Individual magnetostrictive nanobars and arrays comprised of magnetostrictive nanobars were recently introduced as a high performance biosensor platform. In this paper, we report the fabrication and characterization of magnetostrictive nanobars based on Fe-B alloy. The nanobars were synthesized using a template-based electrochemical deposition method. The composition and microstructure of the Fe-B nanobars are directly related to their performance as a biosensor platform. The Fe-B nanobar arrays and individual nanobar were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as Auger electron spectroscopy (AES). Morphologically, nanobars have a very flat top and a smooth cylindrical surface, which are critical factors for obtaining high performance as sensor platforms. Structurally, electron diffraction reveals that the Fe-B nanobars are amorphous. AES analysis indicates that Fe-B nanobars show no significant compositional variation along the length direction. It is found that the nanobars were covered by an oxidation layer of a typical thickness of ∼ 10 nm. It is believed that this oxidation layer is related to the passivation of nanobars in air. High temperature annealing and subsequent structural analysis indicate that the Fe-B nanobars possess a good thermal stability.

Hydrothermal techniques have been used to synthesize samples of ZnxFe3−xO4 (x=0.0-1.0) starting with ZnSO4.7H2O/FeSO4.7H2O aqueous solution. The sequence of phases, structural and magnetic properties were followed by X-ray diffraction (XRD), Mössbauer spectroscopy and transmission electron microscopy (TEM). Refinement of the XRD spectra yielded the dependence of the lattice parameters of zinc–doped magnetite and zinc ferrite phase as function of the Zn molar concentration x. As well, the particle diameter was derived as a function of Zn content x. As a function of Zn concentration, the phase content of hydrothermally synthesized samples was found to consist of zinc-doped magnetite, goethite and zinc ferrite. Consistent with the XRD results, Mössbauer spectroscopy data indicate the presence of magnetite and goethite at x≤0.2, magnetite and zinc ferrite at x≤0.9 and pure zinc ferrite only at high zinc concentrations. The presence of different magnetite phases was confirmed by TEM and particles with a size of 50 nm were identified. Our results show that zinc ferrite is formed at high zinc concentration by the hydrothermal method and an acicular component of goethite-magnetite is obtained at low zinc content.

We have investigated the effect of Zn-doping on the superparamagnetic relaxation of nanosized nickel ferrite particles. Our temperature-resolved AC-susceptibility data demonstrate that the relaxation of these systems is well described by an Arrhenius-type law, behavior which allows a precise determination of the effective energy barrier to magnetization reversal, Ueff. We observe that the Zn-content dependence of Ueff exhibits a pronounced maximum when half on the magnetic Ni2+ ions are replaced by nonmagnetic Zn2+. The average blocking temperature (measured at a given frequency) shows a similar behavior. The observed increase of Ueff is attributed to an enhanced magnetic anisotropy induced by the crossover between two magnetocrystalline regimes. Our findings demonstrate the ability to control the superparamagnetic relaxation of ferrimagnetic spinel nanoparticles through chemical manipulations.

Cobalt ferrite (CoFe2O4) thin films were deposited on quartz and single crystalline MgO(001) substrates using pulsed laser deposition (PLD) technique. The orientation of the as-deposited films were investigated as a function of substrate temperature (TS) in the range 200°C – 750°C. Films grown on MgO at higher substrate temperature were found to be (001) oriented while the films grown at lower substrate temperature were polycrystalline in nature. Magnetic measurements reveal that films deposited at lower substrate temperature had lower magnetic moment compared to that of films grown with higher substrate temperature, indicating the correlation between magnetic order and crystallinity. This is attributed to the presence of ordered magnetic domains in the oriented films even though the microstructure remains the same.

YIG@BaTiO3 composite was synthesized by a sequential process involving the formation of TiO2 by sol-gel reaction and a subsequent hydrothermal transformation from TiO2 to BaTiO3. TiO2 layer was coated on YIG particle via sol-gel reaction which comprised hydrolysis and condensation reaction of titanium n-butoxide. The pH value of the solution was precisely controlled to ensure that YIG particles could be well dispersed in the solution and the concentrations of TBOT and H2O were adjusted to obtain variant thickness of TiO2 layer. Nano-sized BaTiO3 coating on YIG was achieved by a hydrothermal conversion of the TiO2 shell layer. BaTiO3 shell layer was synthesized in an autoclave at 240°C for 12 hours and the concentration ratio of [Ba]/[Ti] was 1.6. Phases and morphology of the composite are identified by X-ray diffraction and SEM, respectively. Magnetic properties of YIG@BaTiO3 composite were investigated by vibrating sample magnetometer. Coercivity of YIG@BaTiO3 composites with different composition were not affected but the saturated magnetization dropped down with increasing of the volume ratio of BaTiO3. Permittivity of YIG was raised by coating of BaTiO3 layer and was varied from 6 to 60 and 75 by tuning up the volume ratio of BaTiO3 in the composite. The mechanism of the formation of YIG@BaTiO3 composite was also discussed in the article.

Magnetic refrigeration based on the magnetocaloric effect (MCE) has been proposed as an attractive alternative to gas compression technology. Some calculations suggest that MCE can be obtained with higher efficiencies than compressor driven refrigeration. We examine the MCE in a system of nickel ferrite nanoparticles with size range of 6 to 15 nm. A peak in the MCE at 55 K is observed that increases with higher magnetic fields. This gives this system a relatively high peak entropy change compared to other ferrite systems. A sensitive radio-frequency (RF) transverse susceptibility measurement has also been used to study the magnetic anisotropy. We show that the MCE peak is not associated with the blocking temperature and is likely a field-driven surface spin reorientation which also has a signature in the transverse susceptibility. Work supported by NSF-CTS-0408933 and ARO- W911NF-05-1-0354

Closely-spaced ferromagnetic nanoparticles are of interest for applications that include data storage, magnetic imaging and drug delivery. Here, we use off-axis electron holography and micromagnetic simulations to study the magnetic properties of iron nanoparticles encapsulated in three-dimensional arrays of carbon nanotubes. The nanotubes constrain the shapes, sizes and separations of the nanoparticles, as well protecting them from oxidation. We record magnetic induction maps from individual particles that each contain a single magnetic domain. We also discuss the use of electron holography to assess magnetostatic interactions between adjacent particles.

Nano sized α-Fe particle was synthesized by modified thermal decomposition method. It resulted in the higher saturation magnetization (Ms) almost equivalent to the value of bulk Fe power (Mbulk = 210 emu/g). To prepare Fe nanoparticles, the Fe2+-(oleate)2 complex was annealed at 400 J in pyrex tube and the prepared Fe3O4 nanoparticle was reduced to Fe crystal structure at 700 J with NaCl under Ar+H2 gas atmosphere and annealed again under high vacuum system of 10−5 torr. The crystallinity and structure of the Fe nanoparticle was investigated by powder X-ray diffraction (XRD). The shape and size was confirmed by transmission electron microscope (TEM) images. The magnetic properties were characterized with coercivity and remanence from hysteresis loop by vibrating sample magnetometer (VSM)

The epitaxial Ni (111) thin film on the oxide substrate could be obtained by a novel epitaxy method, employing pulsed laser deposition (PLD) of NiO (111) epitaxial film on the sapphire (α-Al2O3 single crystal) substrate and successive hydrogen reduction of NiO. The NiO (111) epitaxial film was deposited on the sapphire (0001) substrate at room-temperature by PLD, and then reduced into the Ni epitaxial film by annealing (300 °C to 500 °C) in the hydrogen-atmosphere. On the other hand, the polycrystalline Ni metal thin film was obtained by reduction of the polycrystalline NiO film, indicating necessity of epitaxial growth for the precursor oxide thin film in the metal epitaxy. The present epitaxy method suggests the possible formation of [Ni/α-Al2O3] epitaxial multilayer via selective reduction of oxide multilayer.

The structural and quasi-static magnetic behaviors and the temperature rises of three Dextran-coated maghemite nanoparticles subjected to alternating magnetic field (AMF) were investigated for potential use in magnetic hyperthermia treatments. In order to elucidate the effect of the hydrodynamic particle size on the specific absorption rate, the temperature rises for various hydrodynamic particle sizes were investigated in AMFs of various strengths and frequencies. Structural characterization was performed using a TEM and a SEM as well as by dynamic light scattering, and the quasi-static magnetic hysteresis loops were measured using a VSM. The heating behavior is discussed in relation to the magnetic behavior and particle size. While it was found that the heating mechanism for the ferromagnetic particles was mainly magnetic hysteresis losses, Brownian relaxation losses also contributed to the heating.

Fe-doped SrRuO3 thin films were grown on SrTiO3 (STO) substrates by using the Pulse Laser Deposition (PLD) method. Fe concentrations in the SrRuO3 thin films ranged from 0 % to 11 % to manifest the effect of Fe doping on their microstructure. Lattice constants of the films did not show obvious changes with the Fe doping whereas surface morphologies drastically changed from stepped to island structure with increasing Fe. X-ray reflectivity revealed that the surface and interfacial roughness decreased with increasing concentration of Fe. Surface roughness of the films was confirmed by atomic force microscopy. Therefore, a precise determination of film roughness as well as its growth mechanism using X-ray and AFM is exploited to correlate the Fe doping with structural disorder.

Growth of a Co/Cu/Co multilayer is investigated by molecular-dynamics simulation. The interactions between Co and Cu atoms are calculated in terms of the generic-embedded atom method potential. It is confirmed that two-dimensional island growth of Cu atoms on the Co substrate occurs in the simulations. The roughnesses of the surface and the interface are evaluated by means of the standard deviations of the heights of the surface and interface atoms. Intermixing atoms between the layers are also counted. We conclude that there exists an optimum combination of the incident energies of deposited Cu and Co atoms which minimizes both the roughness and intermixing of the interface.

Cobalt- and manganese-incorporated SnO2 thin films exhibiting room temperature ferromagnetism have been prepared by spray pyrolysis technique. Analysis of structural, magnetic and electrical properties of Sn1−xCoxO2−δ thin films indicates that the origin of ferromagnetism, seen for x<0.125, lies in the polarization of free carriers, leading to the necessary exchange interaction. The films exhibit a Curie temperature > 500K. The XRD study indicates that Sn1−xCoxO2−δ films with x<0.125 is single phasic with no evidence of any Co clusters or magnetic oxides, which supports the intrinsic nature of the ferromagnetism. The electrical transport studies indicate that extra electrons are generated on Co-incorporation in the SnO2 lattice. In the case of Sn1−xMnxO2·δ films, ferromagnetism is observed in a narrow range of manganese (0.075≤x≤0.10) with an associated increase in carrier concentration. The detailed analysis of various properties suggests that Mn-ions have been incorporated in the SnO2 lattice, and there is absence of any Mn-clusters, Mn-related secondary phases.

Exchange-spring nanocomposite permanent magnets have received a great deal of attention for their potential for improved the energy products. Predicted results, however, has been elusive. Optimal properties rely on a uniformly fine nanostructure. Particularly, the soft magnetic phase must be below approximately 10 nm to ensure complete exchange coupling. Inert gas condensation (IGC) is an ideal processing route to produce sub-10 nm clusters method. Two distinct nanostructures have been produced. In the first, Fe clusters were embedded in an FePt matrix by alternate deposition from two sources. Fe cluster content ranged from 0 to 30 volume percent. Post-deposition multi-step heat treatments converted the FePt from the A1 to L10 structure. An energy product of approximately 21 MGOe was achieved. Properties deteriorated rapidly at cluster concentrations above 14 volume due to uncoupled soft magnetic regions (from cluster-cluster contacts) and cooperative reversal. The second nanostructure, designed to overcome those disadvantages, involved intra-cluster structuring. Here, Fe-rich Fe-Pt clusters separated by C or SiO2 were fabricated. Phase separation into Fe3Pt and FePt and ordering was induced during post-deposition multi-step heat treatments. By confining the soft and hard phases to individual clusters, full exchange coupling was accomplished and cooperative reversal between clusters was effectively eliminated. An energy product of more than 25 MGOe was achieved, and the volume fraction of the soft phase was increased to greater than 0.5 while maintaining a coercivity of 6.5 kOe. The results provide new insight into developing high energy product nanostructured permanent magnets.

Nanocomposite particles made from encapsulation of magnetic nanoparticles in an inorganic matrix have a real interest in biomedicine due to their high resistance against biodegradation compared with nanoparticles encapsulated in an organic matrix and little work has been published concerning such materials. In this work we use the laser pyrolysis method for the preparation of magnetic composites of Fe-based nanoparticles dispersed in silica and carbon. The precursor is an aerosol of a precursor which can be easily used in a safe way. Important advantages of the laser pyrolysis method are the reproducibility, simplicity (one step method) and continuity which allows producing significant amounts of nanoparticles. The short reaction times (ms) involved in the nucleation of the powders insure the nanometric particle size of both the magnetic component and the inorganic matrix.

This paper is focused on the synthesis and characterization of the Fe@SiO2 and Fe@C nanopowders generated by laser pyrolysis of ferrocene diluted in toluene and carried to the reaction zone in aerosol form. The silica coating was formed by the addition of tetraethoxysilane (TEOS) to the reactant. The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), specific surface area determination (BET) and magnetic measurements. In the case of Fe@SiO2 the process generates rather homogeneous iron/magnetite particles smaller than 10 nm in diameter surrounded by a SiO2 coating of about 20 nm. In the case Fe@C the process generate iron based magnetic nanoparticles of complex composition smaller than 11 nm surrounded by a graphitic carbon layer of 50 nm. Stable aqueous dispersions at physiological pH were produced for both systems by means of strong oxidation in aqueous solutions, which is a very encouraging result for application in the field of living tissues.

We present the synthesis and magnetic properties of Co nanorods spontaneously organized in superlattices over a surface of several microns. This material results from the thermal decomposition of a cobalt precursor under hydrogen, in the presence of a long-chain amine and a long-chain acid as shape control agents. These nanorod superlattices are ferromagnetic at room temperature and they are characterized by a strong coercive field as a consequence of their large magnetic anisotropy. This system can be considered as a good candidate for high density magnetic recording.

Nd0.5Ca0.5MnO3 (NCMO) and Nd0.5Sr0.5MnO3 (NSMO) nanoparticles have been synthesized using microemulsion synthesis method, with hexamethylene alkyl, a mixture of OP and 1-hexanol, NaOH as oil phase, surfactant, and precipitating agent, respectively. The phase formation of NCMO and NSMO nanoparticles was examined. The final NCMO and NSMO nanoparticles have average particle size of 24 and 50 nm, respectively, and present high-quality crystallinity. Measurements of the magnetic properties suggest that the charge-order state favored for bulk NCMO phase collapses in NCMO nanoparticles. The spin freezing behavior for both NCMO and NSMO nanoparticles was identified.