US3761904A - Magnetic switching devices comprising ni-mo-fe alloy - Google Patents

Abstract

A new family of magnetic alloys containing small amounts of Zr or Be has been developed primarily for use in memories and coincident current switches. These alloys are of particular utility in those applications requiring a terminal heat treatment since they can be optimized to be square looped and essentially nonmagnetostrictive in the heat treated state with coercivities in the range 0.2-3 oersteds. One member of this family, developed for use as the soft magnetic material in the piggyback twistor memory element, has the composition; 80.2 percent nickel, 5.65 percent molybdenum, 0.25 percent zirconium and 0.25 percent manganese.

Description

United States Patent [1 1 Chin et a1.

1 1 MAGNETIC SWITCHING DEVICES COMPRISING NI-MO-FE ALLOY [75] Inventors: Gilbert Yukyu Chin, Berkeley Heights, N .J.-, William Brightman GrupeniThomas Charles Tisone, both of Emmaus, Pa.

[73] Assigneei Bell Telephone Laboratories,Incorporated, Murray Hill, Berkeley Heights, NJ.

[22] Filed: Mar. 18, 1970 [21] Appl. No.: 20,597

[52] US. Cl 340/174 ZB, 75/170, 148/3155,

148/120, 340/174 NA, 340/174 TW [51] Int. Cl Gllc 11/12, C22c 19/00 [58] Field of Search 148/3155, 31.57,

148/120, 121; 75/170; 340/11.4, 166 C, 174 R, 174 EA, 174 NA, 174 QB, 174 PM, 174

1 Sept. 25, 1973 1,715,541 6/1929 Elmen 148/3155 X 1,792,483 2/1931 Elmen 148/3155 2,990,277 6/1961 Post et a1. 148/31.55 X

OTHER PUBLICATIONS Stanley, .1. K.; Metallurgy and Magnetism, Cleveland, 1949 pp. 37, 46-49.

Primary Examiner-L. Dewayne Rutledge Assistant ExaminerW. R. Satterfield Att0rneyW. L. Keefauver [57] ABSTRACT A new family of magnetic alloys containing small amounts of Zr or Be has been developed primarily for use in memories and coincident current switches. These alloys are of particular utility in those applications requiring a terminal heat treatment since they can be optimized to be square looped and essentially nonmagnetostrictive in the heat treated state with coercivities in the range 0.2-3 oersteds. One member of this family, developed for use as the soft magnetic material in the piggyback twistor memory element, has the composition; 80.2 percent nickel, 5.65 percent molybdenum, 0.25 percent zirconium and 0.25 percent manganese.

1 Claim, 6 Drawing Figures PATENTEU 3; 78 1.904

SHEET L [1F 3 I Fla. 2

DRIVE SOFT CURRENT SF #252 4 m w l I I i" VI I! ni W Ir i '1,

G. K CHIN lA/VENTORSZ'W. B. GRUPEN TI 6'. TISO E ATTOR EV MAGNETIC SWITCHING DEVICES COMPRISING NI-MO-FE ALLOY BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is in the field of magnetic alloys intended for use in memories and to perform more general switching operations.

2. Description of the Prior Art A bit of information is stored in a magnetic memory as the direction of remanent magnetization in one of the magnetic elements contained within the memory. The usual operation is binary in which there are two possible remanent states. A signal is read out of the memory when the remanent state is caused to reverse. The signal produced is proportional to the time rate of change of magnetic flux during the reversal. This signal, then, is dependent upon both the total amount of remanent magnetization and the switching speed of the element.

Memories generally can be classified as to the permanence of the stored information. In some memories, the read operation destroys the stored information while some memories contain means for preserving or regenerating the information for later use. One memory of the latter type is the Piggyback Twistor Memory disclosed by W. A. Barrett, Jr. in U.S. Pat. No. 3,067,408 which issued Dec. 4, 1962. The Piggyback Twistor Memory element is formed by wrapping two strands of magnetic material, differing in remanence and coercivity, and adjacent to one another, around a single conducting core. The material possessing higher remanence and coercivity, which will be referred to as the hard material, serves as the storage medium into which the information is written. The material with lower remanence and coercivity, which will be referred to as the soft material, serves as the read out medium which can be switched without disturbing the information written into the hard material. When the read switching field is removed, the remanent magnetization of the bit of hard material restores the adjacent bit of the soft material to its original state so that it can be read out again when required. This device has been successfully fabricated and has proven to be a useful and versatile memory. In order to extend its range of use, development work has continued and a new hard material with improved properties has been developed (E. A. Nesbitt et al., Journal of Applied Physics 39 (1968) 1268).

BRIEF DESCRIPTION OF THE INVENTION The invention disclosed here is the development of an improved soft material and suitable processing conditions for that material. It is required that this soft material possess its desirable properties after a terminal heat treatment step which may be required to develop specific properties of the hard material or to satisfy other device requirements. A family of molybdenumpermalloy alloys with small additions of beryllium and- /or zirconium has been found to exhibit the desired squareness, coercivity and low degree of magnetostriction after a terminal heat treatment. One member of this family particularly suited to a specific contemplated device has the composition including 80.2 percent nickel, 13.65 percent iron, 5.65 percent molybde num, and 0.25 percent zirconium. The bounds of this generally useful family together with recommended processing conditions are presented below.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the Fe-Ni-Mo composition diagram indicating preferred composition ranges;

FIG. 2 is a plane view of a section of piggyback twistor memory wire with the magnetic tapes partially unwrapped to show their situation;

FIG. 3 is a set of curves showing the coercivity as a function of the temperature of the terminal heat treatment for three exemplary alloys varying in beryllium content;

FIG. 4 is a set of curves showing the magnetostriction (expressed as the change in coercivity for a fixed change in stress) and squareness ratio as a function of the temperature of the terminal heat treatment for three exemplary alloys varying in beryllium content;

FIG. 5 is a set of curves showing the coercivity as a function of the temperature of the terminal heat treatment for a number of exemplary wires varying in zirconium content and work history; and

FIG. 6 is a set of curves showing the magnetostriction (expressed as the change in coercivity for a fixed change in stress) and squareness ratio as a function of the temperature of the terminal heat treatment for a number of exemplary wires varying in zirconium content and work history.

DETAIL DESCRIPTION OF THE INVENTION EXEMPLARY DEVICE USE The exemplary piggyback twistor memory wire shown in FIG. 2 is composed of strands of a soft magnetic material 21 and a hard magnetic material 22 in the form of flat tapes wrapped around an electrically conducting wire 23. A drive current in the electrical conductor 24 can be used to interrogate the memory bit by producing a magnetic field such as to cause the bit of soft tape to reverse its magnetization. A larger drive current in conductor 24, possibly in combination with a current passing through conductor 23, can be used to write information into the memory bit by reversing the magnetization of the bit of hard tape. The soft tape 21 is desirably square looped (i.e., its remanent flux (1m, should be nearly equal to its saturation flux, in order to minimize spurious signals during interrogation (shuttle signals). For one proposed use it is required that the coercivity of the soft tape be of the order of 0.7 oersteds and the squareness ratio, be greater than 0.8. However, one could contemplate the use of coercivities from 0.2 oersteds to 3 oersteds or more and many devices can tolerate less squareness. In addition, it is desirable that the finished device be insensitive to mechanical stress.

The hard magnetic tape 22 must have a remanent flux, da which is greater than the saturation flux, tb of the soft tape 21 and a coercivity, I-I more than twice the coercivity of the soft tape 21. Then, after the soft tape is switched by the interrogation signal it is switched back to its original state by the magnetization of the hard tape.

The material properties which make the disclosed alloys suitable for the twistor use are the very same properties which are desirable for a wise variety of other memory devices and more general switching uses.

Alloy Compositions Beryllium and/or zirconium additions in the range of 0.1-1 weight percent of the total 100 percent of the other constituents provide control over the coercivity of this family of magnetic alloys. It is felt that this control stems from the following proposed mechanism: During heat treatment, these materials form nonmagnetic intermetallic type second phase precipitate. Under suitable conditions the precipitate comes out of solution as particles in the size range 200 A to 2,000 A. These particles are most effective in impeding the propagation of domain walls when the particle size is roughly equal to the thickness of the wall (typically 500 A to 1,000 A). [n the disclosed materials this causes a coercivity peak as the heat treatment history is varied to produce precipitate particles through the above size range. High temperature heat treatment (greater than l,000 C) tends to drive the precipitate back into solution and to homogenize the alloys while lower temperature (400 l,000 C) heat treatment tends to cause precipitation. At a given high temperature the longer the time of heat treatment the greater the homogenization. At a given low temperature the longer the time of heat treatment the larger the precipitate size. Additions greater than one percent tend to degrade magnetic performance while additions less than 0.1 percent are inoperative since these materials are soluble to that extent even below 1,000 C.

Using the beryllium or zirconium additions, coercivity can be controlled in this family of high permeability Fe-Ni-Mo alloys in the range 65-85 percent nicket and l-lO percent molybdenum remainder iron (composition expressed in terms of the ternary system). in these alloys the molybdenum serves to alter the electrical resistivity of the alloys thereby changing the eddy currents within the material, which currents influence the switching speed. It is also believed that the molybdenum interferes with the ordering of nickel-iron atom pairs during colling which would explain the insensitivity of the magnetic properties of these materials to cooling rate. However, since molybdenum is a nonmagnetic species, magnetic alloys including it are less magnetic than the parent alloys thereby reducing both the Curie temperature and the saturation magnetization. A practical limit for the disclosed alloys is of the order of percent molybdenum, A. An addition of less than 1 percent is not so operative.

With the discovery that extended bodies of these materials possessed a strong 100 crystal texture (the average orientation of the crystals which make up the body) after heat treatment it was felt that squareness could be improved by making use of the magnetocrystalline anisotropy of these materials. If the composition is adjusted so that the anisotropy constant K,, is positive, the 100 crystalline directions are easy directions for the magnetization (Ferromagnetism, R. M. Bozarth, D Van Nostrand and Company (1951) page 563ff). Thus, the magnetocrystalline anisotropy adds to the shape anisotropy of the extended body in making the axis of the extended body a preferred magnetization direction. This leads to an improved squareness. in order to accomplish this the nickel content should be maintained, depending somewhat on mechanical working and heat treatment, in the range 65-85 percent. K tends to become less positive with higher nickel content, (k for pure nickel is negative) but this tendency is reduced with higher molybdenum content. FIG. 1 shows that, within the preferred 2-8 percent molybdenum range, the higher nickel alloys require a higher molybdenum content.

For those uses requiring the heat treated bodies to possess a particularly low degree of magnetostriction in addition to possessing square loop properties, it is necessary to closely control the nickel content of the alloy. Depending upon the cold work and heat treatment history of the wire, the nickel content should desirably be kept in the range, C, of 805:] percent in order to keep the weight ratio, Ni/Fe M0, in the neighborhood of 4.15. At this nickel content the squareness considerations above indicate a preferred molybdenum content in the range 4-8 percent.

In addition to the above magnetically operative constituents, it is well recognized by those knowledgeable in the art that the addition of small quantities of other constituents may be required by processing considerations or such constituents may be present as accidental impurities in commercial grade materials. For instance, additions of manganese in amounts as great as one percent of the total weight of the other constituents may be incorporated to bind any sulphur which is present as an impurity in commercial grades of the other constituents. Suitable alternatives are known such as magnesium and calcium. This will be beneficial to the hot working properties of the alloy. In addition to sulphur, other accidental impurities such as silicon and phosphorus are commonly found in commercial materials and are tolerable up to levels of the order of two percent of the total weight of the other constituents. Aluminum is frequently added to control oxygen content and may be included in an amount of up to 0.25 percent by weight.

Processing The disclosed alloys can be successfully processed into useful device forms by working schedules including both hot and cold working, swaging, rolling, drawing and the other working methods known in the art. Many magnetic devices make use of round or polygonal wire but some (e.g., the twistor) can make use of flat tapes. The two processes investigated for the conversion of round wire to flat tape use l roll flattening and (2) die drawing. Although both processes are useful they are somewhat different in both the starting material and the end result. (1) Roll flattening tends to make the tape wider than the starting wire leaving the length essentially unchanged while (2) die drawing results in a thin tape which tends to be essentially as wide as the original wire diameter but longer. For instance to produce a 0.003 inch wide tape one may start a roll flattening process with a 0.001 inch diameter wire but a die drawing process with a 0.003 inch diameter wire depending on factors such as the desired tape thickness. The texture present in the roll flattened and die drawn tapes after terminal heat treatment is also somewhat different. They both have a texture along the tape axis. However, roll flattened tape shows a 100 crystal plane in the plane of the tape while die drawn tape shows a 100 crystal plane in the plane of the tape. Both tapes show good squareness characteristics.

During the cold woring schedule, periodic heat treatment is necessary to relieve the working strains which degrade ductility. The heat treatments at the larger diameters have a relatively minor influence on the final magnetic properties of the resulting wires.

The two major types of heat treatment are the strand anneal, in which a strand of wire travels through a hot zone, remaining at an elevated temperature, T,, for a time, 1,, and the coil anneal, in which a coil of wire is placed in a hot zone at an elevated temperature, T for a time, t These heat treatments, which are intended primarily to effect precipitation, usually take place at temperatures below l,O00 C. It was found, generally, that coil anneals at lower temperatures and longer times are equivalent in many respects to strand anneals at higher temperatures and shorter times. In one instance, it was found that a benficial strand anneal for which T, 950 C and t, seconds was generally equivalent to a coil anneal for which T 750 C and t 1 hour. It is a well recognized fact that time and temperature can often be traded off in this way.

Some alloys were shown to benefit from a solution treatment at a temperature above l,O00 C which could take place at some intermediate wire size. This treatment tends to homogenize the alloy and dissolve any precipitate which has formed during the prior processing. A two hour coil anneal at l,l00 C has been used for this purpose. Of course, the magnetic properties of the end product were most critically dependent upon the conditions of the terminal heat treatment.

Examples The alloys investigated here were vacuum melted and case in water cooled molds which produced rods of the order of 1 inch in diameter. It was found that closer control over the relatively volatile beryllium and zirconium was obtained by keeping the temperature of the melt as low as possible. Most of the described tape samples were produced by the following work schedule:

A. Cold Working Schedule 1. Cut off head of ingot and machine to A; inch diameter.

2. Homogenize at l,050 C for 2 hours (H atmosphere).

. Cold swage to 0.328 inch diameter.

. Rod anneal at 870 C for 1 hour (H atmosphere).

. Cold swage to 0.187 inch diameter.

. Rod anneal at 870 C for 1 hour (H atmosphere).

. Cold swage and cold draw to 0.063 inch diameter.

. Rod anneal at 870 C for 1 hour (H atmosphere).

. Cold draw to 0.025 inch diameter.

10. Strand anneal at 950 C by passing the wire at 24 feet per minute in N through a 6 inch hot zone Or coil anneal at temperature 750 C for l or 2 hours in 90 percent N 10 percent H water quench. 11. Cold draw to 2.75 mil diameter. 12. Strand anneal at temperature 0 C for 2-% sec.,

13. Cold draw to 1.28 mil diameter and roll flatten.

B. I-Iot Work Schedule 1. Cut off heat of ingot and machine to /s inch diameter.

2. Homogenize at l,050 C for 2 hours. (H

atmosphere.)

3. Soak at 1,100 C in a H atmosphere, followed by hot swagging to inch diameter.

4. Remaining schedule as above for cold working.

FIGS. 3, 4, 5 and 6 show the effects of the temperature of the terminal heat treatment( 2 /2 seconds strand anneal) on the magnetic properties of beryllium containing tapes and zirconium containing tapes which, for comparison purposes, were all produced by the above Schedule A. They show the wide range of control that can be obtained by a control of the content of beryllium or zirconium and the temperature of the terminal heat treatment. In FIGS. 5 and 6 the legend AP stands for as processed according to the above schedule. The legend ST stands for solution treated an additional two hours coil anneal at l,l00 C at a wire size of 0.025 inch.

What is claimed is:

1. A device comprising a first elongated body consisting of a first magnetic material and a second elongated body consisting of a second magnetic material in which said second magnetic material has a remanent magnetization at least equal to the saturation magnetization of said first magnetic material and a coercivity greater than the coercivity of said first magnetic material, said first magnetic material and said second magnetic material being magnetically coupled to each other, said first magnetic material consisting essentially of 79,58l.5 weight percent nickel, 4-8 weight percent molybdenum with the remainder iron and as an additional portion, at least one member of the group consisting of beryllium and zirconium in the quantity of 0.1-1 weight percent based on one hundred percent of said first three constituents, said first elongated body possessing a coercivity of 0.2-3 oersteds and a ratio of its remanent flux to its saturation flux of greater than 0.8, said first body and said second body having associated therewith at least one electrically conductive path so situated that the passage of current through said path results in a magnetic flux within at least a portion of said first body and said second body.

Patent No. 3,7 1,9 Dated September 25, 1973 Inventor(s) Gilbert Y.Chin, William B. Grupen, Thomas C, Tisone It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, line ll, after "80.2 percent nickel, insert "13.65 percent iron,. Column 2, line 67, "wise" should be wide--. Column 3, line 32, "nicket" should be -nickel- Column 4, line 63, "100" should be ---llO-- Column 5, line 31, case should be -cast-.

Signed and sealed this 19th day of February 197M.-

(SEAL) Attest:

C. MARSHALL DANN EDWARD MFLETCHERJR Commissioner of Patents Attesting Officer FORM uscoMM-oc 60376-P69 L5. GOVERNMENT PRINTING OFFICE 2 I969 0-355-33,

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