Electric field applying magnetic recording method and magnetic recording system
A method for writing information on a highly coercive recording medium stably with an electric field applied through a metal probe and with a magnetic field applied from external and an information recording system that employs the method. The recording medium includes a substrate, a first ferromagnetic layer formed on the substrate, a nonmagnetic layer formed on the first ferromagnetic layer, and a second ferromagnetic layer formed on the nonmagnetic layer. The coercivity Hc 2 of the second ferromagnetic layer is larger than that Hc 1 of the first ferromagnetic layer. A magnetic field H is applied to the magnetic recording medium from a magnetic pole to change the magnetizing direction of the first ferromagnetic layer to a direction of the applied magnetic field, then a positive or negative voltage V is applied between the metal probe and the magnetic recording medium to change the quantum well level energy between the first and second ferromagnetic layers, thereby inducing an exchange magnetic field H E . As a result, the magnetizing direction of the second ferromagnetic layer is changed with both the exchange magnetic field H E and the magnetic field H.
1. A magnetic recording system comprising:
a magnetic recording medium including a substrate, a first ferromagnetic layer formed on said substrate, a nonmagnetic layer formed on said first ferromagnetic layer, and a second ferromagnetic layer formed on said nonmagnetic layer;
a magnetic pole for applying a magnetic field H to invert a magnetizing direction of said first ferromagnetic layer; and
means for applying a positive or a negative voltage V between a metallic probe and said magnetic recording medium,
wherein a coercivity Hc 2 of said second ferromagnetic layer is larger than that Hc 1 of said first ferromagnetic layer;
wherein a quantum well level is formed in said nonmagnetic layer formed between said first and second ferromagnetic layers;
wherein said magnetic field H changes said magnetizing direction of said first ferromagnetic layer to a direction of an applied magnetic field;
wherein applying said positive or negative voltage V changes an energy of said quantum well level between said first and second ferromagnetic layers, thereby inducing an exchange magnetic field H E ; and
wherein said magnetic field H and said exchange magnetic field H E work together to invert said magnetizing direction of said second ferromagnetic layer.
2. The magnetic recording system according to claim 1 , wherein said coercivity Hc 1 of said first ferromagnetic layer, said coercivity Hc 2 of said second ferromagnetic layer, and said magnetic field H are in a relationship of Hc 1 <H<Hc 2 ; and
wherein said exchange magnetic field H E has a relationship of Hc 2 <H+H E with said coercivity Hc 2 of said second ferromagnetic layer and said magnetic field H.
3. The magnetic recording system according to claim 2 , wherein said exchange magnetic field H E has a relationship of H-H E <Hc 1 with said coercivity Hc 1 of said first ferromagnetic layer and said magnetic field H.
4. The magnetic recording system according to claim 1 , wherein said first ferromagnetic layer is formed on an antiferromagnetic layer and magnetization of said first ferromagnetic layer is fixed.
5. The magnetic recording system according to claim 1 , wherein said first and second ferromagnetic layers are magnetized in a longitudinal direction respectively.
6. The magnetic recording system according to claim 1 , wherein said first and second ferromagnetic layers are magnetized in a direction perpendicular to their film surfaces respectively.
7. The magnetic recording system according to claim 1 , wherein said magnetic recording medium further includes:
a third ferromagnetic layer formed between said first ferromagnetic layer and said substrate through a nonmagnetic layer; and
an antiferromagnetic layer formed between said substrate and said third ferromagnetic layer.
8. The magnetic recording system according to claim 1 , wherein a magnetic exchange interaction that works between said first and second ferromagnetic layers is almost zero while said positive or negative voltage V is not applied.
9. The magnetic recording system according to claim 1 , wherein said positive or negative voltage is applied between the metallic probe and a surface of a magnetized region and said magnetizing direction of each of said ferromagnetic layers is read according to a change of a tunnel current value.
10. A magnetic recording system, comprising:
a magnetic recording medium including a substrate, a first ferromagnetic layer formed on said substrate, a nonmagnetic layer formed on said first ferromagnetic layer, and a second ferromagnetic layer formed on said nonmagnetic layer;
a magnetic pole for applying a magnetic field H to invert a magnetizing direction of said first ferromagnetic layer; and
an electrode for applying a positive or negative voltage V between a metallic probe and said magnetic recording medium, wherein a coercivity Hc 2 of said second ferromagnetic layer is larger than that Hc 1 of said first ferromagnetic layer;
wherein said magnetic field H changes said magnetizing direction of said first ferromagnetic layer to a direction of an applied magnetic field; and
wherein applying said positive or negative voltage V inverts said magnetizing direction of said second ferromagnetic layer, thereby recording magnetization information in said second ferromagnetic layer.
11. The system according to claim 10 , wherein application of said positive or negative voltage V induces an exchange magnetic field H E ; and
wherein said exchange magnetic field H E and said magnetic field H work together to invert said magnetizing direction of said second ferromagnetic layer.
12. The magnetic recording system according to claim 10 ,
wherein said coercivity Hc 1 of said first ferromagnetic layer, said coercivity Hc 2 of said second ferromagnetic layer, and said magnetic field H are in a relationship of Hc 1 <H<Hc 2 ; and
wherein said exchange magnetic field H E has a relationship of Hc 2 <H+H E with said coercivity Hc 2 of said second ferromagnetic layer and said magnetic field H.
13. The magnetic recording system according to claim 12 , wherein said exchange magnetic field H E has a relationship of H-H E <Hc 1 with said coercivity Hc 1 of said first ferromagnetic layer and said magnetic field H.
14. An electric field applying magnetic recording method comprising the steps of:
applying a magnetic field H from a magnetic pole to a magnetic recording medium composed of a substrate, a first ferromagnetic layer formed on said substrate, a nonmagnetic layer formed on said first ferromagnetic layer, and a second ferromagnetic layer of which coercivity Hc 2 is larger than that Hc 1 of said first ferromagnetic layer, formed on said nonmagnetic layer, thereby changing a magnetizing direction of said first ferromagnetic layer to a direction of said applied magnetic field;
applying a positive or negative voltage V between a metallic probe and said magnetic recording medium to change an energy of a quantum well level between said first and second ferromagnetic layers, thereby inducing an exchange magnetic field H E ; and
changing a magnetizing direction of said second ferromagnetic layer to a direction of said applied magnetic field with both said exchange magnetic field H E and said magnetic field H.
15. The method according to claim 14 ,
wherein said coercivity Hc 1 of said first ferromagnetic layer, said coercivity Hc 2 of said second ferromagnetic layer, and said magnetic field H are in a relationship of Hc 1 <H<Hc 2 ; and
wherein said exchange magnetic field H E has a relationship of Hc 2 <H+H E with said coercivity Hc 2 of said second ferromagnetic layer and said magnetic field H.
16. The method according to claim 14 , wherein said exchange magnetic field H E has a relationship of H-H E <Hc 1 with said coercivity Hc 1 of said first ferromagnetic layer and said magnetic field H.