What type of magnets are in hard drives

Given some small magnetic domains existing on a hard drive, how is that information read back and retrieved? What type of materials are best for this? As described above, the information is stored in the changing pattern of magnetization: namely, as the hard drive platter is spinning below the part of the hard drive that reads the information the magnetic read head , the magnetic domains change direction and the encodes the information.

When the magnetic domains switch direction, this means that there are two north or two south poles of the domains facing each other: this creates strong magnetic stray fields in that vicinity. So the read head must travel very close to the surface of the platter see below for more on this as it tries to pick up the weak magnetic fields coming from these domain switches — the fields are weak because the domains are so small, only tens of nanometers across for hard drives today!

Therefore one needs to have a material that is very sensitive to magnetic fields and can convert the existence of the stray fields into some electrical signal to be measured to recover the binary information. The basic idea is to use a material system whose resistance depends on the direction of the magnetic field. In a typical device like a hard drive, the voltage V is fixed as given by the power supply — so for a fixed V, the current I will change inversely as the resistance: if R is large then I is small and vice versa.

If the change in R is significant, then the change in I will be easily measured. Thus a magnetoresistive material is needed which will change its resistance R in response to a magnetic field impinging on it: this will change the current I through it at fixed voltage and thus it will act as magnetic field to electrical current converter! So the information will come out as an electrical signal encoded in the current I either high or low representing binary one or zero.

This is all good in theory — but are there magnetoresistive materials that can change their resistance appreciably with magnetic field? The discovery of GMR was even more remarkable as it was of such technological importance that in about a single decade it was already being used in commercial products like hard drives — a fast rate for science to practical technology transfer. What they discovered is that if one makes a layered sandwich structure of two magnetic materials separated by another material, the current going between the two outer magnetic layers depends strongly on whether magnetic fields from the outside act on the sandwich.

In more detail, the schematic on the right shows the layout of a GMR read head. There are two magnetic ferromagnet in the image layers separated by a conductor layer. The current goes from one ferromagnet to the other through the conductor. The bottom ferromagnet can easily change its direction as shown by the arrows, and is typically made of NiFe permaloy : the NiFe can easily change its magnetization direction when an external magnetic field from the domain switches in the substrate is acting on it.

But why does the resistance change? Amazingly, it does so due to quantum mechanical effects of individual electrons! Once you have the hard drive out, you need to clear your work area and get out your trusty screwdriver! The screws are very small so you will need a screwdriver with a very small head. A hard disc drive freshly removed from a computer.

Remove all the visible screws from the outer casing, they may be really tight so make sure you are using the right screwdriver and give yourself plenty of room.

Once you have removed all the visible screws it is likely there will be more pesky screws concealed by stickers on the outside of the drive so remove any stickers that might be concealing screws and unscrew these too. You will need to remove any further screws holding this in place. As the magnets are quite substantial the assembly may feel like it is being held by more screws, however, if you have taken care to remove them all the force you will be able to feel is magnetism.

You will need to get a sturdy screwdriver under the triangle-shaped plates and prise them out. Data are stored in hard disk drives on the basis of magnetism. The surface of the disk is coated with magnetic material that consists of billions or even trillions of tiny magnets. Computer circuit components are able to store data in terms of whether current is present or not, represented by a 0 or 1.

The north and south poles of the tiny neo magnets on the surface of hard disk drives can represent either 0s and 1s, making them perfect for computer data storage. An electromagnetic head is used to store data into these cells since an electromagnet can reverse its own polarity by reversing the direction of current flowing through it—enabling it to rearrange the polls of the tiny hard disk drive magnets.

The same head can also read the data stored on the hard disk drive. Some headphones, voice coil motor and earbuds, too. Cooling Fans A motor is a necessary part of an electrical fan, and all motors contain magnets since they use magnetism and electricity to induce motion.