Perpendicular magnetic recording system and medium with high-moment corrosion-resistant “soft” underlayer (SUL)
View Patent ↗A perpendicular magnetic recording disk has a soft magnetic underlayer (SUL) that has high corrosion resistance as well as high moment. The material of the SUL is an alloy comprising Co, Fe, X, and Y; where X is Ta or Nb, Y is Zr or Hf, and the combined amount of X and Y present in the alloy is between about 10 and 20 atomic percent. The atomic ratio of Co to Fe in the alloy is between about 90:10 to 10:90, preferably between about 25:75 and 35:65. The SUL may be a single-layer SUL or a multilayer SUL formed of multiple soft magnetic layers separated by an interlayer film or films.
1. A perpendicular magnetic recording medium comprising:
a substrate;
a perpendicular magnetic recording layer; and
an underlayer comprising magnetically permeable material between the substrate and the recording layer, the magnetically permeable material being an alloy consisting essentially only of Co, Fe, Ta and Zr wherein the combined amount of Ta and Zr in said CoFeTaZr alloy is greater than or equal to 10 atomic percent and less than or equal to 20 atomic percent and the moment (M s ) is greater than or equal to 11 kOe, and wherein said CoFeTaZr alloy exhibits a corrosion current at zero electrical potential in an electrochemical corrosion test and a Co 92 Ta 3 Zr 5 alloy exhibits a corrosion current at zero electrical potential in said test that is at least 15 times the corrosion current of said CoFeTaZr alloy.
2. The medium of claim 1 wherein the amount of Ta in said alloy is 10 atomic percent and the amount of Zr in said alloy is 5 atomic percent.
3. The medium of claim 1 wherein the atomic ratio of Co in said alloy to Fe in said alloy is in the range of about 90:10 to 10:90.
4. The medium of claim 3 wherein the atomic ratio of Co in said alloy to Fe in said alloy is in the range of about 25:75 to 35:65.
5. The medium of claim 1 further comprising an exchange-break layer between the underlayer and the recording layer for magnetically decoupling the recording layer and the underlayer.
6. The medium of claim 1 wherein the recording layer comprises a granular ferromagnetic Co alloy.
7. The medium of claim 6 wherein the recording layer comprises an oxide or oxides of one or more of an element selected from the group consisting of Si, Ta, Ti, and Nb.
8. The medium of claim 1 wherein the underlayer comprises two films of said magnetically permeable material separated by a nonmagnetic film.
9. The medium of claim 8 wherein the nonmagnetic film provides antiferromagnetic coupling of the two magnetically permeable films.
10. A perpendicular magnetic recording system comprising:
the medium of claim 1 ;
a write head for magnetizing regions in the recording layer of said medium; and
a read head for detecting the transitions between said magnetized regions.
11. A perpendicular magnetic recording disk comprising:
a substrate;
a magnetically permeable underlayer on the substrate and comprising an alloy consisting essentially only of Co, Fe, Ta and Zr, wherein the combined amount of Ta and Zr in said CoFeTaZr alloy is greater than or equal to 10 atomic percent and less than or equal to 20 atomic percent and the moment (M S ) is greater than or equal to 11 kOe, and wherein said CoFeTaZr alloy exhibits a corrosion current at zero electrical potential in an electrochemical corrosion test and a Co 92 Ta 3 Zr 5 alloy exhibits a corrosion current at zero electrical potential in said test that is at least 15 times the corrosion current of said CoFeTaZr alloy;
a perpendicular magnetic recording layer comprising grains of a Co-based ferromagnetic alloy having a hexagonal-close-packed (hcp) crystalline structure with the c-axis oriented substantially perpendicular to the recording layer; and
an exchange-break layer between the underlayer and the recording layer for magnetically decoupling the recording layer and the underlayer.
12. The disk of claim 11 wherein the amount of Ta in said alloy is 10 atomic percent and the amount of Zr in said alloy is 5 atomic percent.
13. The disk of claim 11 wherein the atomic ratio of Co in said alloy to Fe in said alloy is in the range of about 90:10 to 10:90.
14. The disk of claim 13 wherein the atomic ratio of Co in said alloy to Fe in said alloy is in the range of about 25:75 to 35:65.
15. The disk of claim 11 wherein the recording layer further comprises an oxide or oxides of one or more of an element selected from the group consisting of Si, Ta, and Nb.
16. The disk of claim 11 wherein the underlayer comprises two films of said magnetically permeable material and further comprising a nonmagnetic film separating said two magnetically permeable films.
17. The disk of claim 16 wherein the nonmagnetic film provides antiferromagnetic coupling of the two magnetically permeable films.