Effects of oblique-incidence evaporation on magnetic properties of Fe20Ni80/Fe70Co30 bilayer film

Evaporative deposition at oblique incidence is shown to enhance the magnetic anisotropy of an Fe₂₀Ni₈₀ magnetic film and induce magnetic anisotropy in an overlying, strongly isotropic Fe₇₀Co₃₀ film. This deposition method for the formation of an underlayer of several lattice parameters in thickness and semi-hard overlayer of a few thousands Angstroms in thickness achieves a significant change in the magnetization process and strong suppression of the coercive forces of Fe₇₀Co₃₀ in the hard magnetization direction. Soft magnetization of the Fe₇₀Co₃₀ overlayer is not achieved when one of the layers is deposited at oblique incidence. It is anticipated that shape magnetic anisotropy is responsible in part for the magnetic anisotropy induced in both in Fe₂₀Ni₈₀ under- and Fe₇₀Co₃₀ overlayer by oblique incidence evaporation.     

Thickness-dependent magnetic properties of Ni81Fe19, Co90Fe10 and Ni65Fe15Co20 thin films

We present results of magnetization and magnetic anisotropy measurements in thin magnetic films of the alloys Ni₈₁Fe₁₉, Co₉₀Fe₁₀ and Ni₆₅Fe₁₅Co₂₀ that are commonly used in magnetoelectronic devices. The films were sandwiched between layers of Ta. At room temperature the critical thickness for all the films to become ferromagnetic is in the range 11–13 Å. In Co₉₀Fe₁₀ the coercivity and the anisotropy field both depend strongly on layer thickness.     

Nd28Fe66B6/Fe50Co50双层纳米复合膜的结构和磁性

利用磁控溅射法制备了Nd₂₈Fe₆₆B₆/Fe_{50Co50 双层纳米复合磁性薄膜，研究了其结构和磁性.经873K退火处理15min 后，利用x射线衍射仪测定薄膜晶体结构，采用俄歇电子能谱仪估算薄膜厚度和超导量子干 涉仪测量其磁性.磁性测量表明，1)该系列薄膜具有垂直于膜面的磁各向异性.从起始磁化曲 线和小回线的形状特征可知，矫顽力机制主要是由畴壁钉扎控制.2)对于固定厚度（10nm） 层的硬磁相Nd-Fe-B和不同厚度（dFeCo=1—100nm）层软磁相FeCo双层纳米复合 膜,剩磁随软磁相FeCo 厚度的增加快速增加，而矫顽力则减少.当dFeCo=5nm 时 ，最大磁能积达到160×１０^３A/m.磁滞回线的单一硬磁相特征说明，硬磁相Nd -Fe-B层和软磁相FeCo层之间的相互作用使两相很好地耦合在一起.剩磁和磁能积的提高是由 于两相磁性交换耦合所致. 关键词： Nd-Fe-B/FeCo双层纳米复合膜 交换耦合 磁性增强}     

Thickness induced magnetic anisotropic properties of Tb-Fe-Co thin films

The influence of Tb₂₅Fe₆₁Co₁₄ thin film thicknesses varying from 2 to 300 nm on the structural and magnetic properties has been systematically investigated by using of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, magnetization, and magneto-optic Kerr effect microscopy measurements. Thin film growth mechanism is pursued and controlled by ex-situ X-ray refractometry measurements. X-ray diffraction studies reveal that the Tb₂₅Fe₆₁Co₁₄ films are amorphous regardless of thin films thicknesses. The magnetic properties are found to be strongly related to thickness and preferred orientation. With an increase in film thickness, the easy axis of magnetization is reversed from in-plane to out-of-plane direction. The change in the easy axes direction also affects the remanence, coercivity and magnetic anisotropy values. The cause for the magnetic anisotropy direction change from in-plane to out-of-plane can be related to the preferred orientation of the thin film which depends on the large out-of-plane coercivity and plays an important role in deciding the easy axes direction of the films. According to our results, up to the 100 nm in-plane direction is dominated over the whole system under major Fe-Fe interaction region, after that point, the magnetic anisotropy direction change to the out-of-plane under major Tb-Fe/Tb-Co interaction region and preferred orientation dependent perpendicular magnetic anisotropic properties become more dominated with 2.7 kOe high coercive field values.     

Interface morphologies and magnetization characteristics of Co70Fe30 thin films deposited on conjugated polymer thin films

The surface and interface morphology and magnetization characteristics of Co₇₀Fe₃₀ thin films deposited on bare glass and p-Si/SiO₂ substrates and on conjugated polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) thin films on such substrates have been studied by atomic force microscopy and magneto-optic Kerr effect. It was found that the average absolute magnitude of the coercive field of Co₇₀Fe₃₀ correlates with the roughness of the underlayer prior to Co₇₀Fe₃₀ deposition. P3HT deposited on p-Si/SiO₂ substrates possesses an increased surface roughness as compared to the p-Si/SiO₂ surface, but displays a decreased surface roughness as compared to the one of a bare glass substrate.     

Magnetic properties of permalloy multilayers with alternating perpendicular anisotropies

This work reports the magnetic properties of sputtered permalloy (Ni₈₀Fe₂₀) multilayers grown changing the anisotropy direction 90° in successive layers. Magnetic measurements show how the saturating field can be controlled by the thickness ratio between different anisotropy layers and how the coercive field is reduced increasing the number of layers. The linearity of the hysteresis loop is also improved when increasing the number of layers. Magnetic measurements are compared to simulations based on a Stoner-Wolfarth magnetization rotation mechanism.     

Electric field-induced magnetoresistance in spin-valve/piezoelectric multiferroic laminates for low-power spintronics

Electric field-induced magnetic anisotropy has been realized in the spin-valve-based {Ni₈₀Fe₂₀/Cu/Fe₅₀Co₅₀/IrMn}/piezoelectric multiferroic laminates. In this system, electric-field control of magnetization is accomplished by strain mediated magnetoelectric coupling. Practically, the magnetization in the magnetostrictive FeCo layer of the spin-valve structure rotates under an effective compressive stress caused by the inverse piezoelectric effect in external electrical fields. This phenomenon is evidenced by the magnetization and magnetoresistance changes under the electrical field applied across the piezoelectric layer. The result shows great potential for advanced low-power spintronic devices.     

Multilevel interaction between layers in layered film structures

An analysis was carried out of the mechanism underlying magnetic interlayer interaction in film structures. The investigation was based on the assumption that interlayer bonding affects film hysteresis. This was based on experimental data on the coercive force, the domain structure parameters, and the microstructure of Fe₁₉Ni₈₁/Cr/Fe₁₉Ni₈₁ and Fe₁₅Co₂₀Ni₆₅/Cr/Fe₁₅Co₂₀Ni₆₅ films. Theoretical estimates show that, as the thickness of the Cr interlayer increases, the exchange interaction between the ferromagnetic layers can be replaced by the magnetostatic interaction whose effectiveness is determined by surface irregularities and layer ‘magnetization ripples’. Fiz. Tverd. Tela (St. Petersburg) 39, 2191–2194 (December 1997)     

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

High saturation magnetization soft magnetic FeCo (=Fe₆₅Co₃₅) 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.     

Magnetoresistive Fe19Ni81/Tb-Co medium with an internal magnetic bias

The magnetization reversal and magnetoresistance of two-layer exchange-coupled Fe19Ni81/Tb-Co films are studied. Amorphous Tb _x Co_{100 − x} layers with 30 < x < 35 are found to have a uniaxial magnetic anisotropy and a rather high coercive force, which ensures magnetic biasing of the adjacent permalloy layers. In addition, the permalloy layers subjected to selective annealing exhibit a significant anisotropic magnetoresistance and a small magnetic hysteresis. These properties make it possible to consider the developed film structure as an effective magnetoresistive medium. This structure is used to form magnetic sensor samples that have an odd transfer function in the absence of external magnetic biasing.     

Enhancement of in-plane magnetic anisotropy in (111)-oriented Co0.8Fe2.2O4 thin film by deposition of PZT top layer

The CoFe₂O₄ and Co_0.8Fe_2.2O₄ single layer (CFO) as well as PZT/CoFe₂O₄ and PZT/Co_0.8Fe_2.2O₄ bilayer thin films were grown using the pulsed laser deposition technique on Pt(111)/Si substrates at 600 °C. All films had a perfect (111)-orientation and the degree of orientation of CFO films was improved by the deposition of a PZT top layer. Precision X-ray diffraction analysis (avoiding the shift of peaks due to sample misalignment) revealed that the CFO films on Pt(111)/Si substrate were under an out-of-plane contraction and the deposition of a PZT top layer led to the increase in the out-of-plane contraction. The (111)-oriented CFO single layer films had a strong in-plane magnetic anisotropy as a result of orientation as well as the stress-induced magnetic anisotropy. The magnetic properties of CFO film were altered by the deposition of a PZT top layer leading to the enhancement of in-plane magnetic anisotropy. The enhanced in-plane magnetic anisotropy was more detectable in PZT/Co_0.8Fe_2.2O₄ rather than PZT/CoFe₂O₄ bilayer film, which could be expected from its higher magnetocrystalline as well as magnetostriction constants.     

Co0.9Fe0.1薄膜面内元素分辨的磁各向异性

利用X射线磁性圆二色技术对Co_0.9Fe_0.1薄膜面内元素分辨的磁各向异性进行了研究，通过剩磁模式测量不同磁化方向的样品组分原子单位空穴磁矩的变化，发现除了在生长的磁诱导方向存在易磁化轴外，在与该轴垂直的方向还存在一个类似易轴的软磁化轴；面内的两个难磁化轴与易磁化轴取向大约成66°夹角，从而构成了面内双轴磁各向异性；对不同组分元素，其单位空穴磁矩随磁化方向的变化趋势基本相同，不同磁化方向Fe原子单位空穴的磁矩值约为Co的对应值的87%，反映了Fe原子和Co原子之间存在着强烈的铁磁性耦合. 关键词： 磁各向异性 X射线磁性圆二色 铁磁耦合 CoFe合金薄膜     

Influence of the inhomogeneity of local magnetic parameters on the curves of magnetization in an ensemble of Fe<Subscript>3</Subscript>C ferromagnetic nanoparticles encapsulated in carbon nanotubes

Methods have been proposed and tested for analyzing local magnetic parameters in a system of single-domain ferromagnetic nanoparticles using their magnetization curves. The magnetic inhomogeneity in ensembles of Fe₃C nanoparticles encapsulated in carbon nanotubes has been investigated. It has been established that the Fe₃C nanoparticles encapsulated in carbon nanotubes are characterized by two-modal distribution functions of the local magnetic anisotropy energy. The particle distribution over the blocking temperature is reconstructed from the experimental temperature dependence of the coercive force. The allowance made for the inhomogeneity of the local magnetic parameters of the Fe₃C nanoparticles, which were studied by the proposed methods, explains the discrepancy between the magnetic anisotropy energy determined by the method of the magnetization approaching saturation and the magnetic anisotropy energy estimated from the coercive force of single-domain nanoparticles.     

Perpendicular magnetic anisotropy in Co50Pt50 and Co50Pt50 ? x Pd x films

Atomic ordering and its effect on the perpendicular magnetic anisotropy and coercive force in Co₅₀Pt₅₀ and Co₅₀Pt_{50 − x} Pd _x (x = 3–10 at %) alloy films are investigated. The dependence of the coercive force on the film thickness is studied. It is shown that thin films of the ordered alloys become magnetically uniaxial with the easy magnetic axis normal to the plane of the film. Such films can be used for magnetic and thermomagnetic data recording and storage.     

Xenon-ion Induced Magnetic and Structural Modifications of Ferromagnetic Alloys

Thin polycrystalline films of permalloy (Ni₇₉Fe₂₁) and permendur (Co₅₀Fe₅₀) have been irradiated with Xe-ions to fluences of 10¹⁴–10¹⁶ ions/cm². Ion-induced structural and magnetic modifications have been measured by grazing angle X-ray diffraction, Rutherford backscattering and magneto-optical Kerr effect. In the case of permendur, the Xe-ion implantation first reduced the coercivity, because of stress relaxation, while higher ion fluences increased the coercivity due to pinning centers generated in the film. The ion irradiation aligned the in-plane easy axis of the magnetization along the direction of the external magnetic field during implantation. Phase shifts obtained from magnetic force microscopy confirmed these modifications. The effects of Xe-ion irradiation in permalloy films are much weaker and underline the importance of magnetostriction in the variation of the coercivity and anisotropy.     

Annealing effect of NiO/Co90Fe10 thin films: From bilayer to nanocomposite

Exchange-biased bilayers are widely used in the pinned layers of spintronic devices. While magnetic field annealing (MFA) was routinely engaged during the fabrication of these devices, the annealing effect of NiO/CoFe bilayers is not yet reported. In this paper, the transition from NiO/Co₉₀Fe₁₀ bilayer to nanocomposite single layer was observed through rapid thermal annealing at different temperatures under magnetic field. The as-deposited and low-temperature (<623 K) annealed samples had rock salt (NiO) and face center cubic (Co₉₀Fe₁₀) structures. On the other hand, annealing at 623 K and 673 K resulted in nanocomposite single layers composed of oxides (matrix) and alloys (precipitate), due to grain boundary oxidization and strong interdiffusion in the NiO/CoFe and CoFe/SiO₂ interfaces. The structural transition was accompanied by the reduction of grain sizes, re-ordering of crystallites, incensement of roughness, and reduction of Ni²⁺. When measured at room temperature, the bilayers exhibited soft magnetism with small room-temperature coercivity. The nanocomposite layers exhibited an enhanced coercivity due to the changes in the magnetization reversal mechanism by pinning from the oxides. At 10 K, the increased antiferromagnetic anisotropy in the NiO resulted in enhanced coercivity and exchange bias in the bilayers. The nanocomposites exhibited weaker exchange bias compared with the bilayers due to frustrated interfacial spins. This investigation on how the magnetic properties of exchange-biased bilayers are influenced by magnetic RTA provides insights into controlling the magnetization reversal properties of thin films.     

高电阻率多层纳米颗粒膜软磁特性及微波磁导率

研究了应用于微波频段的多层纳米颗粒膜的电阻率、软磁特性和微波磁导率.采用多次顺序沉积Co₄₀Fe₄₀B₂₀和SiO₂薄层制备了薄膜.在100kA/m均匀面内磁场经过250℃真空退火2h,制备的Co₄₀Fe₄₀B₂₀/SiO₂多层膜具有难轴矫顽力为210A/m、饱和磁化强度为838.75kA/m、电阻率为2.06×10^{3关键词： 纳米颗粒膜 电阻率 软磁特性 微波磁导率}     

Microstructure and microwave permeability of FeCo thin films with Co underlayer

Microstructure, static magnetic properties and microwave permeability of sputtered FeCo films were examined. Fe₆₀Co₄₀ films (100 nm in thickness) deposited on glass substrates exhibited in-plane isotropy and a large coercivity of 161.1 Oe. When same thickness films were deposited on 2.5 nm Co underlayer, well-defined in-plane anisotropy was formed with an anisotropy field of 65 Oe. The sample had a static initial permeability of about 285, maximum imaginary permeability of 1255 and ferromagnetic resonance frequency of 2.71 GHz. Cross-sectional TEM image revealed that the Co underlayer had induced a columnar grain structure with grain diameter of 10 nm in the FeCo films. In comparison, FeCo films without Co underlayer showed larger grains of 70 nm in diameter with fewer distinct vertical grain boundaries. In addition, the Co underlayer changed the preferred orientation of the FeCo from (1 0 0) to (1 1 0). The improvement in soft magnetic properties and microwave behavior originates from the modification of the film microstructure, which can be well understood by the random anisotropy theory.     

Coercivity and induced magnetic anisotropy by stress and/or field annealing in Fe- and Co- based (Finemet-type) amorphous alloys

Uniaxial magnetic anisotropy has been induced in amorphous Fe_73.5Cu₁Nb₃Si_15.5B₇ (Fe-rich) and (Co₇₇Si_13.5B_9.5)₉₀Fe₇Nb₃ (Co-rich) ferromagnetic alloys by annealing under stress and/or magnetic field. Such anisotropy plays a crucial role on the magnetization process and, consequently, determine the future applications of these materials. The mechanisms involved on the origin of such induced magnetic anisotropy showed significant differences between Fe-rich and Co-rich amorphous alloys. This work provides a comparative study of the coercive field and induced magnetic anisotropy in Fe-rich and Co-rich (Finemet) amorphous alloys treated by stress and/or field.     

Magnetic properties of field-annealed FeCo thin films

Fe₅₀Co₅₀ thin films with thickness of 30 and 4 nm have been produced by rf sputtering on glass substrates, and their surface has been observed with atomic force microscopy (AFM) and magnetic force microscopy (MFM); MFM images reveal a non-null component of the magnetization perpendicular to the film plane. Selected samples have been annealed in vacuum at temperatures of 300 and 350 °C for times between 20 and 120 min, under a static magnetic field of 100 Oe. DC hysteresis loops have been measured with an alternating gradient force magnetometer (AGFM) along the direction of the field applied during annealing and orthogonally to it. Samples with a thickness of 4 nm display lower coercive fields with respect to the 30 nm thick ones. Longer annealing times affect the development of a harder magnetic phase more oriented off the film plane. The field applied during annealing induces a moderate magnetic anisotropy only on 30 nm thick films.