduction of the crystal defects and improvement in Fe-Co atom-filling density through the optimization of the plating solution at lower temperatures and higher concentrations result in resonant frequency and relative permeability improvements up to 6.1 GHz and 325 (real part), respectively. Further, Fe-Co films with only large relative permeability (up to 715) can also be attained through optimization. These nanofilms thus have the potential to be used in gigahertz microwave devices.

The Role of Magnetoelastic Field Related to Underlayers on Magnetic Properties of FeCo Thin Films

In this work, the influence of the magnetoelastic field on the magnetic properties of FeCo thin film is analyzed by the micromagnetic model. Formula of magnetoelastic energy related to the stress between the FeCo and the underlayer are derived to analysis the role of stress on soft magnetic properties. The cubic anisotropy determines the symmetry of the loops. For the magnetoelastic field, the main term Hma has significant influence on the easy-axis coercivity and the cross term Hmb affects the slope of the hard-axis loop. Good in-plane anisotropy of FeCo thin film, which can be obtained by using certain underlayers (such as Cu, NiFe, CoFe), is corresponding to low value of Hma and Hmb. The magnetization 4πMs at amorphous grain boundary has great effect on the properties of FeCo film.

Soft magnetic property and magnetization reversal mechanism of Sm doped FeCo thin film for high-frequency application

A series of (Fe0.67Co0.33)1−xSmx (0≤x<0.25) thin films with thickness around 110nm have been fabricated on silicon(111) substrates by magnetron co-sputtering at ambient condition with a 2.4kA/m magnetic field applied in the film plane during deposition. With the Sm concentration increasing, FeCo grain size gradually decreases and FeCoSm film eventually becomes amorphous, while the isotropic magnetic property changes to in-plane uniaxial anisotropy as long as Sm is doped. The investigation of the angular dependence of coercivity and switching field indicates that the magnetization reversal mechanism of FeCoSm film is domain-wall depinning and coherent rotation when the applied field is close to the easy axis and hard axis, respectively. The anisotropy field and the resonance frequency of FeCoSm films can be tuned in the range of 15.0–109.5kA/m and 5.2–11.8GHz, respectively, by controlling the content of Sm, indicating that FeCoSm films have much potential in high-frequency applications.

Effect of Ion-Beam Gas Species on Magnetic Softness in Fe-Co Thin-Film Etching

The effect of ion-beam (IB) gas species on magnetic softness in etching of Fe-Co thin films was evaluated by means of in situ magnetoresistance (MR) measurements. A 25-nm Fe70Co30 film was etched by Ar, Ne, or Kr IB, and successive MR measurements were performed in the same IB etching chamber. The IB etching and MR measurements were performed alternately in vacuum; therefore, it was possible to evaluate the etching gas effect on magnetic softness of the single sample in nanometer scale without the need to deposit a capping layer. Higher energy IB of 600 V showed larger gas species dependence of the deterioration than lower energy of 250 V. In the case of 600-V etching, Kr IB showed better softness compared with those of Ar and Ne IBs, whose etching surface was the smoothest among the etching conditions. Structural analysis revealed that surface roughness has an important role for magnetic softness and MR ratio in the thinner region of less than about 5 nm.

Optical detection of magnetoelectric effect in the composite consisting of InGaN/GaN multiple quantum wells and FeCo thin film

The magnetoelectric effect has been demonstrated based on the composite of InGaN/GaN multiple quantum wells (MQWs) and FeCo thin film. By applying an external magnetic field, the ferromagnetic layer will be deformed due to magnetostriction. This deformation is transmitted to the piezoelectric layers and results in piezoelectric effect, which induces electric polarization in the piezoelectric layers. The induced electric polarization changes the strain and the built-in internal electric field in the InGaN/GaN MQWs and therefore, the optical properties of the InGaN/GaN MQWs change. The results shown here open up a possibility for the application of nitride semiconductors in magneto-optical and magnetoelectric engineering.

Irradiation Damage in Fe-Co Thin Films With Low-Energy Ion Beam

The authors estimated the effect of ion-beam irradiation damage on saturation magnetic flux density (B s) in Fe-Co thin films, a material expected to be used as a main pole in write heads in the era of Tbits/in2 recording density. Fe-Co thin film deposition and successive ion-beam irradiation at 250 eV and a capping layer deposition were performed in the same ion-beam etching apparatus without breaking vacuum. The etching tests revealed B s of the films with thickness of about 10 nm was decreased by the ion-beam irradiation; about 0.1-0.2 T decrease in B s was observed with several nanometers etching. Regardless of etching depth, about 0.1 T decrease in B s would appear even in the case of shallow etching of about 1 nm. Damage control in the main pole fabrication would be one of the important issues for the write heads.

Initial Permeability and Dynamic Response of FeCo Write Pole

In this work, the microstructure and the magnetostriction effect of the FeCo thin film are considered in micromagnetic simulations; therefore the magnetic properties of the FeCo thin film and write pole can be calculated more accurately. Based on the micromagnetic models, magnetic hysteresis loops of films are calculated. The simulation results show that the magnetostriction has great effect on the coercive force of FeCo films. Furthermore, the initial permeability and the dynamic response of the FeCo write pole are studied. When the easy axis of the write pole is along cross-track direction, a 128 nm-wide and 32 nm × 32 nm-ABS pole tip has a real initial permeability of 8.0 at low frequencies and a roll-off frequency of 5.0 GHz. The effect of the easy axis orientation is also studied. The write field is about 4300 Oe with a reversal time of approximately 0.15 ns. The scaling of the permeability is analyzed by a simple micromagnetic model without microstructure.

Microstructure and magnetic properties of FeCo epitaxial thin films grown on MgO single-crystal substrates

FeCo epitaxial films were prepared on MgO(100), MgO(110), and MgO(111) substrates by ultrahigh vacuum molecular beam epitaxy. FeCo thin films with (100), (211), and (110) planes parallel to the substrate surface grow on respective MgO substrates. FeCo/MgO interface structures are studied by high-resolution cross-sectional transmission electron microscopy and the epitaxial growth mechanism is discussed. Atomically sharp boundaries are recognized between the FeCo thin films and the MgO substrates where misfit dislocations are introduced in the FeCo thin films presumably to decrease the lattice misfits. Misfit dislocations are observed approximately every 9 and 1.4 nm in FeCo thin film at the FeCo/MgO(100) and the FeCo/MgO(110) interfaces, respectively. X-ray diffraction analysis indicates that the lattice spacing measured parallel to the single-crystal substrate surfaces are in agreement within 0.1% with those of the respective bulk values of Fe50Co50 alloy crystal, showing that the FeCo film strain is very small. The magnetic anisotropies of these epitaxial films basically reflect the magnetocrystalline anisotropy of bulk FeCo alloy crystal.

Structure and Magnetic Properties of FeCo Epitaxial Thin Films

FeCo thin films were prepared on MgO(100), MgO(110), and MgO(111) single-crystal substrates by UHV-MBE. The effects of substrate orientation and substrate temperature on the film growth structure and the magnetic properties were investigated. FeCo thin films with (100)bcc, (211)bcc, and (110)bcc planes parallel to the substrate surface grew epitaxially on respective MgO substrates. FeCo(100)bcc single-crystal films were obtained on MgO(100) substrates. FeCo(211)bcc bi-crystalline films grew epitaxially on MgO(110) substrates with two types of domains whose orientations were rotated around the film normal by 180 degrees with respect to each other. FeCo(110)bcc thin films grew epitaxially on MgO(111) substrates with two type variants namely, the Nishiyama-Wasserman and Kurdjumov-Sachs relationships. Atomically sharp boundaries were recognized between the FeCo thin films and the MgO substrates, where misfit dislocations were introduced in the FeCo thin films, presumably to decrease the lattice misfits. A 0.3% reduction of the lattice spacing normal to the substrate surface was observed for an FeCo thin film prepared at a substrate temperature of 100 °C. The lattice spacing reduction decreased with increasing substrate temperature. The magnetic properties of FeCo thin films grown on MgO substrates were influenced by the magnetocrystalline anisotropy and the shape anisotropy caused by the roughness of FeCo islands which form the FeCo thin films.