Patent Grant
7420780
The invention relates to the general field of magnetic disk systems with particular reference to magnetic write heads for perpendicular designs, more specifically to remnant field reduction in single pole heads.
Perpendicular magnetic recording (PMR) is important for the future of the magnetic recording industry because it offers higher areal density than the current longitudinal magnetic recording (LMR). This is due to the fact that the PMR medium is thermally more stable than that used for LMR. At present, LMR has achieved over 100 Gigabits per square inch (Gbpsi) in the laboratory and more than 60 Gpsi in products currently offered at the market place. In order to further extend the LMR recording density, two main obstacles have to be overcome. The first one is the thermal stability of the LMR recording media which arises because its thickness has to decrease to the extent that thermal energy could randomize the recorded bits. The second one is the ongoing increase in the write field needed to record on the high coercivity LMR media.
This high coercivity is needed to achieve high bit resolution and good thermal stability. Both obstacles to LMR would be considerably lowered if PMR were deployed instead. Thicker PMR media with a magnetically soft under-layer film (SUL) could be used to alleviate the thermal stability problem. A PMR writer provides a larger write field than that of LMR, which is limited to the fringe field from its write gap.
An example of a perpendicular writer of the prior art is shown in
Currently, the single pole is usually made of high Bs (saturation flux density—measured in Teslas) material, with values >2T, and has very small dimensions (0.1 μm in width and 0.2 μm in thickness) together with a relatively long yoke. As a result, the single pole has very large shape anisotropy. After the writing process, the remnant field from a single pole can be very large (as high as 2 kOe), which usually causes erasure of written bits. This problem will get more severe with further decreases in device dimensions.
A routine search of the prior art was performed with the following references of interest being found:
In U.S. Pat. No. 5,477,007, Shukh et al describe a top pole having a laminated structure. In U.S. Pat. No. 6,278,590 Gill et al disclose a laminated pole. U.S. Pat. No. 6,396,735 (Michijima et al) shows a laminated memory element. Sasaki teaches that a top pole may be laminated of two or more materials in U.S. Pat. No. 6,255,040. In U.S. Pat. No. 5,621,592, Gill et al disclose a laminated Fe-based/NiMn structure for a write pole while Mallary shows a vertically laminated pole in U.S. Pat. No. 5,108,837. Note that all these references relate to LMR and are not applicable to perpendicular recording systems in the forms and dimensions described.
It has been an object of at least one embodiment of the present invention to provide a magnetic writer suitable for vertical recording.
Another object of at least one embodiment of the present invention has been that the write pole of said writer exhibit low remnant magnetization when not in use.
Still another object of at least one embodiment of the present invention has been that said write pole provide a high write field as well as a low remnant magnetization.
A further object of at least one embodiment of the present invention has been that manufacture of said write pole introduce no significant changes to existing processes for manufacturing the writer.
These Objects have been achieved by giving the write pole the form of a three-layer laminate in which two ferromagnetic layers are separated by an anti-ferromagnetic coupling layer or by a non-magnetic layer. If an antiferromagnetic coupling layer is used, its thickness is chosen to be optimum for antiferromagnetic coupling. In the remanent state (no external driving field), the two laminated ferromagnetic layers will stay antiparallel to each other so as to minimize the interlayer exchange coupling energy and to allow as much magnetic flux closure as possible, leaving the structure with a low net magnetic moment. For the non-magnetic layer, its thickness is chosen so that there can be no ferromagnetic exchange coupling between the ferromagnetic layers, in which case the low net magnetic moment is achieved solely through magnetic flux closure.
We will disclose the present invention by providing a description of a method for generating it, thereby making the structure of the invention apparent as well. Referring now to
Conductive coil 12 is also formed so that it surrounds yoke 11. The various incidences of layer 31 that appear in the figure represent insulating, non-magnetic material that serves to provide mechanical integrity to the structure.
Normally, the next step would be to deposit the full thickness of the write pole. However, in a departure from the prior art, a first (lower) layer of ferromagnetic material 22 is deposited onto the topmost surface of 31 as well as onto the exposed surface of yoke 11, giving the structure, at this stage, the appearance seen in
Now follows a key novel feature of the invention. As seen in
(1) layer 23 is an antiferromagnetic coupling material. In this case, Its thickness is carefully chosen as needed for an effective antiferromagnetic coupling between layers 22 and 24. A wide range of antiferromagnetic coupling materials is available, including Ru, Rh, and Ir, but the choice of thickness will depend on which one is selected. For example, if the antiferromagnetic coupling layer is Ru it will need to be deposited to a thickness between about 3 and 10 Angstroms while if it is Rh it will need to be deposited to a thickness between about 4 and 7 Angstroms.
(2) layer 23 is a non-magnetic material such as Ta, NiCr, Cu, or Al2O3, with NiCr being preferred. Its thickness is between about 5 and 50 Angstroms which is carefully chosen to be just thick enough to prevent any exchange coupling between layers 22 and 24 but still thin enough to allow strong magnetostatic coupling between layers 22 and 24. As a result, these two layers will automatically orient themselves so as to be magnetically antiparallel to one another when no external field is present. However, in the presence of a strong external field, both layers will align themselves in the same direction and act as a single unit.
Note that, as a further refinement, the coupling field between layers 22 and 24 can be adjusted by insertion of a lower coercivity layer at the antiferromagnetic-ferromagnetic interface. For example, if layers 22 and 24 are of CoFe, an adjusting layer of NiFe could be used (see examples c, d, e, and f below).
After the deposition of one or other of the two versions of layer 23, upper ferromagnetic layer 24 is laid down to a thickness between about 500 and 2,000 Angstroms. Suitable materials for layer 24 include CoNiFe, FeCo, and other high Bs alloys of Fe, Co, and Ni, with FeCo being preferred. Preferably, but not critically, layers 22 and 24 will have the same thickness and be of the same material.
Moving on to
We have determined that, provided the materials and thickness ranges are as disclosed above, the resulting laminated write poles have residual fluxes that are less than about 0.1T, while at the same time being able to provide a write field of at least 10 kOe.
We list below several examples of the laminate structure including addition of NiFe for fine adjustment (thicknesses in Angstroms):
This is a divisional application of U.S. patent application Ser. No. 10/610,036, filed on Jun. 30, 2003, now U.S. Pat. No. 7,064,924, which is herein incorporated by reference in its entirety, and assigned to a common assignee.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5108837 | Mallary | Apr 1992 | A |
| 5621592 | Gill et al. | Apr 1997 | A |
| 6255040 | Sasaki | Jul 2001 | B1 |
| 6278590 | Gill et al. | Aug 2001 | B1 |
| 6396735 | Michijima et al. | May 2002 | B2 |
| 6477007 | Shukh et al. | Nov 2002 | B1 |
| 20030076629 | Minor | Apr 2003 | A1 |
| 20030133224 | Minor et al. | Jul 2003 | A1 |
| 20030197976 | Van der Heijden et al. | Oct 2003 | A1 |
| 20040004786 | Shukh et al. | Jan 2004 | A1 |
| 20040066574 | Crue et al. | Apr 2004 | A1 |
| 20040201918 | Guan et al. | Oct 2004 | A1 |
| 20040252415 | Shukh et al. | Dec 2004 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20060203382 A1 | Sep 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10610036 | Jun 2003 | US |
| Child | 11435053 | US |
