A simple apparatus is described for measuring the magnetic loss as a function of magnetic field for ferrites at a frequency of 10,000 mc. The width of the ferromagnetic resonance curve is as important a factor in designing microwave devices as is the resistivity of these materials. The method of preparing ferrites and the physical properties of polycrystalline nickel ferrites as affected by preparation and firing techniques are discussed. It is shown that pores in the ferrite body substantially increase the width of the ferromagnetic resonance curve. The direct-current resistivity can be made to vary from 10 ohm-cm. to lo9 ohmcm. by changing the firing temperatures. The variation in the relative permeability with the bulk density of the body is discussed with reference to domain rotation and domain wall movement.
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