Electrical devices are powered by one property
of electrons -- charge.
Electrons are more than just charge, however. Electrons can also
be spin up or spin down -- properties analogous to a top spinning clockwise
or counterclockwise. Spintronics researchers are looking for ways to control
and use electron spin.
Researchers from Cornell University and Yale University have brought
the field a step forward by showing that a flow of electrons that all
have the same spin can transfer angular momentum to magnetic material.
The method could eventually be used to produce microwave emitters
for communications devices and to control magnetic fields in devices like
random access memory. The technique can potentially enable such devices
at sizes not much bigger than molecules.
The researchers found that the torque from spin-polarized electrons
can make a magnetic field oscillate in several different ways. They also
found that these oscillations cause a large change in the material's electrical
resistance, making voltage flowing through the material oscillate at microwave
frequencies and thus emit microwaves.
The effect is the inverse of that used in devices like computer
disk drives, which sense the magnetic orientations of bits by measuring
how they change a flow of electrons.
It will take about five years to determine whether the effect
can be used in practical applications. It will take another five years
to build a practical system, according to the researchers. The work appeared
in the September 25, 2003 issue of Nature.
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