Spin transport in a thin graphite flake
J. Barzola-Quiquia
•
P. Esquinazi
Received: 4 November 2010 / Accepted: 31 January 2011 / Published online: 12 February 2011
Ó Springer Science+Business Media, LLC 2011
Abstract We have studied the spin transport on a 30-nm
thick and several micrometer long oriented graphite flake
using a spin-valve configuration with four ferromagnetic
Co electrodes of different widths and several lm separa-
tion. A 5-nm thin Pt layer has been introduced in between
the ferromagnetic Co injector/detector and the graphite
surface. In spite of the conductivity mismatch problem,
efficient electrical spin injection and detection in graphite
has been achieved. The magnetoresistance in the local and
half-local electrodes shows clear maxima with symmetry
around zero field. The spin transport can be detected up to
150 K.
Introduction
Due to the large electron mobility and mean free path of
bulk graphite [1], thin crystalline graphite samples are
expected to have some advantages for certain devices in
comparison with single graphene layers fixed on dielectric
substrates. Recent studies, for example, show that the
graphene layers inside graphite have a smaller carrier
density and a much larger mobility even at room temper-
ature than single graphene layers [2]. That large spin dif-
fusion can be expected in graphite should not actually be a
surprise. Already doped Si is a material with relatively low
carrier concentration and large spin diffusion length and
efficiency [3, 4]. Nevertheless, the efficiency of spin
injection between a ferromagnetic electrode and a graphite/
graphene surface is a key point that needs to be studied and
clarified. For example, theoretical calculations [5] indicate
that the interfaces between graphite and (111) fcc or (0001)
hcp Ni or Co surfaces should behave as perfect spin fil-
tering. However, the formation of chemical bonds between
graphite and the d-shell of those elements may diminish the
spin injection. The authors of that theoretical work [5]
proposed that the use of some Cu monolayers in between
may preserve the spin and an ideal spin injection might be
possible. In this study, we have tested the spin transport on
a 30-nm thick and several micrometer long oriented
graphite flake using a spin-valve configuration with four
ferromagnetic (FM) Co electrodes of different widths and
several lm large separation. In contrast to previous stud-
ies[6, 7], a 5-nm thin Pt layer has been deposited in
between the ferromagnetic Co injector/detector layer and
the graphite surface. In spite of the known conductivity
mismatch problem, we show in this study that efficient
electrical spin injection and detection in graphite with the
described configuration is possible. The magnetoresistance
in the local and half-local electrodes shows clear hysteresis
with the common symmetry around zero field and with
resistance maxima. The spin transport can be detected up to
150 K, overwhelming in temperature previous spin valve
devices on mesoscopic graphite basis [6, 7].
Experimental details and sample characteristics
The samples were prepared by rubbing small flakes of
highly ordered pyrolytic graphite (Advanced Ceramics)
(grade ZYA, of rocking curve 0.4°) on a commercial 5 Â
5mm
2
silicon (100) substrate covered with a 150-nm SiN
x
film; for the preparation details see [8]. For the measure-
ments, we selected a graphite flake taking into account the
J. Barzola-Quiquia (&) Á P. Esquinazi
Division of Superconductivity and Magnetism, Institute for
Experimental Physics II, University of Leipzig, Linnestr. 5,
04103 Leipzig, Germany
e-mail: j.barzola@physik.uni-leipzig.de
123
J Mater Sci (2011) 46:4614–4617
DOI 10.1007/s10853-011-5361-7