Magnetic recording medium, method of producing the same, and magnetic storage apparatus
A magnetic recording medium including a substrate having a surface, an orientation control layer disposed above the surface of the substrate, an underlayer disposed above the orientation control layer, and a recording layer having an hcp crystal structure and disposed on a surface of the underlayer. The recording layer is epitaxially grown on the surface of the underlayer to define a plurality of crystal grains, wherein the crystal grains have c-axes that are inclined in a plurality of random directions, but wherein each random direction defines an angle with respect to the surface of the substrate that is within a range that is greater than 0 degrees and less than or equal to 30 degrees. A magnetic storage apparatus including such a magnetic recording medium is also disclosed.
1. A magnetic recording medium comprising:
a substrate having a surface;
an orientation control layer disposed above the surface of the substrate;
an underlayer disposed above the orientation control layer; and
a recording layer having an hcp crystal structure and disposed on a surface of the underlayer,
said recording layer being epitaxially grown on the surface of the underlayer to define a plurality of crystal grains, wherein the crystal grains have c-axes that are inclined in a plurality of random directions, but wherein each random direction defines an angle with respect to the surface of the substrate that is within a range that is greater than 0 degrees and less than or equal to 30 degrees.
2. The magnetic recording medium as claimed in claim 1 , wherein the orientation control layer is made of a non-magnetic material including nitrogen or oxygen.
3. A magnetic recording medium comprising:
a substrate having a surface;
an orientation control layer disposed above the surface of the substrate;
an underlayer, made of Cr or a Cr alloy having Cr as a main component, and disposed above the orientation control layer; and
a recording layer having an hcp crystal structure and disposed on a surface of the underlayer,
said orientation control layer being made of a non-magnetic material including nitrogen or oxygen,
said recording layer being made up of a first magnetic layer, a non-magnetic coupling layer and a second magnetic layer that are successively epitaxially grown on the surface of the underlayer,
said first and second magnetic layers being exchange-coupled and having magnetizations that are mutually antiparallel in a state where no external magnetic field is applied to the magnetic recording medium,
said first and second magnetic layers being made of a ferromagnetic material having an hcp crystal structure and including Co as a main component, defining a plurality of crystal grains, wherein the crystal grains have c-axes that are inclined in a plurality of random directions, but wherein each random direction defines an angle with respect to the surface of the substrate that is within a range that is greater than 0 degrees and less than or equal to 30 degrees.
4. The magnetic recording medium as claimed in claim 3 , wherein the non-magnetic coupling layer is made of a material selected from a group consisting of Ru, Rh, Ir, Ru alloys, Rh alloys and Ir alloys.
5. The magnetic recording medium as claimed in claim 3 , wherein the surface of the substrate includes a plurality of concave portions and/or a plurality of convex portions that respectively extend in a recording direction.
6. The magnetic recording medium as claimed in claim 3 , wherein the substrate has a disk shape, and the surface of the substrate includes a plurality of concave portions and/or a plurality of convex portions that respectively extend in a circumferential direction.
7. The magnetic recording medium as claimed in claim 5 , further comprising:
a seed layer, made of an amorphous material or a crystalline material having a B 2 crystal structure, disposed on the surface of the substrate,
said seed layer having a surface that includes a plurality of concave portions and/or a plurality of convex portions that respectively extend in a recording direction.
8. The magnetic recording medium as claimed in claim 3 , wherein the non-magnetic material including nitrogen or oxygen is selected from a group consisting of NiP, AlV, AlTi, CoW and CrTi.
9. The magnetic recording medium as claimed in claim 3 , wherein the non-magnetic material including nitrogen or oxygen is selected from a group consisting of crystalline metals having a bcc crystal structure and a B 2 crystal structure.
10. The magnetic recording medium as claimed in claim 3 , wherein the non-magnetic material including nitrogen or oxygen has an fcc crystal structure and is selected from a group consisting of Au, Al, Ag, Pt and alloys thereof.
11. The magnetic recording medium as claimed in claim 3 , wherein the underlayer is made of Cr—X1 having a bcc crystal structure, where X1 is selected from a group consisting of W, Mo, Nb, Ta, V and alloys thereof.
12. The magnetic recording medium as claimed in claim 3 , wherein the first and second magnetic layers are made of a ferromagnetic material selected from a group consisting of CoCr, CoCr alloys, CoPt, CoCrPt, CoCrTa and CoCrPt alloys.
13. The magnetic recording medium as claimed in claim 3 , wherein a diffraction ray observed with respect to Co by a θ-2θ scan by an X-ray diffractometer method only corresponds substantially to a (10-11) crystal.
14. The magnetic recording medium as claimed in claim 3 , wherein a diffraction ray observed with respect to Cr by a θ-2θ scan by an X-ray diffractometer method only corresponds substantially to a (110) crystal face.
15. The magnetic recording medium as claimed in claim 3 , a coercivity ratio Hc 1 /Hc 2 of an in-plane coercivity Hc 1 to a perpendicular coercivity Hc 2 of the recording layer, measured by a Kerr rotation angle measuring method, is in a range of 0.34 or greater and 0.41 or less.
16. The magnetic recording medium as claimed in claim 3 , further comprising:
a first soft magnetic layer disposed between the substrate and the orientation control layer.
17. The magnetic recording medium as claimed in claim 16 , further comprising:
a stacked structure, disposed between the substrate and the orientation control layer, and comprising a second soft magnetic layer, a second non-magnetic coupling layer and a third soft magnetic layer that are successively stacked,
said second and third soft magnetic layers being exchange-coupled, and having magnetizations that are mutually antiparallel in a state where no external magnetic field is applied to the magnetic recording medium.
18. The magnetic recording medium as claimed in claim 17 , wherein the stacked structure is stacked on the first soft magnetic layer, and the second and third soft magnetic layers have saturation magnetic flux densities that are larger than that of the first soft magnetic layer.
19. The magnetic recording medium as claimed in claim 17 , wherein said second non-magnetic coupling layer is made of a material selected from a group consisting of Ru, Re, Os, Ir and alloys thereof.
20. A magnetic storage apparatus comprising:
at least one magnetic recording medium including:
a substrate having a surface;
an orientation control layer disposed above the surface of the substrate;
an underlayer disposed above the orientation control layer; and
a recording layer having an hcp crystal structure and disposed on a surface of the underlayer,
said recording layer being epitaxially grown on the surface of the underlayer to define a plurality of crystal grains, wherein the crystal grains have c-axes that are inclined in a plurality of random directions, but wherein each random direction defines an angle with respect to the surface of the substrate that is within a range that is greater than 0 degrees and less than or equal to 30 degrees; and
at least one head part configured to record information on and reproduce information from the magnetic recording medium.