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.     

Layer resolved magnetization reversal study in SmCo5/Fe nanocomposite bilayers

A hard/soft SmCo5/Fe nanocomposite magnetic bilayer system is fabricated on x-ray transparent 100-200 nm thin Si3N4 films by magnetron sputtering.The microscopic magnetic domain pattern and its behaviours during magnetization reversal in the hard and the soft magnetic phases are studied separately by element specific magnetic soft x-ray microscopy at a spatial resolution of better than 25 nm.We observe that the domain patterns for the soft and hard phases show coherent behaviours in varying magnetic fields.We derive local M(H) curves from the images of Fe and SmCo5 separately and find the switches for hard and soft phases to be the same.     

Fine-grained NdFeB magnets prepared by low temperature pre-sintering and subsequent hot pressing

Fine-grained Nd10.79Pr2.8Al0.4B7.72Fe78.29magnets were prepared by low temperature pre-sintering and subsequent hot pressing.The grain size of the magnets is just about 1–3μm because the low sintering temperature results in no grain growth.The orientation degree,microstructure,and magnetic properties were studied.Some grains’easy axes deviate from the orientation direction,possibly due to grain rotation during the hot pressing.By subsequent annealing,the magnetic properties were significantly enhanced.Especially,the squareness of the demagnetization curve was improved greatly.The enhancement of coercivity by annealing can be explained by an improvement of both grain boundaries and magnetic isolation,which decouples the exchange interaction between neighboring grains.     

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

The dependences of soft magnetic properties and microstructures of the sputtered FeCo (=FeFeCo薄膜 溅射条件 软磁性 高饱和磁化强度FeCo film, sputtering conditions, high saturation magnetization, soft magnetic properties2005-10-263/7/2006 12:00:00 AMThe 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.     

Reduction of Ordering Temperature of FePt-Al2O3 Thin Films by N2 Addition During Sputtering

We investigate the effect of N2 addition during sputtering on the microstructure and magnetic properties of FePt-Al2O3 thin films. The texture of FePt phase in FePt-Al2O3 thin films changes from （111） to a more random orientation by N2 addition during sputtering. The ordering temperature of FePt phase reduces about 100℃ with appropriate N2 partial pressure. A larger coercivity of 6.0 × 10^5 Aim is obtained with N2 partial pressure about 15%. Structural analysis reveals that a small quantity of Fe3N phase forms during sputtering and the release of N atoms during the post annealing induces a large number of vacancies in the films, which benefits to the transformation of FePt phase from fcc to fct.     

Effect of Zr Addition on Glass-Forming Ability and Magnetic Properties of Fe-Nd-Al-B Alloys Prepared by Suction Casting

The microstructure and magnetic behaviors of the Fe-Nd-Al-B alloys prepared by suction casting with zirconium addition are investigated. With the small amount of zirconium addition, the magnetic properties of the alloys change from hard magnetic property to soft magnetic property. The proper addition of Zr （6%） not only improves the glass forming ability, but also suppresses the crystallization. From the scanning electron microscopy of the [（Fe0.53Nd0.37 Al0.10 ）0.96B0.04]94Zr6 alloy and the local average elemental compositions determined using energy dispersive spectroscopy analysis, the amorphous phase with a composition of Fe47Nd38Al12Zra in the alloy can be observed. The bulk amorphous Fe47Nd38Al12Zr3 alloy is prepared by suction casting exhibiting good glassforming ability and soft magnetic behavior.     

X-Ray Magnetic Circular Dichroism Measurement of Fe-Co Alloy Films Prepared by Electrodeposition

The macro- and micro-magnetic properties of Fe-Co alloy films eletrodeposited on CaAs（100） are studied by synchrotron radiation x-ray magnetic circular dichroism （XMCD） in combination with the magneto-optical Kerr effect （MOKE） measurements and magnetic force microscopy （MFM）. The orbital and spin magnetic moments of each element in the Fe-Co alloy are determined by the sum rules of XMCD. Element-specific hysteresis loops （ESHL） are obtained by recording the La MCD signals as a function of applied magnetic field. MOKE results reveal that the amorphous films are magnetically isotropic in the surface plane. The MFM image shows that the dimension of the magnetic domains is about 1-2 #m, which is much larger than that of the grains, indicating that there are intergranular correlations among these grains. Both ESHL and MOKE hysteresis loops indicate the strong ferromagnetic coupling of Fe and Co in the alloy films.     

Reactively sputtered Fe3 O4 -based films for spintronics

Half metallic polycrystalline, epitaxial Fe3O4 films and Fe3O4 -based heterostructures for spintronics were fabricated by DC reactive magnetron sputtering. Large tunneling magnetoresistance was found in the polycrystalline Fe3O4 films and attributed to the insulating grain boundaries. The pinning effect of the moments at the grain boundaries leads to a significant exchange bias. Frozen interfacial/surface moments induce weak saturation of the high-field magnetoresistance. The films show a moment rotation related butterfly-shaped magnetoresistance. It was found that in the films, natural growth defects, antiphase boundaries, and magnetocrystalline anisotropy play important roles in high-order anisotropic magnetoresistance. Spin injection from Fe3O4 films to semiconductive Si and ZnO was measured to be 45% and 28.5%, respectively. The positive magnetoresistance in the Fe3O4 -based heterostructures is considered to be caused by a shift of the Fe3O4 e g ↑ band near the interface. Enhanced magnetization was observed in Fe3O4 /BiFeO 3 heterostructures experimentally and further proved by first principle calculations. The enhanced magnetization can be explained by spin moments of the thin BiFeO 3 layer substantially reversing into a ferromagnetic arrangement under a strong coupling that is principally induced by electronic orbital reconstruction at the interface.     

Microstructure and magnetic properties of FeRh thin films with Pt doping

In this paper,the structure and magnetic properties of FeRh alloy thin films with a small amount of Pt doping fabricated onto a glass substrate by sputtering are investigated systematically.XRD results show that the diffraction pattern of as-deposited film exhibits only nonmagnetic γ phase.After annealing,the disordered γ phase transforms to an ordered α' phase.The temperature dependence of saturation magnetization of different annealing times and Pt contents are characterized.The phase transition temperatu...     

Crystal Structure and Magnetic Properties of Sm2 Fe17-Nδ Thin Films Deposited on Si （100） Substrates

This work focuses on the crystal structure and magnetic properties of the hard magnetic Sm2 Fe17 Nδ films prepared by dc magnetron sputtering and the subsequent nitriding process. The XRD, EDS, M-H and M-T data show that N enters the cell structure and the films with the single Th2Zn17 phase are obtained when the nitriding temperature varies from 300 to 400℃, thus the maximum value of the coercivity Hc reaches 2561.7Oe. However, the Sm2Fo17 phase decomposes to the StuN nonmagnetic phase and the α-Fe soft magnetic phase with further increasing nitriding temperature, which corresponds to the decreasing Hc. Furthermore, the easy magnetization direction （EMD） is found to locate randomly in the film plane. This texture can not give an excellent MR/Ms higher than the Stoner-Wohlfarth limitation （MR/Ms = 0.5）, which agrees well with the observed low MR/Ms （0.58）. It is suggested that the magnetization reversal process is dominated by the nucleation mechanism according to the initial magnetization curve and the dependence of Hc on the field H.     

Soft Magnetism and High Frequency Properties of Fe65Co35-MgF2 Granular Thin Films

（Fe65 Co35 ）x （MgF2 ）1-x films with different metal volume fraction x are fabricated by magnetron sputtering. The results reveal that good soft magnetic properties can be obtained in a very wide x range （0.9 〉 x 〉 0.55） with Hc not exceeding 10 Oe, and high resistivity is also realized for the samples. Especially for the sample with x = 0.75, the coercivity in hard and easy axes is 1.6 Oe and 8.5 Oe, respectively, 4πMs = 14.1 kG and p reaches 1.16 mΩ2.cm. The dependence of complex permeability μ =μ′ - jμ″ on frequency shows that the real part μ′is more than 190 below 2.0 GHz and ferromagnetic resonance frequency fr reaches 2.43 GHz, implying that the film is promising for high frequency applications. High resolution transmission electron micrographs show that the films consists of bcc Fe65 Co35 particles embedded uniformly in an amorphous insulating MgF2 matrix with particle size around a few nanometers. The excellent soft magnetic properties and high frequency properties are ascribed to exchange of coupling among magnetic granules, and the exchange coupling variation in a wide x range （0.9 〉 x 〉 0.55） is studied systematically by △M plots.     

Composition-Controlled Low Field Magnetostriction of TbFe Amorphous Films

Amorphous TbFe films are fabricated by dc magnetron sputtering, and their magnetostrictions at low field are examined over a wide range of terbium content （from 32at.% to 70at.%）. It is found that the terbium content plays an important role in the magnetic and magnetostrictive properties of TbFe films. TbFe film soft magnetic properties and low field magnetostriction can be efficiently improved by controlling the terbium at an optimum content. The magnetostriction at lower magnetic field is increased with the increase of terbium content up to 48.2at.%. After reaching the maximum value, further increase of terbium content would result in a great decrease of the low field magnetostriction. By contrast, at higher magnetic field, the magnetostriction is decreased monotonically with the increase of the terbium content.     

Molecular beam epitaxy and superconductivity of stoichiometric FeSe and KxFe2_ySe2 crystalline films

Our recent progress in the fabrication of FeSe and KxFe2_ySe2 ultra thin films and the understanding of their superconductivity properties is reviewed. The growth of high-quality FeSe and KxFe2_ySe2 films is achieved in a well controlled manner by molecular beam epitaxy. The high-quality stoichiometric and superconducting crystalline thin films allow us to investigate the intrinsic superconductivity properties and the interplay between the superconductivity and the film thickness, the local structure, the substrate, and magnetism. In situ low-temperature scanning tunneling spectra reveal the nodes and the twofold symmetry in FeSe, high-temperature superconductivity at the FeSe/SrTiO3 interface, phase separation and magnetic order in KxFe2_ySe2, and the suppression of superconductivity by twin boundaries and Fe vacancies. Our findings not only provide fundamental information for understanding the mechanism of unconventional superconductivity, but also demonstrate a powerful way of engineering superconductors and raising the transition temperature.     

Ferromagnetism in Eu-doped ZnO films deposited by radio-frequency magnetic sputtering

This paper reports that Eu-doped ZnO films were successfully deposited on silicon (100) by radio-frequency magnetic sputtering. The x-ray diffraction patterns indicate that Eu substitutes for Zn in the lattice. Ferromagnetic loops were obtained by using superconducting quantum interference device at 10 K and room temperature. No discontinuous change was found in both of the zero-field-cooled and field-cooled curves. The observed ferromagnetism in Eu-doped ZnO can be attributed to a single magnetic phase. The saturation magnetisation decreased remarkably for the Eu-doped ZnO prepared by introducing 5% of oxygen in the sputtering gas or by the post annealing in O2, suggesting that the defects play key roles in the development of ferromagnetism in Eu-doped ZnO films.     

Structural and photoluminescent properties of ZnO films deposited by radio frequency reactive sputtering

Zinc oxide films with c-axis preferred orientation were deposited on silicon (100) substrates by radio frequency (RF) reactive sputtering. The properties of the sam- ples were characterized by X-ray diffractometer, X-ray photoelectron spectroscopy and fluorescent-spectrophotometer. The effect of sputtering power and substrate temperature on the structural and photoluminescent (PL) properties of the ZnO films was investigated. The results indicated that when the sputtering power is 100 W and the substrate temperature is 300-400℃, it is suitable for the growth of high c-axis orientation and small strain ZnO films. A violet peak at about 380 nm and a blue band at about 430 nm were observed in the room temperature photolumines- cence spectra, and the origin of blue emission was investigated.     

Magnetization reversal of ultrathin Fe film grown on Si（111） using iron silicide template

Ultrathin Fe films were epitaxially grown on Si（lll） by using an ultrathin iron silicide film with p（2 × 2） surface reconstruction as a template. The surface structure and magnetic properties were investigated in situ by low energy electron diffraction （LEED）, scanning tunnelling microscopy （STM）, and surface magneto-optical effect （SMOKE）. Polar SMOKE hysteresis loops demonstrate that the Fe ultrathin films with thickness t 〈 6 ML （monolayers） exhibit perpen-dicular magnetic anisotropy. The characters of M-H loops with the external magnetic field at difference angles and the angular dependence of coercivity suggest that the domain-wall pinning plays a dominant role in the magnetization reversal process.[第一段]     

Transparent conductive reduced graphene oxide thin films produced by spray coating

Reduced graphene oxide thin films were fabricated on quartz by spray coating method using a stable dispersion of reduced graphene oxide in N,N-Dimethylformamide.The dispersion was produced by chemical reduction of graphene oxide,and the film thickness was controlled with the amount of spray volume.AFM measurements revealed that the thin films have near-atomically flat surface.The chemical and structural parameters of the samples were analyzed by Raman and XPS studies.It was found that the thin films show electrical conductivity with good optical transparency in the visible to near infrared region.The sheet resistance of the films can be significantly reduced by annealing in vacuum and reach 58 k?with a light transmittance of 68.69%at 550 nm.The conductive transparent properties of the reduced graphene oxide thin films would be useful to develop flexible electronics.     

Effective Anisotropy in Magnetically Nd2Fe14B/α-Fe Nanocomposite

Considering different contact situations of grains, we effective anisotropies of magnetically soft α-Fe grains, investigate the effects of exchange-coupling interaction on hard Nd2Fe14B grains and NdaFe14B/α-Fe nanocomposite. An expression of effective anisotropy suitable for different degrees of exchange-coupling between grains is presented. The calculation results show that the exchange-coupling interaction increases the average anisotropy of soft grains and decreases that of hard grains. The effective anisotropy of Nd2Fe14B/α-Fe nanocomposite decreases smoothly with decreasing grain size when the grain size is larger than 20 nm while it decreases dramaticaily with further decrease of the grain size. In order to maintain high coercivity in Nd2Fe14B/α-Fe nanoeomposite, the grain size should not be less than 20nm.     

X-ray diffraction study of effect of deposition conditions on α--β phase transition and stress evolution in sputter-deposited W coatings

Pure W and W-Cu-W trilayer coatings were deposited on an Fe substrate by d.c. magnetron sputtering. The α-β phase evolution, intragranular stress evolution in sputter-deposited W layer were investigated by x-ray diffraction. They are directly related to the film microstructure, density and adhesion. Therefore, control of the film stress and phase component transition is essential for its applications. The phase component transition from β-W to α-W and intragranular stress evolution from tensile to compressive strongly depend on the deposition parameters and can be induced by lowering Ar pressure and rising target power. The compressively stressed films with α-W phase have a dense microstructure and high adhesion to Fe substrate.     

Microstructure and magnetic properties of CoFe_2O_4 thin films deposited on Si substrates with an Fe_3O_4 under-layer

The microstructure and magnetic properties of cobalt ferrite thin films deposited by the sputtering method on an Fe3O4 under-layer were investigated at different post-annealing temperatures.Results show that the Fe3O4 under-layer can accelerate the grain growth of cobalt ferrite films due to the phase transformation of the Fe3O4 under-layer at about 400°C-500°C.By introducing the Fe3O4 under-layer,cobalt ferrite nanocrystalline thin films with high coercivity can be obtained at lower post-annealing temperat...