Temperature Dependence of the Initial Permeability of a FerromagneticAmorphous Co–P AlloyJ. G. M. de Lau Citation: Journal of Applied Physics 41, 5355 (1970); doi: 10.1063/1.1658687 View online: http://dx.doi.org/10.1063/1.1658687 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/41/13?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Frequency dependence of the magnetoimpedance in amorphous CoP electrodeposited layers J. Appl. Phys. 87, 4825 (2000); 10.1063/1.373172 A study of the aftereffect of the magnetic permeability in Corich amorphous ferromagnetic alloys J. Appl. Phys. 60, 3258 (1986); 10.1063/1.337714 Hyperfine field studies of amorphous CoP alloys AIP Conf. Proc. 31, 390 (1976); 10.1063/1.30785 Spinwave dispersion and temperature dependence of magnetization in an amorphous CoP alloy AIP Conf. Proc. 29, 172 (1976); 10.1063/1.30568 Magnetic properties of amorphous Co–P alloys J. Appl. Phys. 45, 1406 (1974); 10.1063/1.1663420

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"Ultraviolet-Flash" Effect in Chemically Deposited PbS Layers*

RONALD J. RYERSON AND RICHARD H. BUBE

Department of Materials Science. Stanford University. Stanford. California 94305

(Received 9 July 1970)

It is well known that photodetectors consisting of chemically deposited PbS layers show a deterioration in detectivity when exposed to short-wavelength radiation. The effect has been called the "uv-flash" effect. The deterioration in detectivity results from an increase in dark conductivity with a subsequent decrease in the light/dark conductivity ratio.

As part of a comprehensive study of the mechanism of photo­conductivity in PbS layers, we have investigated the "uv-flash" effect. It is soon clear that the effect arises from the photo­absorption of oxygen on the layers,. this adsorbed oxygen acting to increase the free-hole density in this p-type semiconductor, and to a lesser extent the photoconductivity lifetime and the hole mobility as well. In order to demonstrate the origin of the effect further, we have measured the intensity of the "uv-flash" effect as a function of wavelength and show here that it is identical with the variation of absorption constant with wavelength.

If light must be absorbed within a distance d of the surface of the layer in order to be effective in producing photoadsorption of oxygen, the effectiveness of light of a given wavelength in producing photoadsorption of oxygen will be proportional to the absorption constant O! for that wavelength as long as O!d«1.

Chemically deposited PbS layers prepared by Santa Barbara Research Center were used in this investigation. Before each measurement of photoadsorption at a given wavelength, the layer was annealed in a vacuum for 14 h at 78°C in the dark to recover its initial conductivity. The increase in conductivity during subsequent excitation in air was measured as a function of time for 200 min. Photoexcitation intensities were adjusted to give a constant photon cm-2 secl flux. The layers were about 1-1' thick.

The resul ts are shown in Fig. 1 as a plot of the difference between the conductivity in the light at the end of 200 min and the con­ductivity in the light at the end of 0.1 min at the beginning of photoexcitation, as a function of the photoexciting wavelength. Also shown in Fig. 1 are optical absorption constant data reported by Bount et al.2 and by Gibson3 for chemically deposited layers of PbS. It is evident that the photoadsorption of oxygen and the

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FIG. 1. The circle data points show the variation of the difference between the conductivity in the light at the end of ZOO-min photoexcitation and the conductivity in the light at the end of O.l-min photoexcitation. as a function of the wavelength used for the photoexcitation. The conductivity increase in this experiment is due to the photoadsorption of oxygen. The dash curve gives the dependence of absorption constant on wavelength according to Blound et al.,t and the dash-dot curve gives similar data according to Gibson.' both measured on chemically deposited layers.

absorption constant have the same dependence on wavelength. Both increase rapidly after the photon energy exceeds about 1.3 eV. This increase in absorption constant is found in single crystals as well as chemically deposited layers,4 and is attributed to the second-smallest direct optical transition of M, type at ~.6

* Sponsored by the Air Force Materials Laboratory. Wright-Patterson Air Force Base under Contract F3361S-69-C-1139.

1 S. Espevik. R. J. Ryerson. and R. H. Bube (unpublished). 2 G. H. Blount. R. H. Bube. D. K. Smith. and R. T. Yamada (unpub-

lished). 3 A. F. Gibson. Proc. Phys. Soc. (London). 63B, 756 (1950). 4 D. G. Avery. Proc. Phys. Soc. (London) 67B, Z (1954). 'P. J. Lin and L. Kleinman. Phys. Rev. 142,478 (1966).

Temperature Dependence of the Initial Permeability of a Ferrr agnetic Amorphous Co-P Alloy*

J. G. M. DE LAUt

Gorau Kay Laboratory, Harvard University,

C"mbridge. Massachusetts 02138

(Received 31 July 1970)

The existence of amorphous solids which are ferromagnetic was predicted on theoretical grounds by Gubanov1 in 1960. Since then it has been demonstrated experimentally by a number of investigators.2- 7 There have been several recent reports of mag­netic property measurements on amorphous Fe-containing alloys made by rapid cooling from the liquid state.a-6 Tsuei, Longworth, and Lin4 measured the magnetization as a function of the temperature of an amorphous Fe-P-C alloy and found a Curie temperature much lower than that of pure iron. Miissbauer experiments showed a nonunique hyperfine field at the nuclei which is consistent with a model of a disordered alloy with a spread in interatomic spacing. Sinha6 reported magnetization and paramagnetic susceptibility measurements on Fe-Mn-P-C alloys. He supposed that the magnetic structures are complex in some of the alloys: ferrimagnetism existing in conjunction with parasitic antiferromagnetism. Hasegawa6 found superpara­magnetic clusters and also ferromagnetism in Pd-Fe-Si alloys. The Curie temperature is much lower as a result of the weaker exchange interaction in the amorphous alloy as compared to the corresponding crystalline alloy.

This paper describes the measurements of the initial per­meability of a ferromagnetic amorphous Co-P alloy made by electrodeposition. The permeability of crystalline materials is primarily limited by the presence of crystalline anisotropy. Therefore it is reasonable to expect that the permeability of an amorphous solid will be considerably higher than that of a crystal­line solid at the same composition. With the electrodeposition technique it is possible to prepare relatively thick layers of com­pletely dense material suitable, when in the shape of rings, for high-permeability measurements. The Co-P alloy was chosen because it was known to be ferromagnetic at room temperature. Bagley and TurnbulF had observed magnetic domain structures in thin films of amorphous Co-P alloys made by flash evaporation.

The electrodeposition technique used has been described in detail by Cargill8 and is based on earlier work by Brenner.9 A one-liter solution was made by dissolving 50-g HaPO., 55-g HaP03 , 35.6-g CoCOa, and 167-g CoCb· 6H20 in water. The anode used was a highly purified cobalt rod with a diameter of 5 mm. The cathode was a 0.25-mm-thick copper strip which was covered with an electric insulating layer except for a ring-shaped window with an outer diameter of 25 mm and an inner diameter of 10 mm. During electrodeposition the temperature of the solution was kept between 750 and 80°C; the liquid was vigorously stirred and the cathode was vibrated for reasons described by Cargill.

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FIG. 1. Permeability vs temperature curve of a ferromagnetic amorphous Co-P alloy. Curves 1, 2. and 3 have been obtained by heating up or cooling down as indicated by the arrows, starting from an as-deposited ring (0).

A dc current with a density of 10 A per em' of the cathode sur­face was maintained during 15 h so that a Co-P layer was de­posited on the ring-shaped cathode. This layer was separated from the copper strip by dissolving the copper in a hot aquous solution which contained 500-g CrO, and 50-g H.SO. per liter. The Co-P ring obtained in this way has an average thickness of 0.4 mm but the outer part of the ring tends to be 1.5-2 times as thick as the inner part. The material is fully dense, according to microscopic examination, and contains 20.O-at. % P according to wet-chemical analysis. X-ray diffraction measurements with molybdenum radiation showed only a few broad peaks of the type described by CargillB as being characteristic for the amorphous structure.

For the initial permeability measurements a coil of insulated copper wire was wound around the ring. The self-inductance of the coil with the Co-P core was measured on a Marconi impedance bridge type TF 936 at 1 kHz. The permeability was calculated from the self-inductance according to a formula given by Smit and Wyn.lO Permeability measurements were carried out at temperatures between -197° and 300°C. The results are shown in Fig. 1. Point 0 gives the permeability of the as-deposited ring at room temperature. The curves 1, 2, and 3 have been obtained by successively heating up to 287°C, cooling down to -197°C, and again heating up to 300°C. Measurements on other samples showed that curve 1 is approximately reversible up to temperatures of about 200°C. Heat treatments at higher temperatures give rise to a considerable rise of the permeability at lower temperatures as can be seen by comparing the curves 1 and 2. The maximum annealing effect is already obtained at 250°C. That is, heating to higher temperatures does not lead to higher permeabilities at room temperature. No change in dif­fraction pattern could be observed after annealing at 250°C. The permeability increase upon annealing is probably due to removal of the mechanical stresses as present in the electro­deposited material. Stresses give rise to extra magnetic anisot­ropies in consequence of the magnetostriction and therefore lower the permeability. The initial permeabilities after annealing (curves 2 and 3) are much higher than the highest value, 68 at room temperature,11 reported up till now for crystalline cobalt.

These relatively high permeability values for the annealed amorphous CO-P alloy are due to the absence of a crystalline anisotropy. Actually they are probably lower limiting values since the permeability tends to be higher for thicker rings. The thickness of the ring is small compared to the other dimensions. The surface of the ring which has an uneven appearance is supposed to have a considerable influence on the magnetic domain structure and the domain-wall mobility. The hysteresis effect as shown by curves 2 and 3 is a result of different domain structures as caused by different heat treatments.

The most remarkable feature of the p,-T curves is that they do not show the normal Curie point behavior which is character­ized by a very high permeability at the Curie point followed by a rapid drop~of the permeability towards higher temperatures. The amorphous material shows rather a gradual permeability decrease at high temperatures. The curves 1 and 3 which have been measured during heating up can both be extrapolated to a permeability value of 1 at 300°C. This is a temperature which is very close to the temperature where crystallization starts. Samples heated up to temperatures above 300°C appeared to be crystallized to a two-phase system of Co and Co.P. Permeabilities of this system are too low to be measured, that is lower than five.

More experimental data are needed to find out whether the coincidence of the temperature obtained by extrapolating the p,- T curve and the temperature where crystallization starts is a purely accidental or a more general phenomenon.

The author is indebted to Professor D. Turnbull and Professor R. V. Jones for their advice and helpful discussions.

* This work was supported by the Office of Naval Research, by the Advanced Research Projects Agency I and by the Division of Engineering and Applied Physics, Harvard University,

t Present address: Philips Research Laboratories, Eindhoven, The Netherlands.

1 A. 1. Gubanov, Sov. Phys. Solid State 2,468 (1960). 2 S. Mader and A. S. Nowick, App!. Phys. Lett. 7, 57 (1965). 3 P. Duwez and S. C. H. Lin, J. App!. Phys. 38, 4096 (1967). 4 C. C. Tsuei, G. Longworth, and S. C. H. Lin, Phys. Rev. 170, 603

(1968) . 5 R. Hasegawa, California Institute of Technology, AEC Rep. No.4.

CAL T -822-4. 6 A. K. Sinha, California Institute of Technology, AEC Rep. No.6,

CALT-822-7. 7 B. G. Bagley and D. Turnbull, Bull. Amer. Phys. Soc. 10, 1101 (1965). • G. S. Cargill III, J. App!. Phys. 41,12 (1970). • A. Brenner, D. E. Cough, and E. K. Williams, J. Res. Nat. Bur. Std.

44, 109 (1950). 10 J. Smit and H. P. J. Wyn, Ferrites (Wiley, New York, 1959), p. 123. 1l R. M. Bozorth, Ferromagnetism (Van Nostrand, New York, 1951),

p.266.

Vaporization of Inclusions during Laser Operation

R. W. HOPPER AND D. R. UHLMANN

Department of Metallurgy and Materials Science, Center for Materials Science and Engineering, Massachusetts Institute of Technology,

Cambridge, Massachusetts 0Z139

(Received 23 July 1970)

In a recent paper,! the present authors associated inclusion damage in glass lasers with the temperature rise of metallic particles relative to the surrounding glass. It was shown that under conditions of high-power laser operation, the thermal expansion associated with such heating can produce stresses in the glass adjacent to the particles which can exceed the theoretical strength of the glass and result in failure.

In these calculations, the effects of the vaporization of inclusion material prior to failure were largely neglected. This neglect

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