US3676082A - Magnetic compositions - Google Patents

Abstract

A NEW MAGNETIC MATERIAL COMPRISES THE MOLAR FORMULA MM''2Z3+YX1- WHERE: X CONSISTS ESSENTIALLY OF AT LEAST ONE OF THE CHALCOGENIDES, S2-,SE2-,TE2-;X CONSISTS ESSENTIALLY OF AT LEAST ONE OF THE HALIDES, C1-,BR-,I-; M CONSISTS ESSENTIALLY OD COPPER IONS; M'' CONSISTS ESSENTIALLY OF CHROMIUM IONS; AND Y IS A NUMBER FROM ZERO TO LESS THAN 1. VALUES OF Y EXITS ABOVE WHICH THE MATERIAL BEHAVES AS A CONDUCTOR AND AT OR BELOW WHICH THE MATERIAL BEHAVES AS A SEMICONDUCTOR. THE COMPOSITIONS ARE GENERALLY IN THE SPINEL CRYSTAL CLASS AND ARE USEFUL IN MAGNETIC AND SEMICONDUCTOR DEVICES. A METHOD OF PREPARING THE ABOVE MATERIAL COMPRISES FIRST MIXING THE STARTING MATERIALS COPPER HALIDE, CHROMIUM, CHALCOGEN AND COPPER IN THE MOLAR RATIOS TO GIVE THE DESIRED PRODUCT. THEN PRESSED PELLETS OF THE MIXTURE ARE FORMED AND PLACED IN EVACUTATED QUARTZ TUBES. THE PELLETS ARE THEN FIRED FOR AT LEAST 10 HOURS AT 700-800*C.

Description

July 11 1972 M. RoBBlNs 3,676,082

MAGNETIC COMPOS ITIONS Filed May 19. 1967 2 Sheets-Sheet l N G "l n i@ K Y u s* K? l l l w n w 'n N Q Juanan/M mm/mf aum/.Ww

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KIJrJr/v/rr (afm-mf) l I l 6 i a /0 /z /lf [la/beni renfe/drag mvfwfon Mae/Mr Fou/M5 WWU ATTQRIEY 3,676,082 MAGNETIC COMPOSITIONS Murray Robbins, Trenton, NJ., assignor to RCA Corporation Filed May 19, 1967, Ser. No. 639,798 Int. Cl. C01b I9/00; H011:` 1/00, 1/06 U.S. Cl. 23-367 9 Claims ABSTRACT F THE DISCLOSURE A new magnetic material comprises the molar formula MM'2Z3+yX1 y where: Z consists essentially of at least one of the chalcogenides, $2-, Sez", Tez; X consists essentially of at least one of the halides, Cl, Br, I; M consists essentially of copper ions; M consists essentially of chromium ions; and y is a number from zeno to less than 1. Values of y exist above which the material behaves as a conductor and at or below -which the material behaves as a semiconductor. The compositions are generally in the spinel crystal class and are useful in magnetic and semiconductor devices. A method of preparing the above material comprises rst mixing the starting materials copper halide, chromium, chalcogen and copper in the molar ratios to give the desired product. Then pressed pellets of the mixture are formed and placed in evacuated quartz tubes. The pellets are then tired for at least l0 hours at 70D-800 C.

BACKGROUND OF THE INVENTION This invention relates to a new magnetic material useful in magnetic devices, semiconductor devices and devices requiring the combination of semiconductor and magnetic properties. More particularly, it relates to magnetic materials some of which are semiconductors having 'Curie temperatures near or above room temperature.

Materials having both magnetic and semiconducting properties are known in the art. 'Ihese prior art materials have low Curie temperatures and therefore require cooling means for maintaining the materials below their Curie temperatures. For example, the compounds of gadolinium selenide and yttrium gadolinium selenide disclosed by S. I. Methfessel et al. in IU.S. Pat. No. 3,271,709 have Curie temperatures of from about 55 K. to 80 K The compounds CdCr2Se4 and CdCr2S4, reported to Ibe ferromagnetic semiconductors by P. K. Baltzer et al. in Physical Review Letters 15, 493 (1965), have Curie temperatures of 84 K. and 130 K. respectively. Since magnetic materials are nonmagnetic above their Curie temperature, it is desirable to obtain materials with as high a Curie temperature as possible. Magnetic materials having higher Curie temperatures require less cooling or no cooling. This reduces or eliminates the requirements for cooling and reduces the cost of operating devices employing magnetic materials.

SUMMARY OF THE INVENTION The novel magnetic materials described herein are characterized in that they have Curie temperatures near or above room temperature. These novel materials are believed to include the only presently known materials having the combined properties of a magnetic material and a semiconductor which in addition have Curie temperatures above room temperature.

The novel magnetic materials have the molar formula MMZ3+X1 y wherein Z consists essentially of at least one of the chalcogenides, $2-, Se2, and Te2, and X rice consists essentially of at least one of the halides, C11", Brland I1. M and M consist essentially of copper and chromium ions respectively. The value of y is a number from zero to less than 1. Values of y exist above which the magnetic materials are conductors and at and below which they are semiconductors. For example, in the series of materials represented by the formula `when y is between zero and about 4.5 the material behaves as a semiconductor. That is, its resistivity decreases with increasing temperature as measured for example from liquid nitrogen temperature to greater than room temperature. When y is 'a number greater than about 0.45 the material behaves as a conductor. That is, the resistivity increases with increasing temperature over the same temperature range.

The magnetic conductors are compatible Iwith the magnetic semiconductors disclosed herein, and may be useful as conductive contacts to the semiconductor. For example, in a sandwich type structure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a graph indicating the Curie temperature of the novel magnetic materials represented by the molar formula 'CuCr2Se3HBr1 y as y varies from 0 to l.

FIG. 2 is a graph indicating the magnetic moment of magnetic materials in the series CuCr2Se3+yBr1 y as y varies from 0 to l.

FIG. 3 is a graph of the resistivity of iCuCr2SeBr as a function of temperature showing the semiconductor behavior of this compound.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The novel magnetic materials are generally single phase structures of the spinel type. Typically, these materials are prepared by reacting copper halide, chromium, chalcogen and copper, or for the compounds resulting when y=0, by reacting fCuX and Cr2Z3, in an evacuated quartz tube at about 700-800 C. CuX represents copper iodide, copper bromide, `or copper chloride. Cr2Z3 -represents chromium sulde, chromium selenide, or chromium telluride. The reactants are weighed and mixed such that the molar ratios of the elements in the reactant mixture is equal to the molar ratios of the elements in the desired product. The reactants are mixed together by dry milling for several hours. The milled reactants are then pressed into pellets which are sealed in evacuated quartz tubes. The pellets are then ltired for at least about 10 hours. When it appears after the tiring step that all of the reactants have not been converted to the lnal product it may be desirable to remove the pellets after the rst firing, grind them into a powder, repress new pellets and retire them.

EXAMPLE 1 Magnetic CuCrzSeSBr is prepared by weighing 0.05 mole of CuBr powder, 0.1 mole of Cr metal powder and 0.15 mole of Se powder and placing these materials together in a ball mill. The materials are mixed by dry milling for about 18 hours. The mixed powders are then placed in an apparatus for forming pellets from powder samples by pressing. Pellets are pressed from the powder using a pressure of at least about 5000 p.s.i. These pellets which are about 'V16 inch in diameter and about from 1-2 inches long, are then placed in quartz tubes which are closed at one end. Usually, there is one pellet per tube. Each quartz tube is then evacuated and sealed at the other end while evacuated so as to form an ampoule EXAMPLE 2 Magnetic CuCr2Se3-4BrM is prepared by dry milling a mixture containing 0.03 mole of CuBr powder, 0.1 mole of Cr metal powder, 0.17 mole of elemental Se powder and 0.02 mole of Cu metal powder, for about 15 hours. The milled mixture is then pressed into pellets, sealed in an evacuated quartz ampoule and fired as described in Example 1. The Curie temperature, Tc, of the nal product is about 345 K.

EXAMPLE 3 Magnetic CuCr2Te3I is prepared by dry mixing a mixture containing 0.05 mole of Cul powder and either 0.1 mole of Cr metal powder and l0.15 mole of Te powder or 0.05 mole of Cr2Te3 powder, for about 18 hours. The milled mixture is then pressed into pelets, sealed in the evacuated quartz ampoule and ired as described in Example 1. The Curie temperature of this material is about 294 K.

EXAMPLE 4 Magnetic CuCrzTemIo is prepared by dry milling a mixture containing 0.04 mole of Cul powder, 0.1 mole of Cr metal powder, 0.16 mole of Te powder and 0.01 mole of Cu metal powder, for about 18 hours. The milled mixture is thgnpcessed as described in Example 1. The Curie tempera yreof this material is about 307 K.

g vEXAMPLE 5 Magnetic CuCr2Se3Cl is prepared by dry milling a mixture containing 0.05 mole of CuCl powder, 0.1 mole of Cr metal powder and 0.15 mole of Se powder, for about 18 hours. The milled mixture is then processed as described in Example l.

Other compounds such as CuCrzTesBr and CuCr2S3Br have been prepared by similar procedures. Also, the process has many variations which may be used to prepare the novel composition. For example, it is not necessary to dry mill, milling can be performed in a non-aqueous solvent provided the powder is properly dried prior to pressing and/ or firing. Also, the milling time is not critical but should preferably be greater than about 4 hours.

Although it is preferred to form pressed pellets from the mixed powder, this step is not necessary. However, if pellets are not formed prior to firing the time of firing and number of reiirings required to convert all the reactants to the desired product may be increased. The pressure used to press the pellets is not critical but should be at least great enough to give a mechanically sound pellet.

Firing in a sealed tube is a convenient way of maintaining the partial pressures of volatile components of the reactants and preventing loss of any component. Where the tube is not sealed it may be difficult to control the composition of the final product as the volatile components may be depleted. The sealed tube is preferably evacuated but may contain inert gases.

The slow temperature rise of the furnace is merely a safety precauation to prevent explosion of the ampoule to the exothermic heat of reaction. The ring temperatures should be between about 700 to 800 C. and preferably 4 from about 750 to 800 C. with firing times of at least about 10 hours.

The Curie temperatures, Tc, of several of the novel compositions are shown in FIG. 1. The Curie temperatures of the materials represented by the formula CuCr2Se3+yBr1 y increases steadily from Tc=275 K. when y=0 to To=430 K. when y=1. The compound CuCr2Se4, obtained when y=l, is metallic. The Curie temperature at y=0.45, which is the composition near which the material changes from a semiconductor to a conductor or metal, is about 355' K.

The magnetic strength of the novel materials represented by the molar formula CuCr2Se3+yBr1 y is shown in FIG. 2. The magnetization of these materials increases as the value of y decreases and is highest for the semiconducting compound CuCrzSeaBr. The resistivity of this compound as a function of temperature is shown in FIG. 3. The semiconducting behavior (an increase in resistivity with a decrease in temperature) is shown in the iigure.

The table shows the resistivity of various compositions at room temperature and at liquid nitrogen temperature.

The particular value of y, in the molar formula CuCr2Z3+yX1 y, above which the compositions change from a semiconductor to -a metal may be diierent for different combinations of chalcogende (Z) and halide (X). The preferred maximum value of y is about 0.95. Above this value the change in magnetic moment is not considered significant.

What is claimed is:

1. A magnetic material consisting of a copper chromium chalcogenide halide represented by the molar formula CuCl'2Z3+yX1 y (a) Z consists essentially of at least one chalcogenide selected from the group consisting of S2, Sez, and Te2,

(b) X consists essentially of at least one halide selected from the group consisting of C11, Br, and I1, and

(c) y is a number from zero to less than 1.

2. The magnetic material described in claim 1 wherein y is a number from zero to 0.95.

3. A magnetic semiconductor material consisting of a copper-chromium chalcogenide halide represented substantially by the molar formula CuCr2Z3+yX1ny wherein (a) Z is at least one chalcogenide selected from the group consisting of S2, Sez, and TeZ,

(b) X is at least onehalide selected from the sgroup consisting of C11, Brl, and Il, and

(c) y is a number from zero to a maximum value of less than 1, said maximum being that value above which the material behaves as a conductor.

4. The magnetic semiconductor material described in claim 3, wherein Z is Tez and X is 11'.

5. The magnetic semiconductor material described in claim 3 wherein y is a number from zero to about 0.45.

6. The magnetic semiconductor material described in claim 5 wherein Z is 8e2 and X is Brl,

7. A single phase ferromagnetic semiconductor compound having a spinel crystal structure and represented by the molar formula CuCrgSeaBr.

5 6 8. A single phase ferromagnetic semiconductor com- References Cited pound having a spinel crystal structure and represented FOREIGN PATENTS by the molar formula CuCrzTeaI.

9. A magnetic material comprising a copper-chro- 708,891 5/1965 Canada 252-623 T mium chalcogenide halide lrepresented by the formula 5 OTHER REFERENCES MM 2Z3+YX1Y Wherem: Hahn et al.: Z. fn Anorg. U. Allg. Chem. 303, pp. 107- (a) Z consists essentially of at least one chalcogenide 112 (1960) selected from the group consisting of S2, Se-z, and

Tez OSCAR R. ERTIZ P r E (b) X consists essentially of at least one halide selected 10 V Uma y Kammer from the group Consisting of Cl-i, Br-i, and 1 1, H. S. MILLER, Ass1stant Examiner (c) M consists essentially of copper ions, (d) M consists essentially of chromium ions, and U'S CL X'R (e) y is a number from zero to less than 1. 252-62.3 V, 62.51, 518

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