MAGNETIC ALLOYS OF IRON, NICKEL, AND COBALT 451 



the baked sample the ascending and the descending branches of the 

 loop coincide and the loop is represented by a straight line. For the 

 next higher flux density the loop, for the same heat treatment, begins 

 to have a measurable area. At low values of induction, however, the 

 two branches of the loop for the baked alloy approach each other and 

 often come together completely at the origin. The complete loop for 

 a maximum flux density of 5,000 gauss also shows this peculiar shape 

 for the baked alloy. The loop is constricted in the middle, the two 

 branches almost passing through the origin. The air-quenched alloy 

 also shows tendency of constriction but much less than the baked. 

 The areas of the two loops show that for this value of maximum flux 



4 .8 1.2 1.6 2.0 2.4 2.8 3.2 



Fig. 12 — Hysteresis characteristics for a permlnvar alloy containing 45 per cent Ni, 

 25 per cent Co, 30 per cent Fe. A = air quenched; B = baked. 



density the hysteresis loss for the baked sample is greater than for the 

 air-quenched. This condition is the reverse of that for lower flux 

 densities. 



The last group of alloys of special interest are the permalloys. 

 In Fig. 13 I have taken the curves for initial permeabilities of the 

 iron-nickel series from the solid diagrams for the air-quenched and the 

 annealed conditions and plotted them on the same scale of coordinates. 

 A curve of initial permeabilities for a series of baked alloys is also 

 plotted in this figure. The baking process for these alloys difi'ered 

 from the one we usually employed in that each alloy was baked until 

 no decrease in the permeability resulted from further baking. For 

 some alloys several weeks were required before this condition obtained. 

 The time was shortest for compositions between 60 per cent and 80 

 30 



