J.J. Van Den Broek

Calculation of intrinsic coercivity of magnetic domain walls in perfect crystals

The critical field strength at which a classical domain wall moves through a perfect ferromagnetic crystal of simplified structure is calculated as a function of the ratio between anisotropy energy K and ferromagnetic coupling energy C , taking into account the discrete nature of the spins. When K approaches C intrinsic wall pinning becomes appreciable with critical fields approaching the anisotropy field when K \gg C . For K/C \geq 2/3 , the wall has a thickness of one atomic distance and thus resembles a ferroelectric wall.

Phase transformations in pure and carbon-doped Al45Mn55 alloys

Abstract Pure and carbon-doped Al45Mn55 (at.%) alloys are known to exhibit interesting magnetic properties when they have the metastable L10 (CuAuI) type structure. A study by transmission electron microscopy and diffraction is presented in which the various phase transitions in this complex system are analysed. Experimental evidence is given which indicates that the transition at high temperatures from the disordered A3 to the ordered B19 structure proceeds by a heterogeneous nucleation and growth process whereas the transition from the B19 to the metastable L10 phase occurs by way of a shear transformation whereby the B19 ordering in the close packed planes seems to be conserved and also polytypes are formed as intermediate phases. More drastic structure changes are shown to occur at the decomposition of B19 or L10 into the stable β- and ‘Cr5Al8’ type phases.

Mechanical properties of thin alloy films: Ultramicrohardness and internal stress

On a series of Ag‐Al, Ag‐Au, Ag‐Cu, Au‐Cu, and Au‐Fe thin films, made by vapor deposition, both ultramicrohardness and internal stress were determined as a function of the chemical composition of the deposits. In order to interpret these results microstructural investigations were performed using x‐ray diffraction and transmission electron microscopy, supplemented by electrical resistivity measurements. The observed data on hardness and internal stress can be well understood with the help of the metastable phase diagram of the alloy films. In the case of single‐phase solid solutions, internal stresses are tensile. Compound formation, phase decomposition, or ordering are accompanied with dramatic changes of the internal stresses. With indentation experiments at very low loads the hardness‐concentration dependences were observed in the case of films having a thickness of 1 μm only. Metallic films in general are characterized by a very high defect concentration. Moreover, a dramatic reduction of the average ...

Metal film precision resistors: Resistive metal films and a new resistor concept

Abstract Metal-films for precision resistors combine a very low temperature dependence of the electrical resistance with a tolerance of the resistance of only 0.1%. Corrosion resistance and adhesion to the substrate are of major importance. There are different classes of materials being utilised. For low ohmic applications, we use Cu-Ni alloys with a composition of about 65 at. % (atomic percent) of Cu. For this special alloy, the low temperature coefficient of the resistance (TCR) is a stable, intrinsic property. For most alloys, however, annealing is essential to approach the state of zero TCR. This is the case for the NiCrAl alloys, used for the mid-range of resistances and for SiCrN for high ohmic applications. In high ohmic films, metals are often combined with non-metallic substances like oxides or nitrides. Variation of alloy composition, sputtering conditions and annealing procedures are important for obtaining optimum thin-film properties. Important tools for thin-film characterisation are electron microscopy and related techniques together with high-temperature resistance measurement.

Ultramicrohardness experiments on vapour-deposited films of pure metals and alloys☆

Abstract The ultramicrohardness of thin alloy films is determined by indentation experiments at very low loads. The indentation apparatus is briefly described. We measured the hardness of a number of pure metal films, either vapour deposited or magnetron sputtered. In addition, a detailed study was made of the composition dependence of the hardness of the six binary alloy systems of AgAuCu and AuCoNi. These films were prepared by high vacuum vapour deposition. The thickness of all the films was 1 μm. The hardness data were interpreted with the help of the metastable alloy phase diagram, e.g. as obtained by transmission electron microscopy. The results are discussed in terms of the blocking of the motion of dislocations, solid solution hardening, compound formation, grain size reduction due to alloying, and differences in atomic radii.

Permanent magnetism and microstructure in τ-AlMn(C)

Abstract The lattice transformations by which ferromagnetic AlMn(C) is formed have been studied by transmission electron microscopy and diffraction. After an initial ordering transition, further transformation takes place by a shear mechanism. The ordering in the close packed planes is preserved throughout the shear transformation.

Thermodynamics of the stability of amorphous alloys of two transition metals

A scheme, recently proposed by Miedema and Niessen (MN), by which the concentration range is predicted in which amorphous binary transition metal alloys have high crystallization temperatures, has been tested for several alloy systems. The predictions are based on calculated values of the enthalpies of the amorphous phase and the f.c.c., h.c.p. and b.c.c. solid solutions. Thin films of W-Os, W-Ir, Ta-Re, Ta-Os, Ta-Ir, V-Pd, Nb-Pd and Ta-Pd were deposited at room temperature. The crystallization behaviour of films that were amorphous as deposited was investigated. For the 5d-5d systems, crystallization temperatures from 750 °C to 950 °C were observed. Using transmission electron microscopy and X-ray diffraction, some complex metastable phases were found as crystallization products. In agreement with the MN scheme plots of the crystallization temperature vs. average valence z generally exhibit a maximum around -z = 6.7. However, the range of alloy compositions over which amorphous alloys are formed disagrees, in most cases, with the predicted one. We propose improvements for the calculation of the enthalpy curves.

The composition dependence of internal stress, ultramicrohardness and electrical resistivity of binary alloy films containing silver, aluminium, gold, cobalt, copper, iron or nickel

Abstract Binary alloy films were prepared by high vacuum vapour deposition across the complete concentration ranges. The substrates were at room temperature and film thicknesses were up to 1 microm. The metastable phase diagram of the alloy systems investigated was determined by means of X-ray diffraction and transmission electron microscopy, supplemented by electrical resistivity measurements. It is shown that a close relationship exists between the concentration dependence of the measured properties and the metastable phase diagram of the alloy system. Sharp distinctions can often be made between single-phase and multiphase alloys. The sensitivity of the properties to the observed phase boundaries increases in the sequence electrical resistivity, ultramicrohardness, internal stresses.

Adhesion, internal stress, microstructure and resistivity of thin alloy films of aluminium, copper and silver

Abstract A series of Ag-Cu, Cu-Al and Al-Ag thin films was made by vapour deposition. With a variety of experimental techniques we studied the composition dependence of several properties of the deposits. Microstructural investigations were performed with X-ray diffraction and transmission electron microscopy, supplemented by electrical resistivity measurements. Mechanical properties such as the adhesion of the films to their substrates and internal stresses in the deposits were studied also. In this paper we discuss mutual connections between these physical and mechanical phenomena for the alloy films investigated.

Kinetics of the oxidation of nickel and some of its alloys

Abstract The oxidation of nickel, Ni with 0.5% Cu, Mn or Cr and with 2.5% Cr is investigated. Deviations from the parabolic law in the case of pure Ni can be attributed to “ageing” effects in the oxide layer, and at temperatures above 950°C to the formation of a second layer under the first formed. Both Ni-Cr alloys showed periodic variations in the oxidation rate. These may be due to stress accumulations in the oxide layers.