Among them, GdTbFeCo is preferable since it exhibitsexcellent overwriting characteristics.The material of the metal reflecting layer used in this aspect is not particularly limited as long as the layer satisfies d.gtoreq.40 and 2.0.ltoreq..lambda.d.ltoreq.20 where d denotes the thickness (nm) and .lambda.denotes the thermalconductivity (W/mK)[m: meter], i.e., the unit of .lambda.d is .mu.W/K. More