An avalanche spin-valve transistor switches a current "on"
or "off" depending on whether the magnetizations of two thin
films are parallel (large current) or anti-parallel (small current).
Such a spintronic transistor is somewhat like the giant magnetoresistance
(GMR) read heads in hard drives, but is 10 to 100 times more sensitive.
The usual drawback of spin-valve transistors, a weak output current,
is, in the Harvard lab of Venkatesh Narayanamurti, overcome by using
an avalanche process much like the one used in photodetectors---an incoming
electron ionizes several secondary electrons, each of which ionizes
still more electrons, adding up in the end to a sizable current.
One of the team members, Kasey Russell (firstname.lastname@example.org, 617-496-5471)
says that the extra sensitivity and strong output could lead to use
of the device in magnetic storage technologies. (Russell
et al., Applied Physics Letters, November 8, 2004; lab website