Magnetic recording disk with antiferromagnetically-coupled magnetic layer having multiple lower layers
View Patent ↗A magnetic recording disk has an antiferromagnetically-coupled (AFC) structure that has three lower ferromagnetic layers (LL 1 , LL 2 , LL 3 ) and an upper ferromagnetic layer (UL), all four ferromagnetic layers being antiferromagnetically-coupled together across corresponding antiferromagnetically-coupling layers. The UL has a magnetization-remanence-thickness product (Mrt) greater than the Mrt each of the three lower layers LL 1 , LL 2 , LL 3 , and greater than the sum of the Mrt values of LL 1 and LL 3 . The middle lower layer LL 2 has an Mrt less than the Mrt of each of the other lower layers LL 1 and LL 3 , and as a result the composite Mrt of the AFC structure is less than the composite Mrt of a conventional AFC structure having only a single lower layer. The AFC structure achieves this composite Mrt reduction without increasing the Mrt of any of the three lower layers above the maximum Mrt of the single lower layer in the conventional AFC structure.
1. A magnetic recording disk comprising:
a substrate; and
an antiferromagnetically-coupled (AFC) magnetic recording layer on the substrate and having two remanent magnetic states in the absence of an applied magnetic field, the AFC recording layer comprising
(a) a first lower ferromagnetic layer having a remanent magnetization Mr, a thickness t and a remanent-magnetization-thickness product Mrt; (b) a first antiferromagnetically coupling layer on the first lower ferromagnetic layer; (c) a second lower ferromagnetic layer on the first antiferromagnetically coupling layer and having an Mrt less than the Mrt of the first lower ferromagnetic layer; (d) a second antiferromagnetically coupling layer on the second lower ferromagnetic layer; (e) a third lower ferromagnetic layer on the second antiferromagnetically coupling layer and having an Mrt greater than the Mrt of the second lower ferromagnetic layer; (f) a third antiferromagnetically coupling layer on the third lower ferromagnetic layer; and (g) an upper ferromagnetic layer on the third antiferromagnetically coupling layer and having an Mrt greater than the sum of the Mrt values of the first and third lower ferromagnetic layers;
and wherein the magnetization directions of the upper ferromagnetic layer and the third ferromagnetic layer are substantially antiparallel in each remanent state, the magnetization directions of the second lower ferromagnetic layer and the first ferromagnetic layer are substantially antiparallel in each remanent state, and the magnetization direction of the upper ferromagnetic layer in one remanent state is substantially antiparallel to its magnetization direction in the other remanent state.
2. The disk of claim 1 wherein the lower ferromagnetic layers are formed of substantially the same material, and wherein the second ferromagnetic layer has a thickness less than the thickness of each of the first and third lower ferromagnetic layers.
3. The disk of claim 1 wherein the upper ferromagnetic layer is an alloy comprising Co, Pt, Cr and B, and wherein each of the lower ferromagnetic layers is an alloy comprising Co and Cr.
4. The disk of claim 3 wherein each of the lower ferromagnetic layers is an alloy further comprising Ta.
5. The disk of claim 1 wherein each of the antiferromagnetically coupling layers a material selected from the group consisting of ruthenium (Ru), chromium (Cr), rhodium (Rh), iridium (Ir), copper (Cu), and their alloys.
6. The disk of claim 1 further comprising an underlayer located on the substrate between the substrate and the AFC recording layer.
7. The disk of claim 1 further comprising a protective overcoat formed over the upper ferromagnetic layer.