Protective layers of germanium ceramics

The novel polycrystalline, unoriented or X-ray amorphous carbide, oxide and/or nitride ceramics which have the elemental composition I ##STR1## where M is at least one element from the group consisting of titanium, zirconium, hafnium, thorium, scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, rhenium, iron, cobalt, nickel, ruthenium, rhodium, copper, zinc, magnesium, calcium, strontium, barium, boron, aluminum, gallium, indium, thallium, tin, lead, phosphorus, arsenic, antimony, bismuth and tellurium and x is from 0.01 to 0.7, can be used, in the form of thin layers, as diffusion barriers, anticorrosion layers or interference layers, for protecting surfaces from mechanical abrasion or for protecting magneto-optical recording layers from corrosion. These novel thin polycrystalline, unoriented or X-ray amorphous layers of germanium ceramics can be prepared with the aid of reactive sputtering or reactive magnetron sputtering of a target which consists of the abovementioned elemental composition I.

The present invention relates to polycrystalline, unoriented or X-ray 
amorphous carbide, oxide and/or nitride ceramics which have the elemental 
composition I 
##STR2## 
where M is at least one element from the group consisting of titanium, 
zirconium, hafnium, thorium, scandium, yttrium, lanthanum, cerium, 
praseodymium, neodymium, samarium, europium, gadolinium, terbium, 
dysprosium, holmium, erbium, thulium, ytterbium, lutetium, vanadium, 
niobium, tantalum, chromium, molybdenum, tungsten, manganese rhenium, 
iron, cobalt, nickel, ruthenium, rhodium, copper, zinc, magnesium, 
calcium, strontium, barium, boron, aluminum, gallium, indium, thallium, 
tin, lead, phosphorus, arsenic, antimony, bismuth and tellurium and x is 
from 0.1 to 0.7. 
The present invention furthermore relates to thin layers which consist of 
these germanium ceramics, and their use as diffusion barriers, 
anticorrosion layers or interference layers, for protecting surfaces from 
mechanical abrasion or for protecting magneto-optical recording layers 
from corrosion. 
The present invention also relates to a novel magneto-optical recording 
element which contains at least one thin layer of one of the novel 
germanium ceramics defined at the outset. 
The present invention also relates to a process for the production of thin 
layers which consist of the germanium ceramics defined at the outset. 
Thin polycrystalline or X-ray amorphous layers of carbide, oxide and/or 
nitride ceramics which have the elemental composition 
EQU (Al.sub.x Si.sub.1-x).sub.1-z (M.sub.r.sup.1 M.sub.s.sup.2 
M.sub.t.sup.3).sub.z 
are described in EP-A-0 326 932. 
On the basis of this general formula and observing the conditions according 
to the patent: 
M.sup.1, M.sup.2 and M.sup.3 are each Ti, Zr, Hf, Th, Sc, Y, La, Ce, Pr, 
Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, V, Nb, Ta, Cr, Mo, W, Mn, Re, 
Fe, Co, Rh, Cu, Zn, Mg, Ca, Sr, Ba, B, Ga, In, Tl, Ge, Sn, Pb, P, As, Sb 
and Te, with the provisos that M.sup.1, M.sup.2 and M.sup.3 are different 
from one another, or that they are identical to or different from one 
another when M.sup.1, M.sup.2 and M.sup.3 are each lanthanum or a 
lanthanide, 
x is from 0 to 1, z is r+s+t, 
r and s are each from 0.005 to 0.15 and 
t is from 0 to 0.005, 
it is possible to derive germanium-containing ceramics, for example the 
nitride ceramic 
EQU Al.sub.0.695 Ge.sub.0.15 La.sub.0.155 N 
which however cannot contain more than 15 atom % of germanium. The 
polycrystalline or X-ray amorphous ceramic layers described in EP-A-0 326 
932 are used in particular for protecting magneto-optical recording layers 
of amorphous lanthanide/transition metal alloys from corrosion. 
U.S. Pat. No. 4,661,420 discloses a thin, X-ray amorphous layer which, in 
addition to germanium or germanium and silicon, also contains at least one 
further element from the group consisting of hydrogen, carbon, fluorine, 
nitrogen and oxygen, in amounts of not more than 50, in particular 30, 
atom %. This known thin X-ray amorphous layer is used for increasing the 
Kerr angle of the recording layer of magneto-optical recording elements. 
U.S. Pat. No. 4,661,420 gives no information about the anticorrosion effect 
of the thin X-ray amorphous germanium-containing layer. EP-A-0 326 932 
likewise provides no information about the effect of the polycrystalline 
or X-ray amorphous ceramic layer described therein on the Kerr angle. 
Magneto-optical recording elements are likewise known. In general, they 
contain an optically transparent dimensionally stable substrate (A), a 
thermally alterable recording layer (B) of an amorphous 
lanthanide/transition metal alloy and, at least on that side of the 
recording layer (B) which faces away from the substrate (A), a 
polycrystalline or X-ray amorphous anticorrosion layer (C). These known 
magneto-optical recording elements may furthermore have other layers, such 
as a reflector layer or interference layers. 
These known magneto-optical recording elements are used for recording data 
with the aid of pulse-modulated laser beams, which are focused on the 
recording layers (B) and/or strike them at right angles. 
During recording of data, an auxiliary magnetic field whose field lines are 
oriented at right angles to the surface of the recording layers (B) is 
applied to the recording elements, or the recording layers (B) have a 
correspondingly oriented intrinsic magnetic field. 
It is known that the recording layers (B) consisting of amorphous 
ferrimagnetic lanthanide/transition metal alloys and magnetized at right 
angles to their surface are heated by the laser beam at the point of 
contact during recording of the data. As a result of the heating, the 
coercive force H.sub.c of the alloys decreases. If the coercive force 
H.sub.c falls below the field strength of the applied (external) magnetic 
field or of the intrinsic magnetic field at a critical temperature 
dependent on the particular alloy used, a region which has a magnetization 
direction opposite to the original direction forms at the point of 
contact. Such a region is also referred to as a spot. 
The recorded data can, if required, also be deleted selectively by local 
heating of the data-containing recording layer (B), for example by means 
of a laser beam in an external or intrinsic magnetic field whose field 
lines are oriented with respect to the layer surface, after which 
procedure further data may be recorded, i.e. the recording process is 
reversible. 
Data are read using linearly polarized light of a continuous-wave laser 
whose luminous power is not sufficient to heat the material above the 
critical temperature. This laser beam is reflected either by the recording 
layer (B) itself or by a reflector layer arranged behind the said 
recording layer, an interaction taking place between the magnetic moments 
in the recording layer (B) and the magnetic vector of the laser light 
source. As a result of this interaction, the plane of polarization E of 
the laser light which is reflected by a spot or by a reflector layer 
behind it is rotated through a small angle with respect to the original 
plane. If this rotation of the plane of polarization E occurs during 
reflection of the light at the recording layer (B) itself, this is 
referred to as the Kerr effect and the angle of rotation accordingly as 
the Kerr angle; if, on the other hand, the plane is rotated during passage 
of the light twice through the recording layer (B), the terms Faraday 
effect and Faraday angle are used. 
This rotation of the plane of polarization E of the laser light reflected 
by the magneto-optical recording element is measured with the aid of 
suitable optical and electronic apparatuses and is converted into signals. 
If the Faraday effect is utilized in the known magneto-optical recording 
elements during reading of data, it is essential for the recording 
elements to contain a reflector layer, since the recording layers (B) as 
such are transparent. Moreover, interference layers must be present in 
order to suppress troublesome diffraction phenomena. Of course, the 
reflector layers and interference layers present in the known 
magneto-optical recording elements, and combinations of the said layers, 
act as diffusion barriers which to a certain extent prevent corrosion of 
the extremely oxygen-sensitive and water-sensitive recording layer (B). In 
practice, however, they do not perform this function to a sufficient 
extent because their structure and their composition are not determined 
exclusively by their diffusion barrier action or anticorrosion action but 
mainly by the other functions. Anticorrosion layers (C), which seal the 
magneto-optical recording element from the air, must therefore always be 
present in addition. 
Regarding their adhesion to the other layers present in the known 
magneto-optical recording element, their shelf life, their internal stress 
or their mechanical strength, the conventional anticorrosion layers (C) 
still have disadvantages. However, significant progress has been achieved 
here by the anticorrosion layer (C) described in EP-A 0 326 932, since 
this anticorrosion layer (C) is scratch-resistant and hard, has good 
adhesive strength and mechanical strength, is sufficiently stress-free and 
ensures excellent shielding of the extremely air-sensitive and 
water-sensitive recording layer (B) of magneto-optical recording elements. 
It can also be used as an optically transparent interference layer between 
the substrate (A) and the recording layer (B) and is in this respect 
clearly superior to other interference layers in its optical adaptability, 
its anticorrosive action being fully displayed in this application too. 
Furthermore, it can be readily adapted to the remaining layers of the 
magneto-optical recording elements in its optical and mechanical 
properties and in its adhesion properties. 
As described above, an increase in the Kerr angle is achieved with the aid 
of the thin X-ray amorphous germanium- and nitrogen-containing layer of 
U.S. Pat. No. 4,661,420. However, the patent does not reveal whether this 
is also applicable to the Faraday angle. In addition, the anticorrosion 
action of the said layer is very unsatisfactory, particularly when it is 
intended to shield the magneto-optical recording element from the air. 
It is an object of the present invention to provide novel polycrystalline, 
unoriented or X-ray amorphous carbide, oxide and/or nitride ceramics 
which, in the form of thin layers, are suitable very generally as 
diffusion barriers or as interference layers in optical arrangements or 
for protecting sensitive surfaces from corrosion or mechanical abrasion. 
In particular, the novel polycrystalline, unoriented or X-ray amorphous 
ceramics in the form of thin layers should be suitable for protecting 
magneto-optical recording layers from corrosion without having the 
disadvantages of the prior art. 
We have found that this object is achieved, surprisingly, by 
polycrystalline, unoriented or X-ray amorphous carbide, oxide and/or 
nitride germanium ceramics of which, in addition to germanium and carbon, 
oxygen and/or nitrogen, also contain further elements in exactly defined 
amounts; in view of the prior art, it was not to be expected that 
precisely the novel germanium ceramics with their special composition 
would no longer have the disadvantages described above and moreover would 
have additional advantages. 
The present invention accordingly relates to the polycrystalline, 
unoriented or X-ray amorphous carbide, oxide and/or nitride ceramics of 
germanium which are defined at the outset and have the elemental 
composition I, and which are referred to below as novel ceramic(s) for the 
sake of brevity. 
The novel ceramic is advantageously optically transparent, i.e. for example 
it neither scatters laser light nor absorbs it to any great extent but 
allows the relevant laser light to pass through without any essential 
change in the intensity and the beam cross-section. 
The novel ceramic is polycrystalline, unoriented or X-ray amorphous. 
The polycrystalline or unoriented novel ceramic is composed of crystallites 
(microcrystals) whose size is in the nanometer range but which are still 
capable of diffracting X-ray beams, the crystallites having no preferred 
orientation in the unoriented novel ceramic. 
On the other hand, the X-ray amorphous novel ceramic does not produce any 
diffraction patterns on exposure to X-ray radiation and in this respect 
resembles glass, which is known to be amorphous. 
In its optical properties and performance characteristics and in its 
particularly advantageous action, the polycrystalline or unoriented novel 
ceramic substantially corresponds to the X-ray amorphous novel ceramic, 
although, depending on the intended use, there may be certain differences, 
which however can be advantageously utilized. 
By its very nature, the novel ceramic corresponds to a ceramic material in 
the conventional sense, which was formerly understood as comprising 
inorganic industrial products or engineering materials which are obtained 
by calcining or firing materials such as clays, etc. and which have high 
physical and chemical stability. Owing to the very rapid development in 
the area of the inorganic industrial materials, the meaning of this term 
has been considerably expanded in recent years and it now also covers 
materials which are produced not by calcination or firing but by other 
methods. These materials have a property profile which is superior in many 
respects to that of traditional ceramics and often includes unusual 
properties. These materials are therefore frequently designated modern 
ceramics. The novel ceramic is a new member of these modern ceramics. 
In terms of its composition, the novel ceramic may be regarded as a 
carbide, oxide and/or nitride ceramic, i.e. it consists either of 
carbides, oxides or nitrides or of a mixture of carbides with nitrides, 
oxides with carbides, carbides with nitrides or oxides and carbides with 
nitrides. It has the elemental composition I to be used according to the 
invention, which composition gives an overview of the molar ratio of the 
other components with respect to one another, apart from carbon, oxygen 
and/or nitrogen. This atomic or molar ratio is completely or substantially 
specified from the outset for a given novel ceramic. On the other hand, 
the molar ratio of carbon, oxygen and/or nitrogen to the elemental 
composition I varies, depending on the predetermined elemental composition 
I, in the manner inevitably prescribed by the valence of the atoms and/or 
by the number of positive or negative electric charges present. Thus, the 
carbon, oxygen and/or nitrogen content of a novel ceramic can be readily 
calculated via the particular elemental composition I used, so that an 
exact statement of the particular carbon, oxygen and/or nitrogen content 
is unnecessary below, and simply stating that it is, for example, a novel 
oxide ceramic or nitride ceramic or a novel oxide and nitride ceramic 
having a certain oxygen/nitrogen ratio is sufficient for complete 
characterization of the composition of the relevant novel ceramic. 
The elemental composition I to be used according to the invention contains 
the component germanium as well as the component M. This is at least one 
further element selected from the group consisting of titanium, zirconium, 
hafnium, thorium, scandium, yttrium, lanthanum, cerium, praseodymium, 
neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, 
erbium, thulium, ytterbium, lutetium, vanadium, niobium, tantalum, 
chromium, molbydenum, tungsten, manganese, rhenium, iron, cobalt, nickel, 
ruthenium, rhodium, copper, zinc, magnesium, calcium, strontium, barium, 
boron, aluminum, gallium, indium, thallium, tin, lead, phosphorus, 
arsenic, antimony, bismuth and tellurium. 
The elemental composition I to be used according to the invention may 
contain only one of these elements M. However, it is advantageous if the 
said elemental composition I contains two or three of these elements M, 
since the performance characteristics of the novel ceramics which result 
from the relevant elemental compositions I can then particularly simply 
and advantageously be adapted to specific intended uses. In less frequent 
cases, it may be advisable to introduce more than three, for example four, 
five, six or seven, elements M into the elemental composition I to be used 
according to the invention, although this results in only a comparatively 
small further improvement of the performance characteristics of the novel 
ceramics, which characteristics are in any case already excellent. 
Elemental compositions I which are particularly preferably used according 
to the invention contain scandium, yttrium, lanthanum, aluminum and/or 
silicon, because the novel ceramics based on these elemental compositions 
I are very particularly suitable for the production of anticorrosion 
layers (c) for magneto-optical recording elements. 
In the elemental compositions I to be used according to the invention, 
germanium and the components M have a certain molar ratio with respect to 
one another, which is expressed by the index x of the general formula I 
stated at the outset. Here, x may be any positive number from 0.01 to 0.7. 
Although it is impossible for x to assume values greater than 0.7, for 
example from 0.75 to 0.85, the germanium-containing ceramics which result 
from the relevant elemental compositions no longer fully meet the 
practical requirements. According to the invention, it is advantageous if 
x is any positive number from 0.05 to 0.5, in particular from 0.1 to 0.4, 
because the said elemental compositions I having these molar ratios give 
novel ceramics which have a particularly wide range of uses and display 
their special advantages in a very wide variety of application forms. 
Examples of elemental compositions I which are very particularly preferably 
used according to the invention are listed below: 
List: 
I-1 Ge.sub.0.7 Al.sub.0.2 Sc.sub.0.1 
I-2 Ge.sub.0.8 Al.sub.0.15 Y.sub.0.05 
I-3 Ge.sub.0.8 Al.sub.0.08 Si.sub.0.02 
I-4 Ge.sub.0.95 Al.sub.0.04 La.sub.0.01 
I-5 Ge.sub.0.75 Si.sub.0.2 Y.sub.0.094 La.sub.0.01 
I-6 Ge.sub.0.85 Al.sub.0.1 Sc.sub.0.03 Y.sub.0.02 
I-7 Ge.sub.0.9 Al.sub.0.05 Sc.sub.0.02 La.sub.0.03 
I-8 Ge.sub.0.8 Al.sub.0.15 Y.sub.0.02 La.sub.0.03 
I-9 Ge.sub.0.85 Al.sub.0.08 Si.sub.0.04 La.sub.0.03 
I-10 Ge.sub.0.75 Si.sub.0.2 Sc.sub.0.03 La.sub.0.02 
I-11 Ge.sub.0.785 Si.sub.0.2 Y.sub.0.05 
The novel ceramic can be used in a very wide range of external forms, for 
example as solid spheres, rings, cylinders, blocks or other moldings whose 
shape and composition depend on the particular intended use. However, the 
novel ceramic has very particular advantages in the form of a thin layer, 
the embodiment which is very particularly preferred according to the 
invention. 
The novel thin layers of the ceramics according to the invention may have 
different compositions. If such a novel thin layer consists of, for 
example, oxides and nitrides, the oxygen and nitrogen may be randomly 
distributed in the relevant novel thin layer, i.e. the layer is 
homogeneous and may be polycrystalline, unoriented or X-ray amorphous. In 
addition, the said layer may be an oxide/nitride ceramic which contains 
both microcrystals of oxides and microcrystals of nitrides randomly 
distributed, i.e. the relevant novel thin layer is a polycrystalline 
layer. This also applies in the general sense to novel thin layers which 
consist of oxides and carbides of carbides and nitrides or of oxides, 
carbides and nitrides. 
The polycrystalline, unoriented or X-ray amorphous novel thin layers can, 
however, also have a gradient, for example with respect to the 
distribution of the oxygen and nitrogen over the layer thickness. This 
means that the concentration of nitrogen may increase uniformly starting 
from one side of the novel thin layer to the other side, and the 
concentration of the oxygen then decreases in a corresponding manner 
determined by the stoichiometry. However, this may also mean that the 
concentration of the nitrogen can initially increase starting from one 
side of the novel thin layer and then again gradually, i.e. in a fluid 
manner, or abruptly, decrease, here too the concentration of the oxygen 
decreasing in a corresponding manner and then increasing again. This may 
occur several times over the total thickness of the novel thin layer, 
resulting in a multistratum structure of the relevant layer. This also 
applies in the general sense to the novel thin layers which consist of 
oxide and carbides, of carbides and nitrides or of oxides, carbides and 
nitrides. 
These multistratum novel thin layers may accordingly consist of two or more 
separate strata, and each separate stratum may be a carbide, nitride or 
oxide stratum or a carbide/oxide, carbide/nitride, oxide/nitride or 
carbide/oxide/nitride stratum. 
In most cases, from three to five separate strata are sufficient for 
obtaining an optimum property profile, but in particular cases novel thin 
layers of six, seven or eight strata may be used. The novel thin layers of 
nine, ten or more strata are more rarely used because the higher 
production cost is not always justified by a further increase in the 
properties, which are in any case particularly advantageous. Hence, novel 
thin layers of three to five strata are especially advantageous because 
they can be prepared at comparatively low cost and already have optimum 
properties. 
The strata in these novel thin layers may have different thicknesses. 
However, it is advantageous if they have roughly the same thicknesses. 
Furthermore, the transition from one stratum to the other may be abrupt, 
i.e. there is an exactly defined interface between the strata, for example 
in the transition from a stoichiometric nitride stratum to an oxide or 
carbide stratum. However, the transition may also be fluid. For example, 
the transition zone between z stoichiometric nitride stratum and a pure 
oxide or a pure carbide stratum may be a zone in which the concentration 
of the nitrogen decreases more or less rapidly and the concentration of 
the oxygen or of the carbon increases more or less rapidly. 
According to the invention, a fluid transition from one stratum to the next 
is advantageous. 
Regardless of whether a polycrystalline, unoriented or X-ray amorphous, 
single-stratum or multistratum novel thin layer of nitrides, carbides 
and/or oxides of the elemental composition I to be used according to the 
invention is employed, according to the invention it is particularly 
advantageous if that side of the relevant novel thin layer which faces a 
surface, for example the surface of a magneto-optical recording layer (B) 
to be protected, or is directly adjacent to the said surface, consists 
mainly or exclusively of nitrides. 
Regardless of whether a polycrystalline, unoriented or X-ray amorphous, 
single-stratum or multistratum thin layer of nitrides and oxides, carbides 
and oxides, nitrides and carbides or carbides, oxides and nitrides or a 
polycrystalline or X-ray amorphous novel thin layer of carbides, oxides or 
nitrides is used, the said layer is not more than 1000 nm thick. Because 
of its particular properties and technical effects due to the novel 
ceramics, greater layer thicknesses are unnecessary. Furthermore, the 
greater consumption of material required for this purpose results in only 
a comparatively small further improvement in the property profile, which 
is in any case advantageous. The thickness of the novel thin layers should 
on the other hand not be less than 20 mm, since in this case, for example, 
the barrier effect of the said layers with respect to oxygen and water is 
no longer completely satisfactory. Thicknesses of from 30 to 800 nm are 
advantageous, the thickness range from 30 to 500 nm being particularly 
noteworthy and that from 40 to 250 nm being very particularly noteworthy. 
Within the thickness range from 40 to 250 nm, the range from 40 to 100 to 
nm is in turn of particular importance because novel thin layers having 
this thickness have an optimum property profile with respect to the 
barrier effect, material consumption, production cost, mechanical 
strength, toughness and stability and are therefore particularly useful. 
Accordingly, the range from 40 to 100 nm is an optimum within which the 
thickness of the novel thin layer can be varied and adapted in an 
advantageous and excellent manner to the composition and technical 
parameters of, for example, magneto-optical recording elements. 
Regardless of whether 20-1000 nm thick polycrystalline, unoriented or X-ray 
amorphous, single-stratum or multistratum novel thin layers of nitrides 
and oxides, carbides and oxides, nitrides and carbides or carbides, oxides 
and nitrides or 20-1000 nm thick, polycrystalline, unoriented or X-ray 
amorphous novel thin layers of carbides, oxides or nitrides are used, the 
novel carbide, oxide and/or nitride ceramic of these novel thin layers 
always have the elemental composition I to be used according to the 
invention. 
This means that the novel ceramics of which the novel thin layers consist 
have a uniform or a substantially uniform composition with regard to the 
elemental composition I over their entire volume, i.e. the said layers are 
free or substantially free of concentration gradients with regard to their 
elemental composition I. 
In terms of the method, the preparation of the novel ceramic according to 
the invention has no special features but is carried out by the 
conventional and known techniques for the preparation of modern ceramics. 
The preparation of the novel ceramic in its particularly advantageous 
embodiment of the thin layer is preferred according to the invention. The 
production of the novel thin layers also has no special features with 
regard to the method and is carried out by the conventional and known 
techniques for the production of thin carbide, oxide and/or nitride 
ceramic layers by vapor deposition, reactive vapor deposition, ion 
plating, ion cluster beam deposition (ICB), sputtering or reactive 
sputtering. Among these techniques, reactive sputtering is advantageously 
used and reactive magnetron sputtering is very particularly advantageously 
used. 
In reactive sputtering, it is known that the material of a target is 
converted into the gas phase (sputtered) by bombardment with helium, neon, 
argon, krypton and/or xenon ions under reduced pressure. Further 
components, for example hydrocarbons, oxygen and/or nitrogen, are mixed 
with the gas produced in this manner, the said further components, 
together with the sputtered target material, forming the process gas. From 
this process gas, the sputtered target material is deposited, together 
with the reactive components, as a thin ceramic layer on the surface to be 
coated. In reactive magnetron sputtering, it is known that the target is 
in a magnetic field. 
By varying the process parameters, such as sputtering rate, deposition 
rate, process gas pressure and composition, it is possible to produce 
polycrystalline, unoriented by or X-ray amorphous thin novel layers from 
novel ceramics of the desired composition in a very controlled and very 
exact manner. Suitable process parameters can be selected on the basis of 
the existing technical knowledge in the area of reactive (magnetron) 
sputtering and/or with reference to preliminary experiments. 
According to the invention, the novel thin layers are produced using 
targets which have the elemental composition I to be used according to the 
invention. The targets are in the form of flat disks or sheets and are 
produced by thorough mixing, homogenization and shaping of germanium and 
the components M described above, with the aid of the conventional and 
known mixing and shaping techniques. 
Examples of very particularly suitable target compositions I are the 
elemental compositions I-1 to I-11 from the abovementioned list. 
According to the invention, it is particularly advantageous to sputter this 
target composition having elemental composition I under reduced pressure 
in an atmosphere in which the volume ratio of noble gas to the reactive 
gases is from 1 : 5 to 100 : 1, the noble gas used comprising one or more 
noble gases from the group consisting of neon, argon, krypton and xenon, 
or advantageously a mixture of argon and one or more noble gases from the 
group consisting of neon, krypton and xenon, the volume ratio of argon to 
the other noble gas or gases being from 1 : 5 to 10 : 1. It is also 
advantageous if the process gas contains hydrogen, since in many cases the 
presence of the hydrogen further improves the success of the process. If 
hydrogen is present, the volume ratio of the reactive gases to hydrogen is 
from 2 : 1 to 20 : 1. 
The novel ceramics, in particular in the shape of the thin novel layers, 
are very useful as diffusion barriers, anticorrosion layers or 
interference layers or for protecting sensitive surfaces from mechanical 
abrasion. They are used in particular for protecting the outermost 
air-sensitive and water-sensitive recording layers (B) of novel 
magneto-optical recording elements from corrosion. When performing this 
function, the novel thin layers are referred to as novel anticorrosion 
layers (C). They are that component of the novel magneto-optical recording 
elements which is essential according to the invention. They are produced 
by the methods described above in connection with the production of the 
novel magneto-optical recording elements, the order of the individual 
process steps inevitably arising from the desired structure of the 
particular novel magneto-optical recording element to be produced. 
The further essential component of the novel magneto-optical recording 
element is the optically transparent dimensionally stable substrate (A). 
Advantageous substrates (A) are the conventional and known, disk-shaped, 
optically transparent dimensionally stable substrates (A) having a 
diameter of 90 or 130 mm and a thickness of 1.2 mm. They generally consist 
of glass or of plastics, for example polycarbonate, polymethyl 
methacrylate, polymethylpentene, cellulose acetobutyrate or a mixture of 
poly(vinylidene) fluoride and polymethyl methacrylate or polystyrene and 
poly-(2,6-dimethylphen-1,4-ylene ether). Among these, the substrates (A) 
of plastics are particularly advantageous. 
That surface of the dimensionally stable substrate (A) which faces the 
recording layer (B) may have structures. The structures in the surface of 
the substrate (A) are in the micrometer and/or submicrometer range. They 
are used for exact guidance of the read laser beam and ensure a rapid and 
exact response of the tracking and autofocusing means in the laser-optical 
write and read heads of the disk drives, i.e. they permit tracking. These 
structures may furthermore themselves be data, as is the case, for 
example, in the known audio or video compact disks, or they may serve for 
coding the recorded data. The structures consist of raised parts and/or of 
indentations. These are in the form of continuous concentric or spiral 
tracks or in the form of isolated hills and/or holes. Furthermore, the 
structure may have a more or less smooth waveform. Tracks are preferred 
here. They have, in their transverse direction, a rectangular 
sawtooth-like, a V-shaped or a trapezoidal contour. Their indentations are 
generally referred to as grooves and their raised parts as land. Of 
particular advantage are tracks having 50-200 nm deep and 0.4-0.8 .mu.m 
wide grooves separated by a 1-3 .mu.m wide land. 
The particularly preferably used dimensionally stable substrate (A) is 
produced in a conventional manner by shaping the plastic or plastic blend 
forming the substrate (A), by injection molding under clean-room 
conditions, as described in detail in, for example, German Patent 
Application P 37 27 093.1. 
Dimensionally stable substrates (A) having tracks on one of their surfaces 
are very particularly preferably produced in this manner. 
The other essential component of the novel magneto-optical recording 
element is the magneto-optical recording/layer (B) of an amorphous 
lanthanide/transition metal alloy. The recording layer (B) is from 10 to 
500 nm thick. The lanthanides Pr, Nd, Sm, Eu, Gd, Tb, Dy and Ho and the 
transition metals Fe and Co are suitable for producing the recording layer 
(B). Suitable mixing ratios of lanthanides to transition metals are known 
from the prior art. Furthermore, the amorphous lanthanide/transition metal 
alloy may also contain other elements, such as Sc, Y, La, V, Nb, Ta, Cr, 
No, W, Mn, Ni, Re, Ru, Os, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, B, Al, Ga, In, 
Si, Ge, Sn, Pb, P, As, Sb and/or Bi in conventional and known amounts. 
In the production of the novel magneto-optical recording element, the 
recording layer (B) is produced on the dimensionally stable substrate (A), 
advantageously on a layer present on the substrate (A), by the 
above-mentioned techniques for producing the novel thin layers. 
In addition, the novel magneto-optical recording element may contain 
further layers which are useful for the functioning of the recording 
element. These are the conventional and known interference layers, 
reflector layers or adhesion-promoting layers or further magnetizable 
layers. Furthermore, two of the novel magneto-optical recording elements 
may be connected to one another in the form of a sandwich, so that their 
recording layers (B) face one another and there is a certain distance 
between them, the conventional and known techniques for connecting two 
recording elements being used. 
Usually, a defined magnetization oriented at right angles to the layer 
surface is induced in the recording layers (B) after the production of the 
novel magneto-optical recording elements. 
The particularly preferred novel magneto-optical recording element is the 
novel magneto-optical disk comprising 
1. the particularly preferably used dimensionally stable substrate (A) 
described above, 
2. the first novel anticorrosion layer (C), 
3. the recording layer (B) described above and 
4. the second novel anticorrosion layer (C), 
and, if required, additional conventional and known layers. 
The individual layers of this novel magneto-optical disk are produced by 
the methods described above, the order of the process steps inevitably 
arising from the composition (A), (C), (B), (C). 
Data in the form of magnetically reversed sports can be recorded on the 
novel magneto-optical recording elements in a conventional manner from the 
side of the optically transparent dimensionally stable substrate (A) with 
the aid of a pulse-modulated write laser beam which has a wavelength 
.lambda. of less than 1000 nm and is focused on the recording layers (B) 
and/or strikes the said layers at right angles. The data can then be read 
with the aid of a continuous-wave laser beam which is focused on the 
data-containing recording layers (B) and/or strikes the said layers at 
right angles, the light reflected by the recording layers (B) themselves 
or by any reflector layers present being collected, analyzed and converted 
into signals. In the case of the novel magneto-optical disks, the 
conventional and known laser-optical disk drives having laser-optical 
heads which contain semi-conductor lasers can be used for this purpose. 
Compared with the prior art, the novel magneto-optical recording elements 
have particular advantages which are finally based on the use of the novel 
ceramic for producing the novel anticorrosion layer (C). They have higher 
sensitivity than known magneto-optical recording elements and can 
therefore be recorded on using correspondingly lower laser power. At the 
same laser power, the novel magneto-optical disks can therefore be 
recorded on at higher disk speeds than known disks. Furthermore, their bit 
density is substantially higher compared with the prior art. On reading, 
they give undistorted signals and have a signal-to-noise ratio of more 
than 55 dB. Even after a storage time of more than 1000 hours at 
70.degree. C. and at a relative humidity of 90%, there is no increase in 
the bit error rate, i.e. there is no loss of information. 
As described above, the novel magneto-optical recording elements have at 
least one novel anticorrosion layer (C) which consists of the novel 
ceramic. This novel anticorrosion layer (C) is scratch-resistant and hard, 
has good adhesive strength and mechanical strength, is stress-free and 
shields the extremely air-sensitive and water-sensitive recording layer 
(B) in an excellent manner. If the novel anticorrosion layer (C) is also 
used as an optically transparent interference layer between the substrate 
(A) and the recording layer (B), it is clearly superior to conventional 
interference layers in its optical adaptability. Furthermore, the 
excellent anticorrosive action of the novel anticorrosion layer (C) is 
also fully displayed here. Very particular advantages are obtained if both 
sides of the recording layer (B) are covered with the novel anticorrosion 
layer (C). In particular, this extends the life of the novel recording 
materials beyond the period achieved to date. Moreover, the fact that the 
novel anticorrosion layer (C) can be adapted, in terms of its optical and 
mechanical properties and its adhesion properties, in an excellent but 
simple manner to the other layers of the novel magneto-optical recording 
elements is an advantage. In addition, the novel anticorrosion layer (C), 
when functioning as an interference layer, is capable of increasing the 
Kerr angle and the Faraday angle, making the novel magneto-optical 
recording elements even more attractive in practice.