14 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



where He is in oersteds. The ferromagnetic resonance frequency is 

 given by: 



/res = 2.^He Vl + cc^ megacyclcs (16) 



It is easily shown that the following formula is approximately valid 

 for a ferromagnetic body with a circular or square cross-section 



at saturation. Where: 



n = true dc permeability at saturation 



A'^ = demagnetizing factor in x and y directions. 



If an average value of 1000 is assumed for the dc permeability, then 

 He can be readily computed for various shapes. 

 For a thin disc : 



If, for this case, the resonance frequency is so close to the operating 

 frequency that losses due to ferromagnetic resonance become pro- 



