Dresden 2011 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 70: Gerhard Ertl Young Investigator Award

O 70.4: Vortrag

Donnerstag, 17. März 2011, 12:45–13:15, WIL C307

Measuring Nanosecond Spin Dynamics at the Atomic Scale — •Sebastian Loth — IBM Research - Almaden, San Jose, CA, USA

Transition metal atoms that were placed on a monolayer-thin film of copper nitride (Cu₂N) on Cu (100) exhibit unusually large magnetic anisotropy that enables long electron spin lifetimes. The magnetic atoms exhibit discrete spin states that can be probed by inelastic electron tunneling spectroscopy (IETS). We make use of a quantized analogue of spin-momentum transfer to interact with the local spin. A large spin-polarized tunnel current pumps the spin of the magnetic atoms into highly excited states allowing us to quantify the lifetimes of different spin excitations.

Direct access to the dynamical evolution of magnetic atoms in the time domain can be obtained by combining spin-polarized scanning tunneling microscopy (SP-STM) with an all-electronic pump-probe measurement scheme: a continuous train of fast voltage pulses is applied to the tunnel junction where a pump pulse excites the magnetic atom and a time-delayed weaker probe pulse monitors the post-excitation dynamics with nanosecond precision. We find that the spin relaxation time of a Fe atom on Cu₂N can be increased beyond 200 ns by placing a Cu atom adjacent to it. This enables studies of quantum tunneling of magnetization that occurs in these dimers.

The ability to probe individual nanostructures with atomic spatial and nanosecond temporal resolution opens a new avenue to explore spin dynamics and other dynamical phenomena on the intrinsic length scale of the underlying interactions.