Amaresh Chandra Mishra

Enhanced magnetoimpedance and field sensitivity in microstructure controlled FeSiCuNbB ribbons

Fe73.5Si13.5Cu1Nb3B9 and Fe77.2Si11.2Cu0.8Nb3.3B7.5 nanocomposite materials consisting of nanocrystalline phase in an amorphous matrix were obtained by heat-treatment of their precursor amorphous ribbons. The influence of structural modifications induced during the heat-treatment on soft magnetic properties and magnetoimpedance (MI) effect have been studied. The structural investigations on both these ribbons revealed the presence of two phases, fine grained Fe3Si phase and a residual amorphous phase on heat-treatment. The maximum MI ratio obtained in the present study is 95% at f = 4 MHz, for the optimized heat-treated Fe77.2Si11.2Cu0.8Nb3.3B7.5 ribbon. This is ascribed to the increase in magnetic permeability and decrease in coercive force and intrinsic resistivity. Moreover, a maximum magnetic field sensitivity (ξ) of 8.3%/Oe at f = 2.5 MHz is obtained, for the optimized nanocrystalline Fe73.5Si13.5Cu1Nb3B9 ribbon. This suggests that tailoring of the nanocrystalline microstructures induced by optimum h...

Microstructure, magnetic, and magnetoimpedance properties of electrodeposited NiFe/Cu and CoNiFe/Cu wire: A study on influence of saccharin additive in plating bath

Magnetic thin films of NiFe and CoNiFe were electrodeposited from three different deposition baths on copper wires of 100 μm diameter. The magnetic and magneto-impedance (MI) properties of the samples were investigated as a function of saccharin additive concentration in the plating bath. For all intermediate frequencies, the MI ratio increased with saccharin concentration in the plating bath up to a critical concentration and then saturates. The change in MI with saccharin concentration in electrodeposition bath was attributed to the grain size reducing action of saccharin which in turn reduces the coercivity of the film, making it soft magnetic. The origin of MI lies in the combined effect of domain wall motion and spin rotation which contributes to permeability. Inductance spectroscopy was used to evaluate the magnetic characteristic of the samples by modeling magnetic film-coated wires in terms of equivalent electrical circuit; namely parallel inductance and resistance circuit in series with series A ...

Micromagnetic simulation of hysteresis loop of elliptic permalloy nanorings

Magnetic hysteresis behavior of isotropic permalloy elliptic nanorings of outer semi-major axis length (aout) 100 nm and thickness (t) 20 nm were studied with respect to the variation of two parameters: outer semiminor axis length (bout) and the difference between outer and inner dimensions (r). The outer semiminor axis length (bout) varied from 90 nm to 20 nm which covers from nearly circular nanoring to elliptic nanoring of high aspect ratio. The value of r varied in steps of 10 nm. Micromagnetic simulation of in-plane hysteresis curve of these nanorings revealed that the remanent state of all of these elliptic rings are onion states if the magnetic field is applied along the longer side of the elliptic rings. If the magnetic field is applied along the shorter side, then the remanent states turn out to be vortex state. The hysteresis loss indicated by area of the hysteresis loop was found to be decreasing gradually with the increment of either r or bout. On the other hand, the remanent magnetization increased with increment of r but decreased with the increment of bout. The changes were attributed to three parameters mainly: inner curvature, exchange energy and demagnetization energy. The changes in loop area were discussed in light of variation of these three parameters.

Effects of both diffuse and collimated incident radiation on phototactic bioconvection

Phototaxis denotes swimming towards (positive) or away (negative) from light. The suspension containing phototactic algae is illuminated by both the diffuse and collimated solar radiation. The algae absorb the incident light and scatter it. We use the phototaxis model of Ghorai et al. [“Bioconvection in a suspension of isotropically scattering phototactic algae,” Phys. Fluids 22, 071901 (2010)] and investigate the onset of bioconvection with particular emphasis on the effects of diffuse irradiation. The basic equilibrium state of the bioconvective governing system is defined by assuming that the bulk velocity of the fluid to be zero and the up and down swimming, caused by the positive and negative phototaxis, is balanced with the diffusion. For some values of the parameters, the bimodal steady-state profile transits to a unimodal equilibrium state as the diffuse irradiation is increased. For a small scattering albedo, at the onset of bioconvective instability, this model differs significantly from the up-...