MAGNETIC MATERIALS IN RELATION TO STRUCTURE 



maximum permeability is the maximum value that the ratio BjH 

 attains. 



Hysteresis is also of importance, especially in alternating current 

 applications. The phenomenon of magnetic hysteresis results in a loss 

 of energy in a magnetic material when the material is carried through a 

 magnetization cycle. The loss of energy is proportional to the area 

 of the hysteresis loop. In soft magnetic materials, the aim, in prac- 

 tically all cases, is to keep this loss a minimum. 



A hard or permanent magnet material is characterized by a gradu- 

 ally ascending magnetization curve; that is, the material at all magnet- 



SOFT MAGNETIC MATERIAL 



B 

 15,000-- 



HARD (permanent) MAGNETIC MATERIAL 



B 

 15,000- 



10 



B = FLUX DENSITY IN GAUSS 

 H= MAGNETIZING FORCE IN OERSTEDS 

 I = INTENSITY OF MAGNETIZATION 

 B= H + 4ir I 



jj.= PERMEABILITY = -^ 



Br= RESIDUAL INDUCTION IN GAUSS 



Hc= COERCIVE FORCE IN OERSTEDS 



Fig. 1 — Schematic representation comparing characteristics of soft and permanent 



magnet materials. 



izing forces has a relatively low permeability. To attain practical 

 saturation is difficult, requiring in some alloys magnetizing forces of 

 thousands of oersteds. The important properties are associated with 

 the demagnetization curve, that portion of the hysteresis loop between 

 points (1) and (2) in Fig. 1. In general the hysteresis loop in its en- 

 tirety is of little importance. The constants usually determined in 

 permanent magnet investigations are the residual induction, Br, and 

 the coercive force, H^. The product of these two quantities {Br He), 

 which is roughly proportional to {BH)m3.x. on the demagnetization 

 curve, has been considered by some ^ as a quality index for permanent 

 magnet materials. 



