Uncompensated magnetization in the layered molecular antiferromagnet {N(n-C5H11)4[MnIIFeIII(ox)3]}∞

Studies on the magnetic properties of the molecular antiferromagnetic material {N(n-C5H11)4[MnIIFeIII(ox)3]}∞, carried out by various physical techniques (AC/DC magnetic susceptibility, magnetization, heat capacity measurements and Mössbauer spectroscopy) at low temperatures, have been presented. Different experimental observations complement each other and provide a clue for the observation of an uncompensated magnetization below the Néel temperature and short-range correlations persisting high above TN. It is understood that the honeycomb layered structure of the compound contains non-equivalent magnetic sub-lattices, (MnII–ox–FeIIIA–...) and (MnII–ox–FeIIIB–...), where different responses of the FeIIIA and FeIIIB spin sites towards an external magnetic field might be responsible for the observation of the uncompensated magnetization in this compound at T < TN. The present magnetic system is an S = 5/2 2-D Heisenberg antiferromagnet system with the intralayer exchange parameter J/kB = −3.29 K. A very weak interlayer exchange interaction was anticipated from the spin wave modeling of the magnetic heat capacity for T < 0.5TN. The positive sign of the coupling between the layers has been concluded from the Mössbauer spectrum in the applied magnetic field. Frustration in the magnetic interactions gives rise to the uncompensated magnetic moment in this compound at low temperatures.

Graphical abstractThe honeycomb layered {N(n-C5H11)4[MnIIFeIII(ox)3]}∞ antiferromagnet, where both MnII and FeIII ions have spin S = 5/2, shows anisotropy and an uncompensated moment below TN of 27 K. The Mössbauer spectrum in the applied magnetic field reveals the presence of two FeIIIA and FeIIIB spin sites with different responses towards the external magnetic field that is most probably responsible for the uncompensated magnetization. Breaking the local symmetry of the FeIII sites by the bulky N(n-C5H11)4 cations together with a small difference in g-factors for MnII and FeIII ions and a relatively large zero-field splitting for MnII may be a reason for the two non-equivalent sites within the iron sub-lattice.Figure optionsDownload full-size imageDownload as PowerPoint slide