Magnetic measurements and neutron diffraction study of the layered hybrid compounds Mn(C8H4O4)(H2O)2 and Mn2(OH)2(C8H4O4)

Mn(C8H4O4)(H2O)(2) and Mn-2(OH)(2)(C8H4O4) layered organic-inorganic compounds based on manganese-(II) and terephthalate molecules (C8H4O42-) have been studied by DC and AC magnetic measurements and powder neutron diffraction. The dihydrated compound behaves as a 3D antiferromagnet below 6.5 K. The temperature dependence of its chi T product is typical of a 2D Heisenberg system and allows determining the in-plane exchange constant J approximate to -7.4 K through the carboxylate bridges. The magnetic structure confirms the in-plane nearest neighbor antiferromagnetic interactions and the 3D ordering. The hydroxide based compound also orders as a 3D antiferromagnet with a higher Neel temperature (38.5 K). Its magnetic structure is described from two antiferromagnetically coupled ferromagnetic sublattices, in relation with the two independent metallic sites. The isothermal magnetization data at 2 K are consistent with the antiferromagnetic ground-state of these compounds. However, in both cases, a slope change points to field-induced modification of the magnetic structure. (C) 2011 Elsevier Inc. All rights reserved.