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Effect of annealing on the structure and magnetic properties of graphite encapsulated nickel and cobalt nanocrystalsLarge area arrays of cobalt and nickel particles with truncated conical shapes and diameters of 80-120 nm have been prepared using interference lithography combined with an evaporation and lift-off process. The magnetic hysteresis has been measured and the remanent states of the particles have been compared with a three-dimensional micromagnetic model. The model shows a transition from ''flower'' to ''vortex'' magnetization states as the particle size increases. The distribution of switching fields and the magnetostatic interactions between particles have been characterized. Both lead to a slow approach to saturation in the hysteresis loops. The suitability of such arrays for data storage is discussed.

Changes in the impedance, ≊600%/Oe, at axial fields less than 1 Oe have been observed in the presence of a 90 kHz, few mA current through a soft, nearly zero magnetostrictive wire. In this 125 μm diameter CoFeSiB amorphous wire we observe a total change of 160% at the maxima of the impedance in dc fields less than 2 Oe. A systematic study of the role of induced anisotropy in the axial, circumferential, and helical directions on the magneto-impedance shows that the largest effect is seen in the wire annealed to obtain circumferential easy axis using a 15 mA ac current passing through it. Both the axial hysteresis loops and the observed I-V characteristics reflect the induced anisotropies. The observed dependence of the inductance change on the type of the anisotropy induced in these wires can be modeled in terms of an interplay between the induced anisotropy, reversing ac field, and the axial dc field.

Articles you may be interested inPhotoemission electron microscopy study of remanent magnetic domain states in ferromagnetic wedge films deposited on substrates with micrometer-sized square plateaus J. Appl. Phys. 99, 063904 (2006); 10.1063/1.2174119 Variation of domain-wall structures and magnetization ripple spectra in permalloy films with controlled uniaxial anisotropy J. Appl. Phys. 98, 053905 (2005); 10.1063/1.2033152 Magnetic domain wall transitions based on chirality change and vortex position in thin Permalloy™ films Cross-tie walls and magnetic singularities on the surface of permalloy films (abstract)The Bloch to Néel wall transition is investigated in Permalloy films between 160 and 10 nm thickness using direct integration of the Landau-Lifshitz-Gilbert equation in a three-dimensional Cartesian lattice. At 80 nm, the wall is a symmetric Bloch wall characterized by two adjoining vortices with the magnetization at the wall center pointing perpendicular to the plane of the material throughout the thickness. The Bloch to Néel transition takes place between 35 and 30 nm, below which the wall becomes a symmetric Néel wall. For the Bloch walls, our wall energy per unit area calculations match reasonably well the results of A. Hubert's Ritz method calculations ͓Magnetic Domains ͑Springer, New York, 1998͒, p. 251͔ and A. E. Labonte's numerical calculations ͓J. Appl. Phys. 40, 2450 ͑1969͔͒. For the Néel walls, however, our results indicate an approximately 70% higher energy for thicknesses of 30 nm and below, since the Néel wall tails are included. For thicknesses below 160 nm, the anisotropy energy component is low, and both C-shaped and symmetric Bloch walls are dominated by exchange interaction. As the wall transforms from Bloch to Néel below 35 nm, the energy contribution changes from 76% exchange and 24% demagnetization to 70% demagnetization and 30% exchange, respectively. Wall widths are computed for thicknesses between 10 and 640 nm along with the out-of-plane magnetization due to the presence of the vortex.

An overview of advances of the amorphous wire magnetics over the past 27 years with discoveries of extremely sensitive magnetic effects such as the large Barkhausen effect, the Matteucci effect and the magnetoimpedance effect and their successive applications to security sensor tags, pen‐inputting computer tablets and electronic compasses for mobile phones in commercial productions is presented. An important new topic of biocell magnetic field sensing in vitro and human physiological magnetic field sensing in vivo using a 10 pT amorphous wire magnetoimpedance sensor is also shown that would be improved using thinner glass‐covered amorphous wires. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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