Magneto-optical recording medium

A magneto-optical recording medium containing a first and second dielectric layer, a reflector layer, a magneto-optical recording layer, and a substrate, wherein the substrate comprises a homopolymer or copolymer formed by mass polymerization, without ring cleavage, of a monomer mixture

• comprising at least one polycyclic olefin monomer of the formula I, II, III, IV, V or VI ##STR9## in which R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7 and R.sup.8 are identical or different, and are a hydrogen atom or a (C.sub.1 -C.sub.8)-alkyl radical,
• wherein the substrate is prepared by bulk polymerization of the monomer mixture at a temperature of from 20.degree. to 150.degree. C. and at a pressure of from 0.01 to 64 bar, in the presence of a catalyst which comprises a metallocene and an aluminoxane which is of the formula IX ##STR10## or of the formula X ##STR11## where, in the formulae IX and X, R.sup.13 is a C.sub.1 -C.sub.6 -alkyl group, phenyl or benzyl, and n is an integer from 2 to 50, and
• said metallocene is of the formula XI ##STR12## in which M.sup.1 is titanium, zirconium, hafnium, vanadium, niobium or tantalum,
• R.sup.14 and R.sup.15 are identical or different and are a hydrogen atom, a halogen atom, a C.sub.1 -C.sub.10 -alkyl group, a C.sub.1 -C.sub.10 -alkoxy group, a C.sub.6 -C.sub.10 -aryl group, a C.sub.5 -C.sub.10 -aryloxy group, a C.sub.2 -C.sub.10 -alkenyl group, a C.sub.7 -C.sub.40 -arylalkyl group, a C.sub.7 -C.sub.40 -alkylaryl group or a C.sub.8 -C.sub.40 -arylalkenyl group,
• R.sup.16 and R.sup.17 are a monocyclic or polycyclic hydrocarbon radical which can form a sandwich structure with the central atom M.sup.1,
• R.sup.18 is ##STR13## .dbd.BR.sup.19 .dbd.AlR.sup.19, --Ge--, --Sn--, --O--, --S--, .dbd.So, .dbd.SO.sub.2, .dbd.NR.sup.19, .dbd.CO, .dbd.PR.sup.19 or .dbd.P(O)R.sup.19 where R.sup.19, R.sup.20 and R.sup.20 and R.sup.21 are identical or different and are a hydrogen atom, a halogen atom, a C.sub.1 -C.sub.10 -alkyl group, a C.sub.1 -C.sub.10 -fluoroalkyl group, a C.sub.6 -C.sub.10 -fluoroaryl group, a C.sub.6 -C.sub.10 -aryl group, a C.sub.1 -C.sub.10 -alkoxy group, a C.sub.2 -C.sub.10 -alkenyl group, a C.sub.6 -C.sub.40 -alkylaryl group, a C.sub.8 -C.sub.40 -arylalkenyl group, or a C.sub.7 -C.sub.40 -alkylaryl group, or R.sup.19 and R.sup.20 or R.sup.19 and R.sup.21, in each case with the atoms connecting them, form a ring, and
• M.sup.2 is silicon, germanium or tin, and wherein the substituents R.sup.16 and R.sup.17 in the formula XI are different from one another;
• wherein the magneto-optical recording layer comprises an alloy containing at least one transition metal selected from the group consisting of Fe and Co, at least one rare earth metal selected from the group consisting of Gd, Tb, and Dy and at least one further element selected from the group consisting of Pt, Se, and Cr, wherein the recording layer has an axis of easy magnetization at right angles to an upper surface of the recording medium and a thickness of between about 18 and about 30 nm.