Co-P Amorphous Alloys Research Articles

Evolution of the magnetic anisotropy distribution of Co-P amorphous alloys during crystallization

Crystallization processes of amorphous Co 100- x P x ( x = 7−28) alloys are studied following the gradual changes experienced by the magnetic anisotropy distribution after isothermal annealing at different temperatures. The results indicate the existence of two different behaviours over the whole range of composition, the occurence of which is determined by the phosphorus content of the samples. These phenomena are explained by considering the different types of crystallization processes that take place and the related internal changes in the structure of the samples.

The Curie temperature of Co-P amorphous alloys

A new recipe is presented whereby Co-P amorphous alloys with a high P content can be electrolytically obtained. The Curie temperature of these alloys has been studied directly. A linear behavior in T c versus composition is observed up to 28-29 at% P. For higher concentrations, a constant T c value is observed.

Electrical and magnetic properties in Co-P amorphous alloys

Different anomalies in the Hall effect, electrical resistivity, and magnetic susceptibility of simple Co-P amorphous alloys have been observed. We show that the anomalies detected are due to a transition from “para” to “ferromagnetic” order. The transition, which is not well defined, suggests a large compositional inhomogeneity in the samples with high content in P.

Magnetic annealing in electrodeposited Co-P amorphous alloys

The kinetics of induced anisotropy in multilayered amorphous Co-P films was studied by measuring the coercive force of the samples. The results adapt perfectly to the sum of the three different “Arrhenius processes” with the following activation energies Q = 1.02, 1.17, 1.22 eV and jump frequencies > v 0 = 5.7×10 11; 1.3×10 12 respectively. The percentages of each of the three processes are 44%, 28.4% and 27.6%. These values agree with the fractions which correspond to the large holes in Bernal's model and, hence, suggest its validity for this type of amorphous alloys.

Structural relaxation of Co-P amorphous alloys.

The structural relaxation of ${\mathrm{Co}}_{91}$${\mathrm{P}}_{9}$ amorphous alloys is monitored using coercive-force measurements after isothermal annealing. The coercive force relaxes by 2 orders of magnitude after annealing. The relaxation is analyzed in terms of the spectra of the activation energies. We deduce that four processes contributing to relaxation can be distinguished in the activation energy range from approximately 1.18 to 1.50 eV. Our results suggest that the diffusion of P atoms from ``unstable'' to ``stable'' holes is the main source for the relaxation process. The relation between the four processes observed and the different possible holes is discussed.

On the crystallization of electrodeposited Co-P amorphous alloys

On the crystallization of electrodeposited Co-P amorphous alloys

Reorientation kinetics of induced anisotropy in electrodeposited Co-P amorphous alloys

The kinetics of the reversible reorientation of induced magnetic anisotropy in electrodeposited Co-P amorphous alloys, have been studied from 75 to 151°C. Three different kinetic processes have been detected in each sample, each one of which is in accordance with an Arrehenius-type law. Two of the mechanisms are thought to be controlled by self-diffusion of P and the third is thought to be controlled by a kind of residual defect which remains although the samples were subjected to prolonged preannealing at temperatures higher than those used in this study.

Magnetic annealing in electrodeposited Co-P amorphous alloys

The different diffusion processes that occur in electrodeposited Co-P amorphous alloys when they are subjected to magnetic annealing at different temperatures are studied by Coercive field measurements. Different processes are identified with different activation energies: 0.19 eV (stress relaxation): 0.75 eV (directional order); 2.9 eV (crystallization process). The low value of the activation energy for the first mechanism is identified with the diffusion of H, and that of the second with the diffusion of P.

Hyperfine field, concentration and magnetic anisotropy distributions in amorphous CoB, CoP alloys, a NMR study

The Co 59 NMR spectra in rapidly quenched CoB and electrodeposited CoP amorphous alloys exhibit structures which were found to be very sensitive to the excitation rf field strength. The thorough study of this effect shows that there exists a domain wall mobility distribution in these samples which is closely related to concentration fluctuations. The density of “structural defects” that pin the dws is highest in regions where the average concentration is close to the eutectic composition, while dws move more freely in regions where the average concentration is higher or lower than this composition. Regions of eutectic composition are tentatively identified as zones of highest perpendicular easy axis anisotropy. The particular role of the eutectic composition is emphasized by the concentration dependence of the NMR signal intensity and the effect of annealing treatment; a phase separation is suggested for that composition.

電析Co-P合金の加熱にともなう構造変化

From a Watts-type plating bath (CoSO4-CoCl2-H3BO3) containing different amounts of phosphorous acid, Co-P alloys with compositions ranging from 0 to 14 wt%P were electrodeposited, and their structural changes at elevated temperatures were investigated by differential scanning carolimeter, X-ray diffractometer, transmission electron microscope, and small-angle X-ray scattering. Moreover, the apparent activation energy for the heat-induced structural changes in the Co-P amorphous alloys were determined by Kissinger’s method. The results are summarized as follows: (1) The deposited alloys with 0<P≤4.4 wt%, are supersaturated solid-solutions of P in the hcp Co, and those containing ∼5≤P≤14.0 wt% are amorphous solids. (2) The crystallization process of the Co-P amorphous alloys can be classified into three types depending upon the P content. The alloys with ∼5≤P<9 wt% (region I), hcp Co separates in an amorphous matrix at 550∼610 K and upon further heating the matrix transforms into stable phases of hcp Co and Co2P by eutectic crystallization at 610∼670 K. In the alloys with 9≤P<12 wt% (region II), the amorphous solids convert directly into a lamellar structure of hcp Co and Co2P by eutectic crystallization at 620∼630 K. In the alloys with 12≤P≤14 wt% (region III), Co2P separates in an amorphous matrix at 620∼630 K followed by eutectic crystallization into hcp Co and Co2P at 630∼650 K. (3) The Vicker’s hardness of the alloys increased remarkably when the amorphous matrix crystallized into the eutectic structure. For instance, the value of the Co-14.0 wt%P alloy goes up to about 1300 Hv. (4) The apparent activation energy of the structural changes in the amorphous alloys was obtained to be 215±10 kJ/mol.