NO146381B - MAGNETIC DOMAIN DEVICE - Google Patents

Description

The invention relates to a magnetic domain device with aids for influencing such domains in a magnetic medium.

Amorphous materials are known in the art and can generally be classified as metals or non-metals. The metals are described either by means of the Bernal model (where close arbitrary packing exists) or by means of microcrystalline models. Amorphous metallic materials include Pd-Si-

and Mn-C alloys.

Non-metallic amorphous materials are usually

covalently bonded and the "ovonic" materials (based on the Ovshinsky effect) are an example of such materials. Non-metallic amorphous materials are e.g. Si02_> Si, Ge and Ge-Te alloys.

Non-metallic amorphous materials have been utilized

for various applications including beam-addressable information storage, which appears in US patent document no. 3,530,441. However, this prior art does not include applications of amorphous magnetic materials with uniaxial anisotropy in such applications as magneto-optical devices and bubble domain systems. Nor is the use of amorphous magnetic materials such as permanent magnets known in the art. Such materials should be valuable in many applications in this area. E.g. amorphous materials can be deposited on any type of substrate and they do not have to match the lattice structure of the substrate. Furthermore, inherent substrate effects are not detrimental to the properties of the subsequently deposited amorphous material.

Additional advantages of amorphous materials include

that the composition can be adjusted to optimize the properties without the limitations caused by the stoichiometry of the compound.

This means that limitations caused by the phase diagrams

for the materials to be connected, are not relevant when amorphous materials are to be produced. Furthermore, amorphous materials can be produced at low temperatures and by simple techniques such as evaporation, electrode sputtering, etc.

Especially when it comes to magnetic amorphous materials

no such structural defects occur in the amorphous materials which could damage the movement and nucleation of magnetic domains in the material. Furthermore, these materials can have connections that vary within large areas to improve the selected magnetic properties. The addition of disturbance agents to the connection does not adversely affect the structural or magnetic properties of the layers and can be used to achieve greater flexibility in the design of the connections.

Amorphous films containing multicomponent systems

is treated in the literature. E.g. Sawatzky and others describe in Journal of Applied Physics, 42, 1 January 1972 on page 367 the type of films which are amorphous by electrode sputtering and then crystalline after a curing process. In another article in Material Science Research, Volume 4, 1969, E. Giess and others describe on page 493 gadolinium-iron garnet films with a crystal size between 30 and 50Å. A ferromagnetic amorphous film consisting of an Fe-C-P alloy is described by Duwez and others in the Journal of Applied Physics, 38, 10 September 1967 on page 4096. The amorphous films described in the above publications do not have uniaxial magnetic anisotropy.

Amorphous magnetic films of FeGd are described by

x y

J. Orehotsky in Journal of Applied Physics, 43, 5- May 1972 at

page 2413- In order to explain the non-saturation of these films, the authors propose the presence of right-angle anisotropy, originating from an isotropic stress in the plane of the film.

In connection with the present invention, it has been established that uniaxial anisotropy can be induced in amorphous magnetic films and that anisotropy can be provided as a result of substrate limitations. This means that uniaxial anisotropy can be provided by pairing or by reduced anisotropy. The relevant amorphous compositions may consist of only one element or several elements. Use of these amorphous magnetic compounds in device applications eliminates many of the disadvantages of prior art, where crystalline magnetic material must be used.

The purpose of the invention is to provide a device of the type mentioned at the outset whose domains can be easily propagated without regard to structural defects or contamination in the medium, and which can be produced in a simple way, and at a reasonable price.

This is achieved according to the invention in that the magnetic medium, in which these domains exist, is an amorphous magnetic material with non-magnetocrystalline, uniaxial anisotropy.

Further features of the invention will appear from claims 2-18.

The invention will be described in more detail below with reference to the drawings.

Fig. 1A shows an electron beam micrograph of the deflection pattern for an amorphous magnetic composition according to the invention. Fig. 1B shows an electron beam microphotograph of the deflection pattern for the same material after it has been hardened with the intention of imparting a crystalline structure to the material. Fig.

2A and 2B are photographs of magnetic stripe domains in the amorphous material of FIG. IA, which photographs show the movement of the magnetic domains when the amorphous material is exposed to a magnetic field. Fig. 3A shows a curve for the magnetization 4irM as a function of the cobalt concentration in an amorphous Gd-Co alloy.

Fig. 3B shows another curve of the magnetization 4irM as a function of the composition of the amorphous Gd-Co alloy used to indicate the change in magnetization that occurs

when dopant is added to the amorphous material. Fig. 4A shows

a curve for the inverse characteristic length

which func-

tion of the cobalt concentration in the amorphous Gd-Co alloy. Fig.

4B shows a curve for the length L as a function of the thickness of the magnetic film according to the invention. Fig. 5 shows a curve for the domain boundary energy (4ttow) as a function of the electrode sputtering bias applied to the substrate during the deposition of an amorphous magnetic alloy according to the invention. Fig. 6 shows a curve for the deposition rate as a function of applied high-frequency energy for electrode sputtering of amorphous magnetic alloys, which curve shows the effect of an applied magnetic field of approx. 500 during the deposit process.

Fig. 7 shows a curve for the anisotropy Ku for an amorphous uniaxial magnetic layer as a function of the thickness of the magnetic layer. Fig. 8 shows a curve for the deposition rate on a logarithmic scale as a function of the inverse substrate temperature, which curve illustrates the amorphous-crystalline transformation that occurs at certain deposition conditions. Fig. 9 shows a block diagram of a magnetic bubble domain system using the amorphous magnetic materials as the bubble domain material. Fig. 10 shows schematically but in more detail part of the circuits in fig. 9. Fig. 11 shows schematically and in perspective a magneto-optical light modulator where the relevant amorphous magnetic materials are used as light modulating medium. Fig. 12 shows in perspective a magnetic bubble domain material with an adjacent layer of amorphous magnetic material which acts as a biasing layer for magnetic domains in the bubble domain material. Fig. 13 likewise shows in perspective a tape- or plate-based information processing system where available amorphous magnetic material is used as a recording medium.

Mainly amorphous magnetic compositions having uniaxial anisotropy have been produced and can be used for many magnetic purposes. These compositions can be produced in mass or thin film form, or they can occur as magnetic particles in a supporting binder. When it comes to amorphous materials, the choice of substrate plays no role and factors such as lattice adaptation can be considered irrelevant. This simplifies deposition on substrates of any type, and it greatly increases the profitability of production when materials of the relevant type are used.

These magnetic compositions can consist of a single element or a combination of elements occurring in a multi-component system. At least one of the components must have unpaired electron spin so that the composition acquires a magnetic moment. This means that these are magnetically ordered materials.

These amorphous magnetic materials have a uniaxial anisotropy which may be perpendicular to or parallel to the plane of a film containing these amorphous magnetic compositions. The anisotropy originates from combinations of the following phenomena or one of them:

A. Pair arrangement

B. Shape anisotropy

C. Strain-induced anisotropy.

In the present invention, it is not important that uniaxial anisotropy is achieved in a special way.

The three phenomena mentioned above for providing uniaxial anisotropy in mainly amorphous films according to the invention are generally known in the art and shall not be described in detail here. It should be sufficient to point out that pair arrangement includes combinations of two atoms whose magnetizations pair to form magnetic dipoles. The magnetic pairs are oriented in specific directions which result in the uniaxial anisotropy which is necessary for use in magnetic devices.

Shape anisotropy occurs as a result of the magnetic regions* geometric shape. E.g. will an ordered mass of atoms in an area of mainly disordered material acquire a magnetization which is directed along the longitudinal axis of the mass, as this axis is the preferred one for orientation of magnetic moment. Along the short axis in the area defined as the atomic mass, strong demagnetization fields appear.

Furthermore, compositional variations in the amorphous material provide phase separations which causes this type of anisotropy. Phase separation applies to both the state of the individual compositional areas that are close to each other and the state of nearby areas of the same composition with different structural phase, i.e. that one area is amorphous at the same time as another is crystalline. As an example of phase separation, an amorphous magnetic Gd-Co alloy that can consist of local Co-rich areas and other local GD-rich areas can be mentioned. If these areas occur adjacent to each other, the phase separation will provide uniaxial anisotropy.

Stress-induced anisotropy originates from differences in the lattice parameters of the substrate and local areas in the amorphous film or also from differences in thermal coefficients for the amorphous film and the substrate. This type of strain can also become a participant. end factor when it comes to uniaxial anisotropy in the mainly amorphous films according to the invention.

Amorphous magnetic compositions according to the invention have microcrystalline and/or mainly amorphous structure. Both of these structures differ from polycrystalline and monocrystalline structures known in the art in connection with magnetic compositions. E.g. can the amorphous materials according to the invention have local atomic arrangement. If, however, this atomic arrangement occurs, it exists over distances of between 25 and 100 Å if the material is microcrystalline and below 25 Å if the material is mainly amorphous. It is therefore understood that no significant atomic arrangement can also occur and in that case it is a mainly purely amorphous material.

Amorphous material according to the invention consists of simple magnetic elements or multi-component systems. An example of the latter system is binary or ternary alloys or compositions. Particularly suitable materials are compositions containing rare earth species and metals with state transitions. Gd-Co, Gd-Fe, Y-Co and La-Co can be mentioned here. These compositions can be varied over a large area without the stoichiometry of the composition causing limitations as a result of the phase diagram of the components. Therefore, the magnetic properties of the materials can be specially designed for each individual embodiment. E.g. the composition ranges can be chosen so that the atomic moments for rare earths and metals are practically equalized so that the material gets a small saturation magnetization, which is particularly valuable for a bubble domain material.

These amorphous magnetic compositions have longitudinal magnetic ordering and have uniaxial anisotropy. In their simplest form, they consist of elements that have a magnetic moment. An example of this is the 4f series (rare earth elements) and the 5f_series (actinide elements). Furthermore, the iron group of transition metals of the 3d series is included. In addition, there are elements that have a magnetic moment when they are in a special state, e.g. the elements Mn,

Cr, V and Pd.

For each amorphous composition consisting of a single element, it applies that an arbitrary non-magnetic element can be added in relatively small quantities - without the magnetic properties being disturbed. This means that a dilution with non-magnetic elements, e.g. 0,C,

■i

P and N can be made without adversely affecting the magnetic properties. - Therefore, it can be advantageous to add small amounts"1 usually about 2 atomic percent, of these non-magnetic elements to simplify the production of the amorphous film. If large amounts are added, affected of course the magnetic properties.For example, amounts greater than about 50 atomic percent can disrupt the magnetic arrangement.

Binary compositions which comprise at least one of the previously mentioned elements can also be used for the amorphous magnetic materials according to the invention. Binary compounds are usually easier to work with because they retain their amorphous structure over larger temperature ranges than amorphous single-element magnetic materials. As with amorphous single-element materials, small amounts of non-magnetic elements can also be added to the composition.

Another change that can be made to binary amorphous compositions is the addition of a greater concentration, 2-50 atomic percent of non-magnetic elements to vary the magnetic properties. E.g. cups can be added to weaken the magnetic element.

Ternary compositions of the above-mentioned 3d, 4f and 5f elements can also be prepared to obtain amorphous compositions with uniaxial magnetic anisotropy. As with the binary elements, larger concentrations of non-magnetic material can be added to change the magnetic properties of the ternary compositions. Likewise, small amounts of non-magnetic material can be added to

it should be easier to form amorphous films without adversely affecting the magnetic properties. It is understood that the amount of non-magnetic material that is added is insufficient for the magnetic order in the amorphous film to be lost.

The amorphous magnetic materials according to the invention have

highly magnetic order and are either ferromagnetic, ferrimagnetic or antiferromagnetic. Naturally, it is the magnetic arrangement that gives the uniaxial anisotropy that occurs in these materials, which in turn makes the material very useful for device use.

The magnetic properties of these compositions can be changed during manufacture or after manufacture to adapt to particular embodiments. It has been established that the magnetic properties are highly dependent on the composition range of the components and also on the deposition conditions that occur during the preparation of the composition. However, the dependence of the magnetic properties on the deposition parameters is less than the dependence on the composition ranges of the constituents. Processes such as hardening and ion implantation can be used after the production of these amorphous compositions to modify the magnetic properties. Furthermore, these magnetic materials can be doped with doping agents without the structural magnetic properties of the films being adversely affected. Therefore, the magnetic domain movement in the films is not affected, which is the case with ordinary crystalline magnetic films. Examples of particularly suitable amorphous magnetic compositions are the following applications and tables of materials and their properties at the end of the description.

Depending on the alternating interaction that occurs between these materials, it should be possible to provide insulators, conductors and semiconductors that are mainly amorphous. In metals and semiconductors, such alternating interaction can either be direct as a result of overlapping atomic orbitals or indirectly depending on conduction electrons. They are mechanisms that make amorphous material suitable for magnetic application. However, the switching mechanism in insulators is critically dependent on the bond angles and bond distance. As longitudinal magnetic order does not occur in amorphous material, these exchange conditions cannot be met and no magnetic order can be observed.

Fig. IA and IB are electron beam micrographs illustrating amorphous and crystalline material. The electron deflection pattern in fig. IA is characteristic of an amorphous material while the deflection pattern in fig. IB is characteristic of a crystalline material.

More specifically, fig. IA and IB prepared by electron deflection from <n>a'Gd-Co alloy. The solid line L in fig. IA and IB are used to block the incident electron beam to facilitate the framing of the photos. The deflection pattern in fig. IA is characteristic of an amorphous material.

Fig. 1B is an electron deflection pattern for the material Gd-Co in fig. IA after this has been crystallized by the application of heat. In this case, the amorphous film of FIG. IA retained in the electron beam microscope and heated to approx. 300°C. The deflection pattern in fig. IB is characteristic of the deflection in a crystalline material. Both fig. IA and IB are on the same scale. Both figures mainly illustrate amorphous properties of films produced according to the present invention.

Fig. 2A and 2B show the presence of magnetic stripe domains in the amorphous material according to Fig. IA. In Fig. 2A

and 2B, the reference marking M is written into the film and this marking is used to determine the movement of the stripe domains when a magnetic field is applied to the amorphous material.

In particular in fig. 2A, the magnetic stripe domains D are clearly visible on the amorphous magnetic material. These stripe domains have boundaries generally oriented in the vertical direction of the figure. However, when a magnetic field is applied in the plane of the amorphous material, the strip domains D are inclined. This becomes clear when the position of the domains D in relation to the reference marking M is examined in both figures. Thus illustrates fig. 2A and 2B the presence of domains in the amorphous magnetic material and the movement of the domains as a result of an applied magnetic field. As it will appear

of explanation below, the strip domains D can be made to break the seam into round bubble domains.

Amorphous films with a thickness of approx. l^um is deposited on NaCl, SiO2 and Al20^. These films have uniaxial anisotropy and have

also strip domains. A magnetic field of a few hundred 0 applied at right angles is sufficient to cause the stripe domains to collapse into round bubble domains. Furthermore, the bubble domain is moved when the external magnetic field is moved. The domain pattern in the amorphous material resembles the domain patterns that can be observed in carefully prepared garnet films. This suggests that the amorphous material mangles local inhomogeneities, which is sufficient to provide local retention of domains that would limit the domains' movement. Naturally, this is an advantage in an amorphous magnetic material where crystal structure effects, by definition, do not exist. Nucleation and propagation of magnetic domains in such an amorphous material is not limited by this type of defect.

Depending on the particular application where these amorphous magnetic compositions are to be used, the said magnetic properties are adjustable for optimal results. The regulation of the magnetic properties in these amorphous materials is easily achieved by means of specific methods during the production of the amorphous materials and by means of processes that are utilized after the amorphous compositions have been produced. In contrast to previously known crystalline magnetic materials, the magnetic properties of amorphous films are generally easier to control than corresponding properties in crystalline material. One reason for this is that the compositional variations that are permitted in an amorphous material are much wider than the permitted variations in a crystalline material, because amorphous compositions are characterized by metastability rather than by thermodynamic equilibrium. Different magnetic properties will be treated separately to illustrate the flexibility that amorphous material offers.

Saturation magnetization Mg.

The magnetization is easily changed in an amorphous magnetic material by the addition of a magnetic atom which couples with a normal magnetic atom in the amorphous material, or an atom in the amorphous material which is magnetic in a certain state, e.g. Mn, Cr, etc. To reduce the magnetisation, the material to be added to the amorphous composition is coupled antiferromagnetically with the magnetic atoms in the amorphous material. To reduce the magnetization in amorphous Gd-Co alloys, e.g. the ratio Gd/Co so that the material's magnetic moment is virtually eliminated.

To increase the magnetization in an amorphous material, magnetic atoms are added to the composition which couple ferromagnetically with the magnetic atoms in the amorphous composition. E.g. addition of Nd to an amorphous composition of Gd-Co provides an increase in the magnetization of the composition. As another example, the addition of Co to an amorphous composition of Y-Co increases the magnetization.

These additions are made during production and are carried out in the following manner. A mixture of the components is melted and cast into a disc-shaped plate to be used as a target for electrode sputtering. The composition can be regulated during target preparation or the composition of the film can too. is varied during the atomization process by means of regulation of the bias voltage on the substrate for preferred re-atomization of a part of one or more of the components. Alternatively, a second measure of the additive element can be placed in the atomization system so that one of the additive elements is introduced into the deposited film.

When thin films are produced by vacuum evaporation, the concentration of the additive can be varied in the evaporation source or a supplementary source of the additive element can also be used.

In fig. 3A shows a curve for the magnetization at room temperature as a function of the concentration of cobalt in an amorphous Gd-Co alloy. From this curve it appears that the amount of magnetis. atomic Co in the amorphous alloy determines the alloy's magnetization. As a result, the alloy's magnetization changes when material is added to the amorphous alloy, which changes the Gd/Co ratio and thus the degree to which the material's magnetic moment is cancelled,

The composition range close to the magnetization minimum is particularly suitable for material with a low magnetic moment and a high Curie point. Because the low magnetization for compositions near 79 atomic percent cobalt originates from a lowering of the Gd-Co moments rather than from dilution effects, the Curie point, which is largely determined by Gd-Co interaction, is not affected. Consequently, the magnetization of the material at room temperature can be changed while maintaining Tq within certain limits.

Another way to change the magnetization of an amorphous alloy is to add small amounts of N^ when the amorphous alloy is electrodeposited. When e.g. GdGOj electrodes are sputtered in argon,

if small amounts of N2 are added (approx. 1 volume percent N2 in the argon gas), the stripe domains in the material will decrease markedly in size. This in turn indicates an increase in the magnetization 4 Ti Mg. This means that the antiferromagnetic coupling of Gd and Co

is affected so that the magnetization increases without the amorphous material's ..anaxial anisotropy being increased. Nitrogen binds with Gd and this reduces the antiferromagnetic coupling between Gd and Co. The moment for the Co"-"'' sublattice is less effectively canceled by the Gd sublattice moment so that the magnetization increases.

Fig. 3B shows a curve of the magnetization Ms in arbitrary units as a function of the composition for the amorphous Gd-Co alloy also in arbitrary units. This is a minimum of magnetization at a certain composition of Gd-Co.

If the Gd-Co composition is normal for composition A and the composition is prepared in the presence of N2, a shift in the magnetization appears as if an increase in the cobalt content were to occur. Therefore, the magnetization becomes larger. If, on the other hand, one starts with a composition C and adds nitrogen, the magnetization of the produced film will change towards a minimum. Therefore, the magnetization Mg can be changed by simply adding Ng to the material to change the exchange connection between the constituents in the composition to higher or lower magnetization in accordance with where one is on the magnetization composition curve for this material.

Coercive force H .

c

The coercive force in the magnetic material is a primary factor in determining the possibility of moving magnetic domains in the material. Adjustments with respect to the coercive force usually involve changing the magnetic material's grain size because the coercive force is dependent on the grain size. Generally speaking, the coercive force•is maximum for a certain value of the grain size and decreases for grain sizes smaller than and larger than what gives the maximum coercive force. E.g. the coercive force is large in magnetic material where the grain size approaches the domain boundary width.

The grain size can be affected by the addition of the doping material such as e.g. NgOg. These additions change the magnetic order in the amorphous film so that it becomes different from or equal to the domain boundary width £ . If 6 is greater than the arrangement,

is H c small because if £ is equal to order D en H c is maximal,

Ion implantation to a certain depth is normally advantageous when it is not desirable to heat the amorphous material. Heating above a certain temperature changes the amorphous material to the crystalline state which may not be a reversible state. Curing for crystallization of the amorphous film to provide grains of the desired size can also be used.

Other methods to influence the coercive force include surface treatment such as e.g. sputter etching and ion etching to make the surface structure uneven. This affects on

in turn, the movement of the domains in the amorphous magnetic material. Curie temperature Tc.

c

Such amorphous magnetic materials are easy to alloy

to increase the Curie temperature without affecting the material's structure

in an unfavorable direction. Accordingly, no limiting effect is exerted due to a phase diagram as is the case for crystalline material. Alloy area with a large extent of approx. 50 atomic percent) can be used as long as the uniaxial anisotropy in the material is not affected. In general, the Gurie temperature follows linearly the amount of magnetic atoms present. The Curie temperature in these amorphous materials is easier to control than in crystalline magnetic materials.

The alloying conditions are used to change the Curie temperature in amorphous magnetic materials. For example, an amorphous Gd-Co alloy added to magnetic atoms with less torque, e.g. Ni, Cr, Mn or non-magnetic atoms e.g. Cu, Al, Ag, Pd, Ga, In, etc. lower the Curie temperature while addition of

an element such as Fe increases the Curie temperature. The strength of the magnetic coupling in the material is changed by the added elementsr Faraday rotation 0„r.

Increased Faraday rotation or Kerr rotation in a light beam falling on amorphous magnetic material is achieved by amorphous material with a strong magnetic moment. Doping material in the form of rare earth species, e.g. Tb, Dy, Ho, can be added to the amorphous material or alloy additions can be added to the material. When it e.g. for the amorphous Gd-Co alloy, increasing the amount of Co will mean increased Faraday rotation. Also adding Fe to the material will increase the Faraday rotation. For high Faraday rotation, it is desirable for the magnetization 47TM to have as large a value as possible (eg 8000 - 10000 Gauss).

Characteristic length (L parameter).

The parameter L is a quantity that is particularly applicable when designing magnetic bubble domain systems. A more detailed description of this parameter has been made by A.A. Thiele in Journal of Applied Physics No. kl page 1139 (1970).

The parameter L is very dependent on the extent of the constituents in the amorphous alloy. Thus shows e.g. fig. Have variety

tions in the parameter L (more precisely

as a function of

the magnetic ion concentration in an..amorphous magnetic alloy. In this particular case, the composition is Gd-Co and the horizontal axis is the Co concentration. From this it appears that the parameter L can be varied by changing the composition of the amorphous alloy. The curve in fig. 4A is plotted for different compositions of Gd-

Co where all manufacturing parameters are kept constant for each individual sample. The same compositions produced under other conditions have different values for the parameter L. As a result of the fact that the composition range for an amorphous material can easily be varied within wide limits, which deviates from the relationship for crystalline magnetic material,

it is relatively easy to vary the parameter L.

Fig. 4B shows the parameter L depending on the thickness H of the amorphous magnetic layer. Below a critical thickness for each composition, sufficient right-angled anisotropy cannot be achieved to support the bubble domains and therefore the curve is shown with a dashed line below the critical thickness. For the special composition in question here, 20 atomic percent Gd and 80 atomic percent Fe,

a thickness of 0.2yum provides sufficient right-angle anisotropy to promote the bubble domains.

Domain boundary energy <s .

w

The Dbmene limit energy a was related to the L parameter of the amorphous material. The domain boundary energy is also directly proportional to ^~^u where A is the material's exchange constant and Ku is the material's uniaxial right-angled anisotropy constant.

Fig. 5 shows a curve for the domain boundary energy kTTø wi erg/cm measured as a function of the substrate bias used during the electrode sputtering of amorphous Gd-Co alloys containing 80-85 atomic percent Co. This substrate bias is a voltage on the substrate measured in relation to earth. In the direct current electrode atomization device used to produce the curve of fig. 5, it is printed approx. 2000 volts between the anode and the cathode to provide the deposition of the amorphous Gd-Co composition. Application of substrate bias enables control of the deposition and the magnetic properties of the deposited amorphous material. In this way, the domain boundary energy can be varied within a wide range. The domain boundary energy can also be changed by changing the exchange constant A or the anisotropy K . The exchange constant A represents the strength of the magnetic coupling in the material and is proportional to the Curie temperature T . Consequently, the constant A varies from one material to another. Changes in anisotropy will be discussed below.

Anisotropy K .

The material's anisotropy can be varied by changing the method used to produce the amorphous composition. E.g. the composition is a decisive factor as is the thickness of the deposited film. Generally speaking, Ku is a function of the material composition and structural conditions. These factors shall be described in more detail below.

Domain size and domain border width.

T/7T

The domain boundary width is equal to v — Ku Where A is the exchange constant of the material and Ku is the anisotropy of the material. As previously mentioned, the anisotropy Ky depends on the thickness of the amorphous film and on the deposition rate. Therefore, the domain boundary width £ can be varied by changing the anisotropy K . This, in turn, is a function of the composition of the amorphous layer, its range of constituents and of the deposition method used in the preparation of the amorphous material. In the part of the description that concerns production methods, there are curves illustrating the variation of anisotropy Ku with the layer thickness and the deposition rate.

The domain size is a function of the characteristic length L and the thickness of the film. In general, the domain size is chosen so that the desired effect is optimal. For magnetic bubble domain systems, the characteristic length L is given by the equation:

Consequently, the characteristic length and thus the domain size can be changed by changing the magnetization M s , the anisotropy K u and the exchange constant A.

The exchange constant is a quantity that represents the strength of the magnetic coupling in a certain material. It is proportional to the Curie temperature and is greater for materials that have a higher Curie temperature T . As mentioned earlier, the anisotropy Ku is a function of the material composition and the other conditions used in the production of the material. The magnetization Ms originates from magnetic spins and their orientation (parallel or antiparallel). This size is temperature-dependent and can be varied by changing the composition of the amorphous film and the parameters relevant to the production of the amorphous film. Therefore, the domain size can be easily changed within wide areas. Manufacturing methods.

The amorphous magnetic materials can be produced in mass form or thin film form. In general, any known film deposition technique can be used including electrode sputtering and evaporation.

For the preparation of a bulk film of amorphous magnetic material, immersion cooling can be a useful method. In this way, the film components are heated and spread out in liquid form on a cold surface so that the components solidify and form an amorphous mass film. This results in rapid solidification from the liquid phase.

Uniaxial anisotropy can be provided in pulp films by subjecting these to atomic bombardment in an applied magnetic field or by curing in a magnetic field at a temperature below the crystallization temperature of the film. Another method of providing bulk film is continuous evaporation.

The production of thin amorphous film according to the invention can take place by deposition from the vapor phase, rapid cooling from the liquid phase or ion implantation to adjust the anisotropy. Usually, these amorphous films depend on the rate of deposition of atoms on the substrate, the temperature of the substrate and the angle of incidence of the atoms that are deposited on the substrate. If the incoming atoms are unable to achieve a certain equilibrium state, the tendency to form amorphous films increases. In this connection, reference should be made to "The Use of Thin Films in Physical Investigations" by S. Mader published by J.C. Anderson (Academic, New York, 1966) page 433. See also U.S. Patent No. 3,427,154 relating to the preparation of amorphous thin films.

To promote pairing as a means of providing uniaxial anisotropy in these films, it appears essential that the deposition atoms strike the substrate at an angle of incidence other than 90°. This means that the incident atoms must have a certain velocity component parallel to the substrate surface to achieve uniaxial anisotropy in the film. Such an angle gives an atomic movement parallel to the substrate, which in turn promotes pairing because the incoming atoms can move and choose a position that lowers the energy in the system via the material's demagnetization field. Phase separation is promoted, and this leads to the formation of anisotropy because clusters of similar atoms are grouped together at a place where the energy in the system decreases. This, in turn, leads to compositional groupings and, as previously mentioned, these lead to anisotropy in the film.

Another factor in achieving uniaxial anisotropy is the deposition rate of the incoming atoms. If the deposition rate is too great, incoming atoms cannot move to a greater extent on the substrate surface, which limits mobility parallel to the substrate. In this connection, reference should be made to fig. 6 which is a curve showing the deposition rate in Å per second as a function of high-frequency energy used in a sputtering system for the deposition of amorphous material. In this case, the amorphous magnetic material is Gd-Co. In fig. 6 shows a critical deposition rate of 4 Å per second for a specific substrate temperature and composition. This •means that at a deposition rate of 4Å per secondly, the relevant Gd-Co-r test, which contains approx. 80 atomic percent Co, have a domain pattern characteristic of uniaxial right-angle anisotropy in the amorphous magnetic alloy.

In fig. 6, the deposition is carried out with a magnetic field

of 500 at right angles to the substrate and without the presence of the magnetic field to determine the effect of the magnetic field during the deposition. The effect of the magnetic field is not great, although it improves the efficiency of the atomization to a certain extent.

As the substrate bias used by the sputtering system increases, the anisotropy generally increases. This is because the bias causes incoming atoms to be released from the surface of the film. Consequently, the atoms have more mobility parallel to the substrate surface so that they can reach the desired locations leading to composition grouping or pairing.

Fig. 7 shows a curve for the anisotropy Ku (erg/cm ) as a function of the thickness H of the magnetic amorphous film measured in yum.

For this film of amorphous GdFe material, a critical anisotropy of approx. 1.2 x 10 5 erg/cm 3 to promote the domains in the film, which is expressed in the stabilization state K ~? 27TM.

us This critical anisotropy occurs at a film thickness of 0.2 µm.

For the deposition of amorphous magnetic material, the substrate temperature is kept relatively low. These films can be deposited at room temperature or lower and are normally deposited at a temperature below the temperature that will cause crystallization of the material. E.g. for amorphous Gd-Co material, the upper limit for the substrate temperature is approx. 300°C, i.e. the crystallization temperature.

Fig. 8 shows a curve of the deposition rate on a logarithmic scale as a function of the substrate temperature for Gd-Co and Gd-Fe alloys. From this curve it appears that amorphous magnetic film can be produced over a wide range of substrate temperature depending on the deposition rate. In general, depending on which deposition rate is used, the substrate temperature must be lower than that at which crystallization occurs, in order to provide amorphous magnetic material in accordance with the invention.

Stress-induced anisotropy can also be used for

to provide the relevant magnetic materials. This type of anisotropy can be used together with the other methods, e.g. pairing etc. to achieve anisotropy or stress generation can be used alone. For stress-induced anisotropy, the substrate is selected in relation to the magnetostriction of the film to be deposited in such a way that anisotropy is provided in the amorphous film. The film can be subjected to a certain stress at room temperature if the film and the substrate have different coefficients of thermal expansion.

As mentioned earlier, many substrates can be used. As there is no restriction with regard to crystallographic adaptation when producing amorphous films, the choice of substrate is completely free. These substrates can consist of any known materials such as metals and insulators, and also semiconductors. Non-rigid substrates, e.g. plastic can also be used.

Films with in-plane anisotropy can be changed to films with perpendicular anisotropy by hardening. E.g. changes hardening of Gd-Co films at approx. 300 - 400°C from in-plane anisotropy to right-angled anisotropy. As the film thickness increases, the probability of perpendicular anisotropy naturally increases. E.g. have Gd-Co films with a thickness of at least 2000Å normal perpendicular anisotropy.

The amorphous magnetic materials according to the invention can be used for a myriad of applications, e.g. in bubble domain systems, beam addressable archives, light modulators, permanent magnets and recording media on tape and disc. Each of these applications must be treated together with the associated parameters.

Bubble domain systems.

In the case of magnetic bubble domain systems, it is important that sizes 4 M look small and that the material has uniaxial, perpendicular anisotropy. Furthermore, the goodness-of-fit factor Q = H cL M7TM should be much greater than one, where

H a is the uniaxial anisotropy magnetic field and M is the material's saturation magnetization. Furthermore, the coercive force HQ for the material should be small to facilitate the movement, nucleation and breakdown of the magnetic domains in the amorphous magnetic material. As the goodness-of-fit factor Q should be greater than one to provide stable bubble domains, systems with weak magnetization are usually used, because it is difficult to provide strongly induced anisotropy fields H a.. In ferromagnetic systems, it is possible to reduce the magnetization Ms by dilution with a non-magnetic element , but because the magnetic Curie temperature follows the magnetization, a sufficiently small value of 4n^M can be obtained in alloys with a working temperature close to the Curie temperature.

Low magnetic moment with high arrangement temperature like this

that the amorphous material becomes suitable for use, and which works at room temperature, is achieved in a ferromagnetic system containing two or more species of magnetic atoms with opposite spins. This type of order is achieved in amorphous rare earth alloys, primarily transition metals. Amorphous alloys of rare earth metals, e.g. Go^ Co^ " of suitable composition can be provided where the atomic moments of the rare earth metal and the metal nearly cancel, leading to a material with a suitably low value of 4 ff M .

pp

Suitable examples are Gd-Co alloys with 70-90$ Co and

amorphous Gd-Fe alloys with 70-90$ Fe. In the case of thin film shapes, the anisotropy is provided either by strain, pairing or shape anisotropy.

As previously mentioned, usually little coercivity is required

force Hc for bubble domain material. Consequently, the bubble domain boundary width should be such that, on average, the same mean potential prevails everywhere in the amorphous material. The size é should be approximately equal to or somewhat larger than the type of atomic arrangement encountered in the amorphous material. If local deviations (phase separations, grain size, etc:) in the amorphous material are smaller than the boundary width 6 >, the effect of this is negligible for the domain boundary movement. Furthermore, microcrystals of the order of 25-100Å are not necessary-

appear harmful to the domain movement. Until the grain size in the amorphous material reaches the boundary width 6, the coercive force H is cliten.

The domain boundary width 6 follows the Curie temperature Tc

because the exchange constant A follows T o W=A). If large domain boundary widths are desired, it is therefore necessary to provide large switching constants. However, the boundary width cf should not be too large because the anisotropy energy increases, which has an unfavorable effect on mobility. For amorphous bubble domain material, it is normally desirable to provide a low cutoff energy <? W, which means that materials with a low Curie point Tc should be used. As previously mentioned, amorphous magnetic materials can be easily alloyed to change the Curie point. The limitations regarding the Curie temperature T c for amorphous bubble domain materials are essentially the same as for crystalline bubble domain materials. However, it is easier to control the Curie temperature Tc in an amorphous magnetic material than in a crystalline material.

The choice of substrate is free when amorphous magnetic bubble domain materials are used. Suitable substrates include

ter semiconductors insulators and metals e.g. NaCl, glass, SiO2, Si,

Ge, GaAs and AlgO^. A particularly suitable amorphous magnetic film consists of GdGo^ which is electrodeposited on a NaCl substrate. This electrode sputtering takes place from an arc-shaped blank of Gd-Co,-, where the substrate is water-cooled at approx. 20 oC and is provided with a gallium coating to ensure thermal contact with the cooling device. Stripe domains are observed using an electron microscope in a film with a thickness of approx. 750Å. The occurrence of ferrimagnetic ordering was observed by heating the sample to the condensation point Tor to disrupt the Gd ordering, at which point in-plane domains were observed. Perpendicular domains formed on cooling to room temperature. The electron deflection pattern was typical of an amorphous material. These magnetic strip domains with right-angle magnetization could be observed in the free-standing film detached from the NaCl substrate, indicating that the anisotropies were not strain-induced, but probably of the pair-order type.

About. l^urn thick films were deposited in separate processes under the same manufacturing conditions on substrates of NaCl, SiOg and cl^ 0. 7. These films -also had stripe domains when observed by means of the Bitter pattern and by means of the Kerr effect. A perpendicular magnetic field of a few hundred 0 was sufficient to cause the stripe domains to collapse into round domains. By moving the external magnetic field, it is possible to move the domains in the amorphous magnetic film. This domain pattern is similar to that observed in carefully prepared garnet films, suggesting that the amorphous material lacks local inhomogeneities, which would be sufficient to cause local retention of the domains. Naturally, this is an advantage of amorphous materials where crystal structure effects do not exist. The magnetic bubble domains;-and their movement are not limited by this type of defect. Fig. 9 shows a magnetic bubble domain system where an amorphous magnetic material 10 is used as medium, which promotes the magnetic bubble domains in the medium. Fig. 10 schematically shows part of the circuits in fig. 9- The embodiment in fig. 9 and 10 only have the task of showing a bubble domain device where the present amorphous magnetic material can be used, and therefore the system itself is not described in detail. Below follows a brief explanation of this bubble domain system using an amorphous material such as e.g. the magnetic medium 10. Fig. 9 shows a block diagram of a storage system using cylindrical magnetic domains (bubble domains), which system provides recording, storage, decoding, blanking and reading. The amorphous magnetic sheet 10 consists of one of the previously mentioned compositions. A suitable material is an amorphous

Gd-Co alloy or an amorphous Gd-Fe alloy. The properties of

the amorphous film required for use in a bubble domain system is mentioned above. The sheet 10 has a biasing magnetic field H perpendicular to its plane to preserve the diameter of the cylindrical magnet domains in the magnetic sheet 10. The biasing field H is provided by a biasing field source 12 which can wet an outer coil. If desired, the bias field can be provided by a permanent magnet layer or another magnetic sheet which is alternately coupled with the magnet sheet 10.

When the domains are to be moved by means of attracting magnetic poles, which consist of magnetically soft material arranged near the magnetic sheet 10, a propagation field H is provided by the propagation field source 14. The propagation field H is a reorientation magnetic field in the plane of the magnetic sheet 10, which field provides attracting and repulsive magnetic poles along the magnetically soft material which is in the vicinity of the magnetic sheet 10. The propagation field source 14 consists of outer coils which are arranged around the magnetic sheet 10 and which are alternately pulsed to provide a magnetic field in the desired direction. In fig. 9 is the propagation field H is rotating magnetic field-which is directed in one of the directions 1, 2, 3 and 4.

Although the bubble domain conditions are to be described in particular in relation to a propagating means comprising magnetically soft material, it is understood that other propagating means e.g. wire loops can also be used. The bias field source 12 and the propagation field source 14 are activated by the field control circuit 16 which supplies current to the sources 12 and 14 to provide the bias field H and the propagation field H.

The domains move in closed paths in each of the 2^ . the shift register. The domains represent binary information in that the presence of a domain indicates a binary 1 while non-occurring domains indicate a binary 0. To each shift register 1,2,...2N belongs a domain generator 18-1, 18-2,...l8-2N. These generators record information in the shift registers in accordance with input signals supplied by recording pulse source 20 to the lines W1,W2,...W2<N>.

If desired, recording decoders can be used together with the domain generators 18-1 etc. for recording information in a selected shift register.

A reading decoder 22 belongs to the shift register. The readout decoder receives 2N input signals supplied from a decoding pulse source 24. Depending on the input signals supplied from the readout decoder 22, any of the slide regions can be selected for information reading.

After selection by means of the readout decoder 2, the information in the selected register passes a dump device 26 which is activated by a source 28. The source 28, the decoding pulse source 24 and the recording pulse source 20 are selectively controlled from the control circuit 30 which supplies input signals to each of these sources to activate them at the right time. The emptying device 26 sends the domains in the selected shift register to one of two paths depending on whether the information is to be read destructively or yoke destructively. If destructive reading is to be used, the domains in the selected register are fed directly to the detector 32 which may be a magneto-resistive reading element, an inductive loop, a magneto-optical reading device or another detection means. The detector includes a domain disruptor that causes the domains to collapse. The output signal from the detector 32 is supplied to a consumer 34 which can be an arbitrary external circuit that utilizes the binary information contained in the selected shift register.

If destructive reading is not relevant, the emptying device 26 directs the domains from a selected register to a domain separator 36-1, 36-2....36-2N. The separator divides the input domains into two parts, one part being supplied to the detector 32 for destructive reading, while the other goes back to the selected shift register for continued circulation in this shift register loop, In fig. 9, the shift register, read/write decoders 22 and blanking device 26 are shown as separate, distinct components for the sake of simplicity, but it is clear that the decoders having a blanking device are integrated into the shift registers. Consequently, the lines 46 and 44 represent the shift register loops 1,2....2N in which the decoders 22 comprising the emptying device 26 are accommodated.

The block diagram in fig. 9 shows a complete storage system of the cylinder domain type where information is selectively recorded in 2 N shift registers for storage. The information content of the shift register can be selectively addressed by means of input signals to the reading decoder 22. Depending on the activation of the emptying device 26, domains in the selected register will be read destructively or non-destructively. If destructive reading is indicated by the blanking device, the domains in the selected register are destructively read - by the decoder 32. In case of destructive reading, the control circuit 30 activates the recording pulse source 20 which in turn activates the domain generators 18-1, 18-2,...l8-2N which belongs to the relevant register which is read destructively. Thus, new information is recorded in the destructively read shift register.

If the emptying device indicates that information is to be read non-destructively from selected shift registers, the domains from this shift register are fed to a domain separator where they are split into two new domains. One of the new domains goes to the detector 32 for destructive reading while the other is returned to the selected shift register for continued circulation in this shift register.

Selection of one or all shift registers for destructive or non-destructive reading is possible as a result of the binary input signals fed to the reading decoder. In fig.

10 is shown part of a shift register SR14 to show decoding

and the emptying functions. The magnet sheet is not shown here.

The domains, e.g. 53 moves to the right in the direction of arrow 46 in the slide register. It is understood that the majority of this shift register loop is not shown and that the loop extends further to the left to accommodate the decoding loop D1-D2'

on fig. 9 and provide sufficient storage space. In accordance with well-known principles, the rotation of the propagation field forms attracting poles in T- and l-shaped permalloy elements 54 for movement of the domains in the direction of the arrow 46. On the magnetic sheet 10 and above the selected permalloy element 5^ the conductors are used for the decoding loops D3, D3' , D4, and D4'. On the magnetic sheet 10 and on suitable parmelloy elements 4, the emptying loop CL is also a conductor loop, e.g. of copper. From this it appears that the decoding loops D3 and D4' have extended sections within the areas where they intersect the T-shaped elements in the direction 46, in that the decoding loops D3' and D4 do not have extended sections where these pass the T-shaped elements in the direction 46. This implies that currents in the decoding loops D3' and D4 do not affect the passing of the domains in the direction 46.

On the magnetic sheet 10 there is also a permalloy domain separator 36-11 which in this case comprises an upper permalloy layer and a lower permalloy layer which is shown in dashed lines.

When using binary input signals 10100110 for the decoding inputs Dl and Dl'...DV for selective reading of the shift registers, there is no current in the decoding loops D3 Qg D4'. As previously mentioned, the currents in the decoding loops exert D3'

and D4 no influence on the function of the sliding register 14. Consequently, the domains 53 are propagated in the direction of the arrow 46 to the pole position 2

for the T-element 56. Then the domain 53 will either follow the path indicated by arrow 38 or the path indicated by arrow 40. If the discharge loop CL is activated by a current pulse, no attracting magnetic pole will be produced in the pole position 3' for element 46. Therefore, domains located at pole position 2 of element 56 will be attracted upwards to pole position 4 of element 56 when the propagation field H has the direction 4. Then the domains will be moved to the pole position 1'' of the T element 58 when the propagation field H has the direction 1. Movement in the direction of arrow 38 continues as H is twisted, bringing the domains to detector 32 for destructive reading.

The detector 32 is shown as a magnetostrictive detector

in connection with an element 60. The magnetostrictive reading detector 32 consists of a magnetostrictive reading element 62 and a constant current source 64. The reading element 62 turns the magnetization vector when a domain's 53 scattering magnetic field interacts with the element. This causes a resistance change in the reading element 62 which is expressed in a voltage signal V s. The element 60 has an elongated permalloy pattern 66 to which the domains 53 move after the reading when H rotates in the direction 4, the domains 53 being moved to the pole position 4 on the element 66. When H rotates, the domains 53 are moved to the corner of the element 66 and are closed there even when H rotates to the directions 2 and 3, because the pole position 3 is far away from the corner of the element 66. When H is in position 3, the localized field at the corner becomes repulsive and the domains collapse.

If no current pulse occurs in the discharge loop CL when the domains 53 are located at pole position 2 of the element 56, these domains will propagate along the path as indicated by the arrow 40 when the propagation field H rotates. Thus, the domains are fed to the domain separator 36-14. As previously mentioned, this separator comprises an upper permalloy layer as indicated by drawn elements T and I and a lower permalloy layer with drawn elements. Under the influence of the rotating propagating element H, domain '-'53 which is supplied to the separator 36-14 is divided into two parts. A part is led to the detector 32 via the lower layer and follows attracting poles a-b-c in the direction of the arrow 42. These domains then follow the path J>Q to the detector.

The second part of the split domains goes to successive pole positions a'-b'-c' on the element 68 when the propagating field H rotates. These domains follow the path indicated by the arrow 44 for recirculation in the shift register 14.

Accordingly, this bubble domain system provides storage and logic functions on a single sheet of amorphous magnetic material. The various components that can be used in previously known bubble domain materials can also be used here. In the present case, the amorphous magnetic materials are easier to provide on any kind of substrate and can have chosen thickness and lateral dimensions.

Although the permalloy pattern is shown for the propagation of domains, it is understood that the conductor loop pattern can also be utilized as well as the wedge pattern. Furthermore, the recording and reading devices can be varied without going beyond the scope of the invention.

Light modulation on.

Because the amorphous magnetic materials according to the invention promote magnetic domains, it is possible to provide a light modulator which modulates the brightness of an incident light beam. In the present case, it is desirable to have a large magnetic moment klf M s , a small coercive force H c, a high Curie temperature Tq and an anisotropic field H& which should be greater than the magnetic moment 4tt M s. This is preferably fulfilled in such amorphous materials as Y-Co, La-Co, Ca-Co, Nd-Co and Pr-Co.

As magnetic domains in a sheet of amorphous magnetic material have their magnetization either parallel or antiparallel to the direction of the incident light beam, the beam will be affected in a different way depending on the direction of the magnetization in the area of the magnetic sheet that the beam hits. With input-polarized light, the polarization is twisted differently depending on the direction of magnetization in the domains where the brightness passing the amorphous magnetic material can be changed by changing the direction of the domains' magnetization.

Fig. 11 shows a light modulator where a laser 70 delivers a light beam that passes a pdarizing element 72 before it hits the amorphous magnetic material <;>74. Near the film 74 is arranged a domain propagating device 76. In this case, the propagating device 76 is a T- and an L-shaped element that provides attractive magnetic poles for relocating a domain 78

in the sheet 74 in accordance with the orientation of the propagation magnetic field H produced by the propagation source 80. After passing through the sheet 74, the light beam strikes the analyzer 82 before being detected by the photocell 84.

Depending on the occurrence or not of a domain 78 where the light beam hits the sheet 74, the polarization of the light beam will be twisted differently. For a certain twist of the polarization, the light beam will be able to pass the analyzer 82 and hit the photocell 84, which gives a current through the resistance R. In the second case, the twist of the polarization of the light beam is such that the beam does not pass the analyzer 82 and, consequently, no voltage is detected across the resistance.R. A light modulator is thereby provided by means of a suitable sheet of amorphous magnetic material containing domains.

In connection with fig. 11 it is understood that the light can be caused to be reflected from the amorphous sheet 74 instead of being propagated through it. In both cases, the effect is the same, namely that the light has its polarization affected, differently depending on the direction of the magnetization in the domains at the point where the light beam enters.

Permanent magnet.

The amorphous magnetic materials according to the invention can be used as permanent magnets. In this case, it is desirable that the magnets have the greatest possible coercive force Hc, large magnetic moment 47TM s and high Curie temperature T c. Appropriate compositions are Y-CQ which is doped with oxygen, nitrogen or carbon.

A particularly suitable embodiment of a permanent magnet layer where an amorphous material is used is a bias layer in connection with a magnetic sheet in which the bubble domains occur. The magnetic sheet which promotes the bubble domains can be a crystalline magnetic sheet or an amorphous magnetic sheet in accordance with the invention. In contrast to the crystalline permanent magnet material which depends on the crystal properties for strong bias fields, the present amorphous permanent magnets are easy to manufacture with desired properties in accordance with what is mentioned above.

Fig. 12 shows the use of an amorphous permanent magnet layer 86 which is used to provide biasing of a magnetic bubble domain sheet 88. A propagating field source 90 and control logic circuits 92 are provided for influencing the domains in the bubble domain material 88. This material can be a known material with a garnet structure, e.g. (Eu,Y)^ (Ga, Fe)^ 0l2 or an amorphous material in accordance with the present invention. When producing the embodiment in fig. 12, it is not critical that the crystal properties are preserved because amorphous material does not follow the rules that apply to the production of crystalline compositions.

The general structure comprising an amorphous magnetic layer on a substrate of any kind is shown in fig. 12. In this general case, the structure can have any application and the layer 86 is an amorphous magnetic layer according to the present invention. The layer 88 is any suitable substrate, e.g. a semiconductor, an insulator or metal. Furthermore, the substrate can be flexible or rigid and aids can be arranged to move the composition of amorphous magnetic film and substrate.

Drawing subsystem.

It is possible to deposit the present amorphous magnetic material in the form of a recording material on a substrate, e.g. a semiconductor, an insulator or a metal. The substrate can be tape or plate. Furthermore, the amorphous magnetic material can be produced as magnetic particles in a binder, e.g. a common resin type binder for application to any substrate.

Fig. 13 shows a tape or disc recording medium 9^

which contains amorphous magnetic film according to the present invention, above which a reading-recording head 96 is arranged. The head 96, which is used for recording information in magnetic domains in the tape or disc 9H and for reading the stored information, is well known. For this purpose, electrical signals are sent from the clearing medium 84 to the readout amplifier 98 and then to a consumer 100 which can be any circuit used in normal

computer engineering.

The use of an amorphous film according to fig. 13 has many advantages. The sheet or strip substrate can be either flexible or rigid. This enables application in all types of information processing systems. Furthermore, the amorphous material is easy to deposit on any type of substrate in a similar manner so that uniform magnetic properties are achieved everywhere.

Example.

Amorphous magnetic composites with uniaxial anisotropy can be produced using direct current and high frequency electrode sputtering and electron beam evaporation. In general, films have been produced which have amorphous properties such as is determined by the electron beam deflection technique. Film has been produced where the magnetic anisotropy is parallel to the plane of the film or at right angles to the plane of the film.

I. Electron beam evaporated films.

In this method for the production of magnetic film, a polycrystalline blank is first provided using conventional techniques, e.g. small pieces of the components to be used in the item are melted in an inert gas atmosphere, e.g. using argon. The melting takes place on a water-cooled copper hearth in an electric arc furnace common on the market. The temperature is increased to the melting temperature of the constituents to obtain an arc-melted ingot. Generally, this is a polycrystalline blank. In the laboratory, samples have been produced from blanks of arc-melted GdCo etc.

The workpiece is then placed in an ultra-high vacuum evaporator with a base pressure of approx. 10 -9 torr. The ingot is placed on a water-cooled copper hearth and heated using an electron beam from an electron gun in the evaporator. Accelerating voltages of approx. 10Kv is used together with a beam current of approx. 100 milliamps.

The substrate used for the deposition of these films has been chosen arbitrarily and substrates such as glass, polished hardened quartz, rock crystal and sapphire have been used with advantage. The substrate is cooled with liquid nitrogen and has a temperature of approx. 100°K during the pre-evaporation. The deposition rate is generally 30 Å per second.

In one case, films with a thickness of 400 and 4000Å have been produced. These films are Gd-Co alloys which are found to become amorphous upon electron beam deflection. The atoms in the deposition material strike the substrate at an acute angle to provide a uniaxial anisotropy as described above. Perpendicular domains are observed in this film.

In another film deposition, the substrate temperature was 273°K. The same substrate was used and also BaTiO^ substrate and cleaved quartz substrates. The blank composition GdCo^ was the same as that used for the films with thicknesses of 400 and 4000 Å. Only the substrate temperature was changed by this composition. In the present case, the film had crystals located in a generally amorphous matrix, indicating that the substrate temperature was critical in an electron beam deposition process. In order to obtain substantially amorphous films, the substrate temperature had to be lowered from 273°K.

In another electron beam deposition, the blank composition was GdCo2 and the substrate was cooled with liquid nitrogen. The produced film was amorphous with uniaxial magnetization in the plane of the film. It seemed that the surrounding magnetization TT M Sved this composition was

way too big so that the relationship

was not exactly correct for

transportation of domains with perpendicular magnetization.

II. Electrode sputtered films:

Many amorphous films have been produced by direct current and high-frequency electrode sputtering with varying values for the sputtering parameters. These films had perpendicular magnetic anisotropy and parallel magnetic anisotropy and were uniaxial. Many values for the magnetization and other magnetic parameters were obtained in accordance with the guidelines described above.

Various devices are described above where the magnetic compositions have uniaxial magnetic anisotropy with mainly amorphous structural properties. These compositions can be produced in mass or thin film form and the magnetic properties can be controlled within wide limits.

Furthermore, many other applications than those mentioned for such films can be imagined, especially in view of the easy possibility of variation of the properties and composition. As a result of the fact that the strict requirements for the substrate that normally exist in crystal production are not present in this case, these films can be used in any environment with any type of substrate.

It is understood that the magnetic and/or

structural properties of these films can be varied with regard to scope and that other methods than those described can be used. Furthermore, other types of preparation can be used in accordance with methods in the art.

Claims (18)

1. Magnetic domain device with auxiliary means for influencing such domains in a magnetic medium, characterized in that the magnetic medium in which these domains exist is an amorphous magnetic material with non-magnetocrystalline, uniaxial anisotropy. 2. Device according to claim 1, characterized in that the said material is found in a microcrystalline structure with localized atomic nuclei in areas with an extent of approx. 100Å or less. 3. Device according to claim 1, characterized in that the said material has localized atomic order in areas with an extent of approx. 25Å or less. 4. Device according to claim 1, characterized in that the said uniaxial anisotropy forms an essentially right angle with the plane of the amorphous magnetic material. 5- Device according to claim 1, characterized in that the amorphous magnetic material consists of a single element with one magnetic moment. 6. Device according to claim 5, characterized in that the element originates from one of the 4f, 5f or 3d element states in the periodic table. 7. Device according to claim 1, characterized in that the amorphous magnetic medium contains a number of elements, of which at least one has an unpaired magnetic spin. 8. Device according to claim 7, characterized in that the amorphous medium consists of an amorphous alloy of a rare earth metal and a metal with a state transition. 9- Device according to claim 8, characterized in that the alloy is a Gd-Co alloy. 10. Device according to claim 8, characterized in that the alloy is a Gd-Fe alloy. 11. Device according to claim 7, characterized in that the amorphous magnetic medium contains an additive which couples antiferromagnetically with a magnetic atom in the medium. 12. Device according to claim 7, characterized in that the amorphous magnetic medium contains an additive which couples ferromagnetically with a magnetic atom in the medium. 13. Device according to claim 7, characterized in that the amorphous magnetic medium contains an additive which changes the atomic order in the medium in relation to the width of its domain boundaries. 14. Device according to claim 7, characterized in that the amorphous medium consists of a ternary alloy which is magnetically ordered. 15. Device according to claim 1, characterized in that the amorphous magnetic medium contains an additive element of 0, N, C or P. 16. Device according to claim 1, characterized in that the amorphous magnetic medium is doped with an element that occurs in an amount of up to and including 50 atomic percent. 17. Device according to claim 1, characterized in that the uniaxial anisotropy is a pairwise anisotropy. 18. Device according to one of the preceding claims, characterized in that the domains are magnetic bubble domains.