We report studies on exchange bias effects in Ni–NiO nanoparticles with different particle diameters/distributions and concentration of metallic nickel, which vary from 0% to 32%. The exchange bias field, Hex, depends strongly upon both particle size and the concentration of metallic Ni, being maximum (∼2.2 kOe) at 5 K for the sample with almost negligible concentration of metallic Ni, whereas the corresponding value for the sample with highest concentration of metallic Ni (∼32±5.0%) is about 0.07 kOe. The structural features of the samples have been investigated thoroughly by using the Reitveld refinement of x-ray diffraction data and high resolution transmission electron microscopy, where as the magnetic properties using superconducting quantum interference device magnetometer.
The development of new magnetoelastic materials, suitable for use in magnetic stress sensors, has a high scientific and technological interest due to growing number of possible applications in automotive industry. In this study, a series of silicon-doped cobalt ferrite samples with compositions of CoSi,Fe2,X04 were prepared by substituting silicon for iron. The samples were made using standard powder ceramic technique. The spinel structure and the presence of residual phases were checked by XRD analysis. To determine the influence of the substitution on the strength of the magnetic exchange interactions, Curie temperature (Tc) measurements were made. A dramatic decrease of Tc with the substitution of Si for Fe was observed. By adjusting the silicon content and the sintering process the material properties could be optimized for industrial application.
Ar ion beam etching was carried out on NiFe(6)/ Cu(1.5)/NiFe(4)/IrMn(20) multilayer spin-valve structure with three different beam voltages in order to optimize the effective beam voltage for patterned Planar Hall device fabrication. VSM characterizations were done on the multilayer structure before and after etching for verification of necessary exchange bias and influence of etching. The multilayer spin-valve structure exhibits exchange bias of 202 Oe for as deposited sample whereas it enhances to 314 Oe after etching for the etching beam voltage of 800 V. Similarly, the corresponding coercivity of the spin-valve structure before etchings is 113 Oe while it is increased to 179 Oe after ion beam etching. Ar ion beam etching was done for subsequent fabrication of patterned junctions of different dimensions of 50x50 gMm2, 20x20 gm2 and 5x5 gm2 using lithography. The PHE measurements were made on all three junctions. Sensitivity has bee found to be more as the size of the patterned junction becomes smaller and smaller.
PACS 75.60. Ej, 75.70.Cn Top and bottom pinned spin valve structures have been fabricated using rf magnetron sputtering to study the depth sensitive exchange coupling. M-H curves of both the configurations in as-deposited and annealed forms have been measured by vibration sample magnetometry (VSM) and transverse Kerr effect spectrometry (TKE) using DC and AC magnetic fields, respectively. The TKE signal was also examined as a function of wavelength in the range from 300-800 nm, to obtain data from the full length of the bottom NiFe free layer covering either side of the interface. Annealing of the samples brings in higher values of exchange bias field compared to as-deposited samples perhaps due to improved uniformity in exchange conditions. The TKE data at 500 nm wavelength point towards energetically favourable spin structure at the pinned interface. Wavelength dependence of the TKE data shows an anamolous trend close to the NiFe-Cu (seed layer) inteface, which was attributed to a periodic Cu diffusion assisted non-specular reflection (diffraction) component.
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