In order for the temperature dependence of the strip out field of a magnetic garnet crystal film (54) to match the temperature dependence of the residual magnetization of a permanent magnet (56) for applying a bias magnetic field in a magnetic bubble memory chip (2) after conductor paterns are formed thereon, it is necessary that the temperature coefficient of the collapse field of the magnetic garnet crystal film (51) be from 0.01 to 0.04%/.degree.C., in terms of an absolute value, greater than the temperature coefficient of the above-mentioned residual magnetization (56). The present invention achieves this by increasing the degree of substitution of Lu ions for Fe ions in the octahedral sites constituting the unit lattice of the magnetic garnet crystal. As a result, an operating temperature range about twice as wide as the conventional operating temperature range is ensured.

A device for propagating magnetic domains, comprising a monocrystalline nonmagnetic substrate of a material having a garnet structure, and a layer of an iron garnet grown epitaxially on the nonmagnetic substrate. In the dodecahedral lattice sites, the iron garnet comprises at least a bismuth ion and a rare-earth ion selected from the group consisting of lutetium, thulium, and ytterbium. Such a magnetic garnet combines very high uniaxial anisotropy with a high domain mobility, which properties make the device extremely suitable for the propagation of magnetic domains having diameters from approximately 1 to approximately 2 .mu.m under the influence of comparatively low driving fields.

Magnetic device having a monocrystalline substrate bearing a magnetic layer, said substrate having a composition on the basis of rare earth metal gallium garnet of the general formula ##STR1## wherein A=gadolinium and/or samarium and/or neodym and/or yttrium B=calcium and/or strontium C=magnesium D=zirconium and/or tin and O<x.ltoreq.0.7; O<y.ltoreq.0.7 and x+y.ltoreq.0.8.

Certain Tm-containing iron garnet compositions provide layers having desirably low values of temperature coefficient of bubble collapse field and permit the fabrication of 1.2 .mu.m diameter magnetic bubble devices. The compositions, based on Tm-substitution on dodecahedral sites of [(La,Bi),(Sm,Eu),R].sub.3 (Fe,Al,Ga).sub.5 O.sub.12, are grown by liquid phase epitaxy onto suitable substrates. Bubble devices that incorporate the layers find applications in high density information storage.

A magnetic device has a monocrystalline garnet substrate bearing a magnetic layer, in particular for use as information storage. Magmetic device having a monocrystalline substrate bearing a magnetic layer, with the substrate having a composition on the basis of rare earth metal gallium garnet of the general formula ##STR1## wherein A=gadolinium and/or smarium and/or neodym and/or yttrium B=calcium and/or strontium C=magnesium D=zirconium and/or tin and 0<x.ltoreq.0.7; 0<y.ltoreq.0.7 and x+y.ltoreq.0.8.