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Microstructure, magneto-transport and magnetic properties of Gd-doped magnetron-sputtered amorphous carbon

L. Zeng·E. Helgren·F. Hellman·R. Islam·D. J. Smith·J. W. Ager III
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Abstract

The magnetic rare earth element gadolinium (Gd) was doped into thin films of amorphous carbon (hydrogenated \textit{a}-C:H, or hydrogen-free \textit{a}-C) using magnetron co-sputtering. The Gd acted as a magnetic as well as an electrical dopant, resulting in an enormous negative magnetoresistance below a temperature ($T'$). Hydrogen was introduced to control the amorphous carbon bonding structure. High-resolution electron microscopy, ion-beam analysis and Raman spectroscopy were used to characterize the influence of Gd doping on the \textit{a-}Gd$_x$C$_{1-x}$(:H$_y$) film morphology, composition, density and bonding. The films were largely amorphous and homogeneous up to $x$=22.0 at.%. As the Gd doping increased, the $sp^{2}$-bonded carbon atoms evolved from carbon chains to 6-member graphitic rings. Incorporation of H opened up the graphitic rings and stabilized a $sp^{2}$-rich carbon-chain random network. The transport properties not only depended on Gd doping, but were also very sensitive to the $sp^{2}$ ordering. Magnetic properties, such as the spin-glass freezing temperature and susceptibility, scaled with the Gd concentration.

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L. Zeng, E. Helgren, F. Hellman, R. Islam, D. J. Smith, J. W. Ager III. 2007-01-26. Microstructure, magneto-transport and magnetic properties of Gd-doped magnetron-sputtered amorphous carbon. https://doi.org/10.1103/physrevb.75.235450

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