US1715647A - Magnetic material - Google Patents

Description

June 4, 1929. G. w. ELMEN ,7 7

v MAGNETIC MATERIAL Filed June 50, 1926 6 Shets-Sheet 1 l I l I l l l l l I l 4L 8 l6 7.4 57. 4O 2 A H b Co, Ni, Fe Silicon STeel Armco \ron J1me 4, 1929. G. w. ELMEN 1,715,647

MAGNETIC MATERIAL Filed June 30, 1926 6 Sheets-Sheet 2 Fly. 7

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UNITED STATES PATENT OFFICE.

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KAGNETIC Application filed June 30,

This invention relates to magnetic materials and more especially to magnetic alloys containing nickel, cobalt, and iron. The particular proportions of the several constituents and the methods of preparation 4 of the material are set forth hereinafter.

There have hitherto been described magnetic alloys exhibiting relatively constant permeability over a range of magnetizing forces and also exhibiting relative y low hysteresis loss. Such a material is described in French Patent No. 606,649 granted March 12, 1926. There have also been known magnetic materials comprising nickel and iron and containing a very small amount of cobalt as an impurity. An example of such an alloy is that described in the paper by Arnold and Elmen entitled Permalloy published in the Journal of the Franklin Institute for May, 1923, volume 195, pages 621 to 632.

, The present invention relates to magnetic materials exhibiting constancy of permeability of an entirely different order than that of the material described in the French patent. It relates, moreover, to compositions in which the cobalt content is in excess of the slight amounts which ordinarily would be present as a result of using good commercial nickel and is sufiicient, when the alloy is given the proper heat treatment, to impart thereto properties not characteristic of previously-known magnetic materials.

A novel and striking property of magnetic materials in accordance with this invention resides in their extraordinarily constant permeability over a considerable range of flux densities extending from zero upward.

Another important property is substantially complete absence of hysteresis over a considerable range of flux densities from zero upward.

Another property is the relatively high initial permeability and high permeability throughout the range of flux densities utilized in magnetic materials for telephone, telegraph and cable circuits and apparatus.

At higher flux densities the hysteresis loss, the remanence, and .the coercive force are low.

At still higher flux densities the hysteresis OF LEONIA, NEW JERSEY, ASSIGNOR '10 WESTERN ELECTRIC OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MATERIAL.

1926. Serial No. 119,623.

loop widens out and assumes a peculiar form, characterized by a constriction at the origin.

The resistivit of magnetic materials in accordance wit this invention compares favorably with that of other magnetic materials and can be controlled byv varying the proportions of nickel, cobalt and iron or by the addition of a fourth element.

The'charaeteristics of constancy of permeability and negligible hysteresis loss which are exhibited by these new materials in the range of flux densities from zero to 900 c, g. S units, more or less, are important in signaling and other applications in which uniformity of characteristics over a wide working range is demanded. The resulting advantages of reduced energy dissipation and reduction of wave distortion will be apparent to those skilled uin the signaling art. However, these materials exhibit many desirable properties at high field strengths and hence are useful for general application as electromagnetic materials. In particular the low hysteresis, low remanence, low coercivity, and relatively high specific resistance are noteworthy.

A particular magnetic material in accordance with the invention consists of approximately 45% nickel, 25% cobalt and 30% iron with about .572, of manganese added to ,increase the workability. This material may be pot annealed and cooled slowly in the furnace in accordance with the first heat treatment hereinafter specified. It has a facecentered cubic crystalline structure. The curves given in Figs. 1 to 9, inclusive, relate to a specimen of this particular composition but are illustrative of the properties of other compositions within the scope of the invention.

Someof the properties of this particular this material as compared with hysteresis Y loops for Armco iron and silicon steel under force of 80 gauss similar conditions, a indicating the'new material, 6 silicon steel, and c Armco lIOIl.

Figs. 4 to 8, inclusive, show in each case half of a hysteresis loop at different magnetizing forces respectively; and

Fig. 9 shows ha f of a hgsteresis loop of the material at a considera ly higher maximum flux density than in the preceding figures.

Figs. 10 to 14, inclusive, illustrate the properties of a specimen of material of approximately 60% nickel, 15% cobalt and 25% iron; Fig. 10 shows both a magnetization curve and a hysteresis loop for B=13250; Fig. 11 is a graph of permeability for varying values of magnetizing force; and Figs. 12 to 14, inclusive, are halves of hysteresis loops for several values of induction; Figs. 13 and 14 also show the magnet- 100 ization curve of the virgin material as well as the hysteresis loops.

Figs. 15 to 18, inclusive, lllustrate the properties of a composition of approximately 73.3% nickel, 6% cobalt, 20.5% Iron and .2% manganese; Fig. 15 1s a graph of permeability with varying values of magnetizing force; and Figs. 16 to 18 illustrate halves of hysteresis loops for several values of induction.

Figs. 19 to 22, inclusive, relate to a material comprising approximately 50% nlckel, 30% cobalt and 20% iron; Fig. 19 1s a graph of permeability for varying values of magnetizing force; and Figs. 20 to 22 are halves of hysteresis loops for several different values of maximum induction.

Figs. 23, 24, 25, 26, 27 and 28 relate to a composition of approximately 10% nickel, cobalt and 20% iron with a small fraction of 1% of manganese; Fig. 23 is a graph of permeability with varying values of magnetizing force; Fig. 24 teresis loop for an applied magnetizing and also a magnetization curve of the virgin material which curve is distinguished from the loop by having dots instead of circles; and Figs. 25 to 28 illustrate halves of hysteresis loops for varying values of maximum induction.

In all the figures of the drawing which involve magnetizing forces and flux densities these quantities are plotted in c. g. s. units.

The curves of Figs. 1 and 2 indicate the remarkable constancy of permeability up to a magnetizing force of almost two gauss. In accordance with Fig. 2 the initial permeability is about 460 for this particular material. The curve of Fig. 1 also shows that the material has the high fiux densit of 15000 .c. g. s. units at a magnetizing orce of 45 gauss.

Curve 0 of Fig. 3 represents the upper shows a half hyshalf of the hysteresis loop for this alloy for flux densities up to 600 c. g. s. units represented as a straight line. By ballistic methods no hysteresis loss could be detected and the coercive force and remanence were indicated as zero. By more accurate inductance bridge methods, applicable to low inductions, the hysteresis loss was found to be .024 10" ergs per cu. cm. per cycle at an induction of 100 c. g. s. units. This value is so nearly negligible that the hysteresis loss could not be represented on any feasible scale that could be used in the drawings and hence the hysteresis loop appears as a straight line.

The hysteresis loss in a nickel-iron alloy containing 78 nickel and 21%% iron, heat treated to develop high initial permeability, is much less than for silicon steel or iron. In a particular sample of such an alloy, the hysteresis loss at an induction of I c. g. s. units was found to be 33 10' ergs per cu. cm. per cycle, which is over 1000 times that found by the inductance bridge method for the specimen composed of 45% Ni, 25% Co, and 30% Fe.

Figs. 4 to 9, inclusive, illustrate half hysteresis loops of the material for various maximum inductions and show the manner of growth of the hysteresis loss with increasing induction. The curve of Fig. 4 is similar to the curve a of Fig. 3, the circles on this graph indicating the ascending branch and the dots the descending branch. The dots and circles fall on a straight line passing through the origin, indicating the absence of hysteresis, remanence and coercive force. The magnetizing force and maximum induction under which this remarkable condition prevails are the same as those for constancy of permeability. Fig. 4 indicates that the magnetic material has an entirely negilgible change of permeability up to inductions of 600 c. g. s. units.

Figs. 5 to 8, inclusive, show the growth of the hysteresis loss as the flux density increases above the highest value shown in Fig.

4. Figs. 5 and 6, for example, but the areas of the loops are comparatively small and the hysteresis loss is not material. When the flux density reaches values of 1500 or more, as shown inFigs. 7 and 8, the hysteresis loss increases rapidly but it is to be noted that the residual magnetization and the coercive force are still practically zero.

Fig. 9 shows "half of the hysteresis loop ppearance of hysteresis is evident in for a flux density of approximately 15,000 I c. g. s. units. This loop has the general shape of the ordinary hysteresis loop obtained with iron and other magnetic materials. It differs radically from the curves ofi Figs. 7 and 8 in v and remanence are considerable although less than in most magnetic materials. This that the coercive force is particularly true of the remanence. The hysteresis loss at this high maximum flux density is also relatively small compared with that of other magnetic materials.

The curves of Figs. 10 to 14, inclusive, relate to a composition consisting of approximately 60% nickel, cobalt and 25% iron. In this case the initial permeabil' ity is 631 and no change of ipermeability appears up to a flux density 0 700 c. g. s.

9 units.

A composition consisting of approximately 70% nickel, 15% cobalt and 15% iron has an initial permeability of 390 and no appreciable change in permeability up to 1nduetions of 200 c. g. s. units.

The curves of Figs. 15 to 18, inclusive, relate to a composition consisting of approximately 73.3% nickel, 6% cobalt and 20.5% iron and .2% man anese which has an initial permeability change in permeability up to inductions of 715 c. g. s. units. The maximum permeability is about 5600 at a magnetizing force of 1.1 gauss. I

A composition of approximately 20% nickel, 50% cobalt and 30% iron exhibits a negligible change of permeability at magnetizlng forces of 4 gauss which produce in this instance a flux density of 450 c. g. s.

- units.

. nickel, 30% cobalt and The curves of Figs. 19 to 22, inclusive, relate to a compositionof approximately 20% iron which possesses an initial permeability of 231 which is constant up to value of B=716 or H==3.1.

Figs. 23 to 28, inclusive, relate to a composition of 10% nickel, 70% cobalt and 20% iron which has contant permeability and zero hysteresis loss up to a flux density of 225, the permeability being 57 in this range.

It will be noted that the iron content.

ranges between 10% and 40% in all of these compositions. Such compositions have small or entirely negligible hysteresis loss for values of B up to 500 or 1000 as well as negligible coercive force and remanence at inductions of 500 to 1000 and very low coercive force and remanence, often approaching zero, at inductions up to 5000 c. g. s. units.

The range of proportions of the materials, nickel, cobalt and iron, may be stated in general as follows: The magnetic material contains nickel in a substantial percentage of the total nickel, cobalt and iron content; cobalt in a percentage whose lower limit is a few percent, and of an upper limit of considerably more than one-half the material, and the balance iron. For the highest values of initial permeability combined with constancy of permeability experiments have indicated that the nickel should comprise at least 20% of the magnetic material content.

I The highest degree of constancy of permeof 1430 and no appreciable bility and low hysteresis loss has been obtained with percentages of iron ranging up to 40% although percentages of iron somewhat above 40% yield materials having to some extent the. desirable properties. herein described.

In order to further illustrate the propert es of these materials the following addit1onal data is given. The composition of 4 nickel, 25% cobalt, and 30% iron, hereinbefore described, has a resistivity of'19 m1cro-ohm-cms.; a maximum permeability of 2075 at H=4.12; remanence of 3400 and coercive force of 1.3after the application of a magnetizing force of H=50 gauss. The hysteresis loss is negligible at a maximum flux density of 570 c. g. s. units, and is 9.54 ergs per cu. cm. per cycle'at 820,- 15.65 ergs at 960, 93.2 ergs at 1500, 1185 ergs at 5050, 2500 ergs at 8480, and 3375 ergs at 14900.

The material comprising 60% nickel, 15% cobalt and 25% iron has a flux density of 13,250 0. g. s. units at H=30.7; a resistivity of 17.5 micro-ohm-cms., remanence and coercive force of 1700 and .7 respectively after an applied field of H=30.7 gauss and a maximum permeability of 2680 at H=2.45. The hysteresis loss is negligible up to B=695, and is 1.24 ergs per cu. cm. per cycle at a maximum flux density of 725 c. g. s. units, 8.4 ergs at 840, 27 ergs at 1050, 88 ergs at 1520, 632 ergs at 5400, 1240 ergs at 8230, and 1508 ergs at 13,250. 1

The material of 73.3% nickel, 6% cobalt, 20.5% iron and 2% manganese has a reslstivity of 15.5 micro-ohm-cms; remanence and coercive force of 2700 and .35 respectively after an applied magnetizing force of H=21 gauss; maximum permeability of 5600 at H=1.1 gauss; and negligible hysteresis loss at flux densities up to 715 c. g. s. units. The hysteresis loss per cu. cm. per cycle is 23 ergs at a flux density of 1520 c. g. s. units, 348 ergs at 5125, and 783 ergs at 11,500.

The materialof 10% nickel, cobalt, and 20% iron with a fraction of 1% ofmanganesehas a resistivity of 15.36 micro-ohmcms.; remanence and coercive force of 9340 and 3.56 after an applied magnetizing force of gauss; maximum permeability'of 1545 at H=6.5; and negligible hysteresis loss at flux densities up to 228 c. g. s. units. The hysteresis loss per on. em. per cycle is 8 ergs at a flux density of 340 c. g. s. units, 150 ergs at 620, 1040 ergs at 17 00, 2740 ergs at 3950, and 14,160 ergs at 15,500 0. g. s. units.

In each case the remanence and coercive force are negligible at flux densities at which the permeability is constant and the hysteresis loss negligible, and small 'at higher values of flux density. The tendency of the remanence and coercivity to remain small after the application of magnetizing forces higher than those at which the permeability remains constant is indicated in the drawings. For example in Fig. 8 the coerclve force and remanence are mdicated as zero after an applied magnetizing force of 3.2

' increase the specific resistance of the mate- 45% nickel, 25% its subsequent removal increases the initial rial or for other purposes.

A peculiar characteristic, often exhibited by magnetic materials in accordance with the invention, is that the application of a direct current or uni-directional magnetizing force of large value and its subsequent reduction to a low value causes the substance to have a greatly increased permeability for superimposed low alternating magnetizing forces. In a particular case the application of a large uni-directional magnetizing force of about 25 gausses to the composition of cobalt and 30% iron and permeability from 435 to 750.

In other words, the permeability curve follows the curve of Fig. 2 for increasing applied magnetizing fields but on decreasing the field by small steps and remeasuring the permeability the values of permeability depart from the curve of Fig. 2. This departure is not great until the point of maximum permeability is reached. To the left of the point of maximum permeability, the value of permeability, after high magnetization, is considerably above the curve, and, in the particular case mentioned above, had an initial value of. 750. When a specimen of material is thus highly magnetized the characteristic of constant permeability for a range of magnetizing forces is impaired. To bring the initial-permeability back to a lower value it is necessaryto demagnetize the material. To restore the constancy of permeability to the fullest extent it is advisable to treatment.

Another characteristic usually exhibited by these materials is that the magnetization curve often lies partly without the hysteresis loop for high values of induct-ion. A

give the material a renewed heat typical case is indicated by Fig. 10 where the magnetization curve (indicated by dots) is shown crossing the lower branch of the hysteresis loop (indicated by small circles) at an induction of B=about 500 and joining it again at an induction of B=about 7000.

In Fig. 13 the magnetization curve lies wholly within the hysteresis loop and in Fig. 14 is shown the case where the magnet- V ization curve crosses and has a small portion lying without the hysteresis loop. For all hysteresis loops of this particular specimen O. in 180 minutes for maximum inductions greater than shown in Fig. 14 the magnetization curve has a portion lying without the hysteresis loop.

Another characteristic is that the hysteresis loss reaches a maximum at a certain value of flux density and does not increase for greater flux densities.

The magnetic properties of materials in accordance with this invention are subject to change under the influence of mechanical strains and stresses and consequently due precautions must be taken in their utilization to avoid excessive strains and stresses.

Magnetic materials, in accordance with this invention, may be prepared by melting the constituents together in an induction furnace. Good grades of material of commercial purity are suitable. The molten metal is cast into rods or bars. These rods or bars are worked by rolling, swaging, or drawing into desired shapes.

After the mechanical fabrication of the parts into their final'sliapes they are heat.

treated in order to produce the desired magnetic properties. The temperature to which the material is heated and the rate of cooling determine ,very largely the relative values of the several magnetic characteristics.

For heat treatment as hereinafter described about 40 grams of the material is prepared in the form of a thin tape which is rolled into a fiat spiral. The thickness of the spiral i. e. the width of the tape is 1/8 inch (3.175 mm.). The internal diameter ,of the spiral is 3 inches (7.62 cm.) and the external diameter 3-1/2 inches (8.89 cm.).

In accordance with a first method of preparation, the material may be pot annealed, using ordinary precautions to prevent oxidation, at about 1100 C. for at least one hour, after which it is allowed to cool slowly to room temperature in the furnace. This is the method which was used in production of the materials, whose magnetic characteristics are shown in Figs. 1 to 28, inclusive. In a particular instance in which this first method was used the material was placed in a nichrome pot. The pot was about l/2 full. A rim around the potprojected above the cover. A layer ofiron filings, placed on the cover, the rim. The pot was placed in an electric furnace when its temperature was about 900 C. In 90 minutes the temperature of the, pot rose to 1100 C. and it was maintained at that temperature for 70 minutes. The material was then allowed to cool in the furnace and reached a temperature of 350 of cooling time. In accordance with a second method the pot annealed material is reheated above. the magnetic transition-temperature i. e., about 725- C. and cooled faster than in the first was retained by ample, by placing case, for example, at about an average rate of 2 C. to 5 0. per second down to about 350 C. and thereafter to room temperature at any desired rate.-

In accordance with a third method the ot annealed material is reheated to about 25 C. and is cooled rapidly as, for exthe spiral of tape weighing 40 grams on a large copper plate in the open air. The 40 grams of material is in the form of thin tape wound into a spiral rin of internal diameter 3 inches (7.62 cm. external diameter 3-1/2 inches (8.89 cm.), and thickness 1/8 inch (3.175 mm.), which is the width of the tape.

Of these methods the first gives the -materials the most nearly constant permeability and the lowest hysteresis loss over a wide range of field strengths.

Treatment in accordance with the second method gives higher permeability, particularly at low magnetizing forces but the permeability is not so constant or not constant over so great a range.

The third method produces still higher permeability particularly in compositions with a high nickel content but with a greater tendency to variations in permeability with increasing magnetizing forces and greater tendency to increase in hysteresis loss at low field strengths.

The methods of heat treatment may be varied as experience may indicate. The particular methods given illustrate the principle that the degree in which the various properties are present is dependent to some extent upon the heat treatment and that various special properties may be obtained to an increased extent not only by proper selection of the proportions of the constitu cuts of the composition but also by selecting a suitable heat treatment.

Among the uses for which this material is adapted are coil or lumped loading and continuous loading of lowand carrier frequency signaling conductors in submarine and land line telephony 'and telegraphy, loading coils for composite telephone and telegraph systems, repeating coils or transformers, especially battery supply coils, wave filter coils, certain important classes of relays, dynamo-electric machinery, high frequency electromagnetic devices, and magnetic circuits of electrical measuring instruments. 1 I

As an illustration of uses of magnetic ma-' terials in accordance with the present invention in order to take advantageof the important characteristic of constant pern1e ability over a range of magnetizing forces, may be mentioned its use for the continuous loading of telephone conductors in accordance with applicants United States Patent 1,586,883 granted June 1, 1926, or the continuous loading of long submarine telegraph cables for high speed signaling in accordance with United States patent to Buckley 1,586,874 granted June 1, 1926. The use of the present material offers great advantages over the use of materials of permeability variable within the range of magnetizing forces employed.

The magnetic material of a continuously loaded conductor may be given the desired magnetic properties by first applying the loading material to the conductor and then heat treating a coil of the conductor of considerable radius in a suitably large furnace in accordance with the methods hereinbefore described.

What is claimed is:

1. A magnetic material including at least two magnetic elements and having negligible variation in permeability over a range of flux densities at least 50 c. g. s. units in width and lying between zero asa lower limit and 5000 e. g. s. units as an upper limit.

2. A magnetic material including at least two elements of the magnetic group having negligible hysteresis loss over a range of flux densities of at least 50 c. g. s. units and lying within the range employed in electric communication circuits.

3. A magnetic material including at least two elements of the magnetic group, having substantially constant permeability for flux densities below the general range of B=500 4. A magnetic material including at least two elements of the magnetic group having negligible hysteresis loss for flux densities below the general range of B=500 to 1000.

5. A magnetic material comprising nickel 10% or ninre, cobalt 5% or more, and iron in a substantial amount but not to exceed about 45%, the n1ckel-cobalt-iron content being at least 85% of the total.

6. A magnetic material having a variation in permeability of less than 2% over a range. of flux densities from zero to at least 50 c. g. s. units. 7

7. A magnetic material having a variation in permeability of less than 2% for flux densities up to at least 600 c. g. s. units.

8. A magnetic composition having a hysteresis loss of less than .15X 10 ergs per cycle per cubic centimeter for a range of magnetizing forces from zero up to at least 50 c. g. s. units.

9. A magnetic-material having negligible variation in permeability over a wide range of flux densities which requires the application of a reverse magnetizing force a few tenths of a c. g. s. unit or less to restore the flux to zero after the application of a magios netizing force suflicient .to produce a value of induction up to B=5000.

10. A magneticmaterial having negligible variation in permeability were wide range of flux densities and having a residual flux of less than a few hundred c. g. s. units after the application of a magnetizing force sufiicient to produce flux densities up to B=5000. 11. A magnetic material containing cobalt and having substantially constant permeability over a range of low magnetizing forces from zero to at least c. g. s. unit.

12. A magnetic composition comprising nickel, cobalt and iron as essential elements thereof characterized in that it forms part at least of a magnetic circuit in inductive n relation to an electric conductor.

13. A magnetic material having negligible variation in permeability over the general range of flux densities below B=500 to 1000 c. g. s. units comprising nickel, cobalt and iron.

14. A magnetic composition comprising nickel, cobalt and iron as essential constitu- 'ents thereof characterized in that the composition has been heat treated to give it a constant permeability over a range of low magnetizing forces extending from zero to at least c. g. s.*unit. v

15. A magnetic composition comprising nickel, cobalt and iron as essential elements thereof characterized in that it has lower hysteresis loss at all inductions than Armco iron.

16. A magnetic composition containing nickel, cobalt and iron having negligible hysteresis loss for values of induction up to at least 500 c. g. s. units.

17 A magnetic composition containing nickel, cobalt and iron as essential constituents thereof having a coercive force of a few tenths of a c. g. s. unit or less for values of induction up to a least 5000 c. g. s. units.

4 cobalt and iron having stant '65 18. A magnetic material having negligible variation in permeability over a wide range of flux densities, comprising nickel, cobalt and iron, in which a magnetizing force of gauss induces a flux of 15,000 c. g. s. units 19. A magnetic composition comprising nickel, cobalt and iron as essential elements thereof characterized in that the hysteresis loss increases very rapidly over a small range of increasing magnetizing forces whlle for smaller forces the hysteresis loss is ized in that the permeability is substantially constant at magnetizing forces from zero to at least around one gauss.

21. A magnetic composition comprising as essential constituents thereof nickel,

substantially conpermeability and substantially no hysteresis, remanence, or coercivity for a 22. A magnet-ic material, comprising as essential constituents thereof nickel, cobalt and iron, having substantially constant permeability at magnetizing forces from 'zero upward to a certain value and having at larger magnetizing forces *a considerably higher permeability, which is retained after a very large magnetizing force is applied and removed.

23. A magnetic material containing nickel, cobalt and iron as essential constituents thereof characterized in that the reversible permeability possessed by the material at low unidirectional magnetizing forces is increased to a higher value by the application and removal of a large magnetizing force.

24. A magnetic material comprising nickel, cobalt and iron in which the cobalt content comprises approximately,10% to 35% of the nickel-cobalt-iron content.

25. A magnetic composition comprising nickel, cobalt and iron as essential elements thereof characterized in that iron constitutes around or less of the nickel-cobalt-iron content.

26. A magnetic composition comprising nickel, cobalt and iron as essential elements thereof characterized in that the iron comprises around 50% or less and the cobalt around 35% or less of the nickel-cobalt-iron composition.

27 A magnetic material comprising nickel, cobalt and iron as essential constituents thereof in which the nickel component comprises 9% to 81% of the nickel-cobalt-iron content.

28. A magnetic material comprising nickel, cobalt and iron as essential constituents thereof in which the nickel component comprises 30% to iron content.

29. A magnetic alloy comprising nickel between 9% and 81%, cobalt between 4% and 80% and iron between 5% and 45% of the entire nickel-cobalt-iron content.

30. A-magnetic alloy comprising nickel between 15% and 81%, cobalt between 15% and 45% and iron between 9% and 45% of the entire nickel-cobalt-iron content characterized by a permeability which varies less than 5% over a range of flux densities from zero to 500 c. g. s. units.

31. nickel, cobalt and iron in the approximate proportions of 60%, 15% and 25%, respectively.

. 32. A magnetic composition comprising nickel, cobalt and iron as essential elements thereof characterized in that it constitutes of the nickel-cobalt,

A magnetic material comprising at least part of a magnetic circuit for an electric circuit designed to operate by impressing upon the composition magnetizing forces of such magnitude as to produce therein maximum flux densities of less than 1000 c. g. s. units.

33. A magnetic composition comprising nickel, cobalt and iron as essential elements thereof characterized in that over a range of low magnetizing forces it has substantially constant permeability and that it forms part at least, of a magnetic circuit upon which are to be impressed a range of such small magnetizing forces that the permeability remains substantially constant.

34. A magnetic composition comprising nickel, cobalt and iron as essential elements thereof characterized in that it constitutes part at least of a magnetic circuit in inductive relation to a signaling conductor.

35. A magnetic composition comprising nickel, cobalt and iron as essential elements thereof characterized in that it constitutes part at least of a magnetic circuit in inductive relation to a signaling conductor in a submarine cable.

36. A magnetic composition including 45% to 75% nickel and caused to have by the addition of suitable alloying elements and heat treatment an initial permeability of 200 or more and a constancy of permeability within up to a magnetizing force of at least .2 c. g. 5. units.

37. A magnetic composition comprising nickel and iron in the proportions of between 50% to 81% nickel and between 50% to 19% iron and caused to have by the addition of suitable alloying elements and heat treatment an initial permeability of at least 200 and constancy of permeability within 5% up to a magnetizing force of .2 c. g. s. units.

38. A magnetic material comprising nickel, cobalt and iron as essential constituents thereof in which the nickel component comprises 50% to (55%, the cobalt component comprises to and the iron component comprises 10% to 30% of the nickelcobalt-iron content.

In witness whereof, I hereunto subscribe my name this 29th day of June, A. D. 1926.

GUSTAF W. ELMEN.

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