A REVIEW OF NEW MAGNETIC PHENOMENA 



1171 



INCOMING — 

 SIGNAL 



FILTER 

 TO PASS 

 CHANNEL t 



FILTER 



TO PASS 



CHANNEL 2 



FILTER 



TO PASS 



CHANNEL 4 



FILTER 



TO PASS 



CHANNEL 3 



Fig. 10 — Schematic diagram showing the proposed use of circulators to sepa- 

 rate the various channels in a multichannel communication system. 



Reggia and Beatty^^ have recently described a coaxial line variable 

 attenuator in which the transmission loss is controlled by variation in 

 an external cross field. 



XII. CONCLUSION 



From the discussion which has gone before, it should be apparent to 

 the communications engineer that a whole new field of applications of 

 magnetic materials has opened up. It is therefore essential that the engi- 

 neer be acquainted with the modern picture of magnetism including the 

 phenomena which have been described here — low frequency resonance, 

 ferromagnetic resonance, and microwave Faraday effect. Some applica- 

 tions have already been made of the high frequency characteristics, 

 particularly of the Faraday rotation. Knowledge of the general high 

 frequency characteristics of magnetic materials will enable the engineer 

 to interpret new experimental information as it becomes available and 

 intelligently to utilize the new materials in a variety of engineering ap- 

 plications. 



I wish to express my appreciation to J. K. Gait, A. G. Ganz, C. L. 

 Hogan, and V. E. Legg for several discussions which aided in the clari- 

 fication of certain points described herein and to Messrs. Ganz and Legg 

 for their careful criticism of the overall presentation. 



REFERENCES 



1. J. L. Snoek, Non-Metallic Magnetic Materials for High Frequencies, Philips 



Technical Review, 8, p. 353, 1946. 



2. A. Fairweather, F. F. Roberts and A. J. Welch, Ferrites, Reports on Progress 



in Physics, 15, p. 142, London, The Physical Society, 1952, 



3. R. L. Harvev, I. J. Hegvi, H. W. Levernz, Ferromagnetic Spinels for Radio 



Frequencies, R.C.A. Review, 11, p. 321, 1950. 



4. H. J. Williams, R. C. Sherwood, M. Goertz and F. J. Schnettler, Stressed 



