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)[(MnFeIII)-Fe-II(ox)(3)]}(infinity), carried out by various physical techniques (AC/DC magnetic susceptibility, magnetization, heat capacity measurements and Mossbauer 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 Neel temperature and short-range correlations persisting high above T-N. It is understood that the honeycomb layered structure of the compound contains non-equivalent magnetic sub-lattices, (Mn-II-ox-Fe-A-center dot center dot center dot(III)) and (Mn-II-ox-Fe-B-center dot center dot center dot(III)), where different responses of the Fe-A(III) and Fe B spin sites towards an external magnetic field might be responsible for the observation of the uncompensated magnetization in this compound at T < T-N. The present magnetic system is an S = 5/2 2-D Heisenberg antiferromagnet system with the intralayer exchange parameter J/k(B) = -3.29 K. A very weak interlayer exchange interaction was anticipated from the spin wave modeling of the magnetic heat capacity for T < 0.5T(N). The positive sign of the coupling between the layers has been concluded from the Mossbauer spectrum in the applied magnetic field. Frustration in the magnetic interactions gives rise to the uncompensated magnetic moment in this compound at low temperatures. (C) 2009 Elsevier Ltd. All rights reserved.