Exchange and magnetostatic coupling in multilayer rare earth transition metal thin films

Tri-layer structure MSR disks were fabricated and tested using a center aperture detection method. The disks consisted of a GdFeCo read-out layer, a TbFeCo recording layer, and a GdFe intermediate layer. Two samples were prepared with 15 nm and 7.5 nm GdFe thicknesses and one sample contained no intermediate layer. The read-out waveform for the sample with the 15 nm GdFe layer was observed to approach zero in the range 3.3 mW<read-out power (P_r)<3.5 mW and change polarity when P_r>3.5 mW. This anomalous behavior is believed to be the effect of exchange coupling (EC) forces dominating at temperatures below T_Curie of GdFe and magnetostatic (MS) forces dominating above T_Curie of GdFe. Therefore, the read-oat signal approaches zero when the EC and MS forces are equal in magnitude. This phenomenon was observed for the sample with 7.5 nm GdFe for the bi-layer sample