title: Evidence for Spin Glass Ordering Near the Weak to Strong Localization Transition in Hydrogenated Graphene.
abstract: We provide evidence that magnetic moments formed when hydrogen atoms are covalently bound to graphene exhibit spin glass ordering. We observe logarithmic time-dependent relaxations in the remnant magnetoresistance following magnetic field sweeps, as well as strong variances in the remnant magnetoresistance following field-cooled and zero-field-cooled scenarios, which are hallmarks of canonical spin glasses and provide experimental evidence for the hydrogenated graphene spin glass state. Following magnetic field sweeps, and over a relaxation period of several minutes, we measure changes in the resistivity that are more than 3 orders of magnitude larger than what has previously been reported for a two-dimensional spin glass. Magnetotransport measurements at the Dirac point, and as a function of hydrogen concentration, demonstrate that the spin glass state is observable as the zero-field resistivity reaches a value close to the quantum unit h/2e(2), corresponding to the point at which the system undergoes a transition from weak to strong localization. Our work sheds light on the critical magnetic-dopant density required to observe spin glass formation in two-dimensional systems. These findings have implications to the basic understanding of spin glasses as well the fields of two-dimensional magnetic materials and spintronics.
authors.affiliation: Naval Research Laboratory , Code 7130, Washington, DC 20375, United States.
authors.forename: Bernard R
authors.initials: BR
authors.lastname: Matis
authors.affiliation: Naval Research Laboratory , Code 7130, Washington, DC 20375, United States.
authors.forename: Brian H
authors.initials: BH
authors.lastname: Houston
authors.affiliation: Naval Research Laboratory , Code 7130, Washington, DC 20375, United States.
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Baldwin
keywords: 2D magnetic material; hydrogenated graphene; spin glass; transport localization