NL7907616A - GRENADE FOR A MAGNETIC BUBBLE MEMORY. - Google Patents

Description

793474 / amersamers f ^

Applicant s Hitachi, Ltd., Tokyo, Japan »

Short designation: Grenade film for a magnetic bubble memory.

The invention relates to a grenade film for a magnetic bubble device and more particularly to a single crystal grenade film suitable for use in a high density memory in which the bubble diameter is not greater than about 1.5 f. It is known that magnetic bubble memories are becoming increasingly important as a device for storing and processing information, in particular as memory, so that very active developments in this field have been and are being carried out ·

One of the most important functions of a memory device is the memory density, which is determined by the diameter of the magnetic bubble.

In the conventional magnetic memory devices, the bubble has a diameter of 5 to 5 µm, the memory density can be increased significantly when the diameter of the magnetic bubble can be reduced.

In order to increase the practical field of application of the magnetic bubble memory elements, such that they can replace the other currently known memory elements such as disk memories, semiconductor memories and the like, it is necessary that the memory density is increased considerably by decreasing the diameter of the magnetic bubble memory element to less than 1.5 μπι It is therefore important to provide a material for such a memory that can stably hold and energize a magnetic bubble of such a small diameter ·

For the prior art, reference may be made to the following publications: (1) E.3. Hagedornj AIP Conf. Proc., Vol. 5 »pages 72 - 90» (1972)

This publication describes Yq ^ Gd ^ ^ Lag ^ Pe ^ ^ A1q g0 ^ 2 and 35 other garnet films · (2) D.H. Smith and Al., AIP Conf. Proc., Vol. 5, p. 120 - 123 »(1972)

Described herein are Ετ2ΰά.Α1 ^ Eri 52¾.5 ^ 0.4 ^ 21 39 and other grenade films.

7907616 - 2 -> (3) W.A. Bonner and Al, J. Appl. Phys., Vol. 43, No. 7, page 3226-3228, July, 1972

This publication describes a grenade film of composition Y ^ ^ Eu ^ Aly.Pe ^ y.0 ^ 2 (Σ “1” 5 - 2.0, y «0.7 ~ 1» 2).

5 (4) L.G. banitizes and Al, Mat. Res. Ball., Vol. 6, p. 1185-1200.

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Described herein are Eu ^ ^ Gd1 ^ AlQ ^ Pe ^ ^ 0 ^ 2 and other grenade films.

It is noted that the grenade described in any of the above-mentioned publication 10 is not intended for fine bubble memory while; although the amount of Gd added according to the invention is up to 0.5, this amount in any of the compositions described exceeds 1. Although Gd is added to adjust 4times by magnetization of Gd ions, the addition of Gd results in. an increased temperature dependence of certain properties. like 4irMs and Ho (call collapse field)

It is now noted that although according to the invention the amount of added Eu is 1.4, in the known compositions this value is at least 1.5 so that the gyromagnetic ratio and the magnetic wall mobility decrease, making rapid transfer of the bubbles difficult.

The amount of Al is within the range specified according to the invention, but it is not known from any of the previous publications to add Al to bring the exchange stiffness constant A to a certain value as proposed according to the invention. In the prior art, Al is added to adjust the mismatch between the lattice constant of a substrate crystal and that of a bubble film caused by the addition of Gd and the like.

The invention provides a grenade film for a magnetic bubble memory element in which magnetic bubbles of particularly small diameter can be stably held so that a significant improvement in the memory density is obtained.

To this end, according to the invention, the saturation induction is kept at a low value by substituting a 7907616 ti-3 predetermined amount of iron with aluminum without substantially lowering the Curie point while keeping the other properties at the desired levels by adding predetermined amounts of other elements such as yttrium and gadolinium 5 thereby enabling stable retention of fine bubbles.

Based on Thiele's theory (Bell, Syst, Techn, J 5Q (* 7l) 725), an explanation will be given below of the properties that a material must have if it is to allow the stile presence of fine magnetic bubbles.

When a magnetic grenade film is selected such that the thickness h is substantially equal to the diameter d of the magnetic bubble, d is substantially equal to eight times the characteristic length 1: d - 8 1 .......... .................. (1) 15 In such a case 1 can be expressed by a relation in which the saturation induction (4-WMs), the aniso-trope field (Hk) occur. and the exchange stiffness constant (l) j 1-2 (8WA. <1/2 / (4TTMs) ^ 2 .......... (2)

The Hk can be defined as Hk »q. (4WMs), where q.

20 is a factor representing the stability of a magnetic bubble, d can be expressed by the following equation: d - 16 (8M * 01 // 2 / 4irlis ... o .......... (3 ).

If d is to be small it is necessary that both Δ and q are as small as possible and as large as possible. However, two practical considerations follow (1) In order to prevent unwanted magnetic bubbles from being generated in places other than in the magnetic bubble generator q should preferably have a value greater than 3, In order to ensure easy generation of the magnetic bubble by the magnetic bubble generator, q will preferably have a value up to 10, (2) The transfer of the magnetic bubbles is effected by means of a rotating field. Experiments have shown that the intensity of the rotating field required for the transfer of the magnetic bubbles is substantially proportional to 4WMs, It is then - 7907616

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- 4 - also necessary, to make 4fiMs as small as possible, so that not only is less power required to generate the rotating field, but also the heat development in the winding generating the field is as small as possible · 5 As a result of these "constraints, the free factor in the relationship (3) is only A · In other words, for a material with a small value of d, the value of A must be small.

Already have been proposed as material for a fine bubble grenade film (bubbles with a diameter of about 1 μπι) as 10 Ga-substituted grenade type (EuTm) j (FeGa) <.012, (SuYb) ^ (5'eGa) ^ 012 , (BuLn) ^ (i'eGa ^ 0 ^ 2 and the like ·

If a different type of material has been proposed (SmLu) ^ (PeGa) 5 ^ 12 * Sm occurs instead of Eu, and (SmTm) ^ Ee ^ 0 ^ 2 where

Fe is not substituted · 15 'Compared to the normal grenade type and for magnetic bubble elements, these grenades have the following specific properties in terms of their application in magnetic bubble devices: (1) The saturation induction 4 $ Ms is at least 800G greater than with normal grenade. · (In a material in which there is no Fe substitution, 4 * Ms is greater than or equal to 1200G, but in a 2 μια; / material the following applies, for example: (YSmLuCa) ^ (FeGe) ^ 0 ^ 2, 4flMs * 43> OG and in (YSmlu) 3 (FeGa) 5012.4 * Ms * 380G).

(2) The Curie point is at least 200 ° C and the exchange stiffness constant A is at least about 3 ^ 10 µg / cm.

(3) The anisotropy energy Ku is at least twice as great as that of a material used for magnetic bubbles with a diameter of 2 μια ·

One of the major problems with the use of these magnetic films for the bubble element is that the power consumption required for the bubble transfer increases significantly and that a large heat development occurs in the winding used therefor. This is due to the fact that the power absorption in the winding increases with the quadrate of Ms of the grenade film as follows. It can be stated that the first requirement 790 7 6 1 6 - 5 - for a grenade material applicable for fine magnetic bubbles is that Ms is as small as possible · In order to achieve this, it is necessary to make A small as also follows from the above · Saar A however, it is primarily determined by the interaction of the Fe 5 ions, part of the Fe ions can be replaced by other ions, so that the amount of Fe decreases and the value of A becomes small.

In other words, the more Fe is substituted, the smaller is A 7

However, when the value of A drops below 1.5x10 10 erg / cm, the Curie temperature Tc drops below 150 ° C, as a result of which the temperature dependence of various properties of the magnetic bubbles becomes very large and the temperature range in which the magnetic bubble element can still be used well. is reduced. From a practical point of view, it is necessary that the element can still be used at 100 ° C. However, when Tc is less than 150 ° 0, the practical applicability of the magnetic element is virtually nil.

Ions that can be used to keep the value of A small while Tc is at least 150 ° C are Al ^ +, Ga ^ +, Si ^ +, Ge ^ + 20, and Al ^ + gives the best results. Since Al ^ + is also most effective at reducing the value of A, it is possible to keep 4tMs as small as possible when the fine bubbles are obtained by Al substitution. According to the invention, therefore, Al is used as the ion for substituting a portion of Fe and the substitution amount 7 should be between 0.2 and 0.9 for practical applications.

When the diameter of the fine magnetic bubbles is not greater than about 1.5 µm, the garnet film used to generate such fine magnetic bubbles should be between 550 to 1300 Gauss. When 4flMs is below 550G, it is impossible to stably form fine bubbles with a diameter of up to 1.5 μη unless the film is extremely thin.

On the other hand, when 4range exceeds 13.00G, an anisotropic energy Eu of at least 2 × 10 µg / cm 3 is required to achieve stable bubble transfer. With the current state of the art b___ 7907616 * - 6 - ----—— r -----—, however, a value of Ku of 2x10 erg / cm is the upper limit and above that it is not possible to obtain a stable bubble film # 3+

When the substitution amount y of Al is less than 0.2, 4flMs becomes greater than 1300G, and when y exceeds 0.9, 5 * Ms becomes less than 550G · So y must be in the range of 0.2 to 0.9 ·

Since 7, Gd, Tb, Tm, Lu and La all have small magnetic losses, they are added as to match the grating constant of the garnet film to that of the substrate,

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Eu and Sm are added as E $ they are anisotropy ions and have not only a high anisotropy effect but also relatively small magnetic losses,

The added amount x of Eu or Sm should be within a predetermined range. When the condition is between 5500 and 1300 Gauss, x is required to be in the range of about 0.5 to about 2.0 in order to allow a stable presence of the magnetic bubbles.

When x becomes less than 0.5, the anisotropy energy becomes insufficient, making the magnetic bubbles unstable and preventing their stable transfer.

If x is greater than about 2.0, then the magnetic callers are stably present, but their transfer becomes difficult and a high transfer rate is impossible.

Since Gd, Yb and Tm also exhibit anisotropy, they can be used to obtain a desired desired enisotropy energy in conjunction with Eu and Sm.

However, when the amount of Gd added exceeds 0.5 mol per molecular formula, the temperature dependence of 4 µg increases and the temperature characteristics deteriorate. It is therefore necessary to avoid adding more than 0.5 mol Gd ·

When the amount of Eu exceeds 1.5 mol per molecular formula, the bubble saturation rate becomes small; preferably, Eu is added to 1.4 · Since Sm this. adverse phenomenon 7907616 - 7 -

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the quantity thereof may be greater than 1.4 mol.

Example I

As starting material, oxides, for example 0.5 ^ S TgO ^, 0.87 S SnigO ^, 16 g Fe2 O3 and ° 4 ^ Al § and a flux 5, for example 230 g PbO and 4.6 g B ^ O ^ are heated and homogenized at 1200 ° C for 10 hours in a platinum crucible, and then grown axially in a liquid phase on a Gd ^ Ga ^ O ^ one crystal for 3 min, at 920 ° C. The resulting garnet film has the following properties) IQ Film thickness (h) «bubble diameter (d)» Q, 8 μη characteristic length (l) - 0.09 μη Curie temperature (Tc) 180 ° C.

A - 2.0 x 10-7 ea? A / cm> 4 ^ 3 reduced to JQQG, magnetic wall mobility μν - 250 cm / s.0e, 15 Hk - 1500 Oe.

It has been found that when the bubble element is formed from such a material, a rapid transfer of the bubbles is possible and that the bubbles are sufficiently stable. The primitive force Hc is quite small, 0.80 Oe and the memory has excellent features.

Example II

The liquid phase growth is carried out in the same manner as described in example I, with as starting materials 1.2 g SnigO 0.6 g 16 g Fe ^ 0 ^ and 0.3 g AlgO ^ and a ^ oj ^ part 250 g 25 PbO and 0.5 g B ^.

The resulting garnet film has the following properties: h »d 0.5 μη, 1 0.056 μη, Curie point Tc» 220 ° C, A «2.5 * 10“ 7 erg / cm, 4 * Τ ^ 3 * 950G, μw ** 180 cm / s.0e, 30 Hk - 1700 0e.

It has been found that a magnetic bubble element with a very high density can be obtained with such a grenade film} the bit period is 4 μη.

Example III

The liquid phase growth is performed in the manner as 7907616-8-y. λ described in example I with as starting materials 0.85 g ^ 2 ^ 3 * 0.80 g SmgQj, 1.2 g TmgOj, 15 »5 g and ° * 28 g AlgOj and as flux 255 g PbO and 4« 7 g Β2 ° 3 * The result ',; er®nd-e grenade film has the following properties: 5 h 0.6 μη ,, d «0.4 μη, 1 - 0.05 μιη, Tc» 210 ° C, Δ 2.4 x 10 7 erg / cm, 4T0 £ s - 9000,

It is possible to lower 4Nis over 200G compared to the conventional film in which the same bubble diameter is possible. Since the film uses Eu, Sm and Tm, each of which exhibits a considerable anisotropy effect, Hk may be equal to 2000 ° and the bubble is sufficiently stable.

Example IV

A garnet film with a composition in the molten state as indicated below and grown epitazially on a Gd ^ Ga ^ 15 0 ^ 2 one crystal exhibited the composition jgSm ^ ^ Bd ^ 32 * e4. 38A1q g2012 * d-e bubble diameter at room temperature is 1.0 μη at a film thickness of 1.0 μη. The saturation induction 4 * $ Is of the grenade film is 665G; this is a particularly low value for a fine bubble grenade film. Since this garnet film contains a small amount of Gd, the temperature dependence of 41 X ^ 3 has been reduced. The temperature dependence ratio of the bubble collapsing field is over a temperature range of 0 to 100 ° C between -0.19 and -0.23 $ / ° C. This film has excellent temperature properties.

The composition of the grenade is: 25 (Y203 ...... 0.738 g

SmgOj ....... 0.592 g

GdgOj ....... 0.213 g

Pe203 ....... 15.97 g A1203 ....... 0.537 8 30 Flux

PbO ......... 222 g B203 ........ 4.44 g

As in the other cases, the single crystal film of the invention is formed by epitamial growth on a GdjGajO ^ 35 single crystal.

790 7 6 1 5 λ. 3 - 9 -

The film thickness (h) is chosen so that it is substantially equal to the diameter (d) of the slopes to be formed and the range of the ratio d / h is between 0.5 and 2.0 *

The film according to the invention is particularly suitable for forming bubbles therein and a diameter smaller than 1.5 μη and the. maximum film thickness will generally be about 1.5 μη * It is difficult to obtain a uniform film with a thickness less than 0.3 μη using liquid phase epitaxial growth and, since the properties of a magnetic bubble memory element formed from 10 varying a film of such thickness will preferably use a film thicker than 0.3 μη.

7907616

Claims (4)

Grenade film intended for use in a magnetic bubble memory element with a composition determined by the general formula rI R ** FeR Ai O10 3-xx 5-yy 12, characterized in that R * is at least one element 5 selected from the group including Y, Gd, Yb, Tm, Lu and La; at least one element is selected from the group comprising Sm and Eu, and the values of x and y satisfy the relationship 0.5 <x <2.0, 0.2 <y <0.9 while when as R ^ Gd is used, the amount of Gd does not exceed 0.5 per molecular formula »10 Grenade film according to claim 1, characterized in that the thickness of this film is between about 0.3 and 1.5 µm, 3. Grenade film according to claim 1, characterized in that it is voided on a Gd ^ GagO ^ one crystal »15 Grenade film according to claim 1, characterized in that the amount of Eu per molecular formula is up to 1.4 mol »7907616