Magnetic Film Thickness Research Articles

Magnetic properties of exchange‐spring composite films

AbstractHigh‐density magnetic recording in the Tbit/inch2 range is based on single bit, single domain particles in the nanometer range. In order to fulfil the prerequisites for high‐density recording the following magnetic properties must be guaranteed: Easy axis perpendicular to recording plane, thermal stability up to 200 °C, reversal fields of 1–2 T and switching times in the sub‐ns range. Composite nanoparticles composed of a soft and a hard magnetic layer are suitable to fulfil the above conditions. The magnetic ground states of exchange coupled bilayers are determined by micromagnetism and the corresponding reversal fields determined as a function of the soft magnetic film thickness. It is shown that the magnetic ground states are characterized by three configurations: in‐plane, oblique, and perpendicular magnetization depending on the thickness of the soft magnetic layer. These three ground states are characterized by reversal fields of different magnetization processes: Depinning of a charged Néel wall at the phase boundary for soft layer thicknesses Ls larger than the exchange length of the soft layer, spontaneous rotation of magnetization by a nucleation process for soft layer thicknesses smaller than the exchange length.

Effect of Magnetic Film Thickness on the Spatial Resolution of Magnetic Force Microscope Tips

Magnetic force microscope (MFM) tips were prepared by coating commercial atomic force microscope (AFM) tips of 5 nm radius with Co and CoCrPt magnetic thin films varying the thickness in a range of 10–80 nm. The structural and the magnetic properties of coated magnetic thin films were investigated by scanning electron microscopy, AFM, X-ray diffraction, and vibrating sample magnetometry. The tip radius and the film surface roughness increase with increasing the film thickness. With increasing the film thickness, the MFM signal sensitivity increases, whereas the resolution decreases due to increase of tip radius. The MFM observation resolutions of 10 nm and 23 nm are obtained with the tips coated with 20-nm-thick Co and 40-nm-thick CoCrPt films, respectively. The MFM resolution is influenced by both the tip radius and the magnetic moment of coated material.

Largely enhanced energy density in epitaxial SmCo5/Fe/SmCo5 exchange spring trilayers

In order to enhance the energy density (BH)max as a key property for permanent magnet applications, exchanged-coupled trilayers of SmCo5/Fe/SmCo5 with fixed SmCo5 layer thicknesses (25 nm) and varying soft magnetic Fe film thickness have been epitaxially grown by pulsed laser deposition on Cr buffered MgO(110) substrates. The effect of the increasing soft layer thickness on the reversal mechanism and improved remanence due to the higher Fe-volume fraction was investigated by vibrating sample magnetometry in external fields up to 9 T. As the energy density strongly depends on the volume of the samples, emphasis is put on multilayer architecture investigation and reliable thickness determination. Concerning the latter all applied analysis methods as energy dispersive x-ray analysis, Rutherford backscattering spectroscopy and transmission electron microscopy confirm energy densities with maximum values of 312 kJ/m3 (39 MGOe) for a soft layer thickness of 12.6 nm.

Magnetocapillary phenomenon affected by magnetic films

Behaviors of magnetic fluid have been widely studied due to the potential for developing biochips and other micro devices. In this study, magnetic films are deposited on the capillary, and the influences of capillary gap distance and magnetic film thickness on the magnetocapillary phenomenon are investigated. It is observed that in a wider gap a larger liquid height drop occurs due to the stronger magnetic attraction in magnetic fluids. Film thickness is found to affect the solid-liquid interfacial tension, and it significantly influences the behavior of magnetic fluid in a capillary.

The dc magnetic field, temperature and film thickness dependence of microwave surface resistance of YBCO and DyBCO thin films

We investigated the dc magnetic field and temperature dependences of the microwave surface resistance (Rs) of YBa2Cu3Oy (YBCO) and DyBa2Cu3Oy (DyBCO) superconducting thin films. The YBCO and DyBCO thin films, each with a thickness of 300, 500, or 700nm, were deposited on MgO (100) substrates by the thermal co-evaporation method. The Rs was measured using the dielectric resonator method. A dc magnetic field of up to 5.0T was applied parallel to the c-axis of the superconducting thin films. The results showed that the Rs value had almost the same temperature dependence at various thicknesses in a zero-external field. The Rs of the YBCO and DyBCO thin films increased with the applied dc magnetic field. The DyBCO thin films showed weaker magnetic field dependence of Rs than the YBCO thin films. The Rs ratio (defined as Rs(5T)/Rs(0T)) linearly increased with the film thickness. These results show that pinning strength decreased with an increasing film thickness.

The effect of magnetic fields on the electroless deposition of Co–W–P film

Magnetic fields perpendicular to the copper substrate were applied during an electroless deposition process to obtain Co–W–P thin films from alkaline baths. Effects of different magnetic intensities, pH values and different powers of ultrasonic on the composition, microstructure and magnetic properties of Co–W–P alloys were investigated. Along with the increase of magnetic intensity, deposition speed and film thickness increased gradually as a result of the impacts of magnetic force and micro-MHD effect. Higher magnetic intensity could improve cobalt atomic percentage in the film and increase magnetization of Co–W–P films. Almost all of the deposited films were crystalline and contained hexagonal cobalt with a preferred crystallographic orientation (002). Dissimilar surface morphology could be detected under different pH values when 0.5 T magnetic intensity was introduced, such as rice-like and needle-like structures. When magnetic field was applied during the electroless deposition, grains of films tended to grow perpendicularly to the substrate and hill-like structures would appear with the increase of magnetic intensity. It was also found out that hill-like structure thin films tended to have high coercivities. Hill-like structures could be smoothed when ultrasonic was applied during magnetic electroless deposition. Maximum coercivity (914 Oe) could be obtained when 90 W ultrasonic and B = 0.5 T were introduced.

基于磁流体的新型光纤电流传感器研究

A novel fiber optic Fabry-Perot (F-P) current sensor is developed based on magnetic fluid as the medium in F-P interference cavity. A signal demodulation method based on slanted fiber Bragg grating (FBG) wavelength measurement system is proposed. Theory and principle of electromagnetic-controlled refractive index of the magnetic fluid is described, as well as the structure of the sensor system. Preliminary experiments are carried out, and the results indicate that there is a fairly good linearity of the measurement characteristic. The thickness of magnetic fluid film and initial concentration will affect the measurement results.

400-fold reduction in saturation field by interlayering

The buildup of stress with increasing thickness of magnetic thin films is a common phenomenon that often induces undesirable anisotropies that can convert an otherwise magnetically soft film into a magnetically hard one. We found that by interlayering such a magnetic thin film with films that are either not lattice matched or have a different crystal structure, reductions in the saturation field as large as 400-fold can be achieved. Differences in grain size appear to be responsible.

Enhanced imaging of magnetic structures in micropatterned arrays of Co dots and antidots

A specific technique of numerical treatment of atomic force microscopy (AFM) and magnetic force microscopy (MFM) signal has been developed to enhance the quality of raw images, in order both to improve their contrast and to gain better insight on the sample topography and on the local arrangement of the magnetisation vector. Basically, the technique consists in computing the optimum conformal transformation that allows one to superimpose two AFM images of the same area, acquired performing subsequent scans whose fast scan axis were mutually perpendicular, and applying the inverse transform to the second image. After MFM image superposition, the two datasets were either summed or subtracted, in order to improve the magnetic contrast. Computations have been done in a Matlab ® workspace with the help of Image Processing Toolbox 4.2. Improved MFM images obtained on both dots and antidots thin evaporated Co arrays in the demagnetised state (after performing alternate field demagnetisation parallel and perpendicular to the array plane) have been interpreted. Samples consisting of large-size patterns (1×1 mm) of circular dots/antidots with square/hexagonal lattices and minimum diameters of 1 μm were prepared by optical lithography. The magnetic film thickness was chosen depending on resist thickness, and varied between 25 and 150 nm, with a fixed ratio 1:4 between metal/resist film thickness. MFM was exploited to obtain images of either intra-dot or inter-antidot magnetic structures.

Dynamics of vortexlike domain walls in triaxial magnetic films with the Goss orientation of the surface

The stationary dynamics of vortexlike domain walls in films with three magnetic axes and Goss orientation of the surface is studied for the first time with a micromagnetic method that exactly takes into account all basic types of interaction (including dipole-dipole interaction). Consideration is carried out using a 2D model of magnetization distribution by numerically solving Landau and Lifshitz’s nonlinear equations with attenuation in the Gilbert form. Dynamic configurations of domain walls are established, and the dependences of the domain wall velocity on an applied magnetic field, damping parameter, and magnetic film thickness are found.

Feasibility of an Integrated Self Biased Coplanar Isolator With Barium Ferrite Films

The development of passive devices using a ferrite is a major focus of current research for electronic applications in the microwave range (circulators and isolators). Hexagonal ferrite, such as barium ferrite (BaFe12O19 or BaM), which has a large resistivity and high permeability at high frequencies are indeed of great interest for microwave device applications. In this work we developed an integrated and self-biased coplanar isolator using BaM sputtered films. BaM films, 1-36 mum thick, were deposited under optimized conditions by radio frequency magnetron sputtering on alumina substrates. The films were crystallized using a 800degC thermal annealing. Isolators were then realized using patterning of coplanar waveguides (CPW) with standard lift-off technique. The slots and the central width were 300 mum wide and gold was used for the conductor lines. We evaluated the influence of various parameters on the device performances: the magnetic film's thickness, the positioning of the magnetic film (CPW deposited onto the magnetic film or directly on the substrate), the CPW metallic thickness and the polarizing field. As standard design, the CPW were deposited on the top of the magnetic film. At the remanent magnetization (no polarizing field applied), the transmission coefficients then showed a non reciprocal effect, which reached 5.4 dB per cm of line length at 50 GHz for a 26.5 mum thick BaM film. Both the insertion losses and the non-reciprocal effect measured increased with the magnetic film thickness with a saturation effect. In the second design where the CPW is deposited directly on the substrate after a selective etching of the BaM film, we measured that the non reciprocal effect reached higher values for lower BaM thicknesses than for the first design and that the insertion losses also decreased. The interaction between the field lines created by the conductors and the magnetic film was indeed favored in the second case. Finally, we show the tunability of the isolator with the polarizing field.

Depth dependence of Néel wall pinning on amorphous Co xSi 1−x films with diluted arrays of elliptical antidots

Diluted arrays of elliptical antidots have been fabricated by optical lithography, electron beam lithography and plasma etching on amorphous Co 74Si 26 magnetic films with a well-defined uniaxial anisotropy. The magnetic behavior of two identical antidot arrays but with different hole depth in comparison with film thickness has been studied by transverse magneto-optical Kerr effect. Significant differences appear in the coercivity depending on whether the magnetic film is completely perforated or not, indicating a much more effective domain wall pinning process when the depth of the holes is smaller than the magnetic film thickness.

Magnetooptical properties of perforated metallic films

It is shown that optical transmittance and the magnetooptical (MO) Faraday rotation in the heterostructure of a periodically perforated metallic layer attached to a smooth magnetic dielectric thin film demonstrate resonance dependences on the wavelength and magnetic-film thickness. It is possible to adjust geometrical and MO parameters of the system in order to get these resonance peaks close in wavelength and get enhanced Faraday rotation (by a factor of 5–10) along with sufficient transmittance (30–40%). The phenomenon is explained in terms of the excitation of the surface plasmon polaritons waves coupled with waveguided modes of the magnetic film.

Influence of magnetic film thickness on the escape anisotropy of the electrons emitted in the presence of a stripe domain structure

Angular distributions of the escape of electrons, emitted by the surface of a magnetic film containing a stripe domain structure (SDS) are calculated. It is shown for the films of cobalt and ferrite-garnet that the film thickness and the parameters of the magnetic materials significantly influence the conditions of escape blocking and channelling of the electrons near the sample surface. A primitive model of particle channelling along the domain boundary gives a qualitatively correct description of the thickness influence on the shadow size and the critical channelling angle along the boundary of a stripe domain.

Magnetic field dependence of the dynamical properties of ferromagnetic semiconducting thin films

The effect of external magnetic field, temperature and film thickness on the spin wave energy and the spin-wave damping in thin ferromagnetic semiconducting films is studied using the s–d interaction model and a Green's function formalism beyond the random phase approximation.

Particle size and magnetic field-induced optical properties of magnetic fluid nanoparticles

Magnetite nanoparticles with diameters of 7, 9, and 12 nm have been prepared by a chemical coprecipitation method. The transmission of light through magnetic fluid containing these nanoparticles has been investigated as a function of film thickness with wavelength between 400 and 750 nm, and applied magnetic fields up to 275 Oe. The transmission threshold shifts to the lower wavelength side with decreasing magnetic fluid film thickness as well as the particle size. For a given film thickness, the transmittance increases with increasing magnetic field for films with a particle size of 7 and 9 nm, but decreases in the 12-nm film. This is attributed to the competition between the van der Waals and dipole-dipole interaction.

Magneto-optical additivity in ferromagnetic bilayers separated by nonferromagnetic spacers

We show that for some ultrathin multilayer structures the proportionality of the longitudinal Kerr ellipticity signal to the magnetic film thickness does not take place. Instead, thinner magnetic layers give even twice larger contributions than the thicker ones located a few monolayers deeper. This effect is demonstrated both experimentally and theoretically on ultrathin Fe∕Cr∕Fe sandwich systems prepared on GaAs(001) surfaces. Such a behavior is explained by a depth variation of phase relations between the optically reflected wave and the wave generated by the magneto-optical interaction. This mechanism becomes very effective close to the phase where the magneto-optical ellipticity cancels.

Large magnetoresistance at room-temperature in small-molecular-weight organic semiconductor sandwich devices

We present an extensive study of a large, room temperature magnetoresistance (MR) effect in tris-(8-hydroxyquinoline) aluminum sandwich devices. The effect is similar to that previously discovered in π-conjugated polymer devices. We characterize this effect and discuss its dependence on magnetic field direction, voltage, temperature, film thickness, and electrode materials. The MR effect reaches almost 10% at fields of 10 mT at room temperature. The effect shows only a weak temperature dependence and is independent of the sign and direction of the magnetic field. Measuring the devices' current–voltage characteristics, we find that the current depends on the voltage through a power-law. We find that the magnetic field changes the prefactor of the power-law. We also studied the effect of the magnetic field on the electroluminescence (MEL) of the devices and analyze the relationship between MR and MEL.

Theoretical and experimental permeability spectra of nano-granular Co-Fe-Al-O films for GHz magnetoelastic device applications

The effects of the various parameters such as saturation magnetization, anisotropy field, film thickness and resistivity of soft magnetic thin films on the permeability spectra are investigated by using the Landau-Lifshitz-Gilbert equation. Both effects of eddy current loss and ferromagnetic resonance loss on the intrinsic permeability are taken into account to obtain the expression for the effective relative permeability. The calculated permeability spectra are in good agreement with experimental results for nano granular Co-Fe-Al-O thin films, even though only one fitting parameter, the damping constant, is used.

Electron delocalization in disordered films induced by magnetic field and film thickness

We have studied the delocalization transition of noninteracting electrons in disordered thin films induced by magnetic field and film thickness. We also report results for two-dimensional systems. We have used for this purpose (i) a numerical technique based on transfer-matrix method for quasi-one-dimensional systems; (ii) self-consistent theory of localization for weak fields generalized to situations lacking time-reversal invariance. Numerical results provide strong evidence for a zero-temperature insulator-to-metal transition (MIT) with both field and film thickness. In self-consistent theory we adopt two procedures which give different results on MIT induced by field, temperature, and thickness. The variance between numerical and analytical results is analyzed.