Magnetic recording medium, magnetic storage and method for reproducing information from magnetic recording medium
View Patent ↗A magnetic recording medium includes a first magnetic layer; and a second magnetic layer formed on the first magnetic layer. The first magnetic layer and the second magnetic layer make exchange coupling therebetween and also, have their magnetizing direction in anti-parallel to one another. A net residual area magnetization of the first magnetic layer and the second magnetic layer is expressed by the following formula: |Mr 1 ×t 1 −Mr 2 ×t 2 | where Mr 1 and Mr 2 denote respective residual magnetizations of the first magnetic layer and the second magnetic layer, and t 1 and t 2 denote respective film thicknesses of them; and the net area magnetization at a first temperature is larger than the net area magnetization at a second temperature lower than the first temperature.
1. A magnetic recording medium comprising:
a first magnetic layer; and
a second magnetic layer formed on said first magnetic layer, wherein:
said first magnetic layer and said second magnetic layer make exchange coupling therebetween and also have their respective magnetizing directions anti-parallel to one another;
a net residual area magnetization of said first magnetic layer and said second magnetic layer is expressed by the following formula:
|Mr1×t1−Mr2×t2|
where Mr 1 and Mr 2 denote respective ones of residual magnetization of said first magnetic layer and residual magnetization of said second magnetic layer, and t 1 and t 2 denote respective film thicknesses of them;
the net area magnetization at a first temperature is larger than the net area magnetization at a second temperature lower than said first temperature; and said first magnetic layer and said second magnetic layer comprise in-plane orientation films.
2. The magnetic recording medium as claimed in claim 1 , wherein:
the net area magnetization at said second temperature is set in a range between 1.26 nTm and 5.02 nTm.
3. The magnetic recording medium as claimed in claim 1 , wherein:
a non-magnetic coupling layer is provided between said first magnetic layer and said second magnetic layer.
4. The magnetic recording medium as claimed in claim 1 , wherein:
said first magnetic layer and said second magnetic layer have film thicknesses approximately equal to one another;
Mr 1 and Mr 2 are different from one another at said first temperature; and
Mr 1 and Mr 2 are approximately equal to one another at said second temperature.
5. The magnetic recording medium as claimed in claim 1 , wherein:
said first magnetic layer and said second magnetic layer comprise vertically magnetized films.
6. The magnetic recording medium as claimed in claim 1 , comprising:
said first magnetic layer formed on a substrate;
a non-magnetic coupling layer formed on said first magnetic layer; and
said second magnetic layer formed on said non-magnetic coupling layer, wherein:
at said first temperature and at said second temperature, Mr 2 ×t 2 >Mr 1 ×t 1 .
7. The magnetic recording medium as claimed in claim 6 , wherein:
Mr 1 ×t 1 at said first temperature is smaller than Mr 1 ×t 1 at said second temperature.
8. The magnetic recording medium as claimed in claim 1 , wherein:
said first magnetic layer and/or said second magnetic layer have ferrimagnetism.
9. The magnetic recording medium as claimed in claim 1 , wherein:
said first magnetic layer or said second magnetic layer comprises material selected from among a group of Ni, Fe, Co, an Ni alloy, an Fe alloy, CoCr, CoPt, CoCrTa, CoCrPt, CoPt-M and a Co alloy containing CoCrPt-M, where M denotes B, Mo, Nb, Ta, W, Cu or an alloy thereof.
10. The magnetic recording medium as claimed in claim 9 , wherein:
said first magnetic layer or said second magnetic layer further contains at least one element from among a group of rare-earth elements of Gd, Tb, Dy, Pr, Nd, Yb, Sm, Ho and Er.
11. The magnetic recording medium as claimed in claim 1 , wherein:
Curie temperatures or compensation temperatures of said first magnetic layer and said second magnetic layer are different from one another.
12. A magnetic recording medium comprising:
a first magnetic layer; and
a second magnetic layer formed on said first magnetic layer, wherein:
said first magnetic layer and said second magnetic layer make exchange coupling therebetween and also have their respective magnetizing directions anti-parallel to one another;
a net residual area magnetization of said first magnetic layer and said second magnetic layer is expressed by the following formula:
|Mr1×t1−Mr2×t2|
where Mr 1 and Mr 2 denote respective ones of residual magnetization of said first magnetic layer and residual magnetization of said second magnetic layer, and t 1 and t 2 denote respective film thicknesses of them;
the net area magnetization at a first temperature is larger than the net area magnetization at a second temperature lower than said first temperature; and
said first magnetic layer formed on a substrate;
a non-magnetic coupling layer formed on said first magnetic layer; and
said second magnetic layer formed on said non-magnetic coupling layer, wherein:
at said first temperature and at said second temperature, Mr 2 ×t 2 >Mr 1 ×t 1 ; and
Mr 1 ×t 1 at said first temperature is smaller than Mr 1 ×t 1 at said second temperature.
13. The magnetic recording medium as claimed in claim 12 , wherein:
the net area magnetization at said second temperature is set in a range between 1.26 nTm and 5.02 nTm.
14. The magnetic recording medium as claimed in claim 12 , wherein:
said first magnetic layer and said second magnetic layer have film thicknesses approximately equal to one another;
Mr 1 and Mr 2 are different from one another at said first temperature; and
Mr 1 and Mr 2 are approximately equal to one another at said second temperature.
15. The magnetic recording medium as claimed in claim 12 , wherein:
said first magnetic layer and said second magnetic layer comprise in-plane orientation films.
16. The magnetic recording medium as claimed in claim 12 , wherein:
said first magnetic layer and said second magnetic layer comprise vertically magnetized films.
17. The magnetic recording medium as claimed in claim 12 , wherein:
said first magnetic layer and/or said second magnetic layer have ferrimagnetism.
18. The magnetic recording medium as claimed in claim 12 , wherein:
said first magnetic layer or said second magnetic layer comprises material selected from among a group of Ni, Fe, Co, an Ni alloy, an Fe alloy, CoCr, CoPt, CoCrTa, CoCrPt, CoPt-M and a Co alloy containing CoCrPt-M, where M denotes B, Mo, Nb, Ta, W, Cu or an alloy thereof.
19. The magnetic recording medium as claimed in claim 18 , wherein:
said first magnetic layer or said second magnetic layer further contains at least one element from among a group of rare-earth elements of Gd, Tb, Dy, Pr, Nd, Yb, Sm, Ho and Er.
20. The magnetic recording medium as claimed in claim 12 , wherein:
Curie temperatures or compensation temperatures of said first magnetic layer and said second magnetic layer are different from one another.