. The Bell System technical journal . n the literature, for instance, the infor-mation that hard steel and very-well-annealed cobalt behave like nickel,shortening continually as the field is augmented. If the rules whichI stated at first are really typical of the respective elements in standardstates, then one may lay what emphasis he chooses on the fact thatthe four consecutive elements which are nickel, cobalt, iron and themanganese which is the essential element of the Heusler alloys areassociated each with a different one of the four conceivable permuta-tions of expansion and contraction.
. The Bell System technical journal . n the literature, for instance, the infor-mation that hard steel and very-well-annealed cobalt behave like nickel,shortening continually as the field is augmented. If the rules whichI stated at first are really typical of the respective elements in standardstates, then one may lay what emphasis he chooses on the fact thatthe four consecutive elements which are nickel, cobalt, iron and themanganese which is the essential element of the Heusler alloys areassociated each with a different one of the four conceivable permuta-tions of expansion and contraction. The change in length, whichever its eventual sign, comes to an endwhen the material is magnetized to saturation. Intensity of magnet-ization is therefore the natural independent variable on which toconsider magnetostriction as depending. Quite the most exciting of the lately-discovered facts about magneto-striction is disclosed in Figure 4a, which consists of curves representing CONTEMPORARY ADVANCES IN PHYSICS 327 0 5000 10000 fSOOO. (B-H) Fig. 4a-Magnetostriction in polycrystalline wires of annealed iron, nickeland various permalloys. (After L. W. McKeehan and P. P. Cioffi.) 328 BELL SYSTEM TECHNICAL JOURNAL change-in-length for iron, nickel, and six permalloys in which thepercentages of nickel are those indicated beside the curves. Theterm permalloy, I recall, is applied to iron-nickel alloys containingmore than 30 per cent of nickel, of which the initial permeability isremarkably high; the heat-treatments which these alloys had under-gone conferred that quality on them, the nickel had been treated inquite and the iron in nearly the same way. The abscissa is intensityof magnetization, for the reason aforesaid; consequently the curvesterminate when this reaches its saturation-value (not, however,attained in the experiments on iron and nickel). These curves display the gradations from a steady lengtheningreminding the onlooker of the initial lengthening of iron (not, however,f
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