Perpendicular magnetic recording medium and system with low-curie-temperature multilayer for heat-assisted writing and/or reading

1. A perpendicular magnetic recording medium comprising:

a substrate;

a first ferromagnetic layer (PM 1 ) on the substrate and having perpendicular magnetic anisotropy;

a second ferromagnetic layer (PM 2 ) on the substrate and having perpendicular magnetic anisotropy;

an antiferromagnetically coupling (AFC) layer between PM 1 and PM 2 ; and

a ferromagnetic switching layer (SWL) between PM 1 and PM 2 and having a Curie temperature (T C-SWL ) less than the Curie temperature (T C-PM1 ) of PM 1 and less than the Curie temperature (T C-PM2 ) of PM 2 , the SWL comprising a plurality of pairs of alternating films of a first film consisting essentially of Co and Ni and a second film selected from Pt and Pd.

2. The medium of claim 1 wherein said first SWL film comprises a Co x Ni 100-x alloy wherein x is between about 25 and 75 atomic percent.

3. The medium of claim 2 wherein said first SWL film has a thickness in the range of about 1 to 6 Å and said second SWL film has a thickness in the range of about 3 to 15 Å.

4. The medium of claim 1 wherein T C-SWL is between about 40 and 100 degrees C.

5. The medium of claim 1 wherein the AFC layer is on PM 1 and the SWL is on the AFC layer.

6. The medium of claim 5 wherein PM 1 has a coercive field (H C-PM1 ), PM 2 has a coercive field (H C-PM2 ), and H C-PM1 is greater than H C-PM2 .

7. The medium of claim 5 wherein PM 1 has a magnetization greater than the magnetization of PM 2 .

8. The medium of claim 1 further comprising a third ferromagnetic layer (PM 3 ) on the substrate and having a coercive field (H C-PM3 ); wherein PM 1 , PM 2 , the AFC layer and the SWL are on PM 3 ; and wherein H C-PM3 is greater than the coercive field of PM 1 (H C-PM1 ) and greater than the coercive field of PM 2 (H C-PM2 ).

9. The medium of claim 8 wherein PM 3 has a magnetization greater than the magnetization of PM 1 and greater than the magnetization of PM 2 .

10. The medium of claim 9 wherein the SWL has a magnetization and wherein the magnetization of PM 1 is approximately equal to the magnetization of SWL plus the magnetization of PM 2 .

11. The medium of claim 1 wherein PM 1 , PM 2 , the AFC layer and the SWL are formed as continuous layers on the substrate.

12. The medium of claim 1 wherein PM 1 , PM 2 , the AFC layer and the SWL are formed as discrete data islands on the substrate separated by nonmagnetic regions.

13. The medium of claim 1 where one or both or PM 1 and PM 2 comprises a material selected from the group consisting of (a) a granular polycrystalline Co alloy; (b) a chemically-ordered alloy selected from alloys of FePt, CoPt, FePd, CoPd, CoPt 3 and CoPd 3 ; (c) a chemically-ordered L 1 0 phase alloy selected from FePt—X and CoPt—X, where the element X is selected from the group consisting of Ni, Au, Cu, Pd and Ag; and (d) a multilayer selected from the group consisting of Co/Pt, Co/Pd, Co/Ni, Fe/Pt and Fe/Pd multilayers.

14. A magnetic recording system comprising:

the medium of claim 1 ; and

a heat source for heating a region of the medium to raise the temperature of the SWL to a temperature greater than T C-SWL but less than T C-PM1 and less than T C-PM2 .

15. The system of claim 14 further comprising a write head for generating a magnetic write field to the heated region.

16. The system of claim 14 further comprising a read head for detecting a magnetic field from the heated region.

17. A perpendicular magnetic recording disk drive comprising:

a perpendicular magnetic recording disk comprising a disk substrate and a recording layer structure (RLS) on the substrate, the RLS comprising

a first ferromagnetic layer (PM 1 ) having perpendicular magnetic anisotropy;

a second ferromagnetic layer (PM 2 ) having perpendicular magnetic anisotropy;

an antiferromagnetically coupling (AFC) layer between PM 1 and PM 2 ; and

a ferromagnetic switching layer (SWL) between PM 1 and PM 2 and having a Curie temperature (T C-SWL ) less than the Curie temperature (T C-PM1 ) of PM 1 and less than the Curie temperature (T C-PM2 ) of PM 2 , the SWL comprising a plurality of pairs of alternating films of a first film consisting essentially of Co and Ni and a second film selected from Pt and Pd;

a heat source for heating a region of the RLS to raise the temperature of the SWL to above T C-SWL ;

a write head for generating a magnetic write field to a region of the RLS; and

a read head for detecting a magnetic field from a region of the RLS.

18. The disk drive of claim 17 wherein said first SWL film comprises a Co x Ni 100-x alloy wherein x is between about 25 and 75 atomic percent, wherein said first SWL film has a thickness in the range of about 1 to 6 Å and said second SWL film has a thickness in the range of about 3 to 15 Å.

19. The disk drive of claim 17 wherein the RLS further comprises a third ferromagnetic layer (PM 3 ) with perpendicular magnetic anisotropy between PM 1 and the substrate and having a coercive field (H C-PM3 ); and wherein H C-PM3 is greater than the coercive field of PM 1 (H C-PM1 ) and greater than the coercive field of PM 2 (H C-PM2 ).

20. The disk drive of claim 19 wherein the SWL has a magnetization and wherein the magnetization of PM 1 is approximately equal to the magnetization of SWL plus the magnetization of PM 2 .

21. The disk drive of claim 17 wherein the RLS is patterned as discrete data islands on the substrate separated by nonmagnetic regions.