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Perpendicular World

There appeared some hope when specialists who were threatened to lose their research and development grants remembered about the perpendicular recording technology, that has actually been know for years already. Not all the simple things are ingenious, but all the great things are truly simple, this is the fact.

The main idea behind the perpendicular recording technology is to aim the magnetic domains not along the heads trajectory but perpendicular to it.

This is what the traditional read-and-write head looks like in case of longitudinal recording:

We can see the reading part of the head – the GMR-element on the left. And on the right there is a horse-shoe shaped writing head. The magnetic field generated by the head is closed between the poles through a special shield directing the domains underneath it this or that way depending on the polarity of the current send to the head. As you can see from the picture above, the domains are directed in the longitudinal plane.

The read/write head for the perpendicular recoding technique looks like this:

Here you should pay attention to two key things. Firstly, the read head hasn’t been changed at all. Secondly, the write had seems to have got thicker on one end.

One pole of the new write head is considerably thicker than the other one. This, together with the special magnetic layer inside the platter, changes the magnetization direction. Now it penetrates the platter from the thin pole of the head goes into the magnetic layer and closes on the thick pole afterwards. The misbalanced density of the magnetic field resulting from different pole geometry allows recoding the data under the thin pole and “keeping them” under the thick pole.

Of course, to ensure that this method does work correctly, they had not just to change the shape of the read/write head but also to modify the platter. They needed to add this magnetic layer and… get rid of aluminum!

This is what the platter for perpendicular recording looks like if you cross-cut it. Beneath the protective overcoat there is the magnetic layer we are talking about. Under this layer there are two soft magnetic under-layers separated by the familiar AFC (AntiFerromagnetical Coupling). Even lower we see an adhesion layer and something else with a mysterious name “Substrate”. I believe here some of you will be astonished: this is a layer of glass!

Everything returns to its natural roots, and we see glass coming back to the hard disk drive industry. We only hope that the new generation adhesion material will boast better adhesive features to connect glass and metal layers.

But let’s return to the Soft Under-Layer. Note that you see a mirror reflection of the head in the magnetic under-layer in the picture with the perpendicular head. It is true, this layer turns into the second head “flying” beneath the magnetic layer.

The funny thing is that if you rotate both heads from the perpendicular recording illustration by 90 degrees to the right, we will see a head from the first picture! Nice perpendicular, eh?

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