M.R.J. Gibbs

Amorphous wires and their applications

Abstract The basic physical and magnetic properties of Fe and Co based amorphous wires are summarised, together with post-production treatments used to modify the properties of the as-quenched alloys. The current status of the core-shell domain model is reviewed in the light of recent studies of the internal stress and easy axis distributions. Finally, a survey of recently proposed applications is presented.

Digital M-H plotter for low-coercivity metallic glasses

A computer-based system for plotting the DC magnetisation loops of amorphous magnetic ribbons is described. The system overcomes the problems associated with very low coercivity materials by using a nonlinear H-field function that can be adjusted for a particular loop. The problem of drift is overcome by the use of a hybrid analogue/digital integrator and software correction. Commonly used magnetic parameters are calculated from the digitised data. In particular, coercivities of less than 1 A m-1 can be reliably measured. Typical results are presented to illustrate the performance.

Anisotropy and magnetostriction in metallic glasses

Abstract Measurements involving M − H and λ − H data and domain images are presented in a discussion of the effects of induced anisotropy on moment canting and magnetostrictive response in metallic glasses. The data are compared with a recent model. It is shown that field annealing involves two distinct processes. Evidence is given to show that metallic glasses can magnetise by almost pure moment rotation under the correct material conditions; the effective moment canting coming close to zero.

High-field magnetization of metallic glasses

Magnetization measurements in fields to 20 T (16 MA/m) have been made at room temperature on as-cast samples of several compositions of metallic glasses, to see whether or not the results are consistent with neutron diffraction and Mossbauer measurements that show moment canting, or incomplete ferromagnetic alignment of moments, in these materials. The results can be interpreted with the ferromagnetic with wandering axis model of Chudnofsky, but the data fit equally well to the spin-wave model used by Pauthenet to fit high-field magnetization data on crystalline ferromagnets. >

Anisotropy and magnetostriction in amorphous alloys

Abstract A review is presented of three routes to control the anisotropy in amorphous alloys. These are field annealing, stress annealing and surface crystallisation. The aim is to highlight the differences in the magnitudes of the uniaxial anisotropies. The causes and consequences of the observed spread in easy axis direction within domains will be discussed. The magnetostrictive response of amorphous alloys will be discussed in terms of the controlling anisotropy. Devices using magnetostrictive response will be discussed, and the constraints imposed in device fabrication outlined.

Magnetic, magnetostrictive and structural properties of iron-cobalt/silver multilayers

Abstract Magnetic and magnetostrictive measurements have been carried out on FeCo/Ag multilayers using a dc magnetometer and the SAMR method, respectively. The samples were deposited by rf magnetron sputtering onto 26 μm polyimide substrates, half of each multilayer being deposited on each side. The Ag thickness was maintained at 2 nm while tFeCo was varied between 2 and 12 nm. The coercivity of the multilayers was much reduced by the presence of Ag from that observed in a homogeneous FeCo film. Magnetostriction values were also altered from those expected from bulk polycrystalline FeCo alloy. X-ray diffraction analysis indicates that the FeCo layers form a bcc structure with no strong crystallographic orientation. It is likely that the Ag layers are not continuous.

Implications of magnetic and magnetoelastic measurements for the domain structure of FeSiB amorphous wires

The field-dependence of magnetization, Youngs modulus and magnetostriction have been used to investigate the domain structure of FeSiB amorphous wires. The experimental observations of the as-cast wire are explained in terms of a modified core-shell model in which the shell is magnetized in a series of domains oriented approximately perpendicular to the wire axis and the magnetization in the core is oriented at an average angle of about 44 degrees to the wire axis. The presence of reverse spike domains in the core at the ends of the wire is also suggested. The critical length below which magnetic bistability is lost may be associated with these reverse domains. The behaviour of wires annealed at 425 degrees C can be interpreted in terms of a similar model, except that the core volume and the length of the reverse spike domains are increased and the average magnetic moment angle in the core is decreased.

Pulse annealing of FeSiB amorphous wires

The magnetic field dependence of magnetization and Youngs modulus of pulse-annealed Fe/sub 77.5/Si/sub 7.5/B/sub 15/ are reported. Coercivity and anisotropy energy density were measured as a function of annealing current and the tensile stress applied during annealing. It is shown that pulse annealing can remove the internal stresses more effectively than furnace annealing. Coercivity and anisotropy energy density fall by a few percent for annealing currents up to 1 A. Currents between 1 A and 1.5 A reduce both quantities by nearly an order of magnitude. Higher annealing currents result in sharp increases in the parameters, as crystallization begins. >

High Resolution /spl delta/E Measurements Of Fe-Si-B Amorphous Wire

The field dependence of Youngs modulus, E(H), of as-cast Fe-based amorphous wire has been investigated using a high resolution vibrating reed system. The E(H) data have been combined with DC M(H) loops and Kerr effect surface domain images to provide information about the effect of the large Barkhausen jump which characterizes the magnetization reversal in this material. At low fields the modulus decreases via an abrupt small step which correlates with the field at which the large Barkhausen jump occurs in the M(H) behavior. It is suggested that the reversal of the magnetization in the core domain leads to a slight rearrangement of domains in the sheath region of the wires. This is supported by the surface domain images and indicates a small asymmetry in the remanence states. >

Domain wall mobility in amorphous wires

Abstract We report measurements of domain wall velocity and mobility in an Fe-based amorphous wire as a function of applied stress. Velocities of 50–200 m s -1 and mobilities of 50–110 m s -1 /A m -1 are found. These are higher than previously reported values. The data are interpreted in terms of the core and sheath model of domains in amorphous wires.