1166 THE BELL SYSTEM TECHNICAL JOUKNAL, SEPTEMBER, 1953 



Fig. 5 — Behavior of a magnetic material in the neighborhood of ferromagnetic 

 resonance. This represents the usual experimental situation, where frequency 

 is kept constant and the external magnetic field is variable. 



field constant at some value iJo and varies the frequency, one will obtain 

 curves similar to those of Fig. 5. This is indicated in Region B of Fig. 3. 

 Furthermore, for a given sample, as i7o increases, the frequency at which 

 resonance occurs increases. 



IX. MICROWAVE FARADAY EFFECT 



If a linearly polarized wave of microwave frequency travels through 

 a ferrite which is magnetized in the direction of propagation of the 

 wave, the plane of polarization will be rotated. The sense of the rotation 

 depends only upon the direction of magnetization of the ferrite and is 

 independent of the direction of propagation of the wave. Thus the effect 

 is anti-reciprocal. 



This phenomenon, which derives its name from the analogous optical 

 effect was demonstrated experimentally by Roberts^"* and has been ex- 

 tensively investigated by Hogan." It occurs at frequencies above the 

 ferromagnetic resonance frequency, that is, in Region C of Fig. 3. In 

 principle, the effect might be expected in any ferromagnetic material 

 but, so far, only the ferrites are sufficiently transparent to microwaves to 

 allow the effect to be detected. The effect is illustrated in Fig. 6. The 

 linearly polarized microwave in waveguide A passes through a transition 

 section into the circular guide B. A tapered cylinder of ferrite is inserted 

 in B. A solenoid, external to B, supplies a steady field parallel to the axis 



