Perpendicular magnetic recording medium and method of manufacturing the medium
View Patent ↗A perpendicular magnetic recording medium is disclosed in which a soft magnetic layer used as a low K u layer can be stably produced with high performance. Thermal stabilization of magnetization, ease of writing by a magnetic head, and SNR also are improved. A method of manufacturing the medium is disclosed. The perpendicular magnetic recording medium includes at least a nonmagnetic underlayer, a magnetic recording layer, and a protective layer formed in this order on a nonmagnetic substrate. The magnetic recording layer includes a low K u layer having a relatively small perpendicular magnetic anisotropy constant (K u value), and a high K u layer in which the K u value is relatively large, and the low K u layer includes a soft magnetic thin film including an iron group element-based microcrystal structure, in which a nitrogen element is added to a ferromagnetic material mainly containing one of metals of Co, Ni and Fe or an alloy of the metal. The thin film has a crystal structure of a face-centered cubic lattice or hexagonal close packed, and a preferred crystal orientation plane parallel to a plane of the film is a (111) plane in the face-centered cubic lattice structure, and a (002) plane in the hexagonal close packed structure.
1. A perpendicular magnetic recording medium, comprising at least a nonmagnetic underlayer, a magnetic recording layer, and a protective layer formed in this order on a nonmagnetic substrate,
wherein
the magnetic recording layer comprises a low Ku layer having a a Ku value≦3.3×10 5 , and a high Ku layer in which the Ku value is relatively large, and
the low Ku layer comprises a soft magnetic thin film in which nitrogen is added to a ferromagnetic material comprising Co, Cr, and Pt and a nonmagnetic oxide, the thin film having a crystal structure that is face-centered cubic lattice or hexagonal close packed lattice, with crystal orientation plane parallel to a plane of the thin film being a (111) plane in the case of a face-centered cubic lattice and a (002) plane in the case of a hexagonal close packed lattice.
2. The perpendicular magnetic recording medium according to claim 1 , wherein the low Ku layer has a Ku value of 1×10 5 erg/cm 3 or less and the high Ku layer has a Ku value of 1×10 6 erg/cm 3 or more.
3. The perpendicular magnetic recording medium according to claim 1 , wherein the low Ku layer includes crystal grains including ferromagnetic metal and nonmagnetic grain boundaries for magnetically separating the crystal grains from one another, and the nonmagnetic grain boundaries contain the nonmagnetic oxide as a main component.
4. The perpendicular magnetic recording medium according to claim 1 , wherein the high Ku layer comprises an alloy thin film that contains Co as a main component to which at least Pt is added, has a hexagonal close packed lattice crystal structure, and has a (002) crystal orientation plane parallel to a plane of the film.
5. The perpendicular magnetic recording medium according to claim 1 , wherein the high Ku layer comprises crystal grains including ferromagnetic metal and nonmagnetic grain boundaries for magnetically separating the crystal grains from one another, and the nonmagnetic grain boundaries contain a nonmagnetic oxide as a main component.
6. The perpendicular magnetic recording medium according to claim 1 , wherein a ratio of a saturation magnetization value (Ms value) of the low Ku layer to an Ms value of the high Ku layer is 0.8 to 1.2.
7. A method of manufacturing the perpendicular magnetic recording medium according to claim 1 , wherein the low Ku layer is formed by sputtering a material exhibiting ferromagnetism using a sputter gas containing a gas material including a nitrogen compound.
8. The perpendicular magnetic recording medium according to claim 1 , wherein the microcrystal structure of the soft magnetic layer has a crystal structure of the iron group elements.
9. The perpendicular magnetic recording medium according to claim 1 , wherein the low Ku layer is formed by sputtering a material exhibiting ferromagnetism using a sputter gas containing N 2 .
10. The perpendicular magnetic recording medium according to claim 1 , wherein the low Ku layer has a hexagonal close packed lattice crystal structure, with crystal orientation plane parallel to a plane of the thin film being a (002).
11. The perpendicular magnetic recording medium according to claim 1 , wherein the low Ku layer has a face-centered cubic lattice close packed lattice crystal structure, with crystal orientation plane parallel to a plane of the thin film being a (111).
12. The perpendicular magnetic recording medium according to claim 1 , wherein elemental nitrogen (N 2 ) is added to the ferromagnetic material.
13. A perpendicular magnetic recording medium, comprising at least a nonmagnetic underlayer, a magnetic recording layer, and a protective layer formed in this order on a nonmagnetic substrate,
wherein
the magnetic recording layer includes first and second Ku layers in which the first Ku layer has a perpendicular magnetic anisotropy constant (Ku value) that is smaller than the second Ku layer, and has an activation grain size≦5.1 nm and
the first Ku layer comprises a soft magnetic thin film in which nitrogen is added to a ferromagnetic material which comprising Co, Cr, and Pt and a nonmagnetic oxide, the thin film having a crystal structure of a face-centered cubic lattice or hexagonal close packed lattice, with crystal orientation plane parallel to a plane of the thin film being a (111) plane in the case of a face-centered cubic lattice and a (002) plane in the case of a hexagonal close packed lattice.
14. A perpendicular magnetic recording medium according to claim 13 , wherein Ku in the first Ku layer is at least 10 fold smaller than Ku in the second Ku layer.
15. The perpendicular magnetic recording medium according to claim 13 , wherein elemental nitrogen (N 2 ) is added to the ferromagnetic material.
16. A perpendicular magnetic recording medium, comprising at least a nonmagnetic underlayer, a magnetic recording layer, and a protective layer formed in this order on a nonmagnetic substrate, wherein the magnetic recording layer comprises:
a low Ku layer comprising a soft magnetic thin film in which nitrogen is added to a ferromagnetic material comprising Co, Cr, and Pt and a nonmagnetic oxide, the thin film having a crystal structure that is face-centered cubic lattice or hexagonal close packed lattice, with crystal orientation plane parallel to a plane of the thin film being a (111) plane in the case of a face-centered cubic lattice and a (002) plane in the case of a hexagonal close packed lattice, the low Ku layer including crystal grains of a ferromagnetic metal and nonmagnetic grain boundaries for magnetically separating the crystal grains from one another, the nonmagnetic grain boundaries containing the nonmagnetic oxide as a main component, wherein the low Ku layer has a Ku value of 1×10 5 erg/cm 3 or less, and
a high Ku layer comprising an alloy thin film that contains Co as a main component to which at least Pt is added, has a hexagonal close packed lattice crystal structure, has a (002) crystal orientation plane parallel to a plane of the film, and comprises crystal grains including ferromagnetic metal and nonmagnetic grain boundaries for magnetically separating the crystal grains from one another, the nonmagnetic grain boundaries containing a nonmagnetic oxide as a main component, wherein the high Ku layer has a Ku value of 1×10 6 erg/cm 3 or more.
17. The perpendicular magnetic recording medium according to claim 16 , wherein elemental nitrogen (N 2 ) is added to the ferromagnetic material.