Magnetic Potassium Clusters in a Nanographite Host System

The magnetism and structure for potassium clusters physisorbed in nanographite-based nanoporous host are investigated. Potassium clusters are subjected to a slight charge transfer to a host nanographite and modify the magnetism of the edge-state spins of nanographite. The localized spins of $4s$ electrons in the potassium cluster interact with each other through a strong antiferromagnetic interaction. Finite size effect and structural disorder around the cluster surface are responsible for anomalous spin fluctuations in the magnetism.

Figure 1

(a) The $K/C$ dependence of the extent of the charge transfer $f_c$ per carbon atom in K-ACFs. (b) The ratio of the ${\mathrm{K}}^{+}$ ion contributing to the charge transfer to ACFs. (c) The spin-gap energy $\Delta E$ (○) and the number of spins per potassium $N_K$ (●) for the antiferromagnetic clusters with various $K/C$ values.

Figure 2

The SAXS profile for ACFs (○) and K-ACFs (●) with $K/C=0.259$. Solid lines are the linear fittings.

Figure 3

(a) Susceptibility $\chi$ vs temperature plot for ACFs and K-ACFs. The ● denotes ACFs, and □, ▿, $+$, ▵, and ◊ denote K-ACFs with $K/C=0.035$, 0.058, 0.214, 0.259, and 0.282, respectively. (b) Change in the susceptibility during the desorption process of potassium for K-ACFs with $K/C=0.214$. The ●, ▿, □, ◊, ▵, and $+$ denote the nonheat-treated sample, the samples heat-treated at 170, 250, 300, 350, and $400°\mathrm{C}$, respectively. Solid lines in (a) and (b) are guides for the eyes. (c) Fitting with the unique spin-gap model for $K/C=0.214$. The observed data, the contributions of the nanographite spins and potassium clusters, and the theoretical fitting are denoted by ●, □, ○, and solid line, respectively.