B. Parvatheeswara Rao

Mössbauer study of the system Ni0.65Zn0.35Fe2−xScxO4

Abstract Mossbauer study of the system Ni 0.65 Zn 0.35 Fe 2− x Sc x O 4 , with x values ranging from 0.00 to 0.25, has been conducted at room temperature to analyze the site occupancy of Sc 3+ ions. The results indicated that all of the scandium ions preferentially occupy octahedral sites for x values up to 0.10, whereas for the subsequent increase in x , a small part of the scandium ions occupy tetrahedral sites as well. Ionic distribution for the system is given. The observed variations in the hyperfine magnetic fields and peak–area ratios, isomer shifts and linewidths with composition are discussed.

Soft chemical synthesis and characterization of Ni0.65Zn0.35Fe2O4 nanoparticles

Mixed ferrite nanoparticles of Ni0.65Zn0.35Fe2O4 using metal nitrates were prepared by three different low temperature methods of sol gel in polyvinyl alcohol matrix, coprecipitation with NaOH as coprecipitating base, and sol gel in citric acid matrix, separately to estimate the influence of synthesis on the structural and magnetic parameters of this high saturation magnetization NiZn ferrite composition. In the final stage of the synthesis, the coprecipitated sample was washed and filtered several times before drying and finally heat treated at 350°C for 1h to get the ultrafine powder. Whereas the other two samples, which were transformed into dried gel after mixing and drying, were heat treated at 350°C for 1h, respectively, to find out the dried gel burnt out in a self-propagating combustion manner to form a fluffy powder. X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer measurements are performed on all three samples. Though the composition is the same for all thr...

Translocation of magnetic beads using patterned magnetic pathways for biosensing applications

We have designed, fabricated, and demonstrated a novel system for translocation of magnetic beads at specific sites of the sensor surface on a single chip for biosensor applications. The soft NiFe elliptical (9×4×0.1 μm3) elements are arranged as magnetic pathways connected to the model sensor surface. The patterned NiFe elements can generate different stray magnetic fields when they are subjected to the external rotating magnetic field. The inhomogeneity in stray magnetic fields can govern the magnetic bead motion on the pathways. We demonstrated the motion of Dynabead® M-280 magnetic bead on patterned pathways by controlling the external rotating magnetic field in clockwise and counterclockwise directions. The magnetic beads that were placed on the magnetic elliptical pathways are shown to be transported to the sensor surface, as well as be pulled out away from the surface. This technique enables microtranslocation of the magnetic beads coated with biomolecules to the specific binding sites of the senso...

Thickness dependence of parallel and perpendicular anisotropic resistivity in Ta/NiFe/IrMn/Ta multilayer studied by anisotropic magnetoresistance and planar Hall effect

Ferromagnetic layer thickness dependence of anisotropic magnetoresistivities in Ta∕NiFe(t)∕IrMn (10 nm)∕Ta has been investigated for t=3, 4, 5, 7, 8, 10, 12, 15, and 20 nm by the method of anisotropic magnetoresistance and planar Hall effect. Our results revealed that the parallel and perpendicular resistivity components performed a varying function with increment in NiFe thickness. Both the resistivities at first were observed to increase when the NiFe thickness increases from 3 to 10 nm; then for the NiFe thicknesses from 10 to 20 nm, the resistivities of NiFe layer decrease as the NiFe thickness increases. However, the anisotropic resistivity change, which is the difference between parallel and perpendicular resistivities, was observed to increase for the whole range of thicknesses when the NiFe thickness increases. The measured quantities were found to be in good agreement with the theoretically estimated parameters using single domain model; thus these behaviors are well explained based on the modern...

Template Synthesis of Cobalt Nanowires Using PS-b-PMMA Block Copolymer

Cobalt nanowires with 18 plusmn 5 nm diameter were grown in the self-assembled diblock copolymer templates using electrodeposition technique. The diblock copolymer templates with hexagonally ordered nanoporous structure were successfully synthesized by varying the copolymer thickness from 50 nm to 430 nm and post annealing at temperature 180degC for 24 h. The minimum optimized pore sizes of the template were 18 plusmn 5 nm with well order hexagonal nanoporous structure at copolymer thickness from 350 nm to 430 nm. Cobalt nanowires were then successfully deposited using three electrode configuration potentiostatic electrodeposition methods. To remove the cross linked polystyrene of the template and to display the cobalt nanowires, heat treatment was carried out. The morphology of the templates and cobalt nanowires was observed using Scanning Electron Microscope (SEM). The magnetic properties of the cobalt nanowires are analyzed using Vibrating Sample Magnetometer (VSM).

Doped Cobalt Ferrites for Stress Sensor Applications

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 CoSixFe2-xO4 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.

Depth sensitive exchange coupled spin structure in NiFe∕FeMn bilayer

Magnetization mechanisms in NiFe and NiFe∕FeMn layered systems have been studied using vibration sample magnetometry (VSM) and transverse Kerr effect spectrometry (TKE). The TKE signal was examined at the wavelengths of 300, 500, and 700nm and at various fields from 12to85Oe at each wavelength by aiming at a depth sensitive exchange coupled magnetic profile in the probed ferromagnetic layer. An attempt has been made to correlate the features from the M-H curve profiles measured using VSM under dc magnetic field and TKE with ac magnetic field to the exchange coupled spin structures. The results point toward a short range order of biquadratic exchange coupling near the interface. Based on the data and analysis, possible spin structures were proposed and depth profiles of decomposed magnetization due to biquadratic and bilinear exchange couplings were reported.

Novel Planar Hall Sensor for Biomedical Diagnosing Lab-on-a-Chip

The underlying principle for magnetic biosensing has been elaborately described at first with the examples of different magnetoresistive sensing techniques. Then, the planar Hall resistance sensor has been shown as one of the best sensors for conducting magnetic bead detection experiments. While making an in depth study on the capabilities of a PHR sensor in different configurations and geometries, the sequence of narration ultimately has lead towards describing the evolution of hybrid AMR and PHR ring sensor in spin valve configuration with optimized performance for precise detection of even single magnetic bead. Biofunctionalization experiments were also conducted to ensure that our PHR sensor is capable of biomolecule recognition. Therefore, our present sensor can be used to promote for the biomolecular recognition and other molecular interaction detection. This novel planar Hall effect based sensor has been further demonstrated that it can be easily integrated into a lab-on-a-chip and is feasible for bead detection in the sensing current generated magnetic field (without the external applied magnetic field) so as to ensure it an efficient tool for high sensitive biomolecules recognition.

Compositional Dependence of Magnetostrictive Properties of Cobalt Ferrite

Compositional dependence of magnetostrictive properties of three series of samples with compositions CoMnxFe2−xO4, Co1+xSixFe2−2xO4 and CoSixFe2−xO4 (x = 0 to 0.6) have been investigated. Manganese/silicon substituted cobalt ferrites have shown maximum strain derivative values as compared to pure cobalt ferrite which makes these materials promising for magnetostrictive sensing applications. The results are explained on the basis of cation distribution, valence states of different cations with preferential occupation of lattice sites, and their magnetostrictive contributions.

Enhanced Strain Derivative of Mn/Si Substituted Cobalt Ferrite

Influence of Mn/Si for Fe in Cobalt ferrite has been studied in the direction of improving strain derivative and decreasing Curie temperature while making a comparison between the properties of systems thus studied. Two series of CoMnxFe2−xO4 (CMF) and Co1+xSixFe2−2xO4 (CSF) were prepared with spinel crystal structures. Saturation magnetostriction λs, strain derivative dλ/dH, coercivity and Curie temperature, properties were measured. Higher strain derivatives and a large decrease in Curie temperature were noticed with composition in case of series CSF. The results demonstrate the possibility of optimizing the magnetomechanical properties of cobalt ferrite through atomic substitution.