MAGNETIC ALLOYS 



By H. a. KNOWLTON 



University of Utah 



With respect to their magnetic properties all materials can be 

 divided into three classes : 



(i) Diamagnetic substances, such as bismuth, which, in a 

 magnetic field, set themselves with the long axis of the specimen 

 across the lines of force and tend to move from the stronger 

 to the weaker part of the field. 



(2) Weakly para-magnetic substances, such as many metallic 

 compounds and their aqueous solutions, which are drawn into 

 the strongest part of the field but do not exhibit the phenomena 

 of hysteresis or magnetic saturation. 



(3) Strongly para-magnetic or ferro-magnetic substances, such 

 as iron, including those usually spoken of as magnetic, which 

 are drawn with a considerable force towards the strongest part 

 of the magnetic field and are further distinguished from the 

 weakly para-magnetic substances by the phenomena of magnetic 

 saturation. 



Besides iron, the latter class includes magnetite (Fe304), 

 pyrrhotine (FejSg), nickel, cobalt and a number of alloys, some 

 of which contain one or more of the ferro-magnetic metals, 

 whilst others are composed wholly of metals which are non- 

 magnetic when pure, i.e. either diamagnetic like copper or 

 weakly para-magnetic like manganese. 



The most important example of this latter class is the 

 so-called Heusler alloy, discovered in 1903, which consists of 

 copper, manganese and aluminium. The composition by weight 

 of a typical example may be taken as copper 65 per cent., 

 manganese 23 per cent., aluminium 12 per cent, although 

 equally good quality may be found in samples which diff"er 

 considerably in composition. In any case, the manganese and 

 aluminium should be present in approximately atomic propor- 

 tions, as if more than about 25 per cent, of manganese be used 

 the alloy becomes so hard as to be unworkable. The magnetic 



