Non-crystalline Co thin films have been prepared by pulsed laser ablation deposition. From the M-H hysteresis loops measurements, a soft magnetic behavior is observed. Néel type magnetic domain walls are observed in the as-deposited films. The spontaneous magnetization, Ms(T = 300 K), is ≍ 860 emu/cm3. After annealing at 500 oC, Ms(T = 300 K) is ≍ 1460 emu/cm3. The extrapolated to zero K resistance decreases almost two orders of magnitude from the as deposited samples to the crystallized heated at 500 °C ones. A trilayer Co/Cu/Co has shown a real part magnetic susceptibility of 120 at 100 MHz. In the 100 MHz to 1 GHz frequency range, a perpendicular bias magnetic field increased this value up to 270, remaining almost constant for all range.

We have sputter-grown self-organised faceted NiO-Co epitaxial bilayers on MgO(110). Due to very close lattice parameters, NiO adopts the same NaCl crystallographic structure as the substrate but it minimises its surface energy growing in a stripe-shaped morphology elongated along [001] MgO direction. The Co layers then deposited on NiO adopt a fcc structure. They consist of a set of connected nanowires whose height is about 50 Å, length is near to 1 µm and lateral periodicity ≍ 100 Å. Magnetic properties of the Co layers were investigated by magneto-optical Kerr effect from 10 K to room temperature. They are dominated by a strong shape-induced uniaxial anisotropy and exchange coupling with the antiferromagnetic underlayer. Magnetisation loops recorded along the easy axis exhibit a perfect squareness and switch in a field range smaller than 10 Oe. Transverse measurements indicate that switching occurs by domain nucleation and/or domain wall propagation. On the contrary, close to the [110] hard axis, magnetic switching occurs by coherent rotation. The bi-stable Co magnetisation state along its easy axis has been used for ordering the NiO spins configuration from room temperature to 10 K. Sign and value of exchange bias induced by such a thermal treatment can be modulated thanks to a wide magnetocrystalline or local exchange path energies distributions.

We have investigated the batch method of thermal fixing for multiplexed holograms. The batch fixing process is pictured and analyzed, for the first time to our knowledge. The batch procedure of thermal fixing includes optical erasure of electronic gratings by subsequent recordings both in the same batch and in different batches, ionic compensation during thermal fixing in one batch, smoothing of ionic gratings during thermal fixing of subsequent batches, and revealing of ionic gratings. The inter-batch optical erasure time constants of LiNbO3:Fe:Ce crystals are measured in experiment.

The hysteretic behavior of two-phase permanent magnets for high-temperature applications is examined. A variety of systems have been synthesized and investigated, including Sm-Co-Cu-Ti bulk magnets, SmCo5:Cu-Ti thin-film materials, and mechanically milled Sm-CoZr magnets. The hybrid character of the material leads to very high room-temperature coercivities, between 30.2 and 43.6 kOe, and to the survival of a comparatively large part of the coercivity at high temperatures (12.3 kOe at 500 °C for SmCo 6.5Cu0.8Ti0.3). The coercivity reflects the structure and chemical composition of the material. When ferromagnetic grains are separated by a ferromagnetic boundary phase, the boundary phase acts as a pinning center, but when the grain-boundary phase has a comparatively low Curie temperature, the high-temperature magnetism of the system is that of a weakly interacting ensemble of magnetic particles. In spite of some residual paramagnetic exchange coupling, which is discussed in this work, this mechanism enhances the coercivity.

Magnetic nanocomposites have been successfully prepared by encapsulating nanosized entities of iron, cobalt, and nickel compounds in poly(amido-amine) (PAMAM) dendrimer hosts. Problems related to the instability of the magnetic structures under the influence of an external electromagnetic field have been overcome by using a solid polystyrene matrix to embed the dendrimer hosts containing the magnetic guests. SQUID magnetometry measurements on these nanocomposites showed that after subtraction of the diamagnetic polymer background, at 300 K all samples exhibited paramagnetic behavior, with susceptibilities of 1.14, 1.68, and 0.70 × 10−6 m3/kg for Fe-, Co-, and Ni-containing samples respectively. The temperature dependence for T<300 K showed typical paramagnetic behavior, with the susceptibility increasing for decreasing temperatures. Curie-Weiss (1/M vs. T) graphs displayed a linear behavior at high temperatures, with temperature axis intercepts (θ) occurring at –139 K (Fe), –16 K (Co), and 0 K (Ni). Negative deviations from Curie-Weiss behavior occurred at T<175 K for the Fe and T<25 K for the Co samples. Magnetic moments calculated from the high temperature Curie constant indicated that Fe, Co, and Ni possessed effective moments of 3.5, 4.4, and 2.8μB. The negative intercepts and the fact that these moments are larger than those expected for metallic transition metals are indicative that these species are probably present in an oxidized form. The low-temperature behavior indicates either superparamagnetic or soft ferromagnetic behavior.

Super-resolution near-field structure (Super-RENS) was prepared by a heliconwave-plasma sputtering method to improve the disk property that is combined with a magneto-optical (MO) recording disk. Antimony and silver-oxide mask layers were prepared by the method and refractive indices were measured. Recording and retrieving of signals beyond the resolution limit (<370 nm) were achieved for both mask cases. Attempts to optimize the disk structure were also made using a conventional sputtering method. The smallest mark size was around 200 nm and the highest carrier-to-noise ratio (CNR) was 30 dB for 300-nm mark and 22 dB for 250-nm, when using a laser wavelength of 780 nm and a numerical aperture of 0.53. We have found that there is a competing super-resolutional mechanism besides Super-RENS that appears when high readout laser power is applied. This mechanism played rather an important role at least in the mark-size range of 200-370 nm.

The ferromagnetic bulk metallic glass (BMG) Nd60Fe30Al10system exhibits extremely large coercivities at low temperature and moderate coercivities near room temperature. The magnetic hardness, as best evidenced by the onset of magnetic irreversibility, was studied in bulk suction-cast and melt-spun alloys with the nominal composition Nd60Fe30Al10. Systematic x-ray diffraction studies of the degree of crystallinity performed as a function of position within the bulk suction-cast samples is found to correlate with the variation in the room-temperature magnetic hysteresis character. X-ray diffraction data clearly shows the presence of both crystallites and amorphous material on the samples' outmost surfaces; the amorphous phase content increases with distance into the cast sample. These results underscore the importance of solidification conditions and attendant nanophase selection, on the resultant magnetic properties of this class of alloys.

Magnetization reversals in sputtered Co electrodes of a magnetic tunnel junction are studied using transport measurements, magneto-optic Kerr magnetometry and microscopy. Using the tunnel magneto-resistive effect as a probe for micromagnetic studies, we first evidence the existence of an unexpected domain structure in the soft Co layer. This domain structure originates from the duplication of the domain structure of the hard Co layer template into the soft layer via ferromagnetic inter-electrode coupling. A detailed analysis of the kerr microscopy images shows that all features appearing in the variation of tunnel resistance as a function of the applied field are associated to the domain phase evolution of each electrode. By tailoring the magnetic properties of the hard Co layer, we have demonstrated that the appearance of the domain duplication is driven by the magnetic anisotropy of the hard layer. Finally, a brief theoretical description of the domain duplication process allows us to extract the main parameters governing the effect.

The spin polarization of Sb overlayers on the semi-Heusler alloy NiMnSb is investigated in terms of the Landau-Ginzburg approach. The half-metallic semi-Heusler alloy NiMnSb acts as a ferromagnetic perturbation and induces a spin polarization in the semimetallic Sb overlayer. Using a Gaussian approximation, the propagation of the spin perturbation in the overlayer is calculated. The results are compared with spin-polarized inverse photoemission spectroscopy (SPIPES) results and with recent spin-dependent envelope-function approximation (SDEFA) predictions. The Landau-Ginzburg parameters are both band-structure and temperature dependent, and it is argued that thermal spin excitations lead to an injection depth decreasing as 1//T law at high temperatures.

A new approach is proposed to obtain fast crystallizing materials based on a conventional GeSbTe alloy for rewritable phase change optical data storage. By means of co-sputtering, Ge1Sb2Te4alloy was mixed with Sn1Bi2Te4alloy so as to form pseudo-binary alloys (Ge1Sb2Te4)1-x(Sn1Bi2Te4)x (x is a mole fraction). From structural and optical analyses of the co- sputtered and annealed alloy films, the formation of stable crystalline single phases was observed along with a Vegard's law behavior, suggesting a homogeneous mixing of the two alloys. By use of a 4 layered disk with (Ge1Sb2Te4)0.85(Sn1Bi2Te4)0.15 recording layer, a preliminary test of writing and erasing was carried out and the results were compared with the case of the disk with Ge1Sb2Te4recording layer. The (Ge1Sb2Te4)0.85(Sn1Bi2Te4)0.15 recording layer was found to yield markedly higher erasibility, especially with increasing disk linear velocity.

Stimulated by recent experimental observations of room{temperature ferromagnetism of MnxCd1−xGeP2, we investigate the structural, electronic and magnetic properties of these systems as a function of Mn concentration by means of first–principles density-functional-theory-based codes. Moreover, we investigate the effect of the anion substitution (P vs As) in Mn-rich chalcopyirites. Our calculations indicate that the antiferromagnetic alignment is the most stable ordering for all the systems studied, at variance with that experimentally reported. Moreover, we find that there is a slight reduction of the total magnetic moment per Mn atom from ∼5 µB in all the Cd-rich P-based chalcopyrites to ∼4 µB in the Mn–rich MnGeP2 and MnGeAs2 systems.

The magnetic behaviour of the glass-covered metallic microwires with a wide compositional range of composition with soft and hard magnetic character is presented. The effect of conventional furnace and dc current annealing under dc axial magnetic field or without it as well as of a chemical etching on the magnetic properties of Co and Fe-based glass coated microwires has been studied. Such treatments modify the magnetic parameters. In particular, annealing under applied magnetic field (field annealing) can improve significantly such magnetic parameters as permeability. Such phenomenology can be interpreted considering the noticeable magnetic anisotropy induced by the combined effects of the magnetic field and strong internal stresses arising from the coating. Giant magnetoimpedance (GMI) effect was observed in nearly-zero magnetostrictive amorphous microwires. Upon careful heat treatment, FeCuNbSiB amorphous microwires devitrificate into nanocrystalline structure with large variety of magnetic parameters. Hard magnetic materials with coercivity up to 800 Oe were obtained as a result of decomposition of metastable phases in Co-Ni-Cu microwires as well as after crystallization process of FeCuNbSiB amorphous microwires.

A series of experiments have been conducted to evaluate the magnetotransport properties of RF diode sputter deposited giant magnetoresistive (GMR) multilayers with either copper or copper-silver-gold nonferromagnetic (NFM) conducting layers. The study revealed that RF diode deposited multilayers utilizing Cu80Ag15Au5 as the NFM conducting layer posses significantly superior giant magnetoresistance to otherwise identical device architectures that used pure copper as the NFM conducting layer. To explore the origin of this effect, copper and Cu80Ag15Au5 films of varying thickness have been grown under identical deposition conditions and their surface morphology and roughness investigated. Atomic force microscopy revealed significant roughness and the presence of many pinholes in thin pure copper films. The surface roughness of the Cu80Ag15Au5 layers was found to be much less than that of pure copper, and the alloying eliminated the formation of pinholes. Molecular statics estimates of activation barriers indicated that both silver and gold have significantly higher mobilities than copper atoms on a flat copper surface. However, gold is found to be incorporated in the lattice whereas silver tends to segregate (and concentrate) upon the free surface, enhancing its potency as a surfactant. The atomic scale mechanism responsible for silver's surface flattening effect has been explored.

Thin silver oxide films used as mask layers in super-Resolution Nearfield Structure (super-RENS) disks for high density optical data storage were reactively sputter-deposited and their composition was determined by spectroscopic means. We found that the stoichiometry of the films changed with the oxygen content in the sputtering gas atmosphere. With a stepwise increase in the percentage of O2 from 0 - 100%, the corresponding layers consist of Ag, mixtures of Ag and Ag2O, Ag2O, mixtures of Ag2O and AgO and AgO. Laser activation of such oxidic phase containing deposits results in the decomposition of the material and excitation of strong local plasmons in the remaining silver clusters. This was confirmed by acquiring surface enhanced Raman spectra (SERS) of benzoic acid (BA), copper phthalocyanine (CP) and internal carbon impurities on silver oxide substrates. From this data, we conclude that the sub-wavelength resolution obtained in super-RENS disks is mediated by local surface plasmons on small silver particles forming in the mask layer.

Bulk rods with diameters up to 3 mm prepared by suction casting and respectively mould casting and melt-spun amorphous ribbons with thicknesses in the range 25 – 150 μm with compositions Nd90−xFexAl10 (x = 35; 40; 45; 50) were investigated by XRD, DSC and magnetic measurements in the temperature range 5 – 600 K. The microstructure and magnetic properties are strongly dependent on the cooling rate, preparation process and Fe content. The large values of the coercive field, which amount to 320 kA/m in the as-cast state as well as the increase with decrease of the temperature and cooling rate result from the formation of very small metastable or nonequilibrium magnetic clusters.

Magnetoresistance of the nanocomposite Fex(SiO2)1−x (x≍0.6) at high enough magnetic field is logarithmic function of the magnetic field. Such a dependence does not fall into the known theory of giant magnetoresistance of ferromagnetic nanocomposites. This paper examines the giant magnetoresistance of such a system in terms of a simple model where the non-ordinary quasi-logarithmic magnetic field dependence of nanocomposite magnetoresistance is related to the non-spherical granules' distribution over their shapes.

The modification of conventional longitudinal recording media by ion-beam irradiation is of both scientific and technological interest. In particular, patterning by irradiation through a stencil mask at the 50 nm length scale may fulfill the promise of a commercially viable patterned media architecture. In this context, the magnetic properties and microstructural evolution of high-coercivity longitudinal thin film media were investigated after ion-beam irradiation. TRIM simulations were used to calculate the depth profiles and damage distributions as a function of energy and dose for carbon, nitrogen, and chromium ions and three different media (C, Cr, no capping layer). Corresponding implantations were carried out and hysteresis curves were measured using a vibrating sample magnetometer (VSM). Using chromium ion implantation at 20 keV, both remanence and coercivity were reduced to zero, i.e., rendering the ferromagnetic thin film paramagnetic, at doses as low as 1×1016 cm−2. For C+ implantation at 20 keV, remanence and coercivity were also reduced to varying extent up to doses of 5×1016 cm−2 after which further irradiation had no effect. Slight decreases in remanence and coercivity were observed for 20 keV N2+ irradiation. XRD measurements indicate that the hexagonal cobalt alloy phase remains intact after irradiation. The physical and magnetic domain structures at the surface were assessed by atomic force and magnetic force microscopy. Combined with the development of a suitable stencil mask, such chromium ion implantation can be used to develop a viable patterned media with nanoscale dimensions, consisting of locally defined ferromagnetic and paramagnetic regions. This work is in progress.

The iron manganites FexMn(3−x)O4 synthesis by soft chemistry method have been studied. The main difficulty is to obtain single phase spinel with high Mn content (0.4< x < 1.3). Oxalate precursor powders of these materials with controlled shape and nanoscopic size have been prepared. The precursors are then heat treated with a H2/H2O/N2 gas mixture at low temperature. The resulting stoechiometric spinels are metastable phases with high specific surface area and are highly reactive toward oxygen. Therefore, these oxide can be oxidized in air at low temperature in order to produce mixed valence defect manganites FexMn(3−x)O4+δ with a good reproducibility on the oxygen content. Although, some problems persist for the higher Mn contents, as the oxygen partial pressure for the reduction must be controlled precisely in order to produce the stoechiometric spinel at low temperature. The development of a low temperature reduction system, with oxygen partial pressure controlled by oxygen electrochemical pumping, is in progress.

The magnetostriction of as-sputtered and annealed 400 nm thick Co films has been studied in longitudinal and transverse magnetic fields. The appreciable change of the magnetostriction behavior after annealing above 250 °C is correlated to grain growth and to the related change of the texture (from nearly randomly distributed hcp-Co crystallites to a c-axes texture perpendicular to the film plane). The magnetostriction behavior in the annealed samples cannot be explained by a domain magnetization within the film plane. It is assumed that a rotation of the spontaneous magnetization out of the film plane occurs due to the development of a perpendicular magnetic anisotropy.

The stability of the individual elements of a two-dimensional (2D) regular array of single domain particles is investigated. The variance in the statistical distribution of up- and down switching fields of the elements leads to premature switching for the low coercivity particles, and incomplete overwriting for the high end of the distribution. The distribution of the interaction fields from surrounding elements on a 2D array depends the saturation magnetization of the elements, their packing density, and the recorded information. The non-ellipsoidal shape of the elements leads to reduced switching fields as a result of non-collinear magnetization around the corners and edges. The thermal stability of 2D arrays, switching by (incoherent) rotation of the magnetization, is enhanced compared to bulk/contiguous media, due to the lack of low energy barrier domain wall motion processes. However due to the fast decrease of the anisotropy, stability at elevated temperatures is still a problem. Experimental data for a model 2D square array of single crystalline, strongly uniaxial, single domain garnet particles illustrate the effects on stability of statistics, shape, and thermal excitation.