Exchange Coupling and Giant Magnetoresistance in Electrodeposited Co/Cu Multilayers

Abstract

We present the results of the transport and magnetization measurements of electrodeposited Co/Cu multilayers grown in a single electrolyte based on C0SO4, H3BO3 and CuSO4. The samples are deposited on glass substrate covered by a 500 Å thick Cu buffer layer. X-ray diffraction performed on the samples shows fee structure of both Co and Cu layers with preferential (111) orientation. Resistivity measurements show a giant magnetoresistance effect of about 4% at room temperature for multilayers with Co and Cu thickness between 4 nm ≤ tco ≤ 6 nm and 3 nm ≤ tcu ≤4 nm respectively. For Co thickness tCo ≤ 15 nm, the magnetoresistance completely vanishes indicating that there is no more continuous Co layer. The indirect antiferromagnetic exchange coupling between magnetic Co layers is relatively large for 4 nm thick Cu spacer layer and gives rise to a temperature dependence of about 30% between room temperature and 4.2 K.

Giant Magnetoresistance and Structure of Electrodeposited Co/Cu Multilayers: The Influence of Layer Thicknesses and Cu Deposition Potential

“…A variety of baths have been used for the preparation of ED Co/Cu multilayers [4], the simplest one containing merely CoSO 4 and CuSO 4 . Over the last two decades, numerous reports have been published on studying the GMR characteristics of ED Co/Cu multilayers from the pure sulfate bath (containing at most some buffering agents) [5][6][7][8][9][10][11][12][13][14][15]. In this list of references, we have included only those works from the much larger number of reports [4] in which the ED Co/Cu multilayers were prepared from the sulfate bath at or close to the electrochemically optimized Cu deposition potential EC Cu E [5,10,16] where neither Co dissolution, nor Co codeposition can occur during the Cu pulse.…”

“…By looking at former reports, [5][6][7][8][9][10][11][12][13][14][15] it can be established that in most cases not completely systematic studies on layer thicknesses have been carried out for ED Co/Cu multilayers from the sulfate bath. For example, there were several studies of the GMR dependence on layer thicknesses, where one of the layer thicknesses was fixed and the other layer thickness was only varied.…”

“…Over the last two decades, numerous reports have been published on studying the GMR characteristics of ED Co/Cu multilayers from the pure sulfate bath (containing at most some buffering agents). [5][6][7][8][9][10][11][12][13][14][15] In this list of references, we have included only those works from the much larger number of reports 4 in which the ED Co/Cu multilayers were prepared from the sulfate bath at or close to the electrochemically optimized Cu deposition potential E EC Cu 5,10,16 where neither Co dissolution, nor Co codeposition can occur during the Cu pulse. These features ensure that the actual layer thicknesses will be fairly close to the nominal values and that the spacer layer will not contain magnetic Co atoms.…”

Microstructure and Giant Magnetoresistance of Electrodeposited Co-Cu/Cu Multilayers

“…The relatively inexpensive and simple electrodeposition method can also be applied for producing magnetic or nonmagnetic multilayers, including the Co-Cu system, with good GMR properties. 7 Numerous studies [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] have been reported on the preparation and characterization of electrodeposited Co-Cu/Cu multilayers in which the magnetic layer is, as a result of the nature of the electrodeposition method, not pure Co but rather a Co-rich Co-Cu alloy with magnetic properties very similar to those of pure Co. In spite of these efforts, the observed room temperature GMR in electrodeposited Co-Cu/Cu multilayers 12,[14][15][16][17][18][19][20]22,23,25 has remained below 20%, which is much smaller than the value found in sputtered Co/Cu multilayers.…”

“…11, in which a 55% room temperature GMR has been reported for an electrodeposited Co-Cu/Cu multilayer; however, this result has not yet been confirmed by other authors.͒ Therefore, a challenge remains to clarify the parameters of electrodeposition that govern the GMR behavior of magnetic or nonmagnetic multilayers. Abundant literature data are available for Co-Cu/Cu multilayered films deposited with either potential [9][10][11][12][13][14][15][16][17][18][21][22][23][24][25][26] or current control. 8,19,20 In this paper, we report results obtained for electrodeposited Co-Cu/Cu multilayers prepared under current control.…”