Nanotechnology-Enabled Sensors

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Chapter 6: Inorganic Nanotechnology Enabled Sensors
materials are able to demonstrate resistance changes by several orders of
magnitude.
6.7.2 Spin Valves
A spin valve is a GMR-based device (Fig. 6.50). A typical spin valve
may contain two ferromagnetic layers (e.g. alloys of nickel, iron, and cobalt)
sandwiching a thin nonmagnetic metal (usually copper). 114 In such a
structure one of the two magnetic layers is relatively insensitive to moderate
magnetic fields while magnetization of the other magnetic layer can be
changed by application of a relatively small magnetic field. An antiferromagnetic
layer is also in intimate contact with the insensitive magnetic
layer. As the magnetizations in the two layers change from parallel to antiparallel
alignment, the resistance of the spin valve rises typically from 5 to
10%.
There are other ways of forming a spin-valve. The insensitive magnetic
layer can be replaced with a synthetic antiferromagnet which consists of
two magnetic layers separated by a very thin (~10 Å) nonmagnetic conductor,
such as ruthenium. 118 The magnetizations in the two magnetic layers
are strongly antiparallel coupled. As a result, they are also effectively
immune to outside magnetic fields. This structure improves both stand-off
magnetic fields and the operational temperature of the spin valve. Another
method of constructing a spin valve is by using a nano-oxide layer formed
at the outside surface of the soft magnetic film. This layer reduces resistance
due to surface scattering, thereby increasing the percentage change in
magnetoresistance. 127