High-temperature solution phase reaction of iron(III) acetylacetonate, Fe(acac)3, with 1,2-hexadecanediol in the presence of oleic acid and oleylamine leads to monodisperse magnetite (Fe3O4) nanoparticles. Similarly, reaction of Fe(acac)3 and Co(acac)2 or Mn(acac)2 with the same diol results in monodisperse CoFe2O4 or MnFe2O4 nanoparticles. Particle diameter can be tuned from 3 to 20 nm by varying reaction conditions or by seed-mediated growth. The as-synthesized iron oxide nanoparticles have a cubic spinel structure as characterized by HRTEM, SAED, and XRD. Further, Fe3O4 can be oxidized to Fe2O3, as evidenced by XRD, NEXAFS spectroscopy, and SQUID magnetometry. The hydrophobic nanoparticles can be transformed into hydrophilic ones by adding bipolar surfactants, and aqueous nanoparticle dispersion is readily made. These iron oxide nanoparticles and their dispersions in various media have great potential in magnetic nanodevice and biomagnetic applications.

Monodisperse MFe2O4 (M = Fe, Co, Mn) Nanoparticles

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

An overview of the structure and magnetism of spinel ferrite nanoparticles and their synthesis in microemulsions

Nanoparticles are the focus of much attention due to their astonishing properties and numerous possibilities for applications in nanotechnology. For realising versatile functions, assembly of nanoparticles in regular patterns on surfaces and at interfaces is required. Assembling nanoparticles generates new nanostructures, which have unforeseen collective, intrinsic physical properties. These properties can be exploited for multipurpose applications in nanoelectronics, spintronics, sensors, etc. This review surveys different techniques, currently employed and being developed, for assembling nanoparticles in to ordered nanostructures. In this endeavour, the principles and methods involved in the development of assemblies are discussed. Subsequently, different possibilities of nanoparticle-based nanostructures, obtained in multi-dimensions, are presented.

Self‐Assembling Nanoparticles at Surfaces and Interfaces

Ferrimagnets having low RF loss are used in passive microwave components such as isolators, circulators, phase shifters, and miniature antennas operating in a wide range of frequencies (1–100 GHz) and as magnetic recording media owing to their novel physical properties. Frequency tuning of these components has so far been obtained by external magnetic fields provided by a permanent magnet or by passing current through coils. However, for high frequency operation the permanent part of magnetic bias should be as high as possible, which requires large permanent magnets resulting in relatively large size and high cost microwave passive components. A promising approach to circumvent this problem is to use hexaferrites, such as BaFe12O19 and SrFe12O19, which have high effective internal magnetic anisotropy that also contributes to the permanent bias. Such a self-biased material remains magnetized even after removing the external applied magnetic field, and thus, may not even require an external permanent magnet. In garnet and spinel ferrites, such as Y3Fe5O12 (YIG) and MgFe2O4, however, the uniaxial anisotropy is much smaller, and one would need to apply huge magnetic fields to achieve such high frequencies. In Part 1 of this review of microwave ferrites a brief discussion of fundamentals of magnetism, particularly ferrimagnetism, and chemical, structural, and magnetic properties of ferrites of interest as they pertain to net magnetization, especially to self biasing, are presented. Operational principles of microwave passive components and electrical tuning of magnetization using magnetoelectric coupling are discussed in Part 2.

/pdf/microwave-ferrites-part-1-fundamental-properties-124qghgxm4.pdf

Microwave ferrites, part 1: fundamental properties

Magnetic nanoparticles of cobalt ferrite (CoFe2O4) have been synthesized in a homogeneous aqueous solution without any template and subsequent heat treatment. The average particle size could be varied in the range of 2–14 nm by controlling coprecipitation temperature of Co2+ and Fe3+ ions in alkaline solution although the size distribution is pretty wide. As the precipitation temperature increased in the range of 20–80°C, the average particle size also increased. However, there is a considerable change in XRD crystallinity and the average size of the nanoparticles at the precipitation temperature between 40°C and 60°C. While the nanoparticles prepared at the temperature below 40°C show superparamagnetic relaxation at room temperature with blocking temperatures between 75 and 200 K, the samples prepared at the temperature higher than 60°C consist of both superparamagnetic and ferrimagnetic nanoparticles that result in magnetic coercivity at room temperature. Mossbauer spectra of the samples also confirmed their magnetic properties and wide size distribution in each sample. The analysis of the spectra gave a rough estimation of the ratio of superparamagnetic and ferromagnetic nanoparticles in each sample at various temperatures.

/pdf/synthesis-and-characterization-of-cofe2o4-magnetic-40ps8uiegb.pdf

Synthesis and characterization of CoFe2O4 magnetic nanoparticles prepared by temperature-controlled coprecipitation method

Detection of early stage prostate cancer by using a simple carbon nanotube@paper biosensor.

Wustite with NaCl structure is successfully synthesized in a quartz tube sealed under vacuum ( ≒1×10 -3 torr). Hematite in an evacuated quartz tube progressively loses oxide ion at 1373 K. XRD patterns disclose that α-Fe2O3 is transformed into the Fe3O4 after heat treatment at 1373 K for 32 h, and the poorly crystallized FeO is appeared after heat treatment for 48 h. Finally, α-Fe2O3 is completely transformed into the well crystallized Fe 0.935O after heat treatment for 84 h. The electrical resistivity, ac-susceptibility measurement, Mossbauer spectroscopy, and x-ray absorption spectroscopy corroborate the structural phase transition on the iron oxides prepared in a sealed quartz tube depending on the heating time at 1373 K.

A New Synthetic Route to Wüstite

Materials on the scale of nanoscale have widely been used as research topics because of their interesting characteristics and aspects they bring into the field. Out of the many metal oxides, zinc oxide (ZnO) was chosen to be fabricated as nanofibers using the electrospinning method for potential uses of solar cells and sensors. After ZnO nanofibers were obtained, calcination temperature effects on the ZnO nanofibers were studied and reported here. The results of scanning electron microscopy (SEM) revealed that the aggregation of the ZnO nanofibers progressed by calcination. X-ray diffraction (XRD) study showed the hcp ZnO structure was enhanced by calcination at 873 and 1173 K. Transmission electron microscopy (TEM) confirmed the crystallinity of the calcined ZnO nanofibers. X-ray photoelectron spectroscopy (XPS) verified the thermal oxidation of Zn species by calcination in the nanofibers. These techniques have helped us deduce the facts that the diameter of ZnO increases as the calcination temperature was raised; the process of calcination affects the crystallinity of ZnO nanofibers, and the thermal oxidation of Zn species was observed as the calcination temperature was raised.

Fabrication and Thermal Oxidation of ZnO Nanofibers Prepared via Electrospinning Technique

pellet electrode wereinvestigated in aqueous electrolyte solutions. The flat-band potential of this electrode, determined using a Mott-Schottky plot, was +0.18 V vs SCE at pH 4.8 and followed the Nernst equation with respect to pH. Under UVlight illumination, a cathodic photocurrent developed, and molecular hydrogen simultaneously evolved on thesurface of the electrode due to the direct reduction of water without deposition of any metal catalyst. Key Words : CuGaO

https://www.koreascience.or.kr:443/article/JAKO201431057370483.pdf

Don Kim

Papers

Synthesis and characterization of CoFe2O4 magnetic nanoparticles prepared by temperature-controlled coprecipitation method

Detection of early stage prostate cancer by using a simple carbon nanotube@paper biosensor.

A New Synthetic Route to Wüstite

Fabrication and Thermal Oxidation of ZnO Nanofibers Prepared via Electrospinning Technique

Photoelectrochemical Water Splitting on a Delafossite CuGaO 2 Semiconductor Electrode