Antiferromagnetically coupled media for magnetic recording with weak coupling layer
View Patent ↗An embodiment of the invention is a layered magnetic thin film structure that uses antiferromagnetically coupled (AFC) magnetic layers where the top layer structure consists of an upper magnetic layer that is weakly ferromagnetically coupled via a nonmagnetic or weakly magnetic exchange coupling layer (interlayer) to a ferromagnetic exchange enhancing layer that is in turn, AF coupled to the lower ferromagnetic layer of the AFC structure. Preferred materials for the weak coupling layer include alloys of cobalt such as CoRu, CoBRu and CoCr in which the Co content is below the point at which the material would be ferromagnetic. A second embodiment of the invention is a laminated, AF-coupled media structure. In this structure the lower AFC layer that makes up the lower laminate layer includes: the middle magnetic layer, the weak ferromagnetic coupling layer, and the exchange enhancing layer.
1. A thin film magnetic recording medium comprising:
a first magnetic layer;
a spacer layer above the first magnetic layer;
a magnetic exchange enhancing layer above the spacer layer antiferromagnetically coupled to the first magnetic layer;
a weak coupling layer above the exchange enhancing layer, the weak coupling layer being nonmagnetic at room temperature and ferromagnetic below room temperature and ferromagnetically coupling the exchange enhancing layer to a second magnetic layer;
the second magnetic layer above and adjacent to the weak coupling layer;
a decoupling spacer layer above the second magnetic layer; and
a third magnetic layer above the decoupling spacer layer, the third magnetic layer being exchange decoupled from the second magnetic layer.
2. The thin film magnetic recording medium of claim 1 wherein the ferromagnetic coupling between the exchange enhancing layer and the second magnetic layer is less than direct exchange coupling.
3. The thin film magnetic recording medium of claim 1 wherein the weak coupling layer is an alloy of cobalt and ruthenium with from 50 to 80 atomic percentage ruthenium.
4. The thin film magnetic recording medium of claim 1 wherein the weak coupling layer is an alloy of cobalt, ruthenium and optionally boron with from 0 to 15 atomic percentage of boron and from 50 to 70 atomic percentage ruthenium.
5. The thin film magnetic recording medium of claim 1 wherein the weak coupling layer is an alloy of cobalt and chromium with 25 to 40 atomic percentage chromium.
6. The thin film magnetic recording medium of claim 1 wherein the magnetic exchange enhancing layer is an alloy of cobalt and boron with 5 to 30 atomic percentage of boron.
7. The thin film magnetic recording medium of claim 1 wherein the magnetic exchange enhancing layer is a ferromagnetic CoCr alloy.
8. The thin film magnetic recording medium of claim 1 wherein the magnetic exchange enhancing layer is a ferromagnetic alloy of cobalt with 5 to 20 atomic percent boron and up to 20 atomic percent chromium where combined atomic percentage of boron and chromium is less than or equal to 30 atomic percent.
9. A disk drive comprising:
a magnetic head for writing magnetic transitions in a magnetic medium on a disk; and
the disk with the magnetic medium comprising:
a first magnetic layer;
a spacer layer above the first magnetic layer;
a magnetic exchange enhancing layer above the spacer layer antiferromagnetically coupled to the first magnetic layer;
a weak coupling layer above the exchange enhancing layer, the weak coupling layer being nonmagnetic at room temperature and ferromagnetic below room temperature and ferromagnetically coupling the exchange enhancing layer to a second magnetic layer;
the second magnetic layer above and adjacent to the weak coupling layer;
a decoupling spacer layer above the second magnetic layer; and
a third magnetic layer above the decoupling spacer layer, the third magnetic layer being exchange decoupled from the second magnetic layer.
10. The disk drive of claim 9 wherein an effective coupling field created by the weak coupling layer is approximately equal to a write field in the second magnetic layer generated by the magnetic head.
11. The disk drive of claim 9 wherein the weak coupling layer is an alloy of cobalt and ruthenium with from 50 to 80 atomic percentage ruthenium.
12. The disk drive of claim 9 wherein the weak coupling layer is an alloy of cobalt, ruthenium and optionally boron with from 0 to 15 atomic percentage of boron and from 50 to 70 atomic percentage ruthenium.
13. The disk drive of claim 9 wherein the weak coupling layer is an alloy of cobalt and chromium with 25 to 40 atomic percentage chromium.
14. The disk drive of claim 9 wherein the magnetic exchange enhancing layer is an alloy of cobalt and boron with 5 to 30 atomic percentage of boron.
15. The disk drive of claim 9 wherein the magnetic exchange enhancing layer is a ferromagnetic CoCr alloy.
16. The disk drive of claim 9 wherein the magnetic exchange enhancing layer is a ferromagnetic alloy of cobalt with 5 to 20 atomic percent boron and up to 20 atomic percent chromium where combined atomic percentage of boron and chromium is less than or equal to 30 atomic percent.