A research team led by Dr Alan Drew (University of Fribourg, Switzerland and Queen Mary, London) and Dr Elvezio Morenzoni (Paul Scherrer Institute – PSI, Switzerland) is the first one to have tracked the magnetic processes going on within a hard-drive read head – similar to the heads that read the data off computer hard discs.
In their experiment, the researchers implanted muons into their device. Muons are elementary particles that act like small magnets, and can thus show up the magnetic fields in their surroundings. The muons for this experiment were generated in the particle accelerator at PSI and subsequently subjected to heavy deceleration – PSI is the only location world-wide where this process is available. In the long term, this type of experiment will help us to understand the processes going on inside the read head in greater detail, so that engineers can see where they need to concentrate their efforts to optimise the heads.
The fact that computers can store more data and MP3 players have become so much smaller in the past decade is largely due to an effect that physicists call giant magnetoresistance. In 2007, the Nobel Prize for physics was awarded for the discovery of this effect, which makes it possible to produce electronic components with an electrical resistance extremely sensitive to external magnetic fields. By using the effect in hard drive read heads, magnetically coded information can be packed together very densely, and the hard disc can then be extremely small. Without this effect, it would be impossible for a device half the size of a cigarette packet to store all the information contained in 100 CDs and more.
“Unlike in most electronic components, where the electron’s intrinsic charge is used to carry the signal, magnetic read-heads also use the electron’s ‘spin’ that makes the electron into a tiny magnet. Thus the coining of the term ‘spintronics’” explains the initiator of this research project, Dr Alan Drew of the University of Fribourg (Switzerland) and Queen Mary, University of London. The technical term for the relevant component is a “Spin Valve”, consisting of at least three layers: two magnetic outer layers separated by a non-magnetic spacer layer. One of the magnetic layers is magnetised in a fixed direction, while the magnetisation of the other adjusts itself to the external magnetic field. Currents flowing between the two magnetic layers have a smaller resistance if both layers are magnetised in the same direction. However, if they are magnetised in opposite directions, the electron’s progression is inhibited at the second layer because it arrives with the “wrong” spin orientation.
Via NanoWerk
