It has recently been discovered that when a spin-polarized current interacts with a magnet, it can transfer spin angular momentum to the magnet and thereby apply a torque. This spin-transfer torque can be used to manipulate the magnetic-moment direction of small magnets much more efficiently than using magnetic fields. I will describe experiments which utilize 100-nm-scale magnetic devices to investigate the microscopic origin of this effect, the ways in which individual nanomagnets respond to the torque, and potential applications.
In the last part of the talk, I will discuss progress toward extending experiments on spin-dependent transport and magnetic dynamics to even smaller length scales. We have developed a technique for using electromigration to form mechanically-stable nanoscale contacts, for use in single-molecule studies. Even for simple bare contacts (containing no molecules) made of permalloy or nickel, we find an unexpectedly large changes in resistance as a function of the angle of the magnetization. We propose that this effect is the result of quantum interference of electrons within the magnetic device.