Transcript No Slide Title

GIANT MAGENTORESISCANCE
AND MAGNETIC PROPERTIES
OF ELECTRODEPOSITED
Ni-Co-Cu/Cu MULTILAYERS
G. Nabiyouni
Department of Physics, University of Arak, Arak 38156,
Iran
I.Bakonyi
Research Institute for Solid State Physics and Optics,
Hungarian Academy of Sciences. H-1525 Budapest,
P.O.B. 49, Hungary
W. Schwarzacher,
H. H. Wills Physics Laboratory, Bristol BS8 1TL, UK,
Multilayer structures are most commonly
prepare by vacuum based techniques such as
evaporation, sputtering and molecular beam
epitaxy (MBE). However, it has been well
established that nanoscale metallic multilayers can
also be successfully produced by electrodeposition
and at appropriate element and layer thickness
combinations, they can exhibit a significant giant
magnetoresistance (GMR) effect as demonstrated
for the systems Ni-Cu/Cu, Co-Cu/Cu and Ni-CoCu/Cu.
Ni-Co-Cu/Cu multilayers were
electrodeposited from a single bath under
potentiostatic control on (100)-textured
polycrystalline Cu substrates (this texture
proved to be superior to the (110) and
(111) textures for the GMR effect).
The films consist of 100 repeats of Ni-CoCu(3nm)/Cu(1nm) and Ni-CoCu(3nm)/Cu(2nm) respectively.
The starting electrolyte composition
(in units of g/litre H20) was as
follows:
742 g/l Ni-sulphamate (135 g/l Ni
as metal),
13.5 g/l CuSO4 (3.5 g/l Cu as metal)
and 30 g/l H3BO3.
Co metal concentration in solution was as
follow:
X = 0, 1, 2, 3, 5, 7, 10, 14, 18, 21 and 24 g/l
The Co-content of the solution is denoted by
X referring to the amount of Co metal (in g/l
units) in the solution
To introduce Co, CoSO4 was added to the
solution.
(1 g/l Co metal corresponds to 4.46 g/l
CoSO4).
The magnetoresistance (MR)
measurements were performed at room
temperature for magnetic fields up to H
= 8 kOe in the current-in-plane/field-in
plane (CIP/FIP) configuration. The MR
ratio was defined as R/R0 = (RHR0)/R0 where R0 = R(H=0) is the
resistance without a magnetic field and
RH = R(H) that in a magnetic field H.
The magnetoresistance was measured with
four point-probes arranged in a square
making pressure contacts with the sample.
The MR measurements were performed
with the current either predominantly
parallel (“longitudinal magnetoresistance,”
LMR) or perpendicular (“transverse
magnetoresistance,” TMR) to the applied
magnetic field
In the multilayers prepared by sputtering the roomtemperature GMR increases continuously from
about 7 to 55 % when varying the Co-content of the
magnetic layers in Ni-Co/Cu multilayers from 0 to
100 %.
For sputtered Ni-Co/Cu multilayers an optimum
GMR behaviour was found when the Co-content of
the magnetic layer was around 20 to 40 at.% Co.
In the GMR data for electrodeposited multilayers,
also a significant increase has been found when
going from:
Ni-Cu/Cu multilayers to the Co-Cu/Cu system.
Due to the differences in the
electrochemical behaviour of Ni and
Co atoms, the electrodeposition of
Co-Cu/Cu multilayers is less
favourable than that of Ni-Cu/Cu
multilayers. This is because the
exchange reaction between Co and
Cu is stronger than between Ni and
Cu.
All these considerations led us to
perform the present work aimed at
investigating the influence of Cocontent on the GMR and magnetic
properties of Ni-Co-Cu/Cu
multilayers by systematically
increasing the Co ion concentration
in the electrolyte.
It was also of interest to correlate
the magnetic properties and
GMR parameters for a series of
samples with widely differing
magnetoresistance behaviour.
The overall chemical composition
(CNi, CCo and CCu) of the
electrodeposited multilayers was
established for both A and B type
samples by electron probe
microanalysis (EPMA) in a scanning
electron microscope (SEM) after
removing the substrates (table 1&2).
The overall Cu-content didn’t show
a systematic dependence on
electrolyte Co-content (X) and CCu
was 40 ± 3 at.% and 51 ± 4 at.% for
series A and B, respectively
2
M R ,  R /R o ( %)
0
(a) z Co = 0
points: LM R
lines: TM R
-2
-4
(b) z Co = 54 at.%
-6
-8
-10
(c) z Co = 82 at.%
-12
-8
-6
-4
-2
0
2
magnetic field, H (kOe)
4
6
8
The higher Cu-content in series B
reflects the larger Cu-layer
thickness (dCu = 2 nm) in
comparison with series A (dCu = 1
nm).
Acknowledgement
G.Nabiyouni (corresponding
author) acknowledges the
University of Arak for financial
supports.