US3150095A - Ferrite ceramic compositions and method of preparation - Google Patents

Description

United States Patent Oifice 3,150,095 Patented Sept. 22, 1964 3,150,095 FERRITE CERAMIC COMPOSITIONS AND METHOD OF PREPARATION James M. Brownlow, Crompond, and James A. Morrow, Peekskill, N.Y., assignors to International Business Machines Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Nov. 24, 1961, Ser. No. 154,896

8 Claims. (Cl. 252-625) This invention relates to the ferrite compositions which are used in memory and switching circuits in computer mechanisms. These ferrite compositions find application as high speed switching elements in computer circuitry.

In formulating magnetic materials for computer use there are several well recognized objectives in regard to the properties which are required to permit operation of the material as a high speed memory device. These properties are not independent of the several electrical modes of operation that computer designers have developed. In older computer memory designs it was only necessary that the magnetic ferrite have a high B /B ratio and a corresponding high one to zero (signal to noise ratio) in the memory circuit. The switching speed and flux density were not important limitations since the repetition rates were low, 100 kilocycles.

In present day memory design the switching speeds and repetition rates are being pushed to the highest limits by more sophisticated circuit design and modification in materials.

It has been found the ordinary square loop ferrite compositions with fiux densities 1800-2700 ganss, exhibit a thermal effect at fast (25 megacycles) repetition rates, Hysteresis heating on repetitive switching at high rates causes the temperature to rise excessively in the ferrite composition. The power (P) dissipated in the material at a fixed repetition rate is proportional to the flux density (B times the coercive force (H [i.e. P-(B H The coercive force (H can not be lowered too far without loss of switching speed. If the flux density is lowered, stable memory operation is possible because the temperature rise due to hysteresis heating is then within safe limits.

An object of this invention is to provide ferrite compositions and method of making them so that low flux density is achieved while retaining the desirable properties of fast switching and high B /B ratio.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodi ment of thp invention.

It is also desirable to keep the Curie temperature high so that the material can sustain stable operation when the temperature does rise. This eliminates one way of lowering the fiux i.e. by the substitution of zinc or cadmium in Fe O which lowers the Curie temperature and thereby the flux density if the Curie temperature is near 100 C. (Saturation Magnetization and Crystal Chemistry of Ferrimagnetic Oxides by E. W. Gorter, Philips Research Reports, vol. 9, pp. 295420). Such materials are unsuitable because a large temperature rise causes them to approach the Curie temperature where memory operation becomes impossible.

The approach used to solve this problem has been to adjust the composition of the ferrite so that the flux is lowered while the Curie temperature remains high. This requires additions to Fe O which dilute the magnetic moment but do not greatly diminish the number of mag netic inter-actions. It was found the Cr+ and Cu+ act in this way and that Ni+ in small amounts promotes high B /B ratio.

These materials disclosed have been made and tested under memory conditions and found to dissipate less power at high repetition rates (2-5 megacycles) than conventional compositions. They have low magnetic moments, switch at high speed and are useable at 5 megacycles where conventional ferrite compositions are not suitable.

The formulation and processing of these materials follows procedures well known in the art except for the firing step. Here a problem arises because of the high copper content. At 1150l200 C. the Cu+ disassociates partly into Cu Too great an amount of disassociation leads to chemical instability and a foreign phase is formed which results in a 2 phase material with reduced B /B ratio. Careful experimentation with each composition allows a narrow range of firing temperature which is within i50 C. of the optimum firing temperature to be defined for each. In some cases a two step cooling enhances the B /B ratio.

While the firing is critical, the invention is in the unique composition of the ferrite which has a desired combination of magnetic properties namely low fiux density (300- 1600 gauss), high B /B ratio (.7.9), low hysteresis heating effect of the order of /3 to /2 that found in high flux density ferrite composition and capable of operating at high repetition rates (2-5 megacycles) and a Curie temperature (T greater than 150 C.

The range of ferrite ceramic compositions found to be within the scope of the invention are described by the formula expressed in atom numbers:

Fe Cr Cu Mg Ni m wherein y .2-1 z: .5-.8 a=0.2 Zr==0.4

and

A ferrite ceramic composition is defined and understood by those skilled in the art to be a material with a cubic spinel structure which results from the heating (firing) and complete reaction of the component oxides used in preparing the ferrite composition.

The ferrite ceramic composition of the invention may be prepared by mixing together oxides of Fe, Cr, Cu, Mg, and Ni in the amounts shown below in Table II to form a mixture and then subjecting this mixture to an elevated firing temperature from 1100 to 1400 C. for up to 60 hours in an atmosphere containing oxygen to form the ferrite ceramic composition. Thereafter the ferrite ceramic composition may be cooled by air quenching. In some cases a second firing step is used involving a rapid reheating to a temperature lower than the first firing temperature for a specific time and then air quenching. Ordinarily in the two step method the second firing temperature is to 400 lower than the first firing temperature and the second firing time varying from 10 minutes to 2 hours.

The initial mixture is prepared by weighing out the component oxides as specified for any formula number specified in Table II. This mixture is homogenized for four hours in a ball mill with alcohol (e.g. ethyl alcohol) as the suspending agent. The alcohol is removed by drying and the mixture is calcined at 1000 C. for a time of 1 hour. This calcined mixture is again milled in a ball mill with water and 3% by weight of a binder (e.g. polyvinyl alcohol) for a period of time (between four and 24 hours) suificient to reduce the particle size of the calcined mixture to about 1 micron. This material is then dried and reduced to a powder and the powder used to form toroidal sample shapes by pressing in a steel die of suitable design at a pressure of the order of 50,000 lbs. per square inch. Next the toroidal shapes or bodies are fired and cooled according to the temperature and time schedule specified for use in preparing the initial mixture as set forth in Table I. Thus ferrite ceramic compositions are formed which have a cubic spinel' structure.

Table I INITIAL MIXTURE IN GRAMS AND FIRING TREATMENT Weight in grams Step 1* Step 11* Formula No. Temp, Time, Temp, Time,

F6203 CrzO: CuO MgO NiO 0. hrs. 0. hrs.

T 390. 144.0 38.0 55.8 0. 1,200 0.5 T 91.... 120.0 53.2 63.6 0.0 1,200 0.5 T 393- 95. 0 113.8 39. 7 0. 0 1,200 0.5 T 394. 120.0 0.0 39.7 0.0 1,200 16.0 T 95 96.0 68.4 55.8 14.9 1,200 16.0 T 96 80.0 83.6 55.8 14. 9 1,200 16.0 T 9 9 120.0 ,60. 0 39.7 14.9 1,200 16.0 T l00 88.0 83. 6 47. 7' 1419 1,200 16.0 T 103--. 144. 0 38. 0 39. 7 14.9 1,100 00. 0 T 107-" 144. 0 30.4 31. 8 30.0 1,400 0.15 '1 108-.. 144.0 38.0 23.9 22.5' 1,200 3.0 T 1 12 144.0 19.0 47. 7' 11.2 1,150 4.0 T 113 144. 0 15.0 59. 7 7 1, 200 16. 0 T 114-" 120.0 38.0 59. 7 7.5 l, 150 16.0

Firing treatment: Firing done in air atmosphere. air quenched alter each step.

The samples are Table II FINAL COMPOSITIONS IN ATOM NUMBERS AND LEAGNETIG PROPERTIES FOR SYSTEM FeXCr QuzMgaNib Atom numbers Flux Formu1a* density B lB He, '1

o. s oersted C.

x y z a b gauss *These are the final ferrite ceramic compositions obtained by treating mixtures given in Table 1 according to firing treatment set forth therein.

"The unique composition ofzthe ferrite ceramic compositions causes them to exhibit a highly desirable comhination of magnetic properties, namely low flux density (3001600 gauss), high B /B ratio (.7.9), low hysteresis heatingetfect of the order of /3' to that found in high flux density ferrite ceramic compositions that are the invention acomparison of one of the specific compositions of the invention witha manganese containing ferrite i composition currently available in the art is provided a Table 111.

4 Table 111 Type XCll.1 Mure F614 04 T 99C11.5 C Fens N12 04 Wherein 11 is the percent flux switched in a partial switching memory operation. 7 V v v I Power expressed in watts is a measure ofheat dissipated in the magnetic ferrite composition at the high repetition rate expressed in megacycles (me).

The invention shows that low flux density ferrites dissipate less heat at high repetition rates. The Table III shows that the power dissipated at 2 me. is .027 watt in T 99 compared to .073 watt in the high flux density reference material. A similar relation is seen at 5 me. It has been found that the reference material (TypeX) will not operate at 5 mo. unless a liquid refrigerant is forced over the material. The T 99 and other ferrite compositions of this invention will, however, operate in air at this repetition rate. I

In large capacity high speed memory is highly desirable that it operate in air and-without extensive refrigeration.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1-.- A- ferrite ceramic composition having the formula Fe cr cu Mg Ni og wherein x=0.8-1-.8 y=0.21.3 z=0.5-'0;8 a=00-.2" b=0-0.4

and

x+y+z+a+l1=3 2113+ y-2'.3 0.7 a+b,+z1.0

said composition having a flux density (B of less than 1600 gauss, a B /B ratio of at least 0.7 and a T of at least C.

2-. A ferrite ceramic composition having the formula Fe Cr Cu Mg Ni O wherein x=1.21.8 y='0.5-1.3 z='0;5-0.8 a=0 [2:0

and

said composition having a flux density (B of less than 1600 gauss, a B' /Bg ratio of atleast 07 and: a T of at least 150 C. r l i 3. A ferrite ceramic composition having the formula and havinga'flux density (B of 770 gauss, a B /li i ratio of 0.8 anda-T, of C. v 4. A ferrite ceramic, composition havingthe formula v r rt a ttM tz r and having a flux density (B of 740 gauss', a B /B ratio of 0.8 and a T of 175 C.

5. A ferrite ceramic composition having the formula and having a flux desity (B of 1100 gauss, a B /B ratio of 0.9 and a T of 200 C.

6. A ferrite ceramic composition having the formula r.s o.25 0.6 o.2 o.15 4

and having a flux density (B of 1260 gauss, a B /B ratio of 0.9 and a T of 280 C.

7. A method of preparing a ferrite ceramic composition having a flux density (13,) of less than 1600 gauss,

a B /B ratio of at least 0.7 and a T of at least 150 C.

having the formula which comprises mixing in finely divided form oxides of Fe, Cr, Cu, Mg and Ni in proportions such that the ferrite ceramic composition produced by firing has the above formula; subjecting the thus-formed mixture to an elevated firing temperature oetween 11001400 C. for up to hours in an oxygen containing atmosphere to form said ferrite ceramic composition and thereafter air quenching.

8. The method of claim 7 wherein there is a second firing step following the air quenching which comprises a rapid reheating in an oxygen atmosphere to a temperature to 400 C. lower than the first firing temperature, holding at this lower temperature for 9 minutes to 2 hours, and thereafter air quenching and References Cited in the file of this patent UNITED STATES PATENTS 3,031,405 Pierrot et al Apr. 24, 1962 FOREIGN PATENTS 760,035 Great Britain Oct. 31, 1956

Claims (1)

1. A FERRITE CERAMIC COMPOSITION HAVING THE FORMULA