Perpendicular magnetic recording medium with single domain exchange-coupled soft magnetic underlayer and device incorporating same
View Patent ↗A perpendicular magnetic recording disk having a single domain exchange-coupled laminated soft magnetic underlayer (SUL) is disclosed. The SUL is a combination synthetic anti-parallel coupled SUL structure, which has the product (Mst) of saturation magnetization and film thickness of the middle ferromagnetic layer less than the sum of the Mst of the bottom and top ferromagnetic layers. Subjected to a post radial field reset process, this SUL provides single domain state. Moreover, both robustness of stray fields and low permeability are obtained while keeping excellent corrosion resistance and cost effective manufacturability.
1. A method of producing a magnetic recording medium with a single domain soft magnetic underlayer, comprising:
depositing a first soft ferromagnetic layer above a substrate;
depositing a first spacer layer above said first soft ferromagnetic layer;
depositing a second soft ferromagnetic layer above said first spacer layer;
depositing a second spacer layer above said second soft ferromagnetic layer;
depositing a third soft ferromagnetic layer above said second spacer layer, wherein a material of one of the first soft ferromagnetic layer, the second soft ferromagnetic layer, and the third soft ferromagnetic layer is different from a material of another of the first soft ferromagnetic layer, the second soft ferromagnetic layer, and the third soft ferromagnetic layer;
whereby the product of saturation magnetization (Ms) and thickness (t), Mst, of the second soft ferromagnetic layer is less than the sum of the Mst of the first soft ferromagnetic layer and the Mst of the third soft ferromagnetic layer; and
performing a radial field reset such that said first soft ferromagnetic layer assumes a first remanent radial magnetic orientation, said second soft ferromagnetic layer assumes a second remanent radial magnetic orientation anti-parallel to said first remanent radial magnetic orientation, and said third soft ferromagnetic layer assumes said first remanent radial magnetic orientation.
2. The method of claim 1 , wherein said radial field reset is performed by exposure of the soft ferromagnetic layers to a radial magnetic field of strength at least equal to the switching field of the soft magnetic underlayer along the radial direction of the substrate.
3. The method of claim 1 , wherein said radial field reset is performed by exposure of the soft ferromagnetic layers to a radial magnetic field strength that is greater than the saturation field strength of the soft magnetic underlayer along the circuital direction of said substrate.
4. The method of claim 1 , wherein the sum of the Mst of each of said first, second and third soft ferromagnetic layers is equal to or greater than 2.0 memu/cm2 and less than 12.5 memu/cm2.
5. The method of claim 1 , wherein the Mst of said second soft ferromagnetic layer is 75%-99% of the sum of the Mst of said first soft ferromagnetic layer and the Mst of said third soft ferromagnetic layer.
6. The method of claim 1 , wherein each of said second and third soft ferromagnetic layers include cobalt, and at least one other element selected from the group consisting of: iron, nickel, manganese, palladium, tantalum, niobium, zirconium, hafnium, chromium, titanium, molybdenum, vanadium, tungsten, aluminum, silicon, boron, nitrogen, and oxygen.
7. The method of claim 1 , wherein the performing the radial field reset such that said first soft ferromagnetic layer assumes the first remanent radial magnetic orientation, said second soft ferromagnetic layer assumes the second remanent radial magnetic orientation anti-parallel to said first remanent radial magnetic orientation, and said third soft ferromagnetic layer assumes said first remanent radial magnetic orientation comprises:
depositing a nucleation layer above the third soft ferromagnetic layer;
depositing a magnetic recording layer above said nucleation layer; and
performing the radial field reset such that said first soft ferromagnetic layer assumes the first remanent radial magnetic orientation, said second soft ferromagnetic layer assumes the second remanent radial magnetic orientation anti-parallel to said first remanent radial magnetic orientation, and said third soft ferromagnetic layer assumes said first remanent radial magnetic orientation.
8. The method of claim 1 :
wherein the thickness of the first soft ferromagnetic layer is equal to the thickness of the third soft ferromagnetic layer; and wherein the thickness of the second soft ferromagnetic layer is 75%-99% of twice the thickness of the first soft ferromagnetic layer.
9. The method of claim 1 , wherein the first soft ferromagnetic layer, the first spacer layer, the second soft ferromagnetic layer, the second spacer layer, and the third soft ferromagnetic layer provide the single domain soft magnetic underlayer.