Electrons spin magnetic fields

November 5/12, 2003

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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