Copper magnetoresistance

W. H. Butler, X.-G. Zhang, D. M. C. Nicholson, T. C. Schulthess, and J. M. MacLaren, Giant Magnetoresistance from an Elecuon Waveguide Effect in Cobalt-Copper Multilayers , Physical Review Letters 76, pp.3216-3219, (1996). 

Cu and Mn, systems that have partially filled d shells with a degenerate ground state. According to the Jahn-Teller theorem, any degenerate electronic system will spontaneously distort in such a way as to remove the degeneracy (Dunitz and Orgel 1960). The distortions around Cu " have been extensively studied and may play a role in the superconductivity found in some copper oxides (Section 13.3.2), while the distortions around Mn + play an important role in the potentially useful magnetoresistive properties of LaMnOs (Section 13.3.3). 

Thin films of cobalt can be prepared by nebulized spray pyrolysis using Co(acac)2 as precursor in a hydrogen atmosphere. The obtained films show brilliant metallic and magnetic properties. Granular, magnetoresistant cobalt-copper alloys of composition CoigCu82 and C050CU50 are accessible from Co(acac)2 and Cu(acac)2 mixtures under similar reaction conditions. ... 

The effects of thermal treatment and trace impurities on magnetothermal conductivity of good conductors cannot be predicted with confidence. The available experimental data indicate the thermal conductivity can vary by at least a factor of 2 due to differences in composition and thermal treatment. A factor-of-2 decrease in thermal conductivity was also observed when a 6366-kA/m field was applied to the copper and aluminum specimens. A possible solution to this problem is to assume that the Lorenz ratio can be used when the electrical and thermal conductivities involved are actually the magnetoresistivity and magnetothermal resistivity, i.e.,... 

In Table III some experimental values of pg for Cu and Na are given as a function of B. It is clear from the data that sodium exhibits a far lower transverse magnetoresistance effect than copper. 

Comparable data do not seem to exist for sodium, but it is predictable from conductivity theory that the addition of impurities will result in increases in resistivity which are of the same order as those in copper. However, since the magnetoresistance effect in sodium is about a factor of 20 less than that in copper, it can be expected that the purity requirements for sodium will be more severe by about the same factor. This still does not appear to be a requirement outside the capabilities of modern ultra-pure metal technology. In measurements reported by MacDonald [12] on the resistivity of alkali metals, low impurity resistance contributions were found, for specimens with spectroscopically determined purities of 99.95. But Horsley [13] reports practical methods of refining sodium to purities of 99.9995, or 100 times higher purity than those reported by MacDonald in his experiments. 

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