Giant magnetoresistance devic

The electronic and magnetic properties of nanolayers are important in devices formed from electronic materials that are more conventional. We have already discussed quantum well lasers (see Chapter 8) and giant magnetoresistance (GMR) devices used for hard disk read heads (see Chapter 9). Quantum well lasers may be an important component of light-based computers. Other possibilities include magnets with unusual properties (Section 11.2). 

Fig. 1 illustrates the dissipative (i ) and Hall R cy) resistance characteristics of a high mobility device under microwave excitation at 103.5 GHz. Here, the new radiation-induced effect occurs at relatively low magnetic fields, in this instance B < 0.4 Tesla, and the effect includes giant magnetoresistance oscillations. Remarkably, it turns ont that, at the deepest minima, the resistance falls well below the R cx measnied withont photoexcitation, as it vanishes over broad 5-intervals around (4/5)Bf and 4/9)Bf Here, note that the small magnetic fields involved in this low B-field study can be easily realized with small solenoids or commercially available permanent magnets. 

In order to make a spintronics device, the primary requirement is to have a system that can generate a current of spin polarized electrons, and a system that is sensitive to the spin polarization of the electrons. The simplest method of generating a spin polarized current is to inject the current through a giant magnetoresistance (GMR) device. A typical GMR... 

A number of sensitive magnetic field detection devices have been developed as biosensors giant magnetoresistive (GMR) sensors [4], piezoresistive cantilevers [5], inductive sensors [6], superconducting quantum interference devices (SQUIDs) [7, 8], anisotropic magnetoresistive (AMR) rings [9], and miniature Hall crosses [10]. 

Special attention is paid to transport properties (resistance and Hall effect) because they are very sensitive to external parameters being the base for working mechanisms in many types of sensors and devices. The magnetic field and temperature dependences of resistance and Hall effect are considered in the framework of the percolation theory. Various types of magnetoresistances such as giant and anisotropic ones as well as their mechanisms are under discussion. 

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