Amorphous Co-P Research Articles

Radial magnetic anisotropy in amorphous electrolytically prepared CoP and FeP cylindrical layers

The presence of radial magnetic anisotropy with the local axis of the easy magnetization perpendicular to the surface of the layers may be identified in the amorphous cylindrical CoP layers by means of the study of the domain structure using the Bitter technique. This anisotropy is maintained also after undercritical isothermal annealing. In amorphous cylindrical FeP layers the radial magnetic anisotropy is formed — in contrast to CoP layers — only after isothermal annealing below the crystallization temperature. However, the amorphous-crystalline transformation leads in both layers to an apparent disturbance of radial anisotropy, which may be connected with the character of the crystallization of layers and with the new distribution of internal stresses.

Magnetoelastic effects and magnetic anisotropy in amorphous Fe-P alloys

The field dependences of elastic moduli were measured in electrodeposited amorphous Fe-P and Co-P tubes by resonance techniques at about 400 Hz and between 0.2 and 8 MHz. On account of magnetic anisotropies established during preparation (intrinsic anisotropy) and by field annealing, the magnetoelastic effects depended sensitively on the stress modes applied and the direction of the magnetizing field within the samples. The observations are consistent with a picture of the domain structure given in a previous paper Additionally it results that field annealing cannot destroy the intrinsic anisotropy.

Hyperfine-field-distribution of amorphous CoP saturated by high static fields

The hyperfine field distribution of an amorphous CoP sample with 22 at % P has been determined by NMR in large external fields between 1.2 T and 5.2 T. The maximum of the distribution appears at an hyperfine field of 17 T, the mean value is 13.8 T. From the enhancement factor it is found that the quadrupole coupling is very small and has no influence on the shape of the NMR spectrum.

Crystallization kinetics of electrodeposited amorphous Co-P alloys

We have studied the crystallisation of Co-P alloys in a large compositional range (13-35% at P). The samples with higher percentage of P show a polymorphous transformation to a single crystalline phase (Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> P) with a very significant texture. Eutectic crystallisation, as important as the percentage of Co is was detected in the samples with P contents similar or lower to the eutectic equilibrium.

Elastic properties and structural relaxation of amorphous Co-P and Fe-P alloys

The shear modulus G and Young's modulus E of electrodeposited amorphous Co-P and Fe-P tubes and the corresponding ultrasonic attenuation were measured between 0.1 and 10 MHz by a resonance technique. The accuracy was sufficient to evaluate the bulk modulus K and the Poisson ratio nu from G and E. The effect of structural relaxation on the elastic constants was investigated during continuous heating and several isothermal annealing programs. The quantitative analysis of the results is restrained because of the superposition of reversible and irreversible relaxation processes and because of the nearly unknown pre-annealing effects during the heating periods before isothermal treatment starts. But it is possible to derive some ideas concerning short-range order and structural relaxation from the different behaviour of the elastic moduli and the attenuation as functions of time. Relaxation is described mainly by a homogenisation of the material with respect to excess free volume. There are striking differences between the properties of the two alloy systems, particularly in the effects of structural relaxation on their elastic moduli and on their attenuation of sound, pointing to different short-range orders.

Enhancement factor of NMR in ferromagnetic materials with broad hyperfine field distribution

A new configuration of sample and r.f.-coil for spin-echo NMR is presented. The main features are a homogeneous r.f. field over the whole surface of the sample and the possibility of calibration of the r.f.- amplitude in the presence of the magnetic material. In connection with Fourier-transformation of the echo-signals this allows for better accuracy in measurements of the NMR-enhancement factor, especially in broad spectra. The method is illustrated by an experiment with amorphous CoP, a ferromagnetic metal with a very broad spectrum.

Positron lifetime study in electrodeposited amorphous Co-P alloys

Positron lifetime measurements were performed on crystalline Co and amorphous Co-P alloys produced by electrodeposition. The lifetime spectra of the amorphous alloys consisted of only one component whose value ranged between 154 and 168 p.s. over the range 17-30 at.% P while those of the electrodeposited Co showed two components, the longer one attributed to trapped positrons in voids. The results showed a relationship between the mean positron lifetime of the amorphous alloy and its P concentration. Analysing the spectra by the RATIO method, the results suggest positron trapping in empty large Bernal holes of the DRP structure of the metallic atoms and in structural defects associated with a metalloid atom lodged in a small Bernal hole. The analysis of the amorphous alloy spectra suggests that a small fraction of positrons annihilate from free states.

Magnetic and structural properties of Co-P amorphous layers in the crystallization region

The crystallization process of electrolytically deposited CoP layers was studied with magnetic and X-ray diffraction techniques. From the results obtained, a two-step transformation model has been proposed for the transition of amorphous Co-P layers to the crystalline state by the following thermal treatments: (1) 500–550 K when precipitation of Co 2P nuclei takes place, and (2) 500–580 K when Co 2P and β-Co phases are formed.

NMR enhancement factor and multiple echoes in amorphous Co-P alloys

Measurements of the NMR enhancement factor η in a-Co-P show as well as the well-known influence of the external field a contribution from the quadrupole interaction. Thus it is possible to estimate the magnitude of the quadrupole interaction. It is correlated with the hyperfine field and shows a maximum of about 0.3 MHz at the center of the broad spectrum. The behavior of multiple echoes is in qualitative agreement with these results.

Magnetic domain structures in deformed and undeformed foils of a metallic glass

The magnetic domain structure of amorphous Co-P films was examined by transmission electron microscopy. A combination of in-situ annealing and magnetisation treatment was used to investigate the relative pinning effects of the surface relief, structural changes and long range stresses associated with the formation of deformation bands.

Induced anisotropy in amorphous Co-P alloys

Anisotropy induced by magnetic annealing has been measured in electrodeposited amorphous Co-P alloys with between 9 and 20 at% P. The maximum induced anisotropy takes place at ≈ 11at% P and cancels out at ≈ 22 at% P. This result is compatible with the binary dense random packed hard spheres (DRPHS) model if the P cannot occupy the tetrahedral holes.

Apparatus to control columnar growth in electroplated alloys

This is a description of the electronic design of an arrangement which can control the columnar growth produced in electroplated amorphous CoP alloys. This method allows for total or partial interruption of the column-like growth, interleaving a series of very thin layers with greater P concentration.

Annealing effects in electrodeposited amorphous Co-P alloys

We observed how perpendicular magnetic anisotropy, present in electrodeposited amorphous Co-P alloys, changes during heat treatment in the presence or absence of a magnetic field. The results show that, apart from “columnar” shape anisotropy, there are other mechanisms of anisotropy present in the samples, first a stress anisotropy which can reach a value close to that reached by shape anisotropy and second directional-order anisotropy of smaller magnitude than that due to stress. The latter only occurs when the sample is heated to over 140°C.

Magnetic domains in multilayered amorphous Co-P alloys

A thorough study has been made of the magnetic structure of electrodeposited multilayered amorphous Co-P alloys. An unconventional electrolytic process has been used, employing a rectangular alternating current. The samples produced in this way are multilayered, and these layers are separated by very thin boundaries that have a greater P concentration. The results suggest that there is 'exchange interaction' between the layers. It has also been observed that the period and amplitude of the zig-zag of the 'charged walls' is strongly affected by a small energy variation. The origin of the in-plane magnetic anisotropy of the samples has also been investigated. Magnetic anisotropy is very susceptible to magnetic annealing. The results suggest that the authors are dealing with anisotropy induced by directional order.

Multilayered magnetic amorphous Co-P films

We suggest a method to produce electrolytically amorphous samples of Co-P with planar magnetic anisotropy, using a rectangular alternating density current which are variable in amplitude and width. The samples are formed by alternate layers of two different concentrations of Co-P. We study the influence of the parameters which define the density of the current used on the thicknesses of the layers and on their relative compositions. In order to show this, compositional analysis has been carried out using Auger spectroscopy. Structural analysis by X-ray diffraction and measures has been taken of the saturation magnetization by the extraction method. Finally, we relate the behaviour of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> , by varying the thickness of the layers which have the greatest Co concentration, with the different types of domain walls which has been observed by Bitter technique.

Electrodeposited amorphous Co-P alloys with variable magnetic anisotropy

A method is indicated for obtaining electrodeposited amorphous Co-P alloys with differing anisotropies, employing an alternating current density of very low frequency. The method allows samples of a high degree of permeability to be obtained with the result that, in the case of a current density at 5 Hz with amplitude between +0.6 and -0.2 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the magnetic properties are similar to those found by Dietz and coworkers, in samples deposited on rotating cylindrical substrates. In the case of samples without perpendicular anisotropy, there can be observed a distribution of the magnetization in the plane, with 180° domains.

Magnetic anisotropy of electrodeposited Co--P amorphous alloys

The development of magnetic anisotropy with regard to thickness in amorphous electrolytic Co-P alloys (15 at % P) has been observed in the range of thicknesses between 0.06-7.00μm. The study has been undertaken starting from the ratio M <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> /M <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> of the hysteresis loops. The results obtained indicate that for thicknesses below 4000 Å the samples show an axis of easy magnetization in the plane. In the case of greater thicknesses, the axis of easy magnetization develops gradually out of the plane, reaching a perpendicular position near 10 μm. Our results suggest that what we are dealing with here is a shape anisotropy such as that proposed by Cargill, III et al.

NICKEL AND COBALT ELECTRON DISTRIBUTION IN AMORPHOUS METALLIC Ni-P AND Co-P

2p 3/2-3d emission and absorption spectra of nickel and cobalt in amorphous metallic Ni-P and Co-P have been studied. No modification of the emission spectrum with respect to the pure crystallised metal is observed. As a consequence, it may be deduced that the 3d filled distribution of both materials is similar. But, differencies appear in the absorption spectrum ; by comparison with an APW calculation of density of states, we can identify the part of the Ni distribution which is involved in this modification. By combinating X-ray and ESCA measurements, we may conclude that there is no shift observed in the position of the Fermi level, when the nickel is amorphised by the presence of about 15 % phosphorus atoms. From our experiments, similar results seem to be observed for the amorphous metallic Co-P.

Time effects in ferromagnetic amorphous Fe-P alloys

Additionally to previous investigations on amorphous Co-P the time variation of the initial permeability μ of amorphous Fe-P alloys was measured. The changes of μ observed in different temperature ranges below crystallisation were attributed to a superposition of several changes in short range order. According to this the measured curves were fitted by a superposition of functions used before to describe the results from Co-P. Moreover some of the physical processes driving the changes of μ could be explained.

Structural characterization of amorphous electrodeposited cobalt-phosphorus alloys

The structure of amorphous electrodeposited Co-P alloy foils has been examined by x-ray scattering techniques. Samples with phosphorus contents from 18 to 26 at.% have been examined with large-angle x-ray scattering. Atomic arrangements in these alloys are described in terms of radial distribution functions. Effects of alloy composition on randomness of short-range order, atomic-pair distances, and strength of long-range order have been observed. Evidence of large-scale (10–104-Å) composition fluctuations has been obtained from small-angle x-ray scattering on amorphous Co77.5P22.5 samples. The composition fluctuation regions are anisotropically shaped (rodlike) with their largest extent (≳2000 Å) perpendicular to the foil plane and their smallest extent (∼60 Å) in the foil plane.