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I have been having a theoretical discussion with a colleague at work. He proposed the idea of a laser being able to erase a hard drive.

I know that a hard drive is basically a magnetic disc that can be polarised using an electromagnetic write head.

Given that light has an electrical and magnetic field component I would assume it is possible to erase or fry(electrically not thermally) electronics.

My question is this. Is it theoretically possible to erase(not destroy) a hard drive with light in the visible spectrum?

Edit: It appears I was unclear with my earlier question. In this theoretical situation, we are only interested in the effects of the electric and magnetic effects of light. Please ignore thermal effects such as heating the disc until it reaches its Curie temperature.

My personal hypothesis on the matter is that if you could get a very powerful laser that gave off light that was not absorbed by the HDD, and if all that light was in phase, that it might be possible to add up the electrical and magnetic fields to a point where the HDD could be edited(magnetically not thermally) by the light.

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Any erasing would likely be from thermal effects. If the light heats a spot on the disk above the material's Curie temperature, the magnetic field generated by that spot will relax. That may or may not be hot enough to destroy the disk.

You would probably want to use a short pulse from a laser focused on a small spot. This would locally heat the bit in question, and turn off before enough heat was added to raise the temperature of nearby spots.

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  • $\begingroup$ This is definitely an interesting approach that makes sense. However, this discussion evolved from the idea of an EMP being able to destroy electronics and wipe hard drives. to my knowledge EMP stands for electromagnetic pulse seeing as light also contains these electric and magnetic components the question evolved to being "can you erase a hard drive light" $\endgroup$
    – Michael
    Mar 1, 2021 at 21:44
  • $\begingroup$ Yes, but I think the question the OP is asking here is about a possibility of whether or not the rapidly alternating magnetic field that is part of the light could do something more directly to the recording and without the need for heating. $\endgroup$ Mar 1, 2021 at 21:54
  • $\begingroup$ (In particular, a strong alternating magnetic field at much lower frequencies could "degauss" the drive, so the question is whether the extreme frequency fields in light could do the same, and if not, why not. I suppose though that this might be dependent on the fact that much lower frequencies the whole platter is within the blur radius of the "light", while with light-light the wavelength is too small. However, there might be something if we consider that on suitably data-dense hard drives the particles are going to have to be eventually comparable or smaller than a wavelength, $\endgroup$ Mar 1, 2021 at 21:57
  • $\begingroup$ and so they will feel a whole oscillating field.) $\endgroup$ Mar 1, 2021 at 21:57
  • $\begingroup$ (That said, I don't know if current drives reach that level - that's an about 0.25 um^2 magnetic grain size.) $\endgroup$ Mar 1, 2021 at 21:58
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The answer is NO. Gyromagnetic effects limit the rate at which magnetization can be changed. In most situations, magnetization will not respond to frequencies much above a few GHz and certainly not to optical frequencies.

However, all-optical switching of magnetization is a recent and active area of research (for example in 'Nature'). All-optical switching can be extremely rapid. There is some controversy over the exact mechanisms involved. Typically these effects are observed in specialized materials and not at all in the high-coercivity, high-magnetization CoPtCr alloys used in HDDs.

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  • $\begingroup$ Thank you very much. I had no idea that there was a speed limit for magnetization. $\endgroup$
    – Michael
    Mar 3, 2021 at 21:48
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I think your colleague may refer to the Heat-assisted magnetic recording(HAMR) driver. Basically, it is using laser as a heater but not a tool to change the electromagnetic field. For details, you may find more on Wikipedia.

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