1014 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



A Submarine Telephone Cable with Submerged Repeaters. J. J. Gilbert . 

 Trans. A.I.E.E., 70, Part 1, pp. 564-572, 1951. (Monograph 1815). 



Physical Structure and Magnetic Anisotropy of Alnico 5. Part /. R. D. 

 Heidenreich^ and E. A. Nesbitt\ Jl. Appl. Phys., 23, pp. 352-371, 

 March, 1952. (Monograph 1970). 



It is concluded from electron metallograpliic results that the high coercive 

 force and anisotropy of Alnico 5 are caused by a very finel}^ divided precipitate 

 produced by the permanent magnet heat treatment. This precipitate is a transi- 

 tion structure rich in cobalt and is face-centered cubic with ao = lOA and ap- 

 pears as rods growing along the [100] diiections of the matrix crystal when no 

 magnetic field is applied during heat treatment. The size of the i)recipitate rods 

 at oi^timum properties is approximately 75-lOOA l)y 400A long. The spacing 

 between rows of rods is about 200A. The rods are not distinctly resolved in the 

 electron images unless they are grown by aging at 800°C. Their orientation and 

 structure is clearlj' evident in the electron diffraction patterns at all stages of 

 growth. The precipitate responds to a magnetic field applied during heat-treat- 

 ment both bj' suppression of nuclei making an angle greater than about 70° with 

 the field and by the forcing of the rods off the [100] direction into that of the 

 field. The precipitate rods tend to scatter in direction about the field vectoi- when 

 the field is off the [100] but are aligned accurately when the field is along [100]. 



Energy of a Bloch Wall on the Band Picture. I. Spiral Approach. C. 

 Herring'. Phys. Rev., 85, pp. 1003-1011, March 15, 1952. 



It is shown that the band or itinerant electron model of a solid is capable of 

 accounting for the "exchange stiffness" which determines the properties of the 

 transition region, known as the Bloch wall, which separates adjacent ferromag- 

 netic domains with different directions of magnetization. In this treatment the 

 constant spin function usually assigned to each running electron wave is replaced 

 by a variable spin function. At each point of space the spin of a moving electron 

 is inclined at a small velocit.y-dependent angle to the mean spin direction of the 

 other electrons, and this gives rise to an exchange torque which makes the spin 

 direction of the given electron precess as it moves through the transition region, 

 the precession rate being just sufficient to keep it in approximate alignment with 

 the macroscopic magnetization. Physical insight into the mechanisms involved 

 is i)rovided by a rigorous solution of the wall i^roblem for a ferromagnetic free 

 electron gas in the Slater-Fock approximation, although it is known that the 

 free electron gas is not likely to be fei-romagnetic in higher approximations. 

 Rough upper limits to the exchange stiffness constants for actual ferromagnetic 

 metals can be calculated without using an}" empirical constants other than the 

 saturation moment and the lattice constant. The results are only a few times 

 larger than the observed values. 



Elastic and Plastic Properties of Very Small Metal Specimens. C. 

 Herring' and J. K. Galt . Phys. Rev., 85, pp. 1060-1061, March 15, 

 1952. (Monograph 1977). 



'■ Bell Telephone Laboratories 



