PERMALLOY, A NEW MAGNETIC MATERIAL 



105 



ment determined as best for the 80 per cent nickel alloy is used. It 

 is obvious from what has been said above that too much weight must 

 not be given to the actual values recorded at any composition. Had 

 the best heat-treatment been determined for each sample the curve 

 might have been altered considerably in detail, particularly outside 

 the permalloy range. We believe, however, that its general form is 



20 



SO 



IOC 



Fig. 1 



approximately correct. Alloys were made at 5 per cent steps through- 

 out the range except in the vicinity of 80 per cent nickel where a great 

 number of slightly different compositions were investigated. The 

 chemical analysis, rather than the intended composition, was used in 

 every case, although the difference was never considerable. 



The largest value of initial permeability for permalloy at room 

 temperature which we have so far found in the ring permeameter is 

 about 13000, more than 30 times the corresponding value for the 

 best soft iron. How extraordinary this is may be appreciated by 

 considering that this material, although it has a saturation value of 

 magnetic intensity comparable with that of iron, approaches magnetic 

 saturation in the earth's field. Unusual caution must therefore be 

 exercised in measuring the properties of permalloy to protect the 

 sample from the influence of stray magnetic fields. Fig. 2 shows, to 



