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Lead-free Bi0.5(Na0.80K0.20)0.5TiO3 (BNKT) particles were synthesized by using sol-gel method. The samples were investigated by X-ray diffractometry (XRD), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), and vibrating sample magnetometer (VSM). The absorption of microwaves of the lead-free BNKT powders is determined from the magnetic (permeability) and dielectric (permittivity) properties at the frequency range from 2 to 18 GHz. Absorption characteristics of paraffin(wax)-mixed BNKT compounds at different sample thicknesses were also investigated. The microwave absorption properties show that the maximum reflection loss is -21.72 dB (99.9%) at 13.66 GHz with a thickness of 3.2 mm. BNKT composites are thought to be used as a promising microwave absorption material.

Magnetic Fe3O4 nanoparticles are prepared by the coprecipitation method and coated with starch as a surfactant. Their structural and magnetic behaviours are studied by means of X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Raman spectrum, Fourier Transform Infrared (FT-IR) as well as with a Vibrating Sample Magnetometer (VSM). The magnetic Fe3O4 nanoparticles under investigation have an average size of about 14 nm. The coated magnetic nanoparticles exhibit super-paramagnetic behaviours with a blocking temperature of about 170 K and saturation magnetisation ranging between 30 and 50 emu g−1. In addition, the results of FT-IR indicated that interactions between the Fe3O4 particles and starch layers are much improved.

This paper deals with the planar Hall effect (PHE) of Ta(5)/NiFe(tF)/Cu(1.2)/NiFe(tP)/IrMn(15)/Ta(5) (nm) spin-valve structures. Experimental investigations are performed for 50 mumtimes50 mum junctions with various thicknesses of free layer (tF = 4, 8, 10, 12, 16, 26 nm) and pinned layer (tP = 1, 2, 6, 8, 9, 12 nm). The results show that the thicker free layers, the higher PHE signal is observed. In addition, the thicker pinned layers lower PHE signal. The highest PHE sensitivity S of 196 muV/(kA/m) is obtained in the spin-valve configuration with tF = 26 nm and tP = 1 nm. The results are discussed in terms of the spin twist as well as to the coherent rotation of the magnetization in the individual ferromagnetic layers. This optimization is rather promising for the spintronic biochip developments.

High-sensitive stress sensor is simply constructed comprising magnetostrictive 30 μm-thick (Fe80 Co20) 78Si12B10 ribbon acting as a sensitive magnetic core inside an induction coil. The stress can be determined indirectly by measuring the change in the output voltage in the two-coil system. The results show that the sensitivity highly depends on the intrinsic properties of the ribbon cores. The optimum with both a high sensitivity and an almost linear stress dependence of output signal was obtained in the 250°C- annealed ribbon. This is attributed to the correlation between the magnetic and magnetoelastic softness governed by the fine 10 nm nanogram structure. These high sensitivity and simple fabrication sensors are widely applicable to various stress detecting fields. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA. Index Keywords: FeCoSiB ribbons; High-sensitive stress sensors; Nanogram structure; Annealing; Electric potential; Iron alloys; Magnetic cores; Nanostructured materials

Magnetic nanoparticles Fe3O4 were prepared in air environment by the coprecipitation method using molar ratios of Fe2+: Fe3+ = 1: 2. The surface of magnetic nanoparticles was coated with sodium oleate as the primary layer and polyethylene glycol 6000 (PEG-6000) as the second layer. The morphology of the particles was investigated by scanning electronic microscopy (SEM). X-ray diffraction (XRD) indicated the sole existence of inverse cubic spinel phase of Fe3O4 and an average size of about 25 nm. Fourier transform infrared spectroscopy (FTIR) analysis indicated existence of two distinct surfactants on the particle surface. In addition, the results of FT-IR indicated that the coated Fe3O4 particles improved the thermal stability due to the interaction between the Fe3O4 particles and protective layers.

Present paper deals with the planar Hall effect (PHE) of Ta(5 nm)/NiFe(tf)/Cu(1.2 nm)/NiFe(tp)/IrMn(15 nm)/Ta(5 nm) spin-valve structures. Experimental investigations are performed for 50 × 50 μm2 junctions with various thicknesses of free and pinned layer tf = 4, 8, 10, 15, 20 nm and tp = 2, 3, 6, 8, 9, 12 nm. The results show that the thicker free layers, the higher PHE signal is obtained. In addition, the thicker pinned layers, the lower PHE signal. The highest PHE sensitivity S of 15.6 mΩ/Oe is obtained in the spin-valve configuration with tf = 20 nm and tp = 2 nm. This optimum structure is rather promising for micro magnetic bead detections.

The planar Hall effect (PHE) magnetic bead array countermicrochip integrating 24 of single sensors based on a simple NiFe/IrMn bilayer structure with a patterned size of 3×3 μm2 has been fabricated and characterized. Single PHE sensors exhibit a sensitivity of about 2.5 mΩ/Oe. It was well applied for single Dynabeads® M-280 detection, where one bead can induce a signal change, ΔV∼2.2 mV, under the applied magnetic field of 20 Oe and a sensing current of 2 mA. This type of microchip is promising for quickly detecting and identifying multiple biological agents in the environment.