NL7901629A - METHOD FOR FORMING MONOCRYSTALLINE LAYER OF A MAGNETIC IRON OXIDE WITH SPINAL OR GARNET STRUCTURE. - Google Patents

Description

* Λ 28.2.79 1 ΡΗΝ 9355 N.V. PHILIPS »BULB FACTORIES in Eindhoven.

Method for forming a monocrystalline layer of a magnetic iron oxide with a spinel or garnet structure.

The invention relates to a method for forming a monocrystalline layer of a magnetic iron oxide with a spinel or garnet structure on a deposition surface of a monocrystalline substrate crystal, wherein the substrate crystal is immersed in a melt containing a lead flux, which melts is held at a constant temperature and in a super-cooled state and the substrate crystal is immersed in the melt until a layer of the desired thickness has grown epitaxially on the deposition surface.

For various applications it is known to grow monocrystalline layers with a magnetic garnet or spinel composition by epitaxy from a "fluxed melt" on special deposition surfaces of non-magnetic substrates.

For example, applications in magnetic bubble domain memories require thin layers of rare earth garnet with uniaxial anisotropy in which single-wall bubble domains can be generated and advanced 20 (see US patent 3,995 * 093) »and are used in magnetic heads of the thin film type thin layers of spindle ferrite, especially nickel zinc ferrite, and manganese zinc ferrite for the magnetic circuit, required (see Netherlands Patent Application Laid-open No. 7510931) 7901629 + * 28.2.79 2 PHN 9355

Suitable metal oxides for a flux containing parts of an epitaxially grown grenade or. spinel layer dissolves and allows monocrystalline layers to grow at a temperature significantly below that of its melting point are lead oxide, bismuth oxide and boron oxide. These oxides have been found in practice to lead lead oxide, especially in combination with boron oxide, to be the most suitable in terms of viscosity, suitable temperature range for layer growth and impurity contamination in the grown crystals.

As will be explained hereinafter, it provides certain advantages to grenade and spinel layers on natural facets of substrate crystals (in the case of grenades these planes are parallel to the crystallographic (110) or (211) planes; in the case of spinels these planes are parallel to the crystallographic (lil) plane). However, it appears that the use of a lead oxide-based flux in that case results in conical mounds in the surface of the layer. These mounds complicate the further processing of the layers into a bubble domain memory, or into a magnetic head of the thin film type and can moreover hinder domain movement in bubble domain memories because they retain domain walls ("domain wall pinning").

The object of the invention is now to provide a method of the type mentioned in the preamble which provides hilly, smooth layers with garnet or spinel structure, respectively.

The method according to the invention is therefore characterized in that a substrate crystal is provided on which a depositing surface is formed, the normal of which makes an angle of at least 0.5 ° and at most 10 ° with the normal of a natural facet of that substrate crystal.

By growing on a low angle deposition surface with a natural facet, single crystalline garnet and spinel layers can be grown from a lead flux containing melt that does not exhibit conical mounds 7901629 * 28.2.79 3 PHN 9355.

An advantage of the use of a natural facet-related deposit surface is that it offers the possibility of easily adjusting the growth rate to a desired low value.

The use of a deposition surface oriented parallel to an arbitrary crystallographic plane (a (lil) plane in the case of grenades) does not offer this possibility. It is important that the growth rate is kept low, because then it is prevented that a (transitional) layer is formed during the first phase of the growth process, the composition of which varies widely. In the case of a misorientation of the deposition surface with respect to the natural facet of 10 ° and more, the growth rate is equal to that which occurs when growing on a deposition surface oriented parallel to an arbitrary crystallographic plane. A preferred form of the method according to the invention is characterized in that such a combination of supercooling of the melt and orientation of the deposition surface is chosen that the growth rate of the layer is at most half the growth rate of the same layer. a growth surface parallel to a (lil) crystallographic plane is grown.

In particular, in the case of layers with garnet structure, the growth rate can be kept sufficiently low by using a natural facet-related deposition surface to allow the degree of subcooling to be at most equal to 30 ° C and by the angle that the normal of makes the barrier with the normal of the natural facet at most equal to 2 °.

This aspect of the invention is of great importance for submicron bubble domain memories requiring extra thin shell layers (less than 1 µm). In these thin layers, a transition layer (which may have a thickness of 0, lyum or more) makes up a significant portion of the total layer thickness. In such a thin layer, the magnetic properties will also vary in the direction perpendicular to the surface, due to the variation in chemical composition of the transition layer. This is undesirable, and the prevention of the occurrence of a transition layer is therefore of great importance.

When the growth rate cannot be set to a desired low value, as is the case when the deposition plane is a plane oriented parallel to any crystal plane, it is necessary to dip the substrate horizontally in the melt and to rotate a vertical axis to grow thin layers which are as uniform as possible in thickness and of equal composition throughout. The method according to the invention makes it possible to grow at a desired low growth rate.

As a result, a much simpler growth technique can be applied in which the substrate is immersed in a vertical position and in principle does not need to be rotated.

The invention also provides a method as described above for growing a layer of spinel ferrite on a substrate crystal with a cubic crystal structure, the method being characterized in that the natural facet 20 of the substrate crystal is a plane parallel to a crystallographic (III) plane, and the normal of the barrier face makes an angle of at least 0.5 ° and at most 10 ° with the normal of the natural facet.

Good results (sufficiently smooth layer) are obtained with 20 spinel ferrites in particular when the misorientation of the depositing surface (with respect to a natural facet) lies between 1.5 ° and 3 »5 °

Single crystals of magnesium oxide (MgO), zinc gallate (ZnGa ^^), spinel (MgAlgO ^) and sapphire (AlgO ^) are suitable as substrate crystals for epitaxial growth of spinel ferrite layers, but all have their own drawbacks.

A preferred form of the process according to the invention is characterized in that the substrate crystal is zinc ortho titanate (Zn ^ TiO ^). This material has a lattice constant which is very well adapted to that of the spinel ferrites to be grown thereon, in particular MnZn ferrite, and is obtainable in sufficiently large dimensions and with little lattice errors, especially when using 790 1 6 2 9 »28.2.79 5 PHN 9355 of the Bridgman technique has grown.

The invention will be further illustrated by way of example with reference to the following experiments.

Example 1.

To grow layers of type (Υ Gd) ^ (Mh Ga Fe) ^ 012, a melt was composed with a saturation temperature of about 930 ° C from the following components:

PbO 1351.2 grams 1 ° B203 28.05 "

Fe203 107.83 "

Ga203 10.34 Y203 4.24 "

Gd203 4.80 "15 Mn02 9.00"

A first series of gadolinium-gallium garnet substrates was fabricated with faces whose normal was successively angled at 0 °, 1 °, 2 °, 4 °, 6 °, 8 °, and 10 ° with the normal of the crystallographic 20 ( HO) flat.

These substrates were melt-immersed at a temperature of 878 ° C (global 52 ° subcooling) for 3.5 minutes to give layer thicknesses of 3.2 µm for an angle of 0 °, to 6.3 µm for an angle of 10 °.

Smooth layers were found to be formed on the substrates with a misorientation of 2 ° and higher. The growth rate for 0 ° misorientation was 0.94 µm min "" * and the growth rate increased with increasing misorientation to 1.80 µm min "" "for 10 ° misorientation of the deposition plane. The final value of the growth rate is equal to that when using a (III) oriented substrate.

A second series of substrates whose deposition plane was at an angle of 0 °, 1 °, and 4 ° to the normal on the crystallographic (10) plane were placed at a temperature of 913 ° C (approximately 17 ° subcooling) for 6 minutes. melt-dipped to yield layer thicknesses of 0.4 µm for 0 misorientation, 1.9 µm for 1 and 3.9 µm for 790 1 6 29> 28.2.79 6 · PHN 9355 k ° misorientation of the deposition surface of the (110) plane. In this case, smooth layers were found to be formed on the substrates with a misorientation of 1 ° and higher.

The growth rates were 0.067 µm min "" ^ "for 0 ° misorientation, -1 o -1.5 0.32 yva min for 1 misorientation and 0.65 µm min for 4 ° misorientation of the deposition face. 111) orientation, the growth rate at the same immersion temperature was 0.92 µm min

Example 2.

To grow layers of the (YLa) ^ (FeGa) ^ O ^ ^ layers, a melt was composed with a saturation temperature of about 975 ° C from the following components:

PbO 1680.0 grams B2 ° 3 36.92 15 Y203 13.398 "

La203 10.12 »

Fe203 95.13 "

Ga203 18.56 "

A first and a second gadolinium-gallium-grenade substrate were provided with a (III) oriented deposition surface, and a third gadolinium-gallium-grenade substrate with a deposition surface with a misorientation of 2 ° to the (10) plane .

These substrates were melt-immersed at a temperature of about 955 ° C (global 20 ° subcooling) until layers about 1 µm thick had grown on them.

The first substrate was immersed in a horizontal position, and rotated on a vertical axis at a frequency of 4 revolutions per minute, the second and thirds were immersed in a vertical position and not rotated.

The homogeneity of the formed layers was examined using spin wave resonance measurements. This method is described in an article by B. Hoekstra, R.P.

35 van Stapele and J.M. Robertson in Journal of Applied Physics, 4j3, pages 382. (1977). The variation of the magnetic anisotropy, or the magnetization in a layer, can be determined by means of spin wave resonance. The 7901629 28.2.79 7 PHN 9355% so-called perpendicular resonance spectrum was compared in a sub-layer adjacent directly to the deposition surface (the so-called transition layer) with a sub-layer further away from the deposition surface. The difference in the field strengths at which a peak in the resonance spectrum is found (ΛΗ ^) is a measure of the homogeneity.

In the layer grown on the first substrate, an AH ^ of 600 Oe was measured, in the layer grown on the second substrate a HH ^ of 1294 Oe, and in the layer grown on the third substrate a H ^ of 89.

Thus, the homogeneity of the substrate immersed in a vertical position with a slight misorientation of the deposition surface with respect to a natural facet was by far the best.

15 Example 3.

For growing ferrite (ZnFe ^ O ^) layers, a melt with a saturation temperature of about 840 ° C was composed of the following components:

PbO U05 gram 20 B203 12 "

ZnO 4.524 "

Pe203 31.94 "

A series of zinc titanate (Zn2Ti0j ^) substrate crystals was manufactured using the Bridgman process and provided with depositing faces whose normals are successively angled at 0 °, 1 °, 2 °, 3 °, 4 °, 6 ° and 10 ° with the normal of the (lil) plane.

These substrate crystals were equally melt-immersed at temperatures between 750 and 830 ° C, thereby growing layers 3-6 µm thick. (As the misorientation of the deposition face relative to the natural facet increases, the growth rate also increases.) The smoothest layers were found to be formed on the substrates with a misorientation of the deposition face relative to the (lil) 35 plane of 2 ° and 3 °.

Example 4.

Corresponding results were obtained with zinc titanate substrate crystals with different misorientations of the deposition face relative to the (ill) face which were immersed in melts having the following compositions: 4a For growing MgFe 2 O ^: 5

PbO 405 gram B203 13.5 "

Fe203 30.1 »

MgO 0.76 "10 (saturation temperature 825 ° C; growth temperatures between 800 and 820 ° C).

4b For growing NiFe20 ^:

PbO b05 gram 15 b2o3 13.5

Fe203 30.1

NiO 1, b (saturation temperature 850 ° C · growth temperatures between 740 and 840 ° c).

20 4c For the growth of Li Fe--O ,,: —0 »5 2.5 4

PbO 35Ο grams B2 ° 3 57

Fe2 ° 3 38.4 25 Li2Co3 20.1 "(saturation temperature 858 ° C; growth temperatures between 800 and 845 ° C), 4d For growing (MnZn) Fe20 ^ ^ Pb2 Ρ2 ° γ 106 grams

Fe203 11.2 '*

MnC03 66.7 ”

ZnO 0.4 (saturation temperature 1020 ° C; growth temperatures between 35 9 2 5 and 1015 ° C).

7901629

Claims (10)

28.2.79 9 PHN 9355 CONCLUSIONS. 1. A method of forming a monocrystalline layer of a magnetic iron oxide with a spinel or garnet structure on a deposition surface of a monocrystalline substrate crystal, wherein the substrate crystal is immersed in a melt containing a lead flux which melts on maintained at a constant temperature and in a super-cooled state, and wherein the substrate crystal is immersed in the melt until a layer of the desired thickness of epitaxial has grown on the deposition surface, characterized in that a substrate crystal is provided to which a deposit surface is formed, the normal of which forms an angle of at least 0.5 ° and at most 10 ° with the normal of a natural facet of that substrate crystal. 2. A method according to claim 1, characterized in that the melt contains a PbO-B 2 O 2 flux. A method according to claim 1 or 2, wherein the magnetic iron oxide is a rare earth garnet, and the substrate crystal is a rare earth gallium garnet, characterized in that the natural facet of the substrate crystal is attached to a crystallographic (lio) or (21l) plane is parallel plane. Method according to claim 1 or 2, characterized in that a combination of supercooling of the melt and orientation of the depositing surface is chosen such that the growth rate of the layer is at most half of the growth 7901629 28.2. 79 / © PHN 9355 speed of the same layer that is grown on one of an (ill) crystallographic plane parallel deposition surface. 5. A method according to claim 4, characterized in that the melt has a supercooling degree of at most 30 ° C and in that the normal of the depositing surface makes an angle of maximum 2 ° with the normal of the natural facet. Method according to claim k or 5, characterized in that the layer is grown to a thickness of at most 1 ytun. A method according to claim 1 or 2, wherein the magnetic iron oxide is a spinel ferrite, and the substrate crystal has a cubic crystal structure, characterized in that the natural facet of the substrate crystal is parallel to a crystallographic '(lil)' is flat. 8. Method according to claim 7, characterized in that the normal of the depositing surface makes an angle of at least 1.5 ° and at most 3> 5 ° with the normal of the natural facet. 9. A method according to claim 7 or 8, characterized in that the substrate crystal is zinc ortho-tifcanate. A method according to any one of claims 1-9, characterized in that the substrate crystal is immersed in the melt with the depositing surface in vertical position. 25 30 79 016 29 35