Enhancement of spin relaxation time in hydrogenated graphene spin-valve devices

Hydrogen adsorbates in graphene are interesting as they are not only strong Coulomb scatterers, but they also induce a change in orbital hybridization of the carbon network from sp{\textless}math{\textgreater}{\textless}mrow{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}s{\textless}/mi{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}p{\textless}/mi{\textgreater}{\textless}/mrow{\textgreater}{\textless}/math{\textgreater}2{\textless}math{\textgreater}{\textless}msup{\textgreater}{\textless}mrow{\textgreater}{\textless}/mrow{\textgreater}{\textless}mn{\textgreater}2{\textless}/mn{\textgreater}{\textless}/msup{\textgreater}{\textless}/math{\textgreater} into sp{\textless}math{\textgreater}{\textless}mrow{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}s{\textless}/mi{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}p{\textless}/mi{\textgreater}{\textless}/mrow{\textgreater}{\textless}/math{\textgreater}3{\textless}math{\textgreater}{\textless}msup{\textgreater}{\textless}mrow{\textgreater}{\textless}/mrow{\textgreater}{\textless}mn{\textgreater}3{\textless}/mn{\textgreater}{\textless}/msup{\textgreater}{\textless}/math{\textgreater}. This change increases the spin-orbit coupling and is expected to largely modify spin relaxation. In this work, we report the change in spin transport properties of graphene due to plasma hydrogenation. We observe an up to threefold increase of spin relaxation time ??S{\textless}math{\textgreater}{\textless}msub{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}??{\textless}/mi{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}S{\textless}/mi{\textgreater}{\textless}/msub{\textgreater}{\textless}/math{\textgreater} after moderate hydrogen exposure. This increase of ??S{\textless}math{\textgreater}{\textless}msub{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}??{\textless}/mi{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}S{\textless}/mi{\textgreater}{\textless}/msub{\textgreater}{\textless}/math{\textgreater} is accompanied by the decrease of charge and spin diffusion coefficients, resulting in a minor change in spin relaxation length ??S{\textless}math{\textgreater}{\textless}msub{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}??{\textless}/mi{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}S{\textless}/mi{\textgreater}{\textless}/msub{\textgreater}{\textless}/math{\textgreater}. At high carrier density, we obtain ??S{\textless}math{\textgreater}{\textless}msub{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}??{\textless}/mi{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}S{\textless}/mi{\textgreater}{\textless}/msub{\textgreater}{\textless}/math{\textgreater} of 7 ??{\textless}math{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}??{\textless}/mi{\textgreater}{\textless}/math{\textgreater}m, which allows for spin detection over a distance of 11 ??{\textless}math{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}??{\textless}/mi{\textgreater}{\textless}/math{\textgreater}m. After hydrogenation, a value of ??S{\textless}math{\textgreater}{\textless}msub{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}??{\textless}/mi{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}S{\textless}/mi{\textgreater}{\textless}/msub{\textgreater}{\textless}/math{\textgreater} as high as 2.7 ns is measured at room temperature.