Change of the magnetic property of Fe-B-Nd-Nb alloys was investigated with replacing Nb by a glass forming element Zr under constant quenching rate as well as heat treatment conditions. As a result, the coercivity significantly increases up to 1207 kA/m when the half of Nd is replaced by Zr, which is presumably due to grain refinement of the Nd2Fe14B phase. The self-organized nanograin magnets are attractive for future applications since their coercivity can be further improved by reducing the grain size via optimizing the Zr concentration, the quenching rate and the subsequent heat treatment condition.

The study of ferromagnetic transition of Ga1-xMnxAs dilute magnetic semiconductor (DMS) is much of interest mainly due to the potential application in spintronic devices. Based on the mean field approach we present the average contribution of the hole spins by considering the holes in an impurity band (IB) and the critical concentration for the metal-insulator transition (MIT) in this semiconductor. In order to calculate the mean configuration of spins of impurities Mn+2 we use a formalism proposed for a spatial disordered system. The results for the metallic densities around the MIT transition are compared to experimental results and other theoretical findings.

Permalloy (Ni81Fe19) nanoparticles with diameters of hundreds of nanometers have been successfully fabricated by pulsed laser ablation (PLA) in air, distilled water, pure ethanol and sodium dodecyl sulfate (SDS) aqueous solutions. The permalloy nanoparticles made in SDS solutions are typically spherical in shape. Lower laser energy with lower frequency leads to the formation of smaller permalloy nanoparticles. Higher concentration of SDS results in smaller nanoparticles. Lastly, we found some unusual permalloy nanoparticles with interesting morphologies made by PLA in air, distilled water and ethanol.

The local structure around the manganese atom is probed by extended x-ray absorption spectroscopy (EXAFS) measurements in pulsed laser deposited thin films of La11xCaxMnO3 (x=0.1210.53). The thin films were deposited on various single crystal oxide substrates. The effect of the lattice parameter of the substrate on the local structural modifications around Mn atom is investigated. All the x-ray absorption experiments were performed at the National Synchrotron Light Source of Brookhaven National Laboratory. By detailed EXAFS theoretical modeling for the possible local structures and the least square fitting to the EXAFS data using these models, the overall substrate and the Ca concentration effects are probed. The EXAFS results indicate a rigid Mn-O bonding, but response of the Mn-O-Mn bond angle upon variations of the substrate lattice constant and Ca substitution.

In the field of nanostructured magnetic materials, the top-down approach of making ever-smaller magnetic particles has been successful in decreasing the minimum size of magnetic nanoparticles made in this way. Simultaneously, synthetic chemists have employed a “bottom-up” approach to the same problem through discovery of increasingly large molecular magnetic clusters that behave as individual magnets at low temperature. These molecules are called single-molecule magnets, and they have been discovered in a variety of sizes, up to 4 nanometers in diameter. Some display interesting solid-state properties in the crystalline state: bistability through hydrogen bonding or crystallization in potentially useful patterns, such as tubes. The advantage of discrete molecules as nanoscale magnets is the monodispersity of particle size. As the molecular approach and the materials approach to nanoscale magnets brings the possible sizes of particles by each method within range of the other, interdisciplinary research into the complementarity of the two approaches becomes necessary. The magnetism displayed by nanoparticles and molecules alike at this size shows both classical and quantum properties, uniting the two types of production as a window into this area bridging the two major ways of describing the physical world. A discussion of the progress of the synthetic chemistry approach and physics in this area will be made, as well as a discussion of how molecular chemistry may fit in to the field of magnetic nanostructures.

Measuring nonlinear AC dielectric or magnetic properties of ferro and ferri magnetic materials has often required large, extremely high power and bulky equipment configurations for production of the required intense electric and/or magnetic fields. Multiple RF cavities, striplines or waveguide test fixtures may be required. The techniques often require 10s of cubic millimeter too centimeter material volumes. This paper presents results from an initial experimental design of a free space based measurement configuration for small material volumes such as nano and micro particulates or particulate composites. The technique uses wideband radiators and modest variable power radio frequency pumping sources. A second design uses, in concert with a higher power pump, a variable frequency low power probe source at frequencies other than that of the pump. A two dimensional photonic bandgap (PBG) structure is common to both configurations. The photonic structure acts to enhance power density at frequencies associated with localized electromagnetic fields constrained to small volumes of the photonic structures. Field localization is recognized and has been applied in biological diagnostics and treatment [Phys. Rev. v109, 1492; Phys. Rev. B, v55 and 62, n. 19 and 16, pp 13234 and 11230 and Chem.Soc.News, 1998, v27, p241].

Modeling of various measurement configurations is based upon expansion of incident and propagating fields in characteristic modes external and within the structure. A proper choice of photonic structure, material and pump frequency is found to localize fields in air, between the structural dielectric members of the photonic structure. This will allow small magnetic or electric samples to be inserted for exposure in these regions. The electromagnetic reflection, transmission, absorption and field/power density multiplier of the photonic structure can be measured at multiple frequencies and reflect the dielectric or magnetic nonlinearity and changed dispersion induced at the pump frequency. One PBG-free space combination will be presented that finds power density multipliers of 10 6. Thus a 10 watt pump source will produce RF magnetic field strengths near 10 Oe. This magnetic field should be sufficient to exceed critical fields for many ferri and ferromagnetic samples inserted in the volume of field localization.

An one-pot procedure was developed for the synthesis of mesoporous silica containing bimetallic PdCo using Pd(NO3)2 and CoCl2, and cetyl trimethyl ammonium bromide (CTAB) as the templating agent, and tetramethoxy silane (TMOS) as the precursor. The materials were characterized using high resolution scanning transmission electron microscopy (HRSTEM), elemental analysis, X-ray diffraction (XRD), and magnetic measurements. The data indicate that the bimetallic Pd-Co nanoparticles are uniformly distributed on the inner pore walls of silica. The magnetic measurements of reduced Pd-Co nanoparticles (4-5 nm) in mesoporous silica reveal a typical ferromagnetic behavior up to 20 K and exhibit superparamagnetic properties above 30 K.

Iron-platinum (FePt) nano-particles were synthesized using a hot metal salt reduction reaction with iron chloride and platinum acetylacetonate as the precursor salts. The synthesis route was based upon work done previously by Sun et Al.[6]. The size and composition of the FePt nano-particles were controlled by varying the surfactant to reagent molar ratio and refluxing time during synthesis. The average size of FePt nano-particles synthesized ranged from 4.08 nm to 5.23 nm. The composition of the nano-particles ranged from Fe60Pt40 to Fe55Pt45. The size was shown to increase as the surfactant to reagent molar ratio was changed from 1:6 to 1:1. The platinum composition increased from 40 % to 45 % with an increase in the refluxing time from 30 minutes to 60 minutes. The X-ray analysis (XRD) showed that the unannealed nano-particles had a FCC crystal structure. The FCC FePt nano-particles were superparamagnetic at room temperature. A blocking temperature (Tb) of 35 K was measured for 5.23 nm Fe55Pt45 nano-particles. Annealing of the Fe55Pt45 nano-particles induced a FCT crystal structure with hard-magnetic properties. Coercivity (Hc) of approximately 13000 Oe was measured at room temperature.

(a) Department of Chemical and Materials Engineering, San Jose State University

(b) Department of Physics and Astronomy, San Jose State University

(c) Department of Biological Sciences, San Jose State University

We have investigated the effect of nanometric grain sizes on Microstructural, electrical-, magneto-transport and magnetic behaviors in nanocrystalline Nd0.67Sr0.33MnO3 CMR manganites. Three nanocrystalline powders of Nd0.67Sr0.33MnO3 were synthesized through chemical route “Pyrophoric Reaction Process” and calcined for 5 hrs at calcinations temperature (TCal = 650°C, 750°C, and 850°C). XRD patterns indicate that all the synthesized powders have pseudo-cubic perovskite structure without any secondary impurity phase. Using Debye Scherrer formula we calculated the crystallites size for three nanocrystalline Nd0.67Sr0.33MnO3 powders (∼ 30, 40, and 54 nm for TCal = 650°C, 750°C, and 850°C respectively). TEM micrographs show that the average particle sizes are in nanometric regime (ψ ∼ 30–50 nm). In AC susceptibility and resistivity measurement we observed that there is an almost constant Curie temperature (TC) has value around 240 K and gradual decrease of metal-insulator transition temperature (TP) (from 200-129 K) with decrease of TCal. The magneto resistance of ultra fine nanoparticles increases with grain sizes. Highest magnetoresistance observed ∼ 24 for Nd0.67Sr0.33MnO3 with TCal = 850°C. Experimental results revels, the effect of nanometric grain sizes has an important impact in magnetic properties and magneto-transport behaviors.

Magnetite (Fe3O4) nanoparticles are prime candidates for biomedical applications due to their biocompatibility and good magnetic properties. However, magnetite is highly susceptible to oxidation when exposed to the atmosphere. In order to preserve their properties, it is important for the particles to maintain their magnetite phase. In this study, magnetite nanoparticles were prepared using the conventional co3precipitation of ferrous (Fe2+) and ferric (Fe3+) chloride salt solutions with sodium hydroxide (NaOH). Thermogravimetric analysis (TGA) was subsequently carried out to identify the transition temperatures. Energy Dispersive X3Ray (EDX) spectrum shows the presence of impurities, such as sodium (Na) and chloride (Cl) ions in the as3synthesized magnetite nanoparticles. The as3synthesized samples were then calcined in a chamber furnace according to TGA data. The calcined samples were next characterised by X3ray Powder Diffraction (XRD), Transmission Electron Microscopy (TEM) and Vibrating Sample Magnetometer (VSM) to determine the changes in phase and magnetic properties of the nanoparticles as a function of different calcination temperatures.

Structural, magnetic and transport properties of Pr0.5Ca0.5Mn1-xNixO3 (x =0, 0.04, 0.07, 0.1) series have been investigated. The substitution of Mn ions by Ni induces drastic changes in the magneto-transport properties of Pr0.5Ca0.5MnO3. The physical behavior depends drastically on O stoichiometry. For the low Ni doping x=0.04, 0.07, spin glass configuration is rather favored than ferromagnetism; while for x=0.10, the ferromagnetic phase is significantly suppressed. Pronounced irreversibility between zero-field cooled (ZFC) and field cooled (FC) magnetization and a kink in the ZFC curve observed for x=0.04 and 0.07 are indicative of spin-glass-like state. Applied hydrostatic pressure of about 10 kbar reduces the temperature of charge ordering in an x=0 sample by about 10 K indicating a pressure induced suppression of the Jahn-Teller distortions and of the electron-phonon coupling. Electron magnetic resonance (EMR) unambiguously evidences appearance of FM phase in Ni doped manganites. Temperature dependence of EMR spectra parameters allow us to speculate on the effect of magnetic inhomogeneities.

Ferromagnetic delta-phase manganese gallium with Mn:Ga ratio between 1:1 to 1.5:1 is grown on wurtzite gallium nitride and scandium nitride substrates, using molecular beam epitaxy. The dependencies of growth properties, e.g. interface formation, surface reconstruction and crystalline quality, on substrate crystallographic structure and polarity are investigated. Results suggest that for growth on wurtzite GaN, Ga-polar surface promotes quicker interface formation, and also results in better crystalline quality of the MnGa film, as compared to N-polar. The crystal orientation and magnetic anisotropy are found to be different than those grown on cubic scandium nitride substrates.

Zirconium-doped hematite particles of the type xZrO2-(1-x)α-Fe2O3 (x=0.1, 0.5) were synthesized using mechanochemical activation and characterized by X-ray diffraction (XRD) and Mössbauer spectroscopy. XRD patterns yielded the dependence of lattice parameters and particle size as a function of ball milling time for each value of the molar concentration x. The Mössbauer spectra were fitted with one or alternatively, four sextets, corresponding to Zr ions substituting Fe ions in the hematite structure and further required the addition of a quadrupole-split doublet, representing Fe substituting Zr in the ZrO2 lattice. We further correlated the structural properties of the zirconium-doped hematite system with the sensing properties. These were measured as function of temperature, gas concentration (carbon monoxide and methane) and variable humidity of air. The material system was found to be sensitive over the entire range of CO concentrations and the linearity of the sensor signal was not affected by the relative humidity of air, which makes it the ideal system for sensing devices. Comparative results obtained for tin-doped hematite nanoparticles are also presented.

Melt-spun Fe73-Si16-B7-Nb3-Cu1 (at%) amorphous strip was pulverized and then crystallized to obtain nano-grain structure at 540° for 1h under a nitrogen atmosphere. Carbon black of 0.1∼ 1wt% and its dispersant were mixed with the nano-grain structured Fe-based powder for 1h via ball milling for 1h. The mixture was tape-cast with a polymer-based organic binder, and dried at 100° to make a thin sheet. The microstructure and electromagnetic wave absorption properties of the sheet were investigated using a network analyzer. As a result, the properties of electromagnetic wave absorption were improved by the increase of dielectric loss, which was mainly caused by the increase of complex permittivity with the addition of carbon black.

The developments of high performance magnetic materials are required in various applications such as high sensitive magnetic sensing and hyperthermia in cancer treatment. Recently, Co-doped TiO2 has been received considerable attention as a candidate for such materials because of their ferromagnetic properties at room temperature. On the other hand, the phase-separated glasses and the derived glass-ceramics having unique micro-nano structure are utilized for various applications. In this study, the phase separated glass-ceramics in CoO-TiO2-SiO2 system with Al2O3 addition were prepared by melt-quenching process. The as-quenched samples consisted of the TiO2-rich phase and the SiO2-rich one which were formed by a nucleation-growth mechanism of phase separation. From the results of XRD measurements, the samples were found to have a TiO2 crystalline phase and a SiO2-rich glassy phase. The samples showed the magnetic property, which were regarded as a mixture of ferromagnetic and paramagnetic phases. The samples also showed the electric conductivity at room temperature. However, the conductivity of the sample decreased with increase of the Co content, and the temperature dependence of the conductivity of the ferromagnetic samples was different from the other ones. As a result, the Co ions in the phase-separated glass-ceramics in TiO2-SiO2 system were found to affect on both the magnetic and the electric conductive characteristics.