Observation of spin-glass behavior in nickel adsorbed few layer graphene
  Nickel-adsorbed graphene was prepared by first synthesizing graphite oxide (GO) by modified Hummers' method and then reducing a solution containing both GO and $Ni^{2+}$. EDX analysis showed 31 atomic percent nickel was present. Magnetization measurements under both dc and ac magnetic fields were carried out in the temperature range 2 K to 300 K. The zero field cooled and field cooled magnetization data showed a pronounced irreversibility at a temperature around 20 K. The analysis of the ac susceptibility data were carried out by both Vogel-Fulcher as well as power law. From dynamic scaling analysis the microscopic flipping time $\tau_{0}\sim 10^{-13} s$ and critical exponent $z\nu=5.9\pm0.1$ were found, indicating presence of conventional spin glass in the system. The spin glass transition temperature was estimated as 19.5 K.   Decay of thermoremanent magnetization (TRM) was explained by stretched exponential function with a value of the exponent as 0.6 .   From the results it is concluded that nickel adsorbed graphene behaves like a spin-glass. 
Sreemanta Mitra, Oindrila Mondal, Sourish Banerjee, Dipankar   Chakravorty
cond-mat.mes-hall cond-mat.mtrl-sci