Magnetic Response of Mn(III)F(salen) at Low Temperatures

Due to a report suggesting Mn(III)F(salen), salen $=$ H$_{14}$C$_{16}$N$_{2}$O$_{2}$, is a $S=$ 2 Haldane system with $J/k_{B}=$ 50 K and no long-range order down to 2 K,\footnote{T. Birk \textit{et al}., Inorg. Chem. \textbf{50} (2011) 5312.} we have studied its magnetic response. Torque magnetometry, down to 20 mK and up to 18 T, revealed a feature at 3.8 T when $T$ \textless\ 400 mK. ESR ($\sim $ 200 GHz) studies, using single crystals at 4 K and in 5 T, have not detected any signal. The low-field, high-$T$ susceptibility is unchanged for $P$ \textless\ 1.0 GPa. Using a randomly-oriented, powder-like, deuterated (12 of 14 H replaced by D) sample, neutron scattering data, acquired with the CNCS at SNS, are not consistent with a uniform system consisting of $S=$ 2 Heisenberg antiferromagnetic chains. The INS data show strong, dispersionless excitations, suggesting the possibility of isolated magnetic clusters.