I. Introduction

Measuring geometry of the Giant Magnetoresistance (GMR) effect:

Fig. 1. Schematics of (a) the CIP and CPP geometries in multilayers, and (b) the CPP geometry in multilayered nanowires.

CPP vs CIP geometry:

• Characteristic length scale: Spin-flip diffusion length vs. mean free path
• Larger effect size
• Separate interface and bulk spin-dependent scattering

Interesting but difficult: Typical sample 1mm² x 1 µm (cross-sectional area x height), R ~ 10^-7 ~10^-8 W
Previous experiements

• SQUID based sensing system / lithography
• Cross-sectional area: 6 ~ 130 µm²

Multilayered nanowires:    ~ 700 nm²

   II. Fabrication: Pulsed Electrodeposition

Fig. 2. Schematic of the applied potential and the deposition current in the three-segment electrodeposition cycle for the Co/Cu multilayers.

Fig. 3. PEELS map in the TEM of electrodeposited Ni(40Å)/Cu(60Å) multilayered nanowires.

IV. GMR results

Fig. 4. Magnetoresistance measurements at (a) 5 K and (b) 293 K of 30 nm nanowires with layered structure [Co(50Å)/Cu(8Å)]1000. The applied magnetic field is perpendicular to the wire.  The corresponding magnetic hysteresis loops at (c) 5 K and (d) 293 K are also shown.
 

 
 
 

Real multilayered nanowires: characteristics of both

VI. Resistivity Enhancement
 
 

Fig. 5. Schematic of the cross-shaped contact pads on top and bottom of the membrane for making electrical contact with a small number of nanowires in the overlapping area.
 

 

	30 nm	400 nm
Measured R (W)	104	30
Expected R using bulk resistivity (W)	400	2
Per interface R (W-m2)	4.0 x 10-15	2.3 x 10-15

Enhancement due to the numerous interfaces & boundary scattering.

References

1. K. Liu, K. Nagodawithana, P. C. Searson, and C. L. Chien, "Perpendicular giant magnetoresistance of multilayered Co/Cu nanowires", Physical Review B 51, (Rapid Communications) 7381 (1995). (Full Article, PDF File)
2. K. Nagodawithana, K. Liu, , P. C. Searson, and C. L. Chien, "Processing and properties of electrodeposited Co/Cu multilayered nanowires" in Proceedings of the Symposium on Nanostructured Materials in Electrochemistry, Electrochemical Society Proceedings Vol. 95-8, edited by P. C. Searson and G. J. Meyer, p.237-243 (1995).
3. Kai Liu, Ph.D. dissertation, The Johns Hopkins University, Baltimore, Maryland, 1998.

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Contact Us

Kai Liu:         kliu@pha.jhu.edu
P. C. Searson:   searson@jhu.edu
C. L. Chien:   clc@pha.jhu.edu

Last Modified 02/07/99 by Kai Liu