1016 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



possible mechanisms of the current multipUcation process in the Tj'pe-A transistor 

 are discussed. One of the mechanisms is based on trapping holes in the collector 

 bai-rier of the semiconductor. B3' means of this trapping model, the effect of 

 emitter curi'ont and temperature cm the current multiplication is predicted. It 

 is shown that these predictions are in reasonable accord with experiment. 

 Furthermore, assuming this model to hold, the trap density and activation energy 

 (produced b}' forming) may be evaluated. 



Faraday Rotation of Guided Waves. H. Suhl^ and L. R. Walker . 

 Phys. Rev., 86, pp. 122-123, April 1, 1952. 



Transistor Forming Effects in n-Type Germanium. L. B. Valdes , 

 Proc. I.R.E., 40, pp. 445-448, April, 1952. (Monograph 1969). 



Some of the effects of electrical forming of the collector of an n-type germanium 

 transistor are discussed. Evidence is presented for the existence of a region of 

 p-type germanium underneath the formed electrode, together with some indica- 

 tion of the size of the formed region. These experiments lend support to the p-n 

 hook mechanism in that they explain the observed high values of alpha in tran- 

 sistors. This relation is discussed. 



Domain Structure of Perminvar Having a Rectangular Hysteresis Loop. 

 H. J. Williams' and M. Goertz\ Jl. Appl. Phys.,-2Z, pp. 316-323, 

 March, 1952. (Monograph 1985). 



An investigation has been made of the magnetic domain structure of Permin- 

 var (43 per cent Ni, 34 per cent Fe, 23 per cent Co) ring specimens having rec- 

 tangular hysteresis loops after heat-treatment in a magnetic field. Domain 

 patterns obtained with colloidal magnetite showed curved domain boundaries 

 extending completely around the rings, forming circles concentric with them. 

 Changes in magnetization occur when an apphed field causes the circular bound- 

 aries either to expand or contract so that there is a change in the relative values 

 of clockwise and counter-clockwise flux. A nucleus of reversed magnetization 

 was formed by making a small notch in a specimen, and this decreased the co- 

 ercive force and hysteresis loss by a factor of two. It was found that in a 180° 

 domain boundary it was possible to make the change in spin orientations, which 

 occurs in going from one side of the boundary to the other, have either a right- 

 or left-hand screw relation, by the application of a field of appropriate sign per- 

 pendicular to the surface. The effect of superposing an applied alternating field 

 was also investigated, and an effective permeabihty of 4,000,000 was obtained. 



Measuring Techniques for Broad-Band. Long-Distance Radio Relay 

 Systems. W. J. Albersheim'. Proc. I.R.E., 40, pp. 548-551, May, 1952. 

 (Monograph 1971). 



Line-up and maintenance of radio relay systems require sensitive yet rapid 

 measurements. These are obtained by scanning the systems response as func- 

 tions of time, frequency, and amplitude. Parameters thus scanned include the 



1 Bell Telephone Laboratories 



