Magnetic nanoparticles with perpendicular anisotropy are attractive for applications in high-density recording media. For these applications, it is highly desirable to have particles with a size below 8 nm, a uniform size distribution, and a reduced ordering temperature to avoid unwanted particle agglomeration upon the required heat treatment to obtain the high anisotropy ordered L10 structure. In this work, FePt nanoparticles embedded in non-magnetic matrices M (M=C, Ag) have been fabricated by sputtering FePt and M multilayered thin films onto single crystal MgO [100] substrates at elevated temperatures up to 650 °C. The transformation from the disordered fcc to the ordered L10 phase in FePt nanoparticles was observed at temperatures as low as 300 °C. Besides the reduced transformation temperature, the deposited material showed an improved [001] texture for FePt/Ag thin films as compared to FePt/C due to lattice parameter matching between Ag and FePt. As the deposition temperature increases, the degree of atomic ordering approaches that of the fully ordered phase as indicated by the shift in the [002] XRD peak. TEM images showed that isolated particles with smaller average particle size (around 7 nm) were formed when the thickness of sputtered film is less than 4 nm. However, with a further increase of thickness of sputtered FePt film, a continuous layer of FePt particles was observed and the coercivity decreased rapidly due to a domain wall motion mechanism.

FePt nanoparticles, ∼ 2nm in diameter, were prepared by the polyol reduction of platinum(II) acetylacetonate and iron(III) acetylacetonate in the presence of oleyl amine and oleic acid surfactants. The particles were dispersed in hexane and the dispersion added to a solution of 11-mercaptoundecanoic acid in cyclohexanone. As the 11-mercaptoundecanoic acid ligands replaced the oleic acid ligands, the particles precipitated. The particles could be dispersed in basic water, made basic either with sodium hydroxide or ammonium hydroxide. X-ray photoelectron spectra showed a peak near 164 eV, sulfur (2p) confirming the presence of the thiol ligand. Similarly, the oleic acid ligands were replaced with either 3-mercaptopropionic acid or 16-mercaptohexadecanoic acid to give FePt particles that could be dispersed in water. Dispersions made with FePt nanoparticles having 11-mercaptoundeacnoic acid ligands and ammonium counter ions were dried on TEM grids to give highly ordered films consisting of close-packed arrays of FePt nanoparticles. When the counter ion was sodium, the particles tended to aggregate, instead of forming ordered arrays.

P-type Si wafers (∼1019 cm−3) were implanted with 300 keV Mn+ ions at 350°C to a dose of 1×1016 cm−2, and then annealed at 800°C for 5 min. The magnetic properties with dependence upon temperature were measured by using a Superconducting Quantum Interference Device (SQUID) magnetometer. The Mn-implanted Si compound shows ferromagnetic ordering above room temperature. The saturation magnetization increases by ∼ 2 × after annealing and the Curie temperature is TC > 400 K. The structural properties have been investigated by means of Secondary Ion Mass Spectroscopy (SIMS) depth profiling and Transmission Electron Microscope (TEM) imaging. Measurements showed that the Mn atoms redistribute in the Si crystal due to the thermal annealing and form a band layer composed of nanoscale structures such as crystallites or defects.

Magnetic nanostructures with desirable properties such as monodispersed size and crystallographic texturing can be fabricated by a number of synthetic techniques. In this paper, we discuss methods for creating nanoclusters with fine control of individual propertiesand their interactions, as well as a promising chemical technique that provides control of several properties simultaneously. Current and potential applications also will be addressed.

Magnetoresistive Biosensors use a new detection method for molecular recognition reactions based on two recently developed techniques and devices: Magnetic markers and XMR –sensors, where XMR means either GiantMagneto- (GMR) or Tunneling-MagnetoResistance (TMR). The markers are specifically attached to the target molecules, and their magnetic stray field is picked up by the embedded magnetoresistive sensor as a change of the electrical resistance. Compared to established, e.g. fluorescent, detection methods, magnetic biosensors have a number of advantages, including low molecular detection limits, flexibility and the direct availability of an electronic signal suitable for further automated analysis. This makes them a promising choice for the detection units of future widespread and easy to use lab-on-a-chip systems or biochips.

Both the measurement technique using XMR-sensors as well as new developments in the preparation of magnetic carriers are discussed here. Different configurations are discussed and the results for Giant Magnetoresistance sensors are compared to an analysis of the same biological systems marked with fluorescence dyes. Down to a concentration of about 10 pg/μl of, e.g., DNA molecules, the magnetoresistive technique is competitive with nowadays standard analysis methods. The capability of the TMR sensors to detect even single markers is additionally demonstrated by a model experiment using the tip of a magnetic force microscope to meamic the presence of a magnetic particle on top of the sensor surface.

The magnetic carriers (beads) usually detected by the sensors consist of paramagnetic magnetite particles embedded in a polymer matrix with sizes from some μm down to about 100nm. They are linked to, e.g., DNA or proteins (often by a avidin-biotin bond) and thereby enable highly specific detection of complementary molecules. These magnetic particles often suffer from their broad size distribution and the relatively small magnetic moment. With the new colloidal synthesis of superpara- or ferromagnetic Co, CoFe and FePt nanocrystals by, e.g., pyrolythic decomposition of CVD precursor molecules, magnetic markers with superior magnetic moments, smaller size and size distribution can be produced. Here, the question about their potential to replace magnetite is addressed. Starting from a magnetic analysis of the corresponding magnetophoretic mobility of Co and FeCo based alloys their synthesis and resulting microstructural and magnetic properties as function of the underlying particle size distribution and the stability of the oleic acid ligand are discussed.

Moreover, the magnetic particles offer an additional feature: They can be manipulated on chip via currents running through specially designed line patterns. We show, that this manipulation can be performed in a precise and reproducible manner, enabling locally enhanced concentration or even the measurement of binding forces with very low loading rates.

When the constitutive materials of photonic crystals (PCs) are magnetic, or even only a defect in PCs is magnetic, the resultant PCs exhibit very unique optical and magneto-optical (MO) properties: The strong photon confinement in the vicinity of magnetic defects results in large enhancement in linear and nonlinear magneto-optical responses of the media. Novel functions, such as band Faraday effect, magnetic super-prism effect and non-reciprocal or magnetically controllable photonic band structure, are predicted to occur theoretically. All the unique features of the media arise from the existence of magnetization in media, and hence they are called magnetophotonic crystals (MPCs) providing the spin-dependent nature in PCs.

This work focuses on the fabrication of magnetic nanowires with specialized geometries, such as Y-junctions, tapers and multilayers, for magnetoresistive sensor arrays. First, anodic alumina nanopores were grown with diameters of 20–250nm and lengths up to tens of microns. These pores were removed from their Al substrates and the barrier oxide was removed. Co nanowires were initially grown inside the pores by electrochemical deposition. It was shown that the coercivity and remnant magnetization could be tripled in (100)-oriented Co by shrinking the pore diameter/interpore spacing from 150/300nm to 40/80nm. These properties were further enhanced by fabricating (002)-oriented Co using the proper pH and applying a magnetic field during growth. The ability to connect two or more nanostructures is critical to the long term success of nanoelectronics and circuits. Here, Y-junctions were grown by subsequent growth of 40nm then 20nm pores such that two smaller pores extended from the bottom of each larger pore. These pores were then filled with Co in order to produce Y-junctions in the magnetic nanowires. Next, multilayered nanowires were fabricated with alternating layers of Cu and Co. The Co layer thickness was varied in order to study the affect of shape anisotropy on the magnetic properties of Co layers inside arrays. Finally, several configurations for magnetoresistive magnetic field sensors were described.

Magnetic bilayers Fe/Sm-Co and Co/Sm-Co have been fabricated with gradient thicknesses of the soft layers in order to systematically study the dependence of exchange coupling on the thickness of the soft layer. The films were deposited in a combinatorial magnetron-sputtering chamber, where the Fe and Co thickness wedges were created by the natural thickness gradient due to the deposition geometry. The soft layer was deposited at two different temperatures (150°C and 300°C) in order to study the effect of deposition temperature on the exchange coupling. The deposition of the Fe layer at the higher temperature (300°C) was found to enhance the interlayer exchange coupling between Fe and Sm-Co. The single-phase-like magnetization reversal critical thickness increases from 12 nm for Fe deposited at 150°C to 24 nm for Fe deposited at 300°C. We attribute the enhanced exchange coupling in Fe/Sm-Co bilayers to the interfacial mixing and the coherent growth of the Fe layer. On the other hand, we found that the exchange coupling between Co and Sm-Co is not sensitive to the growth temperature of the Co layer.

In this paper, we present our recent studies on the synthesis and magnetoresistance of single crystalline Fe3O4 core-shell nanowires and nanotubes. Homogeneous Fe3O4 nanowires/tubes with controllable length, diameter and wall thickness were synthesized. The as-prepared material composition and stoichoimetry have been carefully examined and confirmed with a variety of characterization techniques including XRD, EDS, XPS, and TEM. Magnetoresistance under different temperatures was systemically studied. Up to 1.2% room temperature magnetoresistance was observed in the as synthesized nanowires/tubes under a magnetic field of B = 1.8 T.

Nickel nanowires were fabricated by electrodepositing Ni from an aqueous plating solution onto the step edges of Highly Oriented Pyrolytic Graphite (HOPG). Freshly cleaved HOPG was exposed to a plating solution of nickel and electro chemically deposited by cyclic voltametry. The morphology of the deposited nanoparticles was studied using an Atomic Force Microscope (AFM) in non-contact mode. The magnetic force of interaction between the nanoparticles was studied by magnetizing the particles. The critical force to displace the nanoparticles was estimated using contact mode of AFM.

Pulse Thermal Processing (PTP) using a High Density Infrared (HDI) Plasma Arc Lamp has been investigated as an enabling manufacturing tool for processing nanomaterials and thin-films. HDI is a single source lamp that offers unique capabilities of processing broad areas with power densities approaching those of a laser. The extremely high radiant energies delivered by the plasma arc lamp provides heating rates approaching 600, 000°C/s through a single pulse on a millisecond time frame, thus allowing controlled diffusion on nano-meter scale. The ability to design the functionality of nanomaterials offers tremendous potential to exploit this technology for a wide range of applications based on nanotechnology. This present article discusses application of PTP using high-density plasma arc lamp to perform; a) phase transformation in FePt nanoparticle system for magnetic media applications, and b) crystallization of amorphous Si (a-Si) for photovoltaic and thin-film transistor (TFT) applications.

This paper describes the results of an investigation of modified synthetic protocols to produce monodispersed magnetic ferrite nanoparticles, γ-Fe2O3 and Fe3O4, and their magnetic properties. The synthesis involved thermal decomposition of organometallic precursors followed by oxidation or reduction. In the synthesis of γ-Fe2O3, iron pentacarbonyl was used as the precursor and trimethylamine oxide as the oxidant. In the synthesis of Fe3O4, iron (III) acetylacetonate was reduced by 1, 2-hexadecanediol. The particle sizes ranged from 5–15 nm with high monodispersity. Results from TEM, XPS, and SQUID characterizations of these iron oxide nanoparticles are discussed.

Thin films of magnetic-nanocomposite are prepared using a novel two step ion-implantation technique. Structural assessment via TEM of the ion bombarded iron-polymer composite shows development of fine magnetic nanoparticles (20–50 A) in a carbonaceous matrix. The experimental temperature dependence of conductivity of the composite, in the temperature range 10–300 K, follows the exponential law σ = σo exp [(-To/T)γ], where To and γ are constants. The observed higher values of γ > 1 imply the presence of more than one conducting channel in the composite. The secondary conducting channels, beside hopping conductivity, may arise from the conducting graphitic matrix around Fe nanoparticles. The room temperature magneto-transport measurement indicates a 0.5% change in magnetoresistance at 0.5T field. The observed anomalous Hall voltage confirms the presence of magnetic nature of nanoparticles.

The influence of an in-situ magnetic field on the plume during pulsed laser deposition (PLD) to prepare epitaxial nickel zinc ferrite (NZF) thin films were investigated. An air core coil (solenoid coil) was installed between a target and a substrate, and up to 43 mT of magnetic field was generated by direct current (DC)(Dynamic Aurora PLD method). Application of magnetic field brought about following structural and property changes;

(1) deposition rate was almost doubled, (2) the concentration of Ni and Zn in the film was decreased, (3) lattice parameter was unchanged, and (4) magnetization and coercivity was increased. Since deposition rate was increased by application of magnetic field, films with same thickness was also prepared without magnetic field, however, magnetic properties were unchanged. This indicates that application of in-situ magnetic field improved magnetic properties.

We investigated the effects of V/III flux ratios on the Curie temperature, TC, in Ga1−x Mnx As layers with various Mn mole fractions of x = 0.03 and 0.05. A 75 nm thick GaMnAs layer was grown at the temperature of 250 °C with various V/III flux ratios of 25∼34. The low temperature molecular beam epitaxy (LT-MBE) method for growth of GaMnAs layer caused the defects related by excess As and Mn interstitial, and these leaded the formation of deep level. We investigated that formation of deep level was established with various Mn mole fraction for V/III flux ratio 34. The changes of TC are observed by varying V/III flux ratio with a fixed Mn mole fraction. The TC in the sample grown with a lower V/III flux ratio of 25 is found to be higher comparing to that with higher V/III flux ratio of 34 at a fixed high Mn concentration (x = 0.05). Although the Mn concentration increases, the TC is not much changed when the V/III flux ratio is high of 34. The changes of TC with various V/III flux ratios are explained by the existence of low temperature grown defects, which are clarified by the deep level transient spectroscopy measurement. The prime species of defects are found to be AsGa and MnI etc.

Metallic Ni nanoparticles were embedded in polyimide (PI) films by applying a chemical surface modification technique. The technique consists of a simple alkali treatment of the PI films, an ion exchange reaction, and thermal annealing. The transmission electron microscopic studies showed that the initial alkali treatment time determined the diameter (d) of Ni nanoparticles formed by the annealing at 300 °C.With increasing the annealing time, the thickness of the composite layers containing Ni nanoparticles decreased while the d was almost constant. The shrinkage of the composite layer led to a decrease in the spacing (r) among Ni nanoparticles. The d and r can thus be fine-tuned independently. Electron magnetic resonance study clearly indicated that the tuning of d and r enable us to control the magnetic dipolar interaction in the Ni nanoparticle systems. The present technique opens a new way to realize tailor-made nanomagnetic structures.

A 4Mb magnetoresistive random access memory (MRAM) with a novel magnetic free layer and toggle switching mode is presented. The new free layer uses a balanced synthetic-antiferromagnet trilayer structure and a novel write pulse sequence to provide robust switching performance with immunity from ½-select disturbs. This new mode greatly improves the switching performance of the MRAM as compared to conventional MRAM. The intrinsic reliability of the magnetoresistive tunnel junction (MTJ) and the metal interconnect system of MRAM are two other areas of great interest due to the new materials involved. Time dependent dielectric breakdown (TDDB) and resistance drift were the two main failure mechanisms identified for intrinsic memory bit reliability. Results indicated that a lifetime over 10 years is achievable under the operating conditions. Finally data retention is demonstrated over times that are orders of magnitude longer than 10 years.

Polycrystalline β-Ga2O3 doped with Fe3+, (Ga1−x Fex)2O3 (x=0.02, 0.05, 0.08 and 0.1), has been prepared by a solid-state reaction. Ferromagnetic ordering is observed at room temperature for samples prepared by β-Ga2O3 and Fe(NO3)3·9H2O and sintered at low temperatures below 900 °C, while the sintering at temperatures above 900 °C leads to the paramagnetic behavior. X-ray diffraction analysis for the samples sintered at 500 °C reveals that the single phase of β-Ga2O3 can be obtained up to x=0.08 without traces of secondary phase or other impurity. Magnetization as a function of temperature shows superparamagnetic or cluster spin-glass behavior, indicating that long-range ferromagnetic ordering does not exist in the present systems. It is suggested that the inhomogeneous distribution of Fe3+ is responsible for the ferromagnetic behavior.