ARTICLE IN PRESS
N.D. Nikolic et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 2436–2438
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in the ‘‘T’’ configuration of wires that has been used
previously to form nanocontacts to measure ballistic
magnetoresistance (BMR) [5]. In both cases the same
structures reported below are observed.
diameter of thin nickel filaments is approximately same
with diameters of small nickel clusters situated on the
surface of large nickel cluster.
This change of the morphology is unexpected because
the energy introduced by the field is just a very negligible
paramagnetic effect that at RT should not account for
much. However, the great change of the nickel
morphology with a perpendicular oriented magnetic
field can be ascribed to magnetic properties of nickel.
The explanation can be given in terms of the resistance
of the branched structure (i.e. filaments of deposits) due
to domain wall scattering. In the case of deposits with
magnetic properties (as nickel), the resistance of these
filaments depends on whether a magnetic field is applied
or not. In order to grow branched structure, it is
necessary that the effective potential at the end of these
branches to be the same as the applied one. In the
absence of magnetic field, the resistance of nickel
filaments formed in the initial stage of nickel electro-
crystallization is too large, and the effective potential on
their ends is much smaller than needed for their further
growth and branches, i.e. for the electrodeposition of
very developed arboreous bead-dendritic structure. For
that reason, these nickel filaments mutually coalesce
giving a very rough nickel structure, with very large
nickel clusters which consist of small nano-sized nickel
clusters. In the presence of magnetic field, the resistance
of these filaments is much smaller, because the domain
walls are erased and the effective potential at the end of
the branches is large enough for the electrodeposition of
arboreous bead-dendritic structure. The formed nickel
filament do not mutually coalesce, and they continue to
branch out, forming very developed dendritic structure
with thin branches which terminate with as flower nickel
aggregates consisted of thin nickel nanosized filaments.
This is a very striking result because the small energies
involved in the magnetic process can drive, in a very
elegant way, the growth structure in one way or other,
just due to the subtle effect of the magnetoresistance of
the grown filaments, because when the field is applied
the domain walls at the constrictions conforming the
filaments are removed and the filament resistance
diminishes drastically. These are process that should
be common and may regulate delicate matters of nature
and growth.
At potentials of À1000 and À1200 mV=SCE; the
effect of magnetic field onto nickel electrodeposition was
keeping with foreseeing of MHD theory. At potential of
À1300 mV=SCE; a great difference between nickel
morphologies obtained without and with a perpendicu-
lar oriented magnetic field was observed (zero MHD
effect was expected!). The nickel deposit obtained
without magnetic field was very rough, with clearly
visible clustered structure (Fig. 1a). On the other hand,
the nickel deposit obtained with perpendicular oriented
magnetic field was very developed arboreous bead-
dendritic structure (Fig. 1b). The structure of this
deposit was very open, with thin branches, which
terminated with as flower aggregates of nickel. A flower
aggregates of nickel consisted of thin nickel branches (or
filaments) which were formed of small nano-sized nickel
clusters. Also, it can be seen from Fig.1 that one nickel
cluster corresponds to one flower aggregate, and that a
It is necessary to note that a change of morphology
with perpendicular oriented magnetic field is not
observed in case of copper which is a paramagnetic
metal and therefore no magnetoresistance effect exist
under applied magnetic field. The copper deposits
obtained without and with perpendicular oriented
magnetic field were always arboreous bead-dendritic
structures.
Fig. 1. Nickel deposits (in the middle of electrode) obtained at
À1300 mV=SCE: (a) without, (b) with perpendicular orientated
magnetic field of 500 Oe:
This work has been supported by the Spanish
DGICyT.
Nikolic
