Sandhya Dwevedi

Giant magnetoimpedance effect in nanocrystalline ribbons for sensitive magnetic sensors

A systematic investigation of the influence of Al and V on the magnetoimpedance (MI) effect in melt-spun Fe73.5Si13⋅5B8CuNb(3−x)VxAl (x=0, 1, 1.5, and 3) ribbons has been performed in the frequency range 500 kHz–13 MHz and under dc magnetic field (Hdc) up to 60 Oe. MI was measured using impedance analyzer employing contact and noncontact methods. MIs of 61% (contact method) and 104% (noncontact method) were observed for the x=1.0 ribbon. Transverse and in-plane anisotropies were studied from the MI measurements and ferromagnetic resonance. Magnetic domain structure was studied in the ribbons through magnetic force microscopy. When the ribbon was rotated by 90° from the east-west direction, a 37% change in the MI was observed due to the earth’s magnetic field.

Magnetoreactance Studies in Rare Earth-Doped Ni Ferrite

Structural, electrical, and magnetoreactance (mr) characteristics of rare earth-doped Ni ferrite (NiO.Fe_2-xR_xO₃ <i>(x = 0, 0.075, R = Dy, Gd)</i> , and NiO.Fe_1.95R_0.05O₃ <i>(R = Gd, Nd)</i>) were investigated. All the materials formed in the cubic inverse spinel phase with small amounts of RFeO₃ as the additional phase. mr was measured in both longitudinal and transverse configuration. A mr of <i>-1477%</i> was observed for pure nickel ferrite at 10 kHz while it is smaller for the rare earth-doped compounds. With increasing frequency maximum mr value is found to decrease. The resistivity was found to decrease with increasing frequency for all the compounds and dispersion of relaxation times was observed.

Structural, magnetic, and magnetoelectric properties of NiO.Fe2O3 and NiO.Fe1.925Sm0.075O3 thin films

NiFe2O3 and NiOFe1.925Sm0.075O3 thin films were prepared by rf magnetron sputtering on oxidized silicon and lead zirconate titanate (PZT) substrates. Both the films were found to crystallize in inverse spinel structure after the annealing was carried out at 1073 K for two hours. Small hysteresis was observed in both the films at 300 K as well as 1.8 K. The magnetoelectric coefficient αE is seen to have the largest value at 500 Oe and is 4.07 and 3.57 mV cm−1 Oe−1 in NiOFe1.925Sm0.075O3–PZT and NiOFe2O3–PZT composite films, respectively.

Magnetoimpedance In Co‐Rich Ribbons/Thin Films

The magnetoimpedance (MI) effect in the as cast and annealed melt‐spun Co68Mn5Si12B15 ribbons has been studied in the frequency range 500 kHz–13 MHz under dc magnetic field (Hdc) up to 60 Oe. The ribbon annealed at 450 °C has the largest MI of 82% at 0.9 Oe. Amorphous magnetic Co‐Mn‐Fe‐Mo‐Si‐B films, annealed at 350 °C exhibit the largest MI of 14% by non‐contact method.