. The Bell System technical journal . rmalloy at roomtemperature which we have so far found in the ring permeameter isabout 13000, more than 30 times the corresponding value for thebest soft iron. How extraordinary this is may be appreciated byconsidering that this material, although it has a saturation value ofmagnetic intensity comparable with that of iron, approaches magneticsaturation in the earths field. Unusual caution must therefore beexercised in measuring the properties of permalloy to protect thesample from the influence of stray magnetic fields. Fig. 2 shows, to 106 BELL SYSTEM TECH
. The Bell System technical journal . rmalloy at roomtemperature which we have so far found in the ring permeameter isabout 13000, more than 30 times the corresponding value for thebest soft iron. How extraordinary this is may be appreciated byconsidering that this material, although it has a saturation value ofmagnetic intensity comparable with that of iron, approaches magneticsaturation in the earths field. Unusual caution must therefore beexercised in measuring the properties of permalloy to protect thesample from the influence of stray magnetic fields. Fig. 2 shows, to 106 BELL SYSTEM TECHNICAL JOURNAL different scales, the values of initial permeability in similar ringsamples of permalloy and of annealed armco iron, and small portionsof the corresponding ^u-H curves from which these were obtained. We have measured the magnetization of permalloy at saturationand find that it is not sensitive to heat-treatment. The saturationvalues of magnetization per gramatom are known to vary almost 00 000 40 000 30000 t 20000 10000. -FIG. 2 PERMEABILITr CORVESFOR LOW MAGNETIZINGFORCES 5CO00 40000 30000 20000 10000 400 300 ZOO 100 .01 4RMC0 IRON MAGNETIZING FORCE M 02 400 300 ZOO 100 .03 -04 Fig. 2 .00 .06 .01 linearly with composition throughout the nickel-iron series, from 222for iron to 59 for The value 84 which we have found for per cent nickel alloy is therefore not abnormal. The magnetic characteristics of heat-treated ring samples of thesame alloy have also been determined through a wider range of field 4P. Weiss, Faraday Society Trans. 8, 149-156 (1912). PERMALLOY, A NEW MAGNETIC MATERIAL 107 B 16000 ARMCO IROM ■c PERMALLOY 1 5000 MAGfCTIZAI ION CURVES 0 H 20 40 60 SO 100 Fig. 3 12000 AR *k;o iron FT eooo - ■ 1ALL0Y B / 4000 FIG 4-MAGNETIZATION CORVES H <j J j n b i 3 10 Fig. 4 108 BELL SYSTEM TECHNICAL JOURNAL 12 0OOr 6000 4000
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