Ferromagnetic Microwires Research Articles

Glass-coated magnetic microwires for technical applications

Glass-coated Fe- and Co-rich ferromagnetic microwires exhibit excellent magnetic properties: magnetic bistability enhanced magnetic softness and GMI effect. Large stress sensitivity of magnetic characteristics has been observed. Conventional and field annealing permit to tailor such magnetic parameters as coercivity or magnetic permeability. A number of technological applications based on magnetic bistability and GMI effect are introduced.

Residual quenching stresses in glass-coated amorphous ferromagneticmicrowires

The calculation of the residual stress tensor components inglass-coated amorphous ferromagnetic microwire is carried out on the basisof the theory of viscoelasticity. The approach takes into account therelaxation of the stresses both in a metallic core and a glass shell of thewire within a certain temperature interval near the point of the wire'svitrification. The distribution of the residual stresses is investigated asfunction of mechanical characteristics of metallic core and glass shell atdifferent ratios of the metallic core radius to the total wire radius. Themagnetic behaviour of a glass-coated amorphous microwire with smallnegative magnetostriction is analysed and is shown to be consistent withthe experimental data.

Broadband permeability measurement of ferromagnetic thin films or microwires by a coaxial line perturbation method

A new method to measure the microwave permeability of ferromagnetic thin film or microwires from 50 MHz up to 18 GHz is presented. In contrast with all previous permeameters based on perturbation techniques, our permeameter does not require any reference sample for calibration, which is a definite advantage, as it is very difficult to have a reference magnetic sample of known permeability. In our technique, a network analyzer detects the small perturbation of the impedance of a coaxial line cell loaded by the magnetic sample. Satisfactory sensitivity is achieved, even for magnetic volume fraction as low as 10−4. To assess the validity of this new technique, comparisons are performed with three other methods on different samples, in particular on ferromagnetic wires. It is shown that in the case of very soft magnetic materials, the shape of the sample affects the permeability measured with a conventional permeameter.

Magnetic microwires as macrospins in a long-range dipole-dipole interaction

The long-range dipole-dipole interaction in an array of ferromagnetic microwires is studied through magnetic hysteresis measurements and Monte Carlo simulation. The experimental study has been performed on glass-coated amorphous ${\mathrm{Fe}}_{77.5}{\mathrm{Si}}_{7.5}{\mathrm{B}}_{15}$ microwire with diameter of 5 \ensuremath{\mu}m and lengths from 5 to 60 mm. Hysteresis loops performed at room temperature for an array of N microwires $(N=2, 3, 4,$ and 5) exhibit jumps and plateaux on the demagnetization, each step correspondent to the magnetization reversal of an individual wire. A model has been constructed taking into account the fact that the magnetization reversal is nucleated at the ends of each wire, under the influence of a dipolar field due to all other wires. Measurements for two wires allowed us to conclude that the dipolar field (or constant coupling) is independent of distance, at least for an array of a few wires. With the exception of three wires, where frustration seems to be present, the predicted reversal fields of our model are in good agreement with measurements. In order to study the role played by the number of wires on the demagnetization process, we calculate hysteresis loops for a large number of wires through the Monte Carlo method.

Magnetoelastic behavior of glass-covered amorphous ferromagnetic microwire

Particular aspects concerning the magnetoelastic behavior of an Fe-rich glass-covered amorphous ferromagnetic microwire (diameter about 20 /spl mu/m) are reported in both the as-prepared state and after various heat treatments. The main feature of such behavior is that related with the bistable behavior exhibited by the microwire. The magnetization process takes place by a single and large Barkhausen jump at a given applied field. For the as-prepared material, the value of this switching field (H*/spl ap/112 Am/sup -1/) is about one order of magnitude larger than that reported for Fe-rich amorphous wires with a diameter of about 125 /spl mu/m (H*/spl ap/8 Am/sup -1/). The effect of the thermal treatment as well as the stress dependence of H* for as-obtained and treated microwire are also reported and discussed in terms of the stress distribution within the microwire.

Magnetic bistability of glass-covered Fe-rich amorphous microwire: influence of heating treatments and applied tensile stress

The influence of heat treatments and mechanical stresses on the magnetic behaviour of an Fe-rich glass-covered amorphous ferromagnetic microwire (diameter about 20 mm) is reported here. The behaviour is characterized by a magnetization process with a single and large Barkhausen jump at a given applied field. For the as-prepared material, the switching field corresponding to this bistable behaviour is around 100 A m−1 and can be significantly modified by adequate heating treatments as well as by application of mechanical stresses. These changes are discussed in terms of the modification of the internal stresses.

LC integrator and nanowebermeter for measuring the saturation flux in ferromagnetic films, tapes and microwires

LC integrator and nanowebermeter for measuring the saturation flux in ferromagnetic films, tapes and microwires