Markayendeyulu G

Magnetoimpedance (MI) effect was studied on amorphous Co33Fe33Ni7Si7B20 ribbons that were irradiated with N+1, Ar+2 and Xe+5 ions, at energy of 75 keV. The (MI)m [maximum MI in each case] values are 9.4% and 11%, 9.9% and 6.5%, the largest, for the as-quenched and N+1, Ar+2 and Xe+5 ion irradiated ribbons respectively, at 2 MHz. The (MI)m value of the N+1 ion irradiated ribbon was observed to be the highest, due to an induced in-plane transverse magnetic anisotropy. The saturation magnetizations of the ion-irradiated ribbons are not seen to change with respect to that of the as-quenched ribbon; a small increase in the Ms was observed only upon irradiation with Xe5+ ions. The interaction between the large number of domains, with large uniaxial anisotropy led to large (MI)m values, at frequencies above 8 MHz in the Ar+2 ion irradiated ribbon.

The giant magnetoimpedance (GMI) effect in amorphous and nanocrystalline Fe73.5Si13.5B8CuV3Al ribbons has been studied as a function of a dc magnetic field, by contact and non-contact methods. In the contact method, an MI of 19% was obtained in the nanocrystalline ribbon while it is of the order of 104 in the non-contact method. The huge sensitivity of the non-contact method is promising with regard to the increase of the sensitivity of the MI sensors. Field dependence of MI has shown double peak behavior in contact method and single peak profile in non-contact method. The domains were found to lie normal to the plane of the ribbon, through MFM studies. All the experimental results were discussed using the Polivanov model. © 2009 Elsevier B.V. All rights reserved.

Magnetoimpedance (MI) has been investigated in the laser and microwave annealed Fe66Ni7Si7B20 ribbons. The largest MI [(MI)m] values of the ribbons annealed using laser with energies of 150, 200 and 250 mJ/pulse (mJp) are 25% (at 7 MHz), 30% (at 5 MHz) and 21% (at 7 MHz) respectively. The effect of domain wall pinning on MI was observed as field insensitive regions in the MI profiles in the ribbon annealed using 150 mJp energy. Flower shaped grains in amorphous matrix in the ribbon annealed with 200 mJp energy are responsible for highest (MI)m due to the least anisotropy. In the ribbons annealed for 40, 45 and 50 min at 400 °C using microwaves, (MI)m values are 35% (at 5 MHz), 46% (at 6 MHz) and 29% (at 7 MHz) respectively. The large DC conductivity and the least anisotropy (smallest Hk values) in the ribbon microwave annealed for 45 min at 400 °C resulted in (MI)m reaching its highest value in the ribbons investigated.

Structural, electrical, and magnetoreactance (mr) characteristics of rare Earth-doped Ni ferrite (NiO.Fe2-xRxO3(x = 0. 0.075. R =- , and NiO.Fe1.95R0.05O3 ) 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 - 1477% 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. © 2009 IEEE.

Magnetoimpedance (MI) has been investigated in the as quenched Fe 66-xCoxNi7Si7B20 (x=0, 33 and 66) ribbons. In plane anisotropy was present in as-quenched x=0, 33 and 66 ribbons. The largest MI values for x=0, 33 and 66 ribbons are 25% (at 7 MHz), 26% (at 8 MHz) and 45% (at 8 MHz) respectively. Largest MI values increased with increasing Co due to reduced magnetic anisotropy. Maximum MI values reduced at higher frequencies due to increased anisotropy fields. © 2014 Elsevier B.V.

Magnetoimpedance (MI) in Co68Fe4Zr10Cu2B16 alloy has been investigated in the frequency range 500 kHz-5 MHz and with the application of external steady magnetic field in the longitudinal direction, up to 100 Oe. MI measurements were carried out on as-cast ribbons and also on conventionally annealed and Joule-annealed ribbons. In as cast ribbons, the maximum MI observed is 13% at a frequency of 500 kHz and it decreases to 5% and 4% with conventional annealing at 100 °C and 150 °C, respectively. On the other hand, MI decreases to 8% and 6% with Joule annealing employing currents of 100 mA and 200 mA, respectively. However, Joule annealing with the application of a magnetic field of 5-10 Oe in the transverse direction causes the MI to decrease to 12% and 11% for currents of 100 mA and 200 mA, respectively. In the as-cast ribbons, double peak behavior is observed in all the frequencies whereas, in the annealed ribbons, double peak behavior in general is observed only at high frequencies. © 2005 Elsevier B.V. All rights reserved.

A systematic investigation of the influence of different types of annealing on the magnetoimpedance (MI) effect in melt-spun (Co1-xFe x)89Zr7B4 [x=0, 0.025, 0.05] and (Co0.88Fe0.12)78.4Nb2.6Si 9B9Al ribbons has been carried out in the frequency range 500 kHz13 MHz and under dc magnetic fields (Hdc) up to 80 Oe. In the stress annealed ribbons, the strain-induced transverse anisotropy is seen to result in large MI. Magnetic domains were investigated in the ribbons through magnetic force microscopy. © 2011 Elsevier B.V. All rights reserved.

The magnetoinductance (mi), AC magnetoresistance (ACMR) and magnetoimpedance (MI) in as cast Co68Fe5Nb12B15 ribbons of length from 1 to 5 cm were studied. The mi, ACMR and MI are large for 5 cm long ribbons. At a frequency of 13 MHz, large value of ACMR (67%) compared with the mi and MI is observed. This is explained as due to the decrease of the skin depth with increase of frequency. With the application of the external steady magnetic field the skin depth increases resulting in a large ACMR. The larger values of mi, ACMR and MI ratios for 5 cm long ribbons compared to those in the smaller ribbons may be due to smaller demagnetizing fields. © 2006 Elsevier B.V. All rights reserved.