US3801290A

US3801290A - Method of producing a single crystal of or thoferrite and thin platelets thereof by means of the floating zone method

Info

Publication number: US3801290A
Application number: US00181035A
Authority: US
Inventors: H Makino; K Matsumi
Original assignee: Nippon Electric Co Ltd
Current assignee: NEC Corp
Priority date: 1970-10-09
Filing date: 1971-09-16
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02
Also published as: JPS4933520B1

Abstract

An orthoferrite single crystal is grown by the floating zone method with the growth direction of the crystal perpendicular to the easy axis of magnetic anisotropy by using a starting seed crystal whose easy axis is disposed perpendicular to the growth direction. The thus produced crystal is then cut into thin platelets in which the plane surfaces thereof are perpendicular to the easy axis of magnetic anisotropy.

Description

United States Patent 11 1 Makino et al.

[ METHOD OF PRODUCING A SINGLE CRYSTAL OF ORTHOFERRITE AND THIN PLATELETS THEREOF BY MEANS OF THE FLOATING ZONE METHOD [75] Inventors: Hiroshi Makino; Koichi Matsumi,

both of Tokyo, Japan [73] Assignee: Nippon Electric Company, Limited,

Tokyo, Japan [22] Filed: Sept. 16, 1971 [2]] Appl. No.: 181,035

[30] Foreign Application Priority Data Oct. 9, 1970 Japan 45-89112 [52] US. Cl. 23/305, 23/DIG. 1., 23/301 SP, 252/6257, 423/263, 423/594 [51] Int. Cl B01j 17/10 [58] Field of Search 23/305, 301 SP, DIG. 1, 23/51, 300; 252/6257; 423/594, 263

[56] References Cited UNITED STATES PATENTS Barnes 23/301 tmj 3,801,290 [45 Apr.'2,- 1974 3,009,788 Daimon 23/301 1 1 1961 3,272,591 9 1966 Rudness.... 23 301 3,414,372 12/1968 Paulus 23 301 3,429,818 2/1969 Benedetto 23/305 2,809,136 10/1957 Mortimer 23/301 OTHER PUBLICATIONS Akashi, et al., Prep. of Ferrite Single Crystals by New Floating Zone Tech., IEEE Trans. Mag., -Vol. Mag. 5, pp. 285-289, (9/69).

Primary Examiner-Wilbur L. Bascomb, .lr.

Assistant Examiner-R. T. Foster Attorney, Agent, or Firm-Sandoe, Hopgood and Calimafde; Eugene J. Kalil ABSTRACT An orthoferrite single crystal is grown by the floating zone method with the growth direction of the crystal perpendicular'to the easy axis of magnetic anisotropy by using a starting seed crystal whose easy axis is disposed perpendicular to the growth direction. The thus produced crystal isthen cut into thin platelets in which the plane surfaces thereof are perpendicular to the easy axis of magnetic anisotropy.

4 Claims, 5 Drawing Figures PATENTEDAPR 2:914 3.801.290

INVENTORS A l/P0567 MA/f/IVO BY A o/cw/ M47504 MWW METHOD OF PRODUCING A SINGLE CRYSTAL OF ORTHOFERRITE AND THIN PLATELETS THEREOF BY MEANS OF THE FLOATING ZONE METHOD This invention relates to a method of producing a single crystal of orthoferrite by the floating zone method and thin platelets thereof.

BACKGROUND OF THE INVENTION motions and moreover restrict the size of the effective area of the device.

. OBJECTS OF THE INVENTION It is therefore an object of this invention to provide a method of producing an orthoferrite single'crystal from which improved bubble domain devices can be producted. I

Another object is to provide a method of manufac-- turing wide-area thin platelets of orthoferrite.

It is still another object to provide a method of manufacturing bubble domain devices having a substantially wide or large area and substantially without defects.

SUMMARY OF THE INVENTION According to this invention, a method is provided of producing an orthoferrite single crystal by floating zone method, said crystal having a uniaxial magnetic anisotropy, wherein the improvement resides in the step of growing the crystal along an axis perpendicular to the' easy axis of magnetic anisotropy.

According to one embodiment of the invention, there is provided a method of manufacturing thin platelets out of an orthoferrite single crystal produced by floating zone method, the crystal having a uniaxial magnetic anisotropy, wherein the improvement comprises the steps of growing the crystal along an axis perpendicular to the easy axis of magnetization, the single crystal thus produced is cut into thin platelets having parallel surfaces perpendicular to the easy axis of magnetization.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the essential portion of an apparatus for growing a single crystal by floating zone method, which is used in carrying out the method according to this invention;

FIG. 2 is a schematic perspective view of a single crystal of orthoferrite grown by a conventional method;

FIG. 3 is a like view of a single crystal of orthoferrite cut into thin platelets according to a conventional method;

FIG. 4 isa schematic perspective view of a single crystal of orthoferrite grown in accordance with the invention; and

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. I, the essential portion of an apparatus for growing a single crystal by floating zone method comprises a lower axle I having a lower chuck 2 for holding a seed 3 of crystal onwhich a singlecrystal 4 is to be grown. The apparatus further comprises an upper axle 5 having an upper chuck 6 for supporting a polycrystalline rod 7 to be subjected to the floating zone method. By axial movement of the axles l and 5, the seed 3 and the rod 7 are brought into contact at a predetermined position where the heat from a heat source (not shown) is caused to melt the interface portions of the seed 3 and the rod 7. With the relative position unchanged, the axles l and 5 are lowered in the direction shown by arrows D. The single crystal 4 grows on the seed 3 from-molten zone 8 which moves upwards relative to the axles l and 5.

With the apparatus of this type, it is already known that a single crystal 4 can be grownalong a particular crystallographic axis when that axis of the seed 3 is placed parallel to the direction D. It has now been found that a so-grown single crystal 4 of'orthoferriteor a substance, such as'an oxide, having a large ionization tendency has a specific crystal habit and a characteristic shape. f v

' It should be noted here that'the floating zone 8 is subjected to localized heat to a temperature above the melting point. As a result, the single crystal 4 grown on the seed 3 passes through a steeptemperature gradient whereby thermal stresses are imposed on the crystal. When the single crystal 4 has a habit of growing into a generally rectangular parallelepiped configuration (an elongated crystal), the stress'is marked at the four corners transverse to the longitudinal axis. More particularly, the four corners are characterized by many dislocations which probably result from crystallographic slip due to the imposed high thermalstresses,

Referring to FIGS. 2 and 3, an elongated single crystal 9 of the orthoferrite having the easy axis of magnetization in the direction of the 00l axis is grown along the 001 axis, that is, along-longitudinal axis X-X Cutting the single crystal 9 perpendicular to the axis of growth, thin platelets l0, l1, 12, etc., are obtained. When, for example, the platelet 10 is etched by hot phosphoric acid after polishing, it is observed by a metallurgical microscope that the etch pits are abundant at the four corners l3, l4, l5 and 16 and scarce at the other surface portion between the corners. The etch pits show the dislocations caused by high thermal stresses set upon the single crystal 9 at the four comers l3, l4, l5 and 16 formed in accordance with the habit.

Since the single crystal is imperfect because of the abundant dislocations at the four comers, the performance of the bubble domain devices formed of thin platelets 10 is adversely affected where the magnetic domains are driven two-dimensionally within platelet 10. This is because the dislocations impede the movement of the magnetic domains. A bubble domain device is usually manufactured by cutting the four corners l3, l4, l5 and 16 away. However, it is necessary that the device have the largest or widest possible area and also that the magnetic domains should be movable throughout the area. Thus, the conventional method of manufacturing bubble domain devices has certain inherent disadvantages in that the serviceable area of the device is markedly reduced.

Referring to FIGS. 4 and 5, an elongated single crystal'l7 of orthoferrite having the easy axis of magnetization in the direction of the l axis is grown with the 0l0 axis of the seed 3 held parallel to or coaxial with the axis of the apparatus, the longitudinal axis YY of the crystal being perpendicular to the 00] axis. in accordance with the habit, a cross section 18, namely, the (010) surface taken perpendicular to the axis of growth has a generally rectangular shape having the longer sides parallel to the 00l axis. The etch pits observed as mentioned with reference to FIG. 3 are abundant at the four

corners

19, 20, 21 and 22 of the rectangle. Even with this invention, it is impossible to obviate the dislocations. It is, however, possible to cut the single crystal 17 into a multiplicity of thin platelets, such as 23, 24, 25 and 26.

Thin platelets

24, 25, with a substantial decrease in or having no dislocations are quite useful in bubble domain devices and have larger areas despite the fact that they are cut from a single crystal l7 having almost the same volume as the conventional single crystal 9 shown in FIGS. 2 and 3. It will be noted, however, that the area of working faces of

platelets

24 and 25 without the dislocations are much larger than the area of working faces of

platelets

10, 11 and 12 o-fFIG; 3. I I

I EXAMPLE 1 A single crystal of yttrium orthoferrite (YFeO was grown on the seed of the same material placed with the 0l0 axis parallel to the axis of the apparatus for growing the single crystal by floating zone method. The single crystal had the dimensions shown in FIG. 4. With the initial and the last grown portions of the crystal of a length of about l0 mm each cut away, the 30 mm long single crystal remaining is then cut with a slicing machine into eight sheets of thin platelets with the planes thereof being the (001) planes. Four of the platelets had no portions abundant with the dislocations. With each of the thin platelets 30 mm long and 5.5 mm wide, 'it was possible to drive the bubble do mains over the whole area without any impediment.

As a reference, a single crystal of the same material was grown along the 00I axis in accordance with the conventional method. The single crystal had the dimensions shown in FIG. 2. With the initial and the last grown portions ofa length of mm each cut away, the 30 mm long single crystal remaining is then cut into thirty-eight sheets of thin platelets having the (001) planes. Each thin platelet of the generally square shape of 6 mm by 6 mm had only an effective area of4 mm by 4mm as a bubble domain device on account of the four-corner portions in which the dislocations were abundant.

The-effective area attained in accordance with this invention is more than ten times as wide or larger as is obtained with the conventional method.

EXAMPLE 2 A single crystal of yttrium orthoferrite (YFeO was single crystal had the dimensions illustrated in FIG. 4 except the axesand 0l0 are interchanged.

The crystal was cut with a slicing machine into eight sheets of thin platelets in the manner shown in FIG. 5. Four of them were free from the portions in which the dislocations were abundant. With each of the thin platelets 30 mm long and 5.5 mm wide, it was possible to drive the bubble domains over the whole area as was the case with Example l.

EXAMPLE 3 The same results as described in conjunction with Example 1 were achieved for a single crystal of terbium orthoferrite (TbFeO except the single crystal was grown on the seed of terbium orthoferrite.

EXAMPLE 4 The same results as described in conjunction with Example 2 were attained for a single crystal of terbium orthoferrite (TbFeO except the single crystal was grown on the seed of terbium orthoferrite.

EXAMPLE 5 wherein Co ions were substituted for a portion of Fe ions.

EXAMPLE 7 The same results as described in connection with Examples l and 2 were achieved for a single crystal of a cobalt-titanium substituted yttrium orthoferrite (YFe- Co,, Ti,, O wherein an equal number of Co ions and Ti ionswere substituted. for a portion of Fe ions. I

From the Examples described above,-this invention is apparently applicable to single crystals of all kinds of orthoferrite, wherein each has'a uniaxialmagnetic anisotropy and is manufacturable by the floating zone method. Furthermore, it is possible to manufacture those thin platelets of a single crystal of orthoferrite which have (001) surfaces, by growing the single crystal along an axis, such as 1 10 axis, that is perpendicular to the 00l axis. it should be noted here that the notations of the crystallographic axes and planes mentioned above are not limitative. For example, thin platelets having (100) surfaces are manufacturable in accordance with this invention from a single crystal of orthoferrite, such as samarium orthoferrite, wherein the easy axis of magnetic anisotropy is the l00 axis.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are consid- 6 growth and perpendicular to said easy axis of magneti'zation.

2. A method as claimed in claim 1 wherein said crystal cutting step is carried out at that portion of the single crystal in which the dislocations are substantially reduced.

3. A method as claimed in claim 1 wherein the easy axis of magnetization is the axis 00l and said para] lel surfaces are (001) planes.

4. A method as claimed in claim 1 wherein the easy axis of magnetization is the axis l00 and said parallel surfaces are planes.

Claims

2. A method as claimed in claim 1 wherein said crystal cutting step is carried out at that portion of the single crystal in which the dislocations are substantially reduced.
3. A method as claimed in claim 1 wherein the easy axis of magnetization is the axis <001> and said parallel surfaces are (001) planes.
4. A method as claimed in claim 1 wherein the easy axis of magnetization is the axis <100> and said parallel surfaces are (100) planes.