Anomalous Hall effect in monodisperse CoO-coated Co nanocluster-assembled films

We have fabricated the uniform CoO-coated Co nanocluster-assembled films at various oxygen gas flow rates (fO) by using a plasma-gas-condensation method and studied their anomalous Hall effect (AHE). The longitudinal resistivity (ρxx) of all the films exhibits a minimum at a temperature of Tmin. With the increase of fO, Tmin shifts from 150 to 300 K and has no longer change when fO is up to 0.10 sccm. The saturated AHE resistivity (ρxyA) presents a near linear increase as fO rises. The anomalous Hall coefficient (Rs) at fO=0.20 sccm is 4.9×10−9 Ω cm G−1 at 300 K, which is almost three orders of magnitude larger than bulk Co. Moreover, at fO=0 and 0.05 sccm, the scaling exponents γ=1.2 and 1.24 in ρxyA∝ρxxγ are obtained in the region of 325-375 K; At fO=0.10, 0.15 and 0.20 sccm, ρxyA decreases with the increase of ρxx on a double-logarithmic scale, following a new scaling relation of log(ρxyA/ρxx)=a0+b0logρxx in two temperature ranges of 5-300 K and 325-375 K.