ELECTRODEPOSITED GIANT MAGNETORESISTANCE IN FeCoNiCu/Cu AND CrFeCoNiCu/Cu MULTILAYERED NANOWIRES PRAJON RAJ SHAKYA, B.E. M.S. in ELECTRICAL ENGINEERING ADVISOR: Dr. DESPINA DAVIS 16th December, 2010
Overview Motivation of the Research Discovery and Historical perspective Introduction Related Research Experimental Details Results and Discussions Conclusion and Future Work References Acknowledgements
Electrons are arranged in antiparallel to each other.
Magnetoresistance (MR) ratio is defined as the ratio of the change in resistivity (due to change in configuration of electrons from antiparallel to parallel) to the resistivity in parallel configuration of electrons.
MR is due to spin of electrons and was first observed in ferromagnetic materials as AMR (Anisotropic Magnetoresistance).
AMR shows increase in resistance along and decrease in resistance across the lines of magnetization. 
2. Discovery and Historical Perspective
This effect of MR was also observed in multilayers with alternating layer of ferromagnetic (FM) and Non Magnetic (NM) layer as GMR (Giant Magnetoresistance).
Fert et al. and Grunberg et al. were first to observe GMR in Fe/Cr multilayers with the method of MBE (Molecular Beam Epitaxy). [1, 3, 4 ]
Figure 1: Giant Magnetoresistance in (a) Fe/Cr multilayers by Fert et al. (left) [1, 3] and (b) Fe/Cr/Fe tri layers by Grunberg et al. (right) [1, 4]
Piraux et al. was first to study GMR in electrodeposited multilayered nanowires. They observed around 15% GMR at room temperature in Co/Cu layers. 
Blondel et al. observed GMR of 14% for Co/Cu and 10% for FeNi/Cu multilayered nanowires. 
Liu et al. investigated Co/Cu multilayerand observed GMR of 11% at room temperature and 22% at 5K . 
CoFeCu/Cu multilayered nanowires were studied by Seyama et al. and observed CPPGMR was twice that of CIP GMR on thin film for the same elements.
Kakuno et al. also studied CoFeCu/Cu but with compositionally modulated alloys and observed 8% GMR at room temperature with polycrystalline deposit of face centered cubic and hexagonal close packed structures. 
Blondel et al. studied CoNi/Cu multilayered nanowires by pulsed potential technique and observed 20% GMR at room temperature with same ferromagnetic and nonmagnetic layer thickness. 
Schwarzacher et al. and Heydon et al. investigated CoNiCu/Cu in polycarbonate membranes and observed 22% GMR at room temperature. The reduction in the dissolution of Co was observed in the deposition of Cu with the addition of Ni.
Evans et al. reported 55% GMR at room temperature and 115% GMR at low temperature on AAO with CoNiCu/Cu multilayers. They also reported that better GMR was observed with AAO template than with PC membranes. 
Huang and Podlaha investigated quaternary system of FeCoNiCu and observed 4% GMR at 300K and 18% at 4K with a Cu layer thickness of 1.8nm. Anodic dissolution during multilayer deposition at low potential pulse was observed and galvanostatic triple pulses with relaxation period were introduced to reduce it. 
J. Gong et al. studied sensitivity of FeCoNiCu/Cu multilayers and observed decrease in coercivity with increase Fe concentration. They reported 9% GMR saturated at less than 0.5KOe and sensitivity of over 0.11% Oe. 
Electrodeposition of Cr
Dolati et al. studied FeCrNiMo alloys using chloride electrolyte and reported increase in Cr content increased the current density. They also observed fine-grain, smooth and compact deposits of FeCrNiMo. 
Xin-Quai et al. investigated pulse electrodeposition of Cr from trivalent bath and reported that thicker coatings and finer grains were observed with lower temperature and current density. [16 ]
Lallemandet al. studied electrodeposition of soft CoFeCr films and reported that the addition of Cr increases the resistivity of the alloy. 
Ericksson et al. investigated the effect of addition of chromium in FeNi alloy. They observed the improvement in crystal anisotropy with improved texture and small grain size that resulted in the decrease of saturation magnetization. 
Choi et al. studied the effect of Cr addition on structure as well as the corrosion resistance in FeTiN nanocrystalline thin films and observed the reduction in coercivity. They also showed that Cr tends to form passivation layer and helps to minimize corrosion  .
Cu top Cu layer Alloy layer Cu bottom Figure 7: Schematic view of electrodeposition technique
Measurement Techniques Figure 8: Lakeshore 7700 Hall Effect Measurement System for GMR measurement (left) and Alternating Gradient Magnetometer (AGM) Micromag 2900 for magnetic measurements (right)
6. Results and Discussions Electrolyte Characterization Table 1: Molar Concentration of baths used for electrodeposition 0
Highest GMR was observed at optimum alloy potential of -2.2V and optimum alloy pulsing time of 1 sec.
Increase in number of bilayers increased GMR percentage with highest GMR obtained as 14.56% for FeCoNiCu/Cu and 5.82% for CrFeCoNiCu/Cu nanowires at 2500 layers.
Highest GMR curves tended to saturate faster which is desirable for read sensors.
Addition of Cr on the alloy region tended to decrease the GMR because Cr being non magnetic and its presence in ferromagnetic region deteriorated interlayer exchange coupling phenomena.
Coercivity of the nanowires was lowered with the addition of Cr because of the regular, granular deposition of Cr that shows proper magnetic interaction between nanowires. Least coercivity values was observed with highest GMR values.
Cr is anti-corrosive in nature and its effect on corrosion of nanowires will be studied .
Variation of Cr concentration and effect of temperature will be explored in the field of CPP GMR magnetic sensors.
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