08-02 Absence of weak electron localization in epitaxial Fe wires on
GaAs(110)
C. Hassel, F. M. Römer, G. Dumpich, and J. Lindner
We have studied the low-temperature magnetoresistance of epitaxial Fe wires on GaAs(110)
to examine the contributions from weak electron localization to the electronic transport.
Continuous epitaxial Fe films are prepared in a UHV chamber. In situ structural analysis (low
energy electron diffraction) of the films verify the epitaxial growth of Fe on GaAs(110).
Magnetic characterization of the films is carried out by ferromagnetic resonance. This method
also allows determining the magnetic anisotropy constants.
The structuring of the films into wires is done by an electron beam lithography process
using negative resist, which is used to mask parts of the Fe film in a wire-geometry. The nonmasked parts of the films are sputtered with 500 eV Ar ions so that only Fe-wires remain.
These Fe-wires are contacted in a second step with gold wires which do not affect the
magnetization of the Fe-wires.
Magnetic force microscopy investigations show that we have succeeded in preparing
wires with strong magnetic anisotropies. This enables us to prepare wires with the effective
easy-axis of magnetization transverse to the long wire axis.
Fig. 1. Resistance as a function of the logarithm of the temperature of a 3 µm wide epitaxial Fe-wire oriented
parallel to the [001]-direction for various external fields applied perpendicular to the film plane.
Magnetoresistance at low temperatures is measured in external magnetic fields
perpendicular to the film-plane. Figure 1 shows the temperature dependence of the resistance
of a 3 µ m wide wire, which is oriented parallel to the [001] direction. We observe for each
applied magnetic field a logarithmic resistance increase towards lower temperatures which is
Fig. 2. ∆G(10) values of various oriented epitaxial Fe wires and polycrystalline Co wires as a function of
wire-width.
classically not expected. For higher magnetic fields, the curves are shifted towards lower
resistances since the overall resistance decreases due to the anisotropic magnetoresistance.
For weak electron-localization, one would expect a variation of the slope of the temperature
dependence of the resistance when the external magnetic field is changed. We find no such
dependence and, thus, no contribution from weak electron-localization. The observed
resistance increase with decreasing temperature can be attributed to the presence of enhanced
electron-electron interaction, which also leads to a logarithmic resistance-increase. However,
the resistance-increase due to enhanced electron-electron interaction is expected to be
independent of the external magnetic field.
To further investigate the enhanced electron-electron-interaction in such wires, we
measured the low-temperature magnetoresistance for differently oriented wires and varying
widths. Figure 2 shows the width-dependence of ∆G(10), which is proportional to the slope of
the temperature dependence of the resistance (Fig. 1) for differently oriented wires. Data for
polycrystalline Co wires are also shown for comparison. We find for all wires that the
influence of enhanced electron-electron interaction increases with decreasing wire-width. This
property can be described by an electron-electron interaction model developed by Neuttiens et
al. (solid line) [2].
References
1. T. R. McGuire, R. I. Potter, IEEE Trans. Mag. 11, 1018 (1975)
2. G. Neuttiens et al., Europhys. Lett. 34, 617 (1996)
3. C. Hassel, F. M. Römer, G. Dumpich, J. Lindner, submitted