The work addresses the correlation between the phase composition and the magnetic characteristics of aligned Fe-filled multi-walled carbon nanotubes (Fe-MWCNTs) grown by pyrolysis of ferrocene on oxidized Si substrates. In a combinatorial approach we exploited the extremely high gradients of the technological parameters temperature and ferrocene flow across the surface of a substrate positioned close to the reactor wall to obtain a large variation in the structural and magnetic properties of the Fe-MWCNTs. In this way, we established several clear correlations between the Fe-filling phase composition and the overall magnetic characteristics of the aligned Fe-MWCNTs. The α-Fe rich samples, which possess a more ordered graphitic sheet structure, a higher degree of preferred crystalline orientation of the metal filling and much larger metal crystallites in comparison with the carbide-rich samples, show a much stronger magnetic anisotropy with easy axis perpendicular to the substrate and unusually high values of the coercive field Hc and the saturation field Hs. The changes in the measured saturation magnetisation Ms and the Hc values correlate well with the variation of the α-Fe content and the filling crystallinity. A special annealing treatment of the samples causes a distinct increase of the α-Fe quantity and an increase of the measured average grain size. The respective magnetic characteristics show a significant increase of the overall magnetic moment and decrease of the coercive field. The correlation between the structural and the magnetic characteristics of the annealed samples matches quite well the respective correlations in the case of as-deposited samples.

This work presents results on modifications of the structure and the magnetic properties of magnetron-sputtered Fe50Co50 films induced by high dose Sin or Xe ion implantation. A combinatorial approach was used in order to screen a wide range of implantation doses from 4 x 10(15) to 1.6 x 10(17) ions/cm(2). Sm-implanted FeCo films are considered as precursors for the synthesis of multi-phase exchange-spring magnetic materials while Xe ion implantation of such films is known as a method to modify film stresses and magnetical properties.Materials libraries of as-implanted films were investigated by energy dispersive X-ray analysis (EDX) and secondary ion mass spectrometry (SIMS) for the film composition and concentration depth profiles, transmission electron microscopy (TEM) and X-ray diffraction (XRD) for the film morphology and crystalline structure, vibrating sample magnetometry (VSM) for the magnetization behaviour and four-point probe measurements for the film resistivity. Three main results were found on the basis of this combinatorial study: (i) The high-dose Sm-implanted samples have an overall Sin concentration above the value necessary for Sm-Fe(Co) alloy formation and show magnetic hysteresis curves corresponding to two-phase or two-layer film stucture; (ii) The two implanted series show quite different magnetic anisotropy in the film plane a negligable one for Xe and a strong one for Sm implantation; (iii) For the Sm-implanted samples a clear local maxima in the coercivity H-c and the anisotropy field H-k can be seen at D-sm >= 1 x 10(16) ions/cm(2). The XRD spectra of the libraries show that the last two effects are closely related to the film strains introduced by the implantation process. (c) 2005 Elsevier B.V. All rights reserved.

AlOx tunnel barriers prepared by oxidizing ultra-thin Al films of various thickness by means of a Rf wave resonance plasma beam source were investigated to understand the influence of the plasma oxidation conditions on the junction resistance Rj, the magnetoresistance ratio (MR) and the switching characteristics of exchange-biased magnetic tunnel junctions (MTJs) with NiMn pinning layer. The junction properties were characterized as a function of oxidation time, plasma power and distance between plasma source and sample. The MR of the as-deposited junction was about 15%. The highest exchange bias fields (17mT) and pinned layer coercivities (23mT) can be achieved with extended annealing at low temperatures T≅320∘C or with a rapid annealing at T≅400∘C, respectively. Short-time annealing (1min) at intermediate temperatures (350°C) and field cooling at 1T leads to the highest MR effect of 35% at room temperature and 55% at 4.2K.

The magnetic properties of annealed Fe–Pt multilayer thin films with a broad composition range were investigated in order to identify the effects of composition and annealing temperature on the achievable coercive field, and to identify its maximum at low processing temperatures. Two types of multilayer systems were deposited as materials libraries to vary the composition from Fe20Pt80 to Fe75Pt25. The first type of multilayer was comprised of alternating opposing wedges, whereas the second type consisted of repeated uniform Fe and Pt layers interspersed periodically with Fe wedge layers. It was found that coercive fields μ0HC>0.7T can be achieved at an annealing temperature of about 300°C (60min) for both types of multilayers as long as the composition is close to 50:50. Higher annealing temperatures are needed for films, which deviate from this composition. Increasing the annealing temperature up to 700°C leads to increased coercivity values. Multilayers with additional Fe layers showed increased remanence but reduced coercive fields.

Fe 57 transmission Mössbauer spectroscopy (TMS) and back scattered conversion electron Mössbauer spectroscopy (CEMS) measurements were carried out on Fe-filled multiwalled carbon nanotubes (Fe-MWCNTs) grown by chemical vapor deposition with ferrocene as precursor. Samples of Fe-MWCNTs material deposited on the inner wall of the quartz tube reactor and samples of aligned Fe-MWCNTs grown perpendicularly to the oxidized Si substrate were characterised by the TMS method. The data show that Fe phases encapsulated within the carbon nanotubes comprise α-Fe, γ-Fe, and Fe3C in different percentage ratio depending on the sample preparation. These results are in a good accordance with the previously measured magnetic characteristics and with the structural data found by x-ray diffraction as well by selected area electron diffraction methods and allow a new complementary characterization of the Fe(Fe-alloy)-MWCNT systems. The CEMS method applied for the characterization of metal containing MWCNTs reveals that close to the top surface of the aligned Fe-MWCNTs samples only the γ-Fe phase is found. This technique shows an additional potential for further investigation of the spatial distribution of the crystalline phases in the depth of aligned Fe-MWCNT samples.

This work addresses the issue of acceleration of the long post-deposition annealing procedures typically used for obtaining the antiferromagnetic (AFM) state of the pinning film in NiMn-based spin-valve systems. It presents results on exchange biasing (EB) bi-layers NiMn(50 nm)/Ni19Fe81(5 nm) grown on a permalloy seed layer after annealing for a very short time at temperatures in the vicinity of the phase transition of the NiMn film.Both the magnetic and the structural characteristics measured after the short annealing procedure reveal clear differences between the samples annealed below and above a specific temperature T* which is lower than the phase transition temperature in the equilibrium NiMn phase diagram. The absence of an EB in the samples short annealed at T-an < T* is related to the dominance of the face-centered cubic (FCC) paramagnetic NiMn phase. In contrast, the significant EB effect in the samples annealed at T-an > T* and the saturation found in H-EB for T-an greater than or equal to 375degreesC are connected with the existence of a dominant stable face centered tetragonal (FCT) AFM NiMn phase. This shows that for the investigated sputter-deposited NiMn pinning films a specific temperature T* exists above which a fast FCC double right arrow FCT (paramagnetic double right arrow AFM) phase transition occurs.The unidirectional EB effect surprisingly found in samples cooled without magnetic field can be explained with a two-step generation model: (i) the formation of specific magnetic anisotropy in the as-deposited permalloy films strongly depending on the phase composition of the NiMn pinning film, on its surface morphology and the stresses in the AFM/ FM interface, respectively, and (ii) recording ("burning in") of the existing magnetic anisotropy through the described fast paramagnetic double right arrow AFM phase transition. (C) 2004 Elsevier B.V. All rights reserved.

The magnetic functionalization of carbon nanotubes or the incorporation of carbon nanotubes into magnetic systems opens up exciting research topics and technological applications. We describe recent results concerning the filling of carbon nanotubes with ferromagnetic materials. In addition, we discuss the aspects and experimental verification of spin-dependent transport phenomena through carbon nanotubes.

Carpet-like flakes (area ≤ 9mm2; thickness < 50μm) of well-aligned Co-filled multi-walled carbon nanotubes were grown by decomposition of cobaltocene. The nanotubes have outer diameters of 50–90nm and a metal core of 15–30nm diameter. They are discontinuously filled with f.c.c.-Co nanowires of up to a few micrometers in length. Magnetometry studies show a weak uniaxial magnetic anisotropy with the easy axis along the nanowires and a high coercivity of about 59mT. Electron holography provides information about the magnetic characteristics of individual nanowires.

We report on the magnetic properties of Fe-filled multiwalled carbon nanotubes (MWNTs) grown by chemical vapor deposition (CVD) on Si substrates with ferrocene as precursor. The MWNTs are aligned perpendicularly to the substrate plane. X-ray diffraction analyses indicate the presence of both bcc and fcc iron with a relatively strong texture. Magnetometry measurements show a pronounced magnetic anisotropy with the easy axis perpendicular to the substrate plane and parallel to the axis of the aligned MWNTs, respectively. The low-temperature behavior suggests a negligible coupling between the two iron phases. We accessed the magnetic properties of individual Fe-filled MWNTs by electron holography using a transmission electron microscope (TEM).

We have investigated the magnetic and the structural characteristics of bi-layer exchange biasing (EB) systems NiMn-Co as function of the antiferromagnetic (AFM) film deposition parameters and of the post-deposition annealing and field-cooling procedures. The effects of sputtering pressure, growth rate, seed layer and of the annealing parameters were studied by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Magneto-Optical Kerr (MOKE) effect measurements. The results yielded optimised deposition conditions and permitted us to establish efficient annealing and field-cooling procedures. The best obtained EB systems with 5 nm Co film reveal coercive field H-c greater than or equal to 35 Oe and exchange bias field H-EB greater than or equal to, 95 Oe and have good stability in air up to at least 200degreesC.The obtained magnetic characteristics are closely correlated with the crystalline structure of the as-deposited samples and with the phase transformation effects. According to our results, the as-deposited samples are a mixture of a nonequilibrium FCC NiMn phase (quenched by the sputtering deposition process) and a variable amount of the equilibrium face centred tetragonal (FCT) phase. The ratio of these two phases depends on the deposition conditions-the amount of the FCT NiMn phase is larger if deposition conditions closer to equilibrium have been used, especially at higher sputtering gas pressure and higher deposition rates. The annealed samples contain dominantly the FCT AFM phase as confirmed by XRD and TEM-diffraction analyses. The transition to this AFM state depends on the initial structure of the as-grown samples and, respectively, on their deposition conditions. (C) 2002 Elsevier Science B.V. All rights reserved.

Thin films (250 nm - 1200 nm) of cubic Y3Fe5O12 (YIG) were deposited on fused silica and monocrystal Y3Al5O12 (YAG) 100 substrates by spray pyrolysis (using ethylene glycol solutions of Y-Fe(III)-citric complexes) and additionally annealed at 950 degrees Celsius in static air for 2 h. The films were afterwards irradiated by a free-running Nd-YAG laser (pulse energy 650 mJ, pulse duration 700 microseconds, energy density 100 mJ/cm2) whose onset was synchronized with that of a magnetic field pulse of nearly-square shape (magnetic induction 0.5 T, pulse duration 900 microsecond). The samples were placed normally to the direction of the magnetic field. The temperature reached at the film surface was estimated to be as high as the melting point, considerably higher than the Curie temperature. The laser-magnetic field treatment causes: a sharp weakening of the YIG/YAG films texturation, highly textured before that treatment; an increase of the crystallites size; change in the phase composition of the YIG/silica films; an increase of the magnetization by more than 45%; an increase (in the case of YIG/silica) and decrease (in the case of YIG/YAG) of the coercive force.

The oxidation of sputtered NiFe(20 wt.%, Permalloy) thin films with a thickness of 180 nm was studied during annealing up to 400°C for 2 h in air. The composition and the thickness of the oxide layer and the compositional change in the NiFe alloy layer as well as the microstructure of the film were investigated by Auger electron spectroscopy, X-ray diffraction, and transmission electron microscopy. Distinct oxidation starts at about 300°C. The formed oxide layer consists of Fe2O3. The Fe concentration in the NiFe layer decreases with the oxidation which leads to changes of the properties of this layer.

Non-reactive d.c. magnetron sputtering by two magnetron sources with inclined geometry was used for deposition of Cr-C thin films with C:Cr ratio in the range 0.08-2.40. The phase composition of the films was investigated by x-ray diffraction, XPS, SEM and resistivity measurements. Four phase compositional regions were distinguished in the investigated large compositional range: films containing mainly microcrystalline Cr or Cr-C solid solution; films containing both the microcrystalline Cr phase and the stoichiometric Cr23C6 carbide phase (beta-phase); amorphous-like films composed of the ultradisperse Cr crystalline phase and different metastable carbides; and amorphous films consisting of a carbon matrix with a limited amount of a high-carbon carbide phase dispersed in it, The films from the first two regions exhibit very high microhardness and good wear resistivity, and at the same time a relatively low electrical resistivity, which make them promising coating materials for electronic applications. Copyright (C) 2000 John Wiley & Sons, Ltd.

Optimal conditions for depositing of high textured (111) TiN films by d.c. reactive magnetron sputtering in Ar+N2 atmosphere on Si substrates at ambient temperature are determined. For that purpose the influence of both the nitrogen flow and the discharge power on the film composition and texture formation has been systematically investigated. The discharge power was varied in the interval 0.1–2 kW and the nitrogen flow was varied from 1 to 20 Pa l s−1 at constant total flow q(Ar+N2)=100 Pa l s−1 and constant total pressure ptot=0.66 Pa. The TiN thin films obtained were investigated by GDOS for chemical composition and by X-ray diffraction for phase composition and texture. The electrical resistivity of all samples was also measured. A comparison of the XRD intensity ratio T=I(200)/I(111) and of the resistivity ρ of the TiN films as a function of the nitrogen flow and of the discharge power clearly demonstrates the dominant effect of the discharge power on T and ρ. Films with best (111) texture (T≤0.015) are obtained at relatively low discharge power (Pd.c.<0.8 kW) and low deposition rate (vdep.≤35 nm/min) for all nitrogen flows. These films have over-stoichiometric composition and relatively high electrical resistivity from 260 up to 600 μΩ cm.

Detailed characterization of a newly developed sputtering system consisting of two symmetrically inclined unbalanced magnetron sputtering devices, to be used for ion-assisted deposition of two component alloy thin films, is made. The working characteristics of the double magnetron system are compared with those of a single magnetron sputtering device with perpendicular geometry and a magnetron with inclined geometry, all of them based on the same unbalanced Sm–Co magnetic assemblage of type II. The experiments were made with Cu targets of 52 mm diam., and 1 mm thickness using Ar at a pressure from 2×10 −3 Torr to 2×10 −2 and for target−substrate distances from 55 mm to 75 mm. The results include the following characteristics of the system : (i) discharge characteristics of the individually and of the simultaneously working magnetrons ; (ii) dependence of the floating potential at isolated substrate and of the currents to grounded and to negatively biased substrate on different parameters of the magnetron discharge ; (iii) homogeneity of the thickness of the deposited films.

A comparison of the working characteristics of two similar planar d.c. magnetron sputtering devices that differ only in the geometry of the build-in magnetic assemblages is made. The comparative study includes the discharge characteristics of the two magnetrons for different pressures of the sputtering gas Ar as well as some parameters characterising the magnetron plasma in the area of the substrates, namely the self-bias electrical potential of the isolated substrate, the current towards the grounded substrate and the current to negatively biased substrate. The values of the measured parameters and the character of the curves obtained show that both magnetron devices are of unbalanced type II. However, the expected strong advantages of the second magnetic system, predicted in our previous investigation on the basis of the magnetic field distributions for the two assemblages, were not confirmed. The experimental data obtained with 1-mm Cu target indicate that the magnetron sputtering source, using the first system, produces higher values of the floating potential, higher values of the current to the grounded substrate and comparable values of the current to negatively biased substrates. These results, together with other advantages shown by the first system, namely the larger working range of the sputtering gas, lower running voltages, significantly larger efficiency of the target utilization and larger homogeneity of the thickness of the deposited films determine the first system as being more appropriate for our future experiments on ion-assisted, thin-film deposition.

A compact and simple planar magnetron design is described based on the known concept for modification of the magnetic field by a co-axially placed solenoid. The magnetron unit ensures sufficient values of the perpendicular B⊥ and the parallel B= components of the magnetic induction above the target surface allowing for a wide range of variation of the operating mode from type I to the unbalanced type II. The following experimental data characterizing the newly developed magnetron system are reported: (i) radial distribution of B= at different distances above the target surface and at different solenoid currents Imi (ii) longitudinal distribution of B⊥ along axes parallel to the central one, measured again at different Imi (iii) VA-characteristics of the magnetron unit (with a graphite target) for different values of Im (from 0 to 2.6 A) and at working gas pressure p ~ = 4 Pa Ar).

A complex investigation of the secondary electron emission coefficient (SEEC) of two types of carbon containing thin film materials, which are among potential candidates for anti-multi-pactoring (AMP) coatings in high frequency devices, such as HF waveguides used for plasma heating in fusion experiments, has been performed. Relations between the dependencies of the SEEC on the energy E and the angle of incidence of the primary electron beam ϑ and other thin film characteristics such as morphology, composition and thermal stability have been established. As a result, the conditions for plasma enhanced chemical vapor deposition of thermally stable C:H films with a SEEC<1 were determined. In addition, it was found that the Si:C films obtained by d.c. magnetron co-sputtering have, for all investigated energies E and angles ϑ, before and after annealing, a SEEC very close to unity and are interesting new candidates for AMP-coatings.