THz Spintronics in Magnetic Heterostructures: The Role of Interfaces
on February 2, 2018 from 11:00 AM to 12:00 PM
THz spectroscopy provides a convenient way to directly probe the
dynamics of photocurrents and spins on the picosecond and sub-picosecond
timescale. Recently it was shown that circularly polarized femtosecond laser
excitation in a Co/Pt bilayer can effectively generate an ultrafast
photocurrent pulse at the interface . The direction of this photocurrent is
parallel to the in-plane magnetization of the Co layer and can be controlled by
both the magnetic polarity of Co and the chirality of the circularly polarized
light. Simultaneously, an ultrafast spin current pulse is generated in the Co
layer, which is converted to a charge current in the Pt layer via the inverse
Spin-Hall effect . This charge current is in-plane and perpendicular to the
magnetization of Co. Moreover, its direction can be controlled by the net spin
orientation of the ultrafast spin current by switching the magnetization
orientation of Co. A convenient way to probe these ultrafast phenomena is to
employ THz time-domain emission spectroscopy. The basic principle of this
method is that the (sub)picosecond currents will generate electric radiation in
the THz frequency that can be probed via a technique called electro-optical
sampling. Since the polarization of THz radiation generated by the two charge
currents are perpendicular with respect to each other, one can study each
phenomenon separately using wire-grid polarizers. The role of the interfaces
between magnetic and non-magnetic layers will be discussed, in particular the
generation of the ultrafast photocurrents in Co/ZnO/Pt, Co/Cu/Pt trilayers. The
separation of the Co/Pt interface with interlayers of different characteristics
is shown to give a better understanding of the role of the interface on the
generation of ultrafast photocurrents.
References:  Huisman, T. J., et al. "Femtosecond control of
electric currents in metallic ferromagnetic heterostructures." Nature
 Kampfrath, T., et al. “Terahertz spin current
pulses controlled by magnetic heterostructures”, Nature nanotechnology (2013).
Guanqiao Li was born in Beijing (China) on August 31 1989. He came to
the Netherlands at the age of 3. He obtained his master’s degree Experimental
Physics (graduated in 2016) from Utrecht University (the Netherlands).
Currently, he is a PhD student in Prof. Alexey Kimel’s group at Radboud
University Nijmegen (the Netherlands). His research focuses on exploring the
field of THz spintronics and (sub)picosecond photocurrent phenomena.
Specializing in THz spectroscopy, and ultrafast photocurrents and spintronics
in magnetic heterostructures.
UC San Diego, Center for Memory and Recording Research, Jack Keil Wolf Auditorium