Characterization of the S = 9 excited state in Fe8Br8 by Electron Paramagnetic Resonance

Abstract

High Frequency electron paramagnetic resonance has been used to observe the magnetic dipole, $\Delta$ M${}_s$ = $\pm$ 1, transitions in the $S=9$ excited state of the single molecule magnet Fe${}_8$Br${}_8$. A Boltzmann analysis of the measured intensities locates it at 24 $\pm$ 2 K above the $S=10$ ground state, while the line positions yield its magnetic parameters D = -0.27 K, E = $\pm$0.05 K, and B${}_4^0$ = -1.3$\times$ 10${}^{-6}$ K. D is thus smaller by 8% and E larger by 7% than for $S=10$. The anisotropy barrier for $S=9$ is estimated as 22 K,which is 25% smaller than that for $S=10$ (29 K). These data also help assign the spin exchange constants(J's) and thus provide a basis for improved electronic structure calculations of Fe${}_8$Br${}_8$.

7 pages, Figs included in text, submitted to PRB