Ultrafast terahertz spectroscopy yields direct insight into
the building block of modern magnetic memories
(July 6, 2015) Mainz/Aveiro/Bielefeld/Berlin.
Modern magnetic memories, such as hard drives installed in almost every
computer, can store a very large amount of information thanks to very tiny,
nanoscale magnetic sensors used for memory readout. The operation of these
magnetic sensors, called the spin-valves, is based on the effect of giant
magnetoresistance (GMR), for which its inventors Albert Fert and Peter Grünberg
were awarded a Nobel Prize in Physics in 2007.
The GMR effect is based on the idea of electrical conduction
in ferromagnetic metals, proposed by Sir Nevill F. Mott as early as in 1936. In
Mott’s picture, the conduction electrons in ferromagnetic metals experience
scattering depending on their microscopic magnetic moment – the spin. That is,
the electrons with one spin orientation scatter less and are therefore more
conductive than the electrons with the opposite spin orientation. This
spin-asymmetry in electron conduction is greatly amplified when the thin films
of ferromagnetic and nonmagnetic metals are combined together to form a
spin-valve in which electrical resistivity becomes very sensitive to the
magnetic field, leading to a GMR effect.