Magnetization reversal in Pt/Co(0.5 nm)/Pt nano-platelets patterned by focused ion beam lithography

Arrays of ultrathin Pt/Co(0.5 nm)/Pt nano-platelets with lateral sizes ranging from 30 nm to 1 μm have been patterned by focused ion beam (FIB) lithography under a weak Ga(+) ion fluence. From polar magneto-optical Kerr microscopy it is demonstrated that nano-platelets are ferromagnetic with perpendicular anisotropy down to a size of 50 nm. The irradiation process creates a magnetically soft ring at the nano-platelet periphery in which domain nucleation is initiated at a low field. The magnetization reversal in nano-platelets can be interpreted using a confined droplet model. All of the results prove that ultimate FIB patterning is suitable for preparing discrete magnetic recording media or small magnetic memory elements and nano-devices.     

Intrinsic magnetic anisotropy versus coupling in arrays of closely spaced circular Fe/GaAs(110) dots,patterned by focused ion beam

We present the results of a detailed magneto-optical Kerr effect and Brillouin light scattering investigation of an epitaxial Fe/GaAs(110) film, 9 nm thick, achieving a quantitative determination of its anisotropy constants. Starting from this film, three different arrays of circular dots with diameter of 200 nm and interdot spacings of 200, 60 and 30 nm, have been produced by focused ion beam patterning. The modification of both the magnetization curves and the spin wave spectrum of the patterned specimens are discussed in terms of structural imperfections, intrinsic magnetocrystalline anisotropy and interdot dipolar coupling.     

Analysis of far-infrared horns, lightpipes, and cavities containing patterned conductive films

A scheme is described for calculating the scattering parameters of patterned conductive films in waveguide. The films can have non-uniform, non-isotropic, and non-local sheet impedances. Once the scattering parameters are known, they can be combined with the scattering parameters of paths, dielectric slabs, and waveguide steps to build up models of complicated components comprising patterned films in profiled lightpipes and cavities. It is then straightforward to calculate the Stokes fields of the total reception pattern, the natural optical modes to which the component is sensitive, the Stokes fields of the individual natural modes, and the spatial state of coherence. The method is demonstrated by modeling an absorbing pixel in a length of shorted multimode waveguide. The natural optical modes change from being those of the waveguide to those of a free-space pixel as the size of the absorber is reduced.     

Preparation of free-suspended polyelectrolyte multilayer films using an alginate scaffold and their ion permeability

Free-suspended polyelectrolyte multilayer (PEM) films were prepared over an aperture (diameter, 1 or 3 mm) in a glass plate to study ion permeation across the PEM films. PEM films were successfully constructed by layer-by-layer deposition of poly(allylamine hydrochloride) and poly(styrene sulfonate) on the surface of glass plate whose aperture had been filled with an alginate gel, followed by dissolution of the alginate gel in an ethylenediaminetetraacetic acid solution. PEM films thus prepared showed selective permeability for inorganic salts such as NaCl, KCl, CaCl₂, Na₂SO₄, K₃[Fe(CN)₆], and K₄[Fe(CN)₆]. The results were rationalized based on the size and charge of the ions and the thickness and surface charges of films.     

Fe:O:C grown by focused-electron-beam-induced deposition: magnetic and electric properties

We systematically study the effect of oxygen content on the magneto-transport and microstructure of Fe:O:C nanowires deposited by focused-electron-beam-induced (FEBID) deposition. The Fe/O ratio can be varied with an Fe content varying between ～ 50 and 80 at.% with overall low C content (≈16 ± 3 at.%) by adding H(2)O during the deposition while keeping the beam parameters constant as measured by energy dispersive x-ray (EDX) spectroscopy. The room-temperature magnetic properties for deposits with an Fe content of 66-71 at.% are investigated using the magneto-optical Kerr effect (MOKE) and electric magneto-transport measurements. The nanostructure of the deposits is investigated through cross-sectional high-resolution transmission electron microscopy (HRTEM) imaging, allowing us to link the observed magneto-resistance and resistivity to the transport mechanism in the deposits. These results demonstrate that functional magnetic nanostructures can be created, paving the way for new magnetic or even spintronics devices.     

A magnetic and magneto-optical investigation of Co-Pt alloy nanowire arrays

We have investigated the magneto-optical properties of highly ordered Co-Pt alloy nanowire arrays embedded in anodic aluminum oxide templates. The magnetic field-dependent Stokes parameters, Faraday rotation angle and ellipticity were investigated by an in-house magneto-optical measurement system. The extracted hysteresis loops are broadly consistent with magnetic hysteresis loops obtained from the vibrating sample magnetometer. The maximum Faraday rotation angle and ellipticity of these samples were examined as a function of nanowire composition. With an increase of platinum content from 9 at.% to 86 at.% in the as-deposited nanowire arrays, the maximum Faraday rotation angle per length decreases linearly from 1.39 x 10(3) degrees/cm to 1.58 x 10(2) degrees/cm. The maximum ellipticity shows a similar behavior with the composition. These linear relationships suggest a dilution model for the magnetic moment in the alloy nanowires. Our results indicate that magneto-optical measurements comprise an effective and sensitive method for monitoring the behavior of AAO-based magnetic nanowire arrays.     

Spin Carrier Exchange Interactions in (Ga,Mn)N and (Zn,Co)O Wide Band Gap Diluted Magnetic Semiconductor Epilayers

(Ga,Mn)N and (Zn,Co)O wide band gap diluted magnetic semiconductor epilayers have been investigated by magneto-optical spectroscopy. In both cases, absorption bands observed below the energy gap allow us to study the nature of the valence and spin state of the incorporated magnetic element. Exchange interactions between magnetic ions and carriers can be observed by analyzing the magnetic circular dichroism in transmission or the exciton Zeeman splitting in reflection for (Zn,Co)O. A first estimation of the exchange integrals can be given for both materials.     

Influence of different conducting substrates on magnetic properties of electrodeposited Ni–Fe thin films

Electrodeposition of Ni–Fe soft magnetic alloy on copper and stainless steel substrates was performed in chloride bath. The deposition parameters such as current density, pH, temperature and deposition time have been investigated. From the investigation the optimized deposition parameters were current density 3.5 mA/cm², pH 3, temperature 30 °C and deposition time 15 min. The Ni–Fe magnetic alloys deposited on copper and stainless steel substrates under optimized deposition parameters are subjected to various characterizations. The structural and surface morphology of the Ni–Fe films were detected by using X-ray diffractogram (XRD) and scanning electron microscope (SEM) respectively. The constituents in the films were determined by energy dispersive X-ray spectroscopy (EDAX) technique. The magnetic properties such as the coercivity (H_c) and saturation magnetization of the films were studied with the help of vibrating sample magnetometer (VSM). From the magnetic studies it is concluded that the grain size are create a considerable impact on magnetic behavior of the films on both the substrates. The films prepared on stainless steel substrate of 0.1 M concentration at optimized deposition parameters exhibits higher coercivity (5010 Oe) which seems to be ideal for magnetic sensor applications.     

Rare earth-yttrium iron-gallium garnet epitaxial films for magnetic bubble domain applications

(RE,Y)₃(Fe,Ga)₅O₁₂ garnets, where RE=Eu or Gd, have been developed for use as magnetic bubble domain materials. Magnetic and crystallographic studies were used to find suitable compositions for epitaxial thin films on nonmagnetic garnet substrate crystals. Properties of films grown by liquid phase epitaxy on Czochralski Gd-Ga garnet (111) substrates are discussed. Uniaxial anisotropy in the films can be interpreted as being the result of a lattice mismatch stress mechanism. The Gd-Y films with uniaxial anisotropy are in tension while the Eu-Y films are in compression as shown by lattice spacing differences between films and their substrates. Uncracked, high stability Eu-Y films with very high compressive stresses were grown. Annealing experiments reveal significant changes in anisotropy which correlate with large changes in film lattice spacing. Thus, it is possible to obtain high uniaxial anisotropy in garnets containing only one kind of rare earth ion together with a nonmagnetic ion such as yttrium. These films support domains with very high wall velocities at typical device drive fields.     

Influence of implanted Fe on the Kerr effect of Co6Ag94 granular films

A magneto-optical chip of Fe–(Co₆Ag₉₄) granular films was fabricated by using of combinatorial Fe ions implanting into co-sputtered Co₆Ag₉₄ films and 16 units with different Fe content were prepared via binary masking scheme. The structures and surface morphologies of as-prepared and annealed Fe–Co₆Ag₉₄ films were analyzed by X-ray diffraction and atomic force microscopy respectively. It reveals that the Co, Fe and FeCo granules precipitate, grow and then form nanoparticles embedded in the Ag matrix during annealing. In addition, the measurement of the magneto-optic polar Kerr effect shows that Kerr rotation increases with increasing Fe content, which contributes to the magnetic moment. Precipitation and growth of the magnetic granules during annealing also increase the Kerr rotation due to the size effects. Further, Mössbauer study confirms that the formation of granules with certain size plays a principal role in the enhancement of magneto-optic polar Kerr effect.     

Ion beam modification of exchange coupling to fabricate patterned media

For bit-patterned media, media with low remanent magnetization (M(r)) and high M(r) regions are needed for storing information, which is usually achieved by lithographically defining magnetic and non-magnetic regions. In this work, we have investigated the use of ion beam modification of media surface to define the low and high M(r) states using a medium that is at a low M(r) state to start with. The low M(r) state is achieved by the use of synthetic antiferromagnetic coupling obtained in Co-alloy/Ru/Co-alloy trilayer structured film. Local ion beam modification at 30 keV energy using Ga+ ions was used to create high M(r) regions. AFM and MFM observations indicated that patterned regions of low and high M(r) can be observed with ion beam irradiation. This technique is a potential method to achieve patterned media without the need of planarization techniques.     

Evolution of etch profile in etching of CoFeB thin films using high density plasma reactive ion etching

Inductively coupled plasma reactive ion etching of CoFeB magnetic thin films patterned with Ti hard mask was studied in a CH₃OH/Ar gas mix. As the CH₃OH concentration increased, the etch rates of CoFeB thin films and Ti hard mask decreased but the etch profiles improved with high degree of anisotropy. The effects of coil rf power, dc-bias voltage and gas pressure on the etch characteristics were investigated. The etch rate increased with increasing coil rf power, dc-bias voltage and decreasing gas pressure. The degree of anisotropy in the etch profile of CoFeB films improved with increasing coil rf power and dc-bias voltage. X-ray photoelectron spectroscopy revealed that the chemical compounds containing Co and Fe components were formed during the etching. However, it was expected that the formation of these compounds could not increase the etch rates of the films due to low volatile compounds despite the improvement in etch profile.     

Spin-orbit-driven ferromagnetic resonance

Ferromagnetic resonance is the most widely used technique for characterizing ferromagnetic materials. However, its use is generally restricted to wafer-scale samples or specific micro-magnetic devices, such as spin valves, which have a spatially varying magnetization profile and where ferromagnetic resonance can be induced by an alternating current owing to angular momentum transfer. Here we introduce a form of ferromagnetic resonance in which an electric current oscillating at microwave frequencies is used to create an effective magnetic field in the magnetic material being probed, which makes it possible to characterize individual nanoscale samples with uniform magnetization profiles. The technique takes advantage of the microscopic non-collinearity of individual electron spins arising from spin-orbit coupling and bulk or structural inversion asymmetry in the band structure of the sample. We characterize lithographically patterned (Ga,Mn)As and (Ga,Mn)(As,P) nanoscale bars, including broadband measurements of resonant damping as a function of frequency, and measurements of anisotropy as a function of bar width and strain. In addition, vector magnetometry on the driving fields reveals contributions with the symmetry of both the Dresselhaus and Rashba spin-orbit interactions.     

Metal phosphate planar waveguides for biosensors

Hard, impermeable, glassy, metal phosphate films have been fabricated inexpensively by the use of a spin-coating and low-temperature-curing technique. Films that are suitable for use as monomode waveguides in biosensors have been identified through an examination of the optical and chemical properties of films containing Fe, Al, Ga, In, Cr, or V. The refractive index is controlled over the range 1.49-1.78 by varying the film composition. The film thickness is controlled over the range 50-1200 nm by varying the spin speed and the deposition temperature. Films can be patterned by photolithography or by embossing. Input coupling through an embossed grating of 833-nm pitch is demonstrated.     

Study of FePt films prepared by reactive sputtering

In the present study, ⁵⁷FePt films are prepared with reactive ion beam sputtering using mixture of argon and nitrogen gases. Energy-dispersive X-ray reflectivity is used to estimate the thickness of the as-deposited films. Structural and magnetic properties of the as-deposited and annealed films are studied using grazing incidence X-ray diffraction (GIXRD), magneto-optical Kerr effect (MOKE) and conversion electron Mossbauer spectroscopy (CEMS). Significant difference in structural and magnetic properties i.e., formation of ordered L1₀ phase and perpendicular magnetic anisotropy are observed for the films prepared with mixture of nitrogen and argon as compared to the film prepared with argon only. From the GIXRD, peaks corresponding to the ordered face-centred tetragonal FePt phase are observed for the films prepared with mixture gas. The results of CEMS clearly show the perpendicular magnetic anisotropy (PMA) for the films prepared with mixture of nitrogen and argon. The observed enhanced chemical ordering and the development of PMA in the films prepared with mixture gas is due to the role played by the defects created as a consequence of nitrogen escape in the films with high temperature annealing.     

Structural, magnetic and magneto-optical properties of ultrathin films of nickel on iridium (001)

A detailed theoretical study of the structural, magnetic and magneto-optical behaviours of ultrathin films of nickel grown by pseudomorphic epitaxy on semi-infinite Ir(001) is given. The crystalline structure is found to be body centered tetragonal. The total energies are calculated by Spin-Polarized Relativistic Linear Muffin-Tin Orbitals with Atomic Sphere Approximation method. The calculation of the magnetic properties shows a ferromagnetic inter-layer coupling. The polar magneto-optical Kerr effect spectra are calculated over a photon energy range extended to 9 eV. The microscopic origin of the most interesting features is explained by the interband transitions between the localized spin projected states. These transitions are characterized by a spin-flip.     

The Faraday rotation angle of Ni nanowire arrays: its dependence on photon energy and nanowire size

The magneto-optical properties of Ni nanowire arrays embedded in anodic aluminum oxide templates are studied, for a selection of photon energies, as a function of their diameter and length for the first time. This was achieved by the determination of Stokes parameters of the transmitted light. The magneto-optical response is found to differ considerably from that of the bulk material. At all photon energies studied, a linear association of the Faraday rotation angle with nanowire length has been observed; moreover, a proportional relationship between rotation angle per unit length and nanowire diameter has also been also observed, consistent with our earlier work on Fe and Co nanowires. The relationship between the Faraday rotation angle per unit length with different nanowire diameters and photon energy has been found to exhibit clear spectroscopic structure.     

Influence of preparation condition and doping concentration of Fe-doped ZnO thin films: Oxygen-vacancy related room temperature ferromagnetism

Fe-doped and Fe-Ga co-doped ZnO diluted magnetic semiconductor thin films on quartz substrate were studied. Rapid annealing enhanced the ferromagnetism (FM) of the films grown in Ar/O₂. All the films grown in Ar are n-type and the carrier concentration could increase significantly when Ga is doped. The state of Fe in the films was investigated exhibiting Fe³⁺. Magnetic measurements revealed that room temperature ferromagnetism in the films were doping concentration dependent and would enhance slightly with Ga doping. The origin of the observed FM is interpreted by the overlapping of polarons mediated through oxygen vacancy based on the bound magnetic polaron model.     

Structures in superconducting YBa2Cu3O7−δ thin films investigated by magneto-optic technique

Using a reflection magneto-optic technique we have investigated natural inhomogeneities and artificial structures in YBCO thin films exposed to an external magnetic field. The artificial structures were mechanically scratched by scanning a diamond tip with different loading over the film surface. Alternatively planar structures with reduced oxygen content could be patterned by heating the YBCO film with a focused laser beam in nitrogen atmosphere. Depending on the laser annealing parameters different screening properties concerning the applied magnetic field could be achieved.As a magneto-optically active layer we used EuS films evaporated on glass as well as bismuth- and gallium-doped lutetium-iron-garnet films grown onto (111) oriented gadolinium-gal lium-gar net substrates by liquid phase epitaxy. In contrast to measurements with EuS films that show only weak faraday rotation for temperatures higher than 20 K the magneto-optic studies have been expanded to about 60 K by using the garnet films.     

Experimental Determination of the Nonuniform Shape-Induced Anisotropy Field in Thin Ni–Fe Films

We have determined the nonuniform distribution of the shape-induced magnetic anisotropy field for patterned thin films of Ni-Fe. To do this, we used integrated microstrip structures with different widths on identically patterned Ni-Fe cores to act as probes of the internal magnetic field. We verified the accuracy of the field profiles by comparing them with M-H loop measurements of the magnetic films