Page 24 - Science at the nanoscale

15:10
RPS: PSP0007 - Science-at-Nanoscale
June 9, 2009
14
Introduction and Historical Perspective
Spin Valve On High Current
Spin Valve Off Low Current
Figure 1.7.
Schematic diagram of a simple spin valve.
device that integrates the multiple functionalities with optoelec-
tronics and magnetoelectronics.
There are a number of spintronics devices that have been
realised. The most widely used spintronics device is the Giant
Magnetoresistive (GMR) device commonly used in magnetic
hard-disk drives. Typically, a simple GMR device consists of two
layers of ferromagnetic materials separated by a very thin spacer
layer which is nonmagnetic. A simple illustration of such a spin
valve device is shown in Fig. 1.7. One of the layers is referred to
as the “pinned” layer where its magnetisation direction remains
in a fixed direction. The other ferromagnetic layer is known as
the “free” layer where its magnetisation direction depends on the
externally applied magnetic field. When the two magnetisation
vectors of the ferromagnetic layers are oriented in the same direc-
tion, an electrical current will flow freely. On the other hand, if the ch01
magnetisation vectors are oriented in the opposite direction, there
is a high resistance to the flow of electrons due to spin dependent
scattering. The magnitude of the change in the resistance at these
two different states is called the Giant Magnetoresistance Ratio.
Hence this GMR device is highly sensitive to the external mag-
netic field which is capable of switching the relative magnetic ori-
entation of the ferromagnetic layers. Thus it is widely used as the
read head for magnetic hard disk drives.
There are many other spintronics devices that scientists and
engineers are working on. These include the spin-based transistor,
spin-polarizer, spintronics solar cell, magnetic tunnel junction,