Thermomagnetic information recorder e.g. for laser beams - has active layer of gadolinium, iron and holmium, dysprosium or terbium

摘要

Information carrier in which registration is accomplished by thermomagnetic means and read-out by magneto-optical means, comprises a substrate carrying an active layer consisting of a thin amorphous layer of a gadolinium-iron material of formula (ZZyGd1-y)xFe-x in which ZA is = one of Ho, Dy and Tb; 0.2 x 0.3; and 0 y 1. The film is appleid with a preferred direction of magnetisation perpendicular to the surface of the layer. The materials are esp. useful as registration media for focussed laser beams, whereby the beam is focussed on the material to produce a local increase in temp. to the Curie temp. whilst the material is in a magnetic field. The named gadolinium-iron materials retain their properties down to very low layer thicknesses. Prods. of the desired registration sensitivity can be made by varying the value "y" in the above formula, by which the Curie temp. of the material can be varied between 20 and 230 degrees C.