H.J. de Wit

Soft‐magnetic properties and structure of Fe/CoNbZr multilayers

The magnetic and structural properties of ion beam sputtered Fe/CoNbZr multilayers were studied as a function of the CoNbZr and Fe layer thickness. Good soft‐magnetic properties (coercivity 1000) are obtained only when the Fe grains are small, which is the case for multilayers with Fe layer thicknesses below 10 nm and CoNbZr layer thicknesses above 4 nm. Thick CoNbZr layers (>4 nm) are amorphous and repeated nucleation of Fe grains is observed. When the CoNbZr layers are too thin (<3 nm) they are crystalline and do not interrupt the Fe grain growth. The resulting columnar growth of Fe throughout the total film thickness leads then to a drastic decrease of permeability and increase of coercivity.

The electrical conduction of As2Se3 glass at high fields

Abstract The electrical conduction of As 2 Se 3 glass has been investigated as a function of the applied field, the thickness and the temperature. It is found that below 4 × 10 5 Vcm −1 the conductivity can be described by the relation σ = σ ( F = 0) exp F / F 0 with F 0 ≈ 10 5 Vcm −1 . Above 4 × 10 5 Vcm −1 the conductivity rises sharply. There a similar relation has been found for thin samples but now with F 0 ≈ 4 × 10 4 Vcm −1 . The relevancy of the Poole-Frenkel model, of space charge limited currents and self heating is discussed. From a comparison with a.c. measurements it is concluded that the number of traps at the Fermi level is between 2 × 10 16 and 2 × 10 18 cm −3 eV −1 . Preliminary experiments on ionic conduction as well as the analysis of the composition of thin layers obtained by evaporation of glassy As 2 Se 3 are described.

Domain patterns and high‐frequency magnetic properties of amorphous metal ribbons

Domain patterns and hysteresis curves were studied on field annealed amorphous ribbons of Co70.3Fe4.7Si15B10. The domain structure was observed with the longitudinal Kerr effect. Hysteresis curves and permeabilities were measured at frequencies up to 10 MHz and in fields up to 2 kA/m in the length direction of the ribbon. The frequency dependence of the permeability and the hysteresis curves in the MHz range, measured after annealing in a field perpendicular to the ribbon axis in the plane of the ribbon, can be fully explained by assuming that only rotation contributes to the magnetization and that losses are due to eddy currents. Specimens annealed in a field perpendicular to the ribbon plane behave similarly. After annealing in a field parallel to the ribbon axis, however, only wall displacements occur, leading in the MHz range to a low permeability and large additional contributions to the losses.

Induced anisotropy of amorphous CoFeSiB and CoNbZr magnetic materials

Uniaxial anisotropy induced by magnetic annealing was studied on amorphous CoFeSiB and CoNbZr layers. The kinetics of inducing the anisotropy is slowed down by a preanneal at 400°C. This effect is much stronger for CoNbZr than for CoFeSiB. An addition of 2% transition metal (TM) atoms does not influence the kinetics after preannealing appreciably. Simultaneously with inducing anisotropy magnetic annealing changes the magnetostriction. Two effects determine the anisotropy, orientation of pairs of different magnetic atoms and a contribution which also occurs in alloys with a single magnetic atom. The latter contribution is independent of type and size of the non-magnetic atom(s) and is attributed to Co - clusters.

Structural and soft-magnetic properties of Fe/CoNbZr and Fe/FeCrB multilayers

The magnetic and structural properties of ion‐beam‐sputtered Fe/FeCrB and Fe/CoNbZr multilayers were studied as a function of the FeCrB and CoNbZr layer thicknesses. Good soft‐magnetic properties (coercivity 1000) are obtained only when Fe grains are small, which requires, on the one hand, multilayers with Fe layer thicknesses below 10 nm and, on the other hand, FeCrB interlayers with thicknesses above 1 nm or CoNbZr interlayers with thicknesses above 3 nm. In this case interlayers are amorphous, which induces repeated nucleation of Fe grains. Only at FeCrB thicknesses of 1 nm are the interlayers crystalline due to interface mixing. This in contrast to CoNbZr interlayers which in addition grow epitaxially in a crystalline structure up to thicknesses of 3 nm. When interlayers are crystalline columnar growth of Fe results. As a consequence coercivity increases and permeability decreases.

Electrical conductivity of Li doped MnO

Abstract Electrical resistivity, thermoelectric force and dielectric losses has been measured on Li doped MnO as a function of temperature. We have found that the slopes of logρ and α vs. 1 T are quite different which can be explained by a hole mobility increasing exponentially with temperature. The depth of the Li acceptors is about 0.4 eV, the activation energy of the mobility of holes is about 0.3 eV. The movement of holes around a Li-ion is also thermally activated. The small polaron character of the holes is thought to be connected with Jahn-Teller deformations caused by the holes.

The dielectric breakdown of anodic aluminum oxide

Abstract The dielectric breakdown field of anodic oxide layers on aluminum is independent of thickness in the region 230- 1700 A and is close to the forming field.

Soft magnetic multilayers

Soft magnetic multilayers are new materials that have been developed for record/play-back heads used in video recorders. For this application a combination of a high saturation magnetization and a high magnetic permeability in the MHz range is required. This has been realized in multilayer materials by making the crystallites of the material smaller than the width of the transition regions between the magnetic domains they contain.

Dielectric losses in As2Se3 glass

Abstract Dielectric loss measurements on As 2 Se 3 glass samples at room temperature in the frequency region 10 2 – 10 10 Hz show losses considerable smaller than published values. Definite evidence for localized states was not found. An upper limit of 2 × 10 18 /cm 3 eV for the density of states at the Fermi level follows from these experiments.

n-type Hall effect in MnO

Abstract A large n-type Hall effect with a Hall mobility of ≈ 10 cm 2 /Vsec was measured in ceramic MnO samples.