Hard Axis Coercivity Research Articles

High-frequency behavior of FeN thin films fabricated by using reactive sputtering

We investigated high-frequency behavior of FeN thin films prepared by reactive sputtering through ferromagnetic resonance (FMR) and its relationship with the static magnetic properties. The FMR was observed in the frequency range from 2 to 18 GHz in the FeN films fabricated at proper nitrogen flow rate (NFR). In those FeN thin films, a decrease of the saturation magnetization and the corresponding decrease of the FMR frequency were observed as NFR was increased during the deposition. The external field dependences of the FMR frequencies were well fit to the Kittel formula and the Land\'e g-factors determined from the fit were found to be very close to the free electron value. The high-field damping parameters were almost insensitive to the growth condition of NFR. However, the low-field damping parameters exhibited high sensitivity to NFR very similar to the dependence of the hard-axis coercivity on NFR, suggesting that extrinsic material properties such as impurities and defect structures could be important in deciding the low-field damping behavior.

ChemInform Abstract: Practical FeCo Films for Perpendicular Writer Pole

AbstractReview: 43 refs.

Magnetic properties of [Fe65Co35–O/SiO2] n multilayer thin films for high-frequency application

A series of [Fe65Co35–O/SiO2]n multilayer thin films with different SiO2 separate layer thicknesses (t=0–3 nm) and fixed Fe65Co35–O layer thickness (5.4 nm) have been fabricated on (100) silicon and glass substrates by reactive magnetron co-sputtering. Microstructure analysis and magnetic measurement results show that Fe65Co35–O grain size and magnetic properties can be adjusted by varying the thickness of SiO2 layers. All films reveal an evident in-plane uniaxial magnetic anisotropy (IPUMA) when the thickness of SiO2 monolayer changes from t=0 to 3 nm. The hard axis coercivity (Hch) reveals a minimum of 9 Oe at t=1 nm while the easy axis coercivity (Hce) exhibits a minimum of 16 Oe at t=2 nm. For t=1 nm and 2 nm, the IPUMA fields (Hk) are 95 and 207 Oe, the saturation magnetizations (Ms) are 1.8 and 1.6 T, the real part of the complex permeabilities (below 3.0 GHz) are more than 217 and 104, and the ferromagnetic resonance frequencies (fr) are 3.6 and 5.2 GHz, respectively.

A polycrystalline model for magnetic exchange bias

This work introduces a realistic model for the magnetic behavior of polycrystalline ferromagnet/antiferromagnet (FM/AF) systems with granular interfaces. It considers that, for strong enough interface exchange coupling, the AF layer breaks the adjacent FM into small-sized domains and that at the interface there exist grains with uncompensated spins interacting with the FM magnetizations; the classification of these grains as unstable (rotatable, responsible for a coercivity enhancement) or stable (adding to the bias) depends on both the anisotropy and the magnetic coupling with the adjacent FM. The distinctive characteristic of the model is that the effective rotatable anisotropy changes when the external magnetic field is varied resulting in a non-zero hard-axis coercivity, a feature commonly observed, though little understood and often ignored. The applicability of this model was checked on a typical magnetron-sputtered IrMn/Co bilayer and excellent agreement between experiment and simulation was achieved.

Practical FeCo Films for Perpendicular Writer Pole

An attempt is made in this publication to review various developments of FeCo films for recording heads in the last decade and to look at emerging developments regarding these films. A series of FeCo films from 100% Fe to 100% Co was sputter deposited, characterized, and analyzed for various magnetic properties such as magnetostriction, uniaxial anisotropy, coercivity, dispersion, and saturation magnetization. Many process parameters, with the most influencing parameter being sputter pressure, play an important role especially influencing dispersion and/or hard axis coercivity (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> ) in these materials. Out of the many developments to date the effect of seed layer(s) in reducing grain size of high moment bcc FeCo films is still intriguing and, hence, a comprehensive review and analysis of seed layer effects are included. Although film stress can play an important role in optimizing H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> , there is no clear trend seen between film stress and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> when viewed across broad processing conditions. Higher H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> evolution with oblique deposition is an interesting phenomenon in these films. Uniaxial anisotropies of nearly 1000 Oe were found. The anisotropy evolution is explained through magnetoelastic energy and through crystal structure. Even though these films are very columnar in nature it was found that there was little to no fiber texture present in these films and there was no difference in texture between fine grained and coarse grained FeCo films.

Soft Magnetic Property of [Fe&lt;sub&gt;80&lt;/sub&gt;Ni&lt;sub&gt;20&lt;/sub&gt;-O/ZnO]&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; Multilayer Thin Films for High-Frequency Application

A series of [Fe80Ni20-O/ZnO]nmultilayer thin films with different ZnO separate layer thicknesses (t, from 0 to 3 nm) and fixed Fe80Ni20-O layer thickness (about 5 nm) have been fabricated on (100)-oriented silicon wafers and glass substrates by reactive magnetron sputtering. Microstructure analysis and static magnetic measurement results indicate that the magnetic properties of the films can be adjusted by the variation of ZnO monolayers thickness. All films reveal an evident in-plane uniaxial magnetic anisotropy (IPUMA). The values of in-plane uniaxial magnetic anisotropy fields (Hk) and resistivity (ρ) can be changed from 8 to 57 Oe and 62 to 168 μΩ•cm respectively with the t increasing. While the values of hard axis coercivity (Hch) and easy axis coercivity (Hce) reveal minimums of 1.5 and 3 Oe respectively at t = 1 nm.

Soft Magnetic Properties of Sequential Deposited Co&lt;SUB&gt;40&lt;/SUB&gt;Fe&lt;SUB&gt;40&lt;/SUB&gt;B&lt;SUB&gt;20&lt;/SUB&gt;/SiO&lt;SUB&gt;2&lt;/SUB&gt; Multilayer Nanogranular Films for High Frequency Applications

Multilayer nanogranular films with good soft magnetic properties and high resistivity desired for high frequency applications have been developed in our work. They were prepared by many sequential depositions of thin layers of Co40Fe40B20 and SiO2. After vacuum annealing at 250 degrees C under a uniform in-plane magnetic field of 100 kA/m for 2 hrs, the [Co40Fe40B20 (1.2 nm)/SiO2 (0.8 nm)]30 multilayer nanogranular films have the hard axis coercivity of 210 A/m, saturation magnetization of 1.05 T, resistivity of 2.06 x 10(3) microOmega.cm. Moreover, they show an in-plane uniaxial anisotropy of 2.78 kA/m.

Magnetic Field Enhancement with Soft Magnetic Flux Guides

In this work, a study of the sensitivity enhancement of spin valve sensors, when located in close proximity to magnetic flux guides, is presented. The magnetoresistance (MR) of spin-valve sensors, lithographically patterned into stripes with lateral dimensions, (length) l = 500 µm, (width) wsensor = 1, 2, 6 µm and placed near one/two Co93.5Zr2.8Nb3.7 (CZN) magnetic flux guide, is characterized at room temperature. CZN has a high permeability that together with a defined microstructured shape, is able to concentrate the magnetic flux in a small area, leading to an increase in sensor's sensitivity. The magnetic field amplification is estimated by comparison of sensor sensitivity with/without magnetic flux guides, in the linear operation range, and studied as a function of different parameters. Besides an enhancement in sensitivity, sensors also exhibit an important increase in the hard axis coercivity and a shift from MR(H=0) = 0.5, both attributed to the magnetic flux guides. Amplification factors of the order of 20 are observed..

Magnetic Anisotropy Dispersion in FeCo Films

We report on our study of magnetic and nonmagnetic parameters such as coercivity, anisotropy , magnetic dispersion, and stress on FeCo films of various thicknesses from 25 A to 500 A . We used 10 A Ru or NiFe seed layers for two sets of FeCo films. All films showed so-called hard-axis coercivity rocking, i.e., the hard-axis coercivity exhibits two local minima close to the nominal hard axis. Magnetic properties and stress change dramatically with FeCo thickness, but with little difference between the two types of seed materials. We found a correlation between the angular separation of the two local coercivity minima and easy-axis coercivity. The results stress the need to differentiate between two levels of dispersion, one at the microscopic and the other at the macroscopic level.

Soft magnetic properties of FeCo films with high saturation magnetization

The magnetic properties of multilayer composed of Fe65Co35 and thin layers of Co (less than 5nm) have been investigated. It is found that the microstructure, crystallographic texture, and magnetic softness of the multilayers depended on the initial layer. Multilayers with saturation magnetic induction higher than 23kG and hard axis coercivity smaller than 2Oe have been successfully prepared by using Co as the initial layer. Furthermore, the structure provided an effective process to tailor the in-plane magnetic anisotropy field without deteriorating the magnetic softness of the multilayers.

Electromagnetic and microwave properties of discontinuous CoFeB/MgO soft magnetic multilayer films

A series of discontinuous multilayers of CoFeB-MgO was fabricated by using DC/RF magnetron sputtering, and the electromagnetic and microwave properties were investigated. The results show that the microstructure and electromagnetic properties of the CoFeB-MgO discontinuous multilayer films can be altered by varying the relative content of the magnetic CoFeB phase and the insulating MgO phase. High performance microwave soft magnetic properties along with high resistivity are achieved in the discontinuous ［Co64Fe24B12(0.7nm)/MgO(0.4nm)］40 multilayer film. This film has the saturation magnetization of 1.3 T, hard axis coercivity of 130 A/m, and resistivity of 3.4 mΩ·cm. Moreover, the resonance frequency is about 2.1 GHz for this film. Both the real part μ′ and the imaginary part μ″ of the measured permeability are larger than 240 at 1.59 GHz and are both larger than 100 from 0.9 GHz to 2 GHz. So this film has potential for serving as the microwave absorbers and electromagnetic compatibility materials in the GHz frequency range.

Soft magnetic properties and microwave permeability of multilayer nanogranular films with high resistivity

The resistivity, soft magnetic properties and microwave permeability of multilayer nanogranular films suitable for high frequency applications have been investigated in this work. These films were prepared by repeated sequential depositions of thin layers of Co40Fe40B20 and SiO2. After vacuum annealing at 250℃ under a uniform in-plane magnetic field of 100kA/m for 2h, the Co40Fe40B20/SiO2 multilayer films have the hard axis coercivity of 210A/m, saturation magnetization of 838.75kA/m, resistivity of 2.06×103μΩcm. Moreover, the results show that the films have an in-plane uniaxial anisotropy of 2.78kA/m. As a consequence, the real part of measured permeability keeps constant at 125 up to 1.6GHz. The resonance frequency was about1.73GHz.

Tb doped CoNbZr soft magnetic films with high anisotropy field for applications in GHz frequency region

Abstract CoNbZr films for an adjustable magnetic anisotropy field H k by doping with rare-earth of different atomic ratio Tb element were obtained in this work. The effect of Tb addition ranged from 0 to 4 at.% on the magnetic properties of the amorphous CoNbZr films was further investigated. The results show that the magnetic anisotropy field H k increases sharply with the addition of Tb while the coercivity H ch along the hard axis and H ce along the easy axis change slightly with increasing Tb content in the films. As a consequence, CoNbZr film doped with 2 at.% of Tb exhibits excellent soft magnetic properties with a saturation magnetization 4 πM s of 8.9 kG, a hard axis coercivity H ch of 1.79 Oe, a easy axis coercivity H ce of 1.4 Oe and a magnetic anisotropy field H k of 87 Oe. The measured ferromagnetic resonance frequency f FMR of this film is 2.30 GHz. The real permeability μ ′ is about 100, which is maintained up to 2 GHz. In addition, there is a broad band of the imaginary permeability μ ″ over a large frequency band, indicating high losses. Therefore, Tb doped CoNbZr film is an excellent candidate for high frequency applications such as electromagnetic interference suppressors.

Soft magnetic properties and high frequency permeability in [CoAlO/oxide] multilayer films

A CoAlO thin film was found to have good soft magnetic properties and gigahertz frequency response when it had a thickness of tens of nanometres. Increasing the thickness by more than 100 nm rapidly increased the coercivity and seriously degraded the high frequency response. A multilayering technique (laminating the magnetic layer with oxide spacers) was exploited to improve the magnetic properties in thick films. AlOx and SiOx were used as the oxide spacing layers in this experiment. For the 105 nm CoAlO films, the easy and hard axis coercivities were reduced by more than 8 times by introducing 2 nm AlOx or 5 nm SiOx spacers. With our optimum lamination [CoAlO (52.5 nm)/AlOx (2 nm)]7, good soft magnetic properties (easy and hard axis coercivities: 21 and 14 Oe and effective anisotropy field: 54 Oe) and high frequency response (real permeability: >200 up to ∼2 GHz) were successfully obtained in a multilayer film at a thickness of 380 nm. The changes in the microstructures and film stress with the introduction of the oxide spacers are discussed in this paper.

Effect of Co underlayer on soft magnetic properties and microstructure of FeCo thin films

High saturation magnetization soft magnetic FeCo (=Fe 65Co 35) films were prepared using a thin Co underlayer. The FeCo/Co films exhibited a well-defined in-plane uniaxial anisotropy with easy axis coercivity ( H ce) of 10 Oe and hard axis coercivity ( H ch) of 3 Oe, and a half reduction of H c with H ce=4.8 Oe and H ch=1.0 Oe was obtained when the composition was adjusted to 25 at% Co. The effective permeability of the films remains flat around 250 to 800 MHz. The saturation magnetostriction was 5.2×10 −5 and the intrinsic stress was 0.8 GPa in FeCo single layer, both were slightly reduced by Co underlayer. The Co underlayer changed the preferred orientation of the FeCo films from (2 0 0) to (1 1 0) but more significantly, reduced the average grain size from ∼74 to ∼8.2 nm. It also reduced the surface roughness from 2.351 to 0.751 nm. The initial stage and interface diffusion properties were examined by TEM and XPS.

Studies on high-moment soft magnetic FeCo/Co thin films

The dependences of soft magnetic properties and microstructures of the sputtered FeCo (=Fe65Co35) films on Co underlayer thickness tCo, FeCo thickness tFeCo, substrate temperature Ts and target-substrate spacing dT−S are studied. FeCo single layer generally shows a high coercivity with no obvious magnetic anisotropy. Excellent soft magnetic properties with saturation magnetization μ0Ms of 2.35 T and hard axis coercivity Hch of 0.25 kA/m in FeCo films can be achieved by introducing a Co underlayer. It is shown that sandwiching a Co underlayer causes a change in orientation and reduction in grain size from 70 nm to about 10 nm in the FeCo layer. The magnetic softness can be explained by the Hoffmann's ripple theory due to the effect of grain size. The magnetic anisotropy can be controlled by changing dT−S and a maximum of 14.3 kA/m for anisotropic field Hk is obtained with dT−S=18.0 cm.

Magnetic and microwave properties of CoFe∕PtMn∕CoFe multilayer films

CoFe ∕ PtMn ∕ CoFe films were deposited on seed layers of Ru or NiFeCr with CoFe film compositions being either Co-10at.%Fe or Co-16at.%Fe. Eight periods of the CoFe∕PtMn∕CoFe trilayers were also prepared. The magnetic properties and ferromagnetic resonance (FMR) of these films were characterized with vibrating-sample magnetometer, and field-sweep FMR system at X band (∼9.5GHz). The Ru-seeded CoFe∕PtMn∕CoFe sandwich films show excellent magnetic softness with a low hard axis coercivity of 2–4Oe, an easy axis Mr∕Ms of &amp;gt;98%, and a significantly enhanced in-plane anisotropy of 57–123Oe when CoFe layer thickness is above 200Å. Contrary to what was observed in the ferromagnetic/antiferromagnetic bilayer systems that have reduced FMR linewidth with the increase of film thickness, the CoFe∕PtMn∕CoFe trilayers with Ru seed layer show a minimum FMR linewidth of 45Oe at an intermediate CoFe layer thickness of 300Å at ∼9.5GHz.

Nano-Granular Co-Fe-AI-O Soft Ferromagnetic Thin Films for GHz Magnetic Device Applications

Co-Fe-Al-O nanogranular thin films were fabricated by RF-magnetron sputtering under an Ar+O₂ atmosphere. High resolution transmission electron microscopy revealed that the Co-Fe-Al-O films are composed of bcc (Co, Fe) nanograins finer than 5 nm and an Al-O amorphous phase. A very large electrical resistivity of 374 μΩcm was obtained, together with a large uniaxial anisotropy field of 50 Oe, a hard axis coercivity of 1.25 Oe, and a saturation magnetization of 12.9 kG. The actual part of the relative permeability was measured to be 260 at low frequencies and this value was maintained up to 1.3 GHz. The ferromagnetic resonance frequency was 2.24 GHz. The resulting Co-Fe-Al-O nanogranular thin films with a high electrical resistivity and high resonance frequency are considered to be suitable for GHz magnetic device applications.

Soft anisotropic Fe/sub 65/Co/sub 35//Co thin films prepared by facing targets sputtering

High saturation magnetization FeCo(Fe/sub 65/Co/sub 35/)/Co films with 4/spl pi/M/sub s/ about 24 kG were prepared by facing targets sputtering (FTS). A well-defined in-plane uniaxial anisotropy and excellent soft magnetic properties were obtained with a hard axis coercivity of H/sub ch/=3 Oe by inserting a thin Co underlayer. The X-ray diffractometry (XRD) results indicate that the Co underlayer changed the main diffraction line from [200] in the FeCo single layer to [110] in the FeCo/Co films. The Co underlayer significantly reduced the average grain size from /spl sim/74 nm for FeCo single layer to /spl sim/8.2 nm for FeCo/Co films. A smoother surface and a narrower grain size distribution were observed in FeCo/Co films.

Optimization of high Bsat FeCo films for write pole applications

FeCo films and their lamination with ultrathin NiFe layers down to 5Å were deposited using dc magnetron sputtering techniques. Soft magnetic FeCo films were obtained at an optimal target power of 500W and an optimal deposition pressure of 2mTorr with high saturation flux density, Bsat&amp;gt;2.4T, and low easy-axis coercivity, Hce⩽15Oe, and hard-axis coercivity, Hch⩽3Oe, at a film thickness of 2000Å. While the magnetostriction remains at ∼4×10−6 the stress was further optimized by applying substrate bias at a controlled level ⩽50V without sacrificing film magnetic softness.