Effect of seed layers on the static and dynamic magnetic properties of CoIr films with negative effective magnetocrystalline anisotropy

The c-axis oriented hcp-Co_(81)Ir_(19)magnetic films were prepared on different seed layers(Ni,Cu,Ir,Pt,Au,and No seed).We systematically investigated the impact that surface-free energy and strain energy have on the orientation and defects and/or internal stress of the grains by increasing the lattice mismatch ratio.Moreover,the initial permeability and the natural resonance frequency were discussed in great detail using a comparison between calculated values and experimental values.We found that the almost unchanged 4πM_(s) andμ_(i) are not affected,while the changed H_(c),intrinsic K_(grain),and f_(r) are strongly dependent on the seed layer and seed layer material.Moreover,the extracted damping constant is sensitive to the defects and/or internal stress and orientation of the grains.Therefore,the soft magnetic properties and microwave properties are adjusted and optimized by seed layers with different materials.

Reduction of Coercivity of Fe-N Soft Magnetic Film by Heat Treatment

200 nm thick Fe-N magnetic thin films were deposited on glass substrates by RF sputtering. The as-deposited films have high saturation magnetization but their coercivity is also higher than what is needed Therefore it is very important to reduce coercivity. The samples were vacuum annealed at 250℃ under 12000 A/m magnetic field. When the N content was in the range of 5-7 at. pct, the thin films consisted of α' +α' after heat treatment and had excellent soft magnetic properties of 4πMs=2.4 T, HC <80 A/m. However, the thickness of a recording head was 2μm, and Hc increased as thickness increased. In order to reduce the Hc, the sputtering power was raised from 200 W to 1000 W to reduce the grain size. 2μm Fe-N thin films were vacuum annealed under the same condition, when the N content was in the range of 5.9-8.5 at. pct, the thin films kept its excellent magnetic properties of 4πMs=2.2 T, HC <80 A/m. The properties of the films meet the need of a recording head material used in the dual-element GMR/inductive heads.

Electrodeposition behavior of nanocrystalline CoNiFe soft magnetic thin film

The electroplating behavior of nanocrystalline CoNiFe soft magnetic thin film with high saturation magnetic flux density (Bs>2.1 T) and low coercivity (Hc) was investigated using cyclic voltammetry and chronoamperometry methods in conjunction with the scanning electron microscopy (SEM/EDX). The results show that, under the experimental conditions, the co-deposition of CoNiFe film behaves anomalously due to the atomic radii of iron series elements following the order of rFe>rCo>rNi. In the case of lower electroplating current density, the co-deposition of CoNiFe film follows a 3-D progressive nucleation/growth mechanism, while in the case of higher electroplating current density, which follows a 3-D instantaneous nucleation/growth mechanism. Meanwhile, the change of nucleation mechanism of CoNiFe film with electroplating current density was interpreted theoretically in the light of quantum chemistry.

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 taxget-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.

Microwave properties and surface topography of soft magnetic films with high resistivity

A single layer of CoFeB and a multilayer of CoFeB MgO films are prepared by means of DC/RF magnetron sputter deposition. The excellent microwave properties and high electrical resistivity are simultaneously achieved in the discontinuous multilayer structure of [Co44Fe44B12（0.7nm）/MgO（0.4nm）]40 film. This film has a high permeability （μ′） （larger than 100 below 2.1 GHz）, a high magnetic loss （μ″） （larger than 100 in a range from 1.5 to 3.3GHz）, a resistivity of 3.3 × 10^3μΩ. cm, a saturation magnetization of 1.2 T, and an in-plane uniaxial anisotropy field of 5.5 kA/m. The microstructure and the surface topography of the film are also analysed. The relatively large surface roughness for the discontinuous film is responsible for the wide frequency band of magnetic loss. The magnetic loss and the high resistivity indicate that the discontinuous CoFeB MgO multilayer film has potential applications in microwave absorbers and electromagnetic interference （EMI） shielding materials in a GHz frequency range.

Excellent soft magnetic properties realized in FeCoN thin films

FeCoN soft magnetic thin films are prepared by using the reactive direct-current magnetron sputtering technique. It is found that the addition of N2 can reduce the coercivity of the FeCoN film, and excellent soft magnetic properties can be obtained when the ratio of N2 flow to total gas flow is 10%. The influences of texture, grain size, and stress on the magnetic properties and the high-frequency behaviors of the films are also discussed.

Excellent magnetic softness in TbFe/FeCoV multilayers

[Tb4oFe6o（x nm）/Fe49Co49V2（y nm）]N multilayers were prepared by multitarget magnetron sputtering using a rotary turn-table technique in a stop-and-go mode. The mulfilayers were investigated using X-ray diffraction, field emission scan electron microscopy and vibrating sample magnetometry. The result shows that the coercive field drops abruptly with increasing number of bilayers, and it remains generally stable when the number of bilayers is 10 or higher. An excellent magnetic softness with a coercivity of 1.0 mT is obtained for x = 5 and y = 5 after annealing at 250℃. A crystalline state is observed in FeCoV layers before and after annealing by X-ray diffraction.

Influence of electroplating conditions on magnetic properties of Fe-36wt.% Ni alloy film

A Fe-Ni soft magnetic film was prepared in sulphate solution by electroplating.The influences of the molar ratio of n[Fe^(2+)]/n[Ni^(2+)],current density,bath temperature,pH and L-ascorbic acid concentration on magnetic properties of Fe-Ni alloy film were investigated.The results show that the saturated flux density(BS)of the film increases initially and decreases after it reaches the specific value with the increase of n[Fe^(2+)]/n[Ni^(2+)]molar ratio,current density,bath temperature and pH.However,the relationship between L-ascorbic acid concentration and BS keeps linear.It is observed that the coercive force(H_(c))is enhanced with the increase of n[Fe^(2+)]/n[Ni^(2+)]molar ratio,current density and pH.By comparison,when the bath temperature increases,Hc always decreases.With the increase of L-ascorbic acid concentration,the coercive force increases initially and then decreases.

Influence of magnetic layer thickness on[Fe_(80)Ni_(20) O/SiO_2]_n multilayer thin films

In the present work, a series of [FesoNi20-O/SiO2]n multilayer thin films is fabricated using a reactive magnetron sputtering equipment. The thickness of SiO2 interlayer is fixed at 3 nm, while the thickness values of FesoNi20-O magnetic films range from 10 nm to 30 nm. All films present obvious in-plane uniaxial magnetic anisotropy. With increasing the FesoNi20-O layer thickness, the saturation magnetization increases slightly and the coercivity becomes larger due to the enlarged grain size, which could weaken the soft magnetic property. The results of high frequency magnetic permeability characterization show that films with thin magnetic layer are more suitable for practical applications. When the thickness of FesoNi20-O layer is 10 nm, the multilayer film exhibits the most comprehensive high-frequency magnetic property with a real permeability of 300 in gigahertz range.

Effect of hydrogen plasma implantation on the micro-structure and magnetic properties of hcp-Co_(80)^(57)Fe_(4)Ir_(16)thin films

We present detailed investigations of structural and static/dynamic magnetic properties of hydrogenated hcp-Co_(80)^(57)Fe_(4)Ir_(16) soft magnetic thin films.Two different kinds of defects,i.e.,destructive and non-destructive,were demonstrated by controlling the negative bias voltage of the hydrogenation process.Our results show that the structure and magnetic properties of our sample can be tuned by the density of the induced defects.These results provide better understanding of the hydrogenation effect and thus can be used in the future for materials processing to meet the requirements of different devices.

Influence of Nanocrystallization on Magnetic Properties of the Co-Based Alloys Thin Films

The rapid recurrent thermal annealing (RRTA) method has been used to amorphous Co-Nb-Zr soft magnetic thin films fabricated by DC sputtering. By using this method, in this paper, the crystalline grains with diameter of about 30~90 nm are formed and the partial nanocrystallization of the films is realized. As a result, the soft magnetic properties of the Co-based nanocrystalline thin films are improved greatly after RRTA: their resistivity is a quarter decreased; the average initial permeability is enhanced from 3 500 to over 5 000; the impedance is increased form 20 ~100 ?(at 1.4 GHz); the resonance peak is moved about 200 MHz down to low frequency. The evident improvement enables the Co-based nanocrystalline thin films to be used over a much wide frequency range of 1 KHz ~1.5 GHz.

MHz频段颗粒型纳米晶T-M-O系软磁性薄膜及其应用

本文介绍高Bs高ρ颗粒型纳米晶T-M-O系软磁性薄膜的主要类型、制备方法、某些膜的特点和主要电磁性能;最后介绍这种膜的应用。

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

A series of FeCo-based thin films were pre- pared 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/SiNx]n multilayer thin film were investigated systematically. When FeCo thin film was doped with Si and N, the resis- tivity and soft magnetic properties of the obtained FeCo- SiN thin film can be improved effectively. The coercivity （He）, resistivity （p） and ferromagnetic resonance frequency （fr） can be further optimized for the [FeCoSiN/SiNx]n multilayer thin film. When the thickness of FeCoSiN layer and SiNx layer is maintained at 7 and 2 nm, the He, p andfr for [FeCoSiN/SiNx]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 （Hoe ≈ 506 A·m^-1） of [FeCoSiN/SiNx]n multilayer thin film can be maintained after annealing at 300℃ in air for 2 h.

High frequency characteristics of (Ni_(75)Fe_2)_x(Zn O)_(1-x) granular thin films with tunable damping coefficient

The effect of the volume fraction of ferromagnetic metal （x） in （Ni75Fe25）x（ZnO）1-x nanogranular thin films on microstructural, soft-magnetic, and high-frequency properties was investigated. Good soft-magnetic properties were obtained in a broad x range, with 0.55 〈 x 〈 0.82. High resolution transmission electron microscopy （HRTEM） observations reveal that the grain size of the samples is lower than 14 nm, and that it decreases with decreasing x. Of special interest, our investigation of the permeability spectra indicates that these films exhibit an adjustable frequency linewidth of resonance peak, dependant upon changing x. Correspondingly, large and adjustable damping coefficients （aeff） from 0.023 to 0.043 were achieved by decreasing x from 0.82 to 0.55. Combined with the HRTEM results, the variation of αeff with x was analyzed in detail.

Influence of bath composition on the electrodeposition of cobalt-molybdenum amorphous alloy thin films

Cobalt-molybdenum （Co-Mo） amorphous alloy thin films were deposited on copper substrates by the electrochemical method at pH 4.0. Among the experimental electrodeposition parameters,only the concentration ratio of molybdate to cobalt ions （[MoO4^2-]/[Co^2＋]） was varied to analyze its influence on the mechanism of induced cobalt-molybdenum codeposition. Voltammetry was one of the main techniques,which was used to examine the voltammetric response,revealing that cobalt-molybdenum codeposition depended on the nature of the species in solution. To correlate the type of the film to the electrochemical response,various cobalt-molybdenum alloy thin films obtained from different [MoO4^2-]/[Co^2＋] solutions were tested. Crack-free homogeneous films could be easily obtained from the low molybdate concentrations （[MoO4^2-]/[Co^2＋]≈0.05） applying low deposition potentials. Moreover,the content of molybdenum up to 30wt% could be obtained from high molybdate concentration; in this case,the films showed cracks. The formation of these cracked films could be predicted from the observed distortions in the curves of electric current-time （j-t） deposition transients. The films with amorphous structure were obtained. The hysteresis loops suggested that the easily magnetized axis was parallel to the surface of the films. A saturation magnetization of 137 emu·g^-1 and a coercivity of 87 Oe of the film were obtained when the deposition potential was -1025mV,and [ MoO4^2-]/[Co^2＋] was 0.05 in solution,which exhibited a nicer soft-magnetic response.

Effect of Annealing on Microstructure and Electrical Characteristics of Doped Poly （3-Hexylthiophene） Films

The effect of annealing on the microstructure and electrical characteristics of poly （3-hexylthiophene） （P3HT） films doped with very small amounts of the electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane （F4-TCNQ） is studied. X-ray diffraction and UV-vis spectrum studies show that unlike the pure P3HT film, the thermal treatment on the doped fihns under an Ar atmosphere can effectively enhance the crystalline order of P3HT films, as well as successfully facilitate the orientation of the polymer chains. This improvement is attributed to the electrostatic force between P3HT and F4-TCNQ molecules. This force induces the polymer chains to crystallize and orient during the annealing process. As a result, annealing significantly improves performance, especially for the Ion/Ioff ratio of the TFTs based on the doped P3HT films.

FeCoNiMnY高熵薄膜的软磁性能及噪声抑制特性

采用电化学沉积法制备了FeCoNiMnY高熵薄膜,利用XRD、VSM和VNA等测试手段对其性能进行表征,并研究了不同Y元素浓度对高熵薄膜晶体结构、软磁性能和噪声抑制特性的影响。结果表明,Y的添加一方面粗化了晶粒尺寸,增加了合金矫顽力(从12.09 kA/m增加至21.7 kA/m);另一方面,元素Y的添加引起的晶格畸变提高了高熵薄膜的电阻率(高达336μΩ·mm)。FeCoNiMnY高熵薄膜的最大功率损耗比在6.1 GHz处可达到0.84。上述结果表明,FeCoNiMnY噪声抑制片在千兆赫频率下的抗电磁干扰应用中具有很大的潜力。

Giant magnetoimpedance effect of multilayered structure(F/SiO_2)_3/Ag/(SiO_2/F)_3 films deposited in a longitudinal magnetic field

The soft magnetic properties and giant magnetoimpedance(GMI) effect of the multilayered structure(F/SiO2)3/Ag/(SiO2/F)3(F≡Fe71.5Cu1Cr2.5V4Si12B9) films,which were prepared by radio frequency sputtering without and with a longitudinal magnetic field of about 72 kA/m,are studied.The results show that the GMI effect almost cannot be detected in the samples deposited without field,whereas,a longitudinal magnetic field applied during deposition process obviously optimizes the soft magnetic properties of the films,and noticeable GMI effect is obtained.The maximum values of the longitudinal and transverse GMI ratios are 45% and 44% at the frequency of 6.81 MHz,respectively.In addition,the dependence of magnetoimpedance ratio,magnetoresistance ratio,magnetoreactance ratio and effective permeability ratio on the frequency has been investigated.We found that the GMI spectrum curves in the longitudinal and transverse cases almost overlap for the field-deposited sample.The GMI effect is mainly a giant magnetoinductive effect at low frequencies.When f 】9 MHz,magnetoreactance ratio changes to a negative,i.e.,the property of reactance changes from inductive to capacitive.

Structure and Magnetic Properties of Magnetostrictive FeGa Film on Single-Crystal(100) GaAs and(001) Si Substrate Fabricated by Pulsed Laser Deposition

FeGa thin film has been deposited on（100）-oriented GaAs and（001）-oriented Si substrates with different film thicknesses and laser energy densities at room temperature by pulsed laser deposition system.Materials structure and static magnetic of FeGa film have great changes depending on the substrate and energy density of pulsed laser.X-ray diffraction reveals the presence of first-order order–disorder structure ofgrain phase and disordered bcc A2 structure on GaAs substrate.The coercivity and remanence of FeGa film on GaAs substrate ratio show a regular dependence on the thickness and energy densities.However,film on Si substrate did not exhibit structure change,which can be attributed to a large lattice mismatch between FeGa and Si.

磁性薄膜材料剩磁分布与弯曲形式的关系探究

磁场驱动的智能软材料在软体机器人、生物医疗诊断、柔性电子等领域具有潜在的应用前景。软材料内部的磁场分布形式决定了材料的变形行为,而材料内部的剩磁分布由其充磁时的弯曲形式控制。该文探究了薄膜状硬磁性软材料内部剩磁分布与其充磁时弯曲形状之间的关系。通过对薄膜充磁时弯曲形式的控制,实现了对其内部剩磁分布的控制。为了验证关系式的合理性,基于力-磁耦合本构模型对几种不同充磁弯曲方式的薄膜的变形行为进行了数值模拟及实验验证。对实验结果和模拟结果进行对比发现两者吻合较好,证明了所给出的两者之间关系式的合理性。