A Review of New Magnetic Phenomena 



By R. E. ALLEY, Jr. 



Manuscript received May 25, 1953 



As a result of new developments, the classical concepts of magnetic 

 materials, characterized by hysteresis loss and eddy currents, are no longer 

 adequate. Study cf the ferrites has revealed new and important magnetic 

 phenomena. These materials, because of their high resistivities and cor- 

 respondingly low eddy currents, exhibit useful magnetic properties at fre- 

 quencies well above those at which magnetic alloys are applicable. This paper 

 reviews the new phenomena — domain wall motion and dimensional effects 

 in the low megacycle region, and ferromagnetic resonance and the Faraday 

 effect in the microwave region — and relates them to modem theory. Some 

 possible microwave applications are discussed briefly. 



I. INTRODUCTION 



Up until a few years ago, the classical concept of magnetic materials, 

 characterized by hysteresis and eddy current effects, was adequate for the 

 communications engineer. Recent new and important developments, 

 however, have made it necessary for him to have a broader knowledge 

 of magnetic phenomena than is given by the old picture. Because of the 

 low resistivities of existing magnetic materials, their properties at high 

 frequencies have been dominated by eddy currents which in many cases 

 have completely masked other magnetic effects. In contrast, the newly 

 developed ferrites have resistivities from 10 to 10 " times greater, and 

 eddy currents are usually negligible. The ferrites are, therefore, useful 

 at far higher frequencies than previously available materials. Further- 

 more they have revealed new and important magnetic phenomena. 



It is the purpose of this paper to present the modern picture of mag- 

 netism from the standpoint of the engineer. It describes the new phe- 

 nomena and relates the experimentally observed behavior of magnetic 

 materials at high frequency to the present physical theory of magnetism. 

 The new phenomena include dimensional and domain wall motion effects 

 in the low megacycle region and ferromagnetic resonance and the recently 

 observed Faraday effect in the microwave region. 



1155 



