Magnetic structure and dynamics of a strongly one-dimensional cobalt$^{II}$ metal-organic framework

Abstract

We investigate the magnetism of the Co$^{II}_4$(OH)$_2$(C$_1$$_0$H$_1$$_6$O$_4$)$_3$ metal-organic framework which displays complex inorganic chains separated from each other by distances of 1 to 2 nm, and which orders at ~5.4 K. The zero-field magnetic structure is determined using neutron powder diffraction: it is mainly antiferromagnetic but posseses a ferromagnetic component along the $\textbf{c}$-axis. This magnetic structure persists in presence of a magnetic field. Ac susceptibility measurements confirm the existence of a single thermally activated regime over 7 decades in frequency ($E/k_B\approx64 K$) whereas time-dependent relaxation of the magnetization after saturation in an external field leads to a two times smaller energy barrier. These experiments probe the slow dynamics of domain walls within the chains: we propose that the ac measurements are sensitive to the motion of existing domain walls within the chains, while the magnetization measurements are governed by the creation of domain walls.