Muon-spin relaxation studies of the low-dimensional molecular compounds Mn(dca)2(pyz) and Fe(NCS)2(pyz)2

We present the results of zero field muon-spin relaxation (μ+SR) studies of the molecular magnets Mn(dca)2(pyz) and Fe(NCS)2(pyz)2 (where dca=[N(CN)2]- and pyz=pyrazine). Both of these materials possess low-dimensional structural motifs resulting in magnetic behaviour consistent with this reduced dimensionality. Mn(dca)2(pyz) is formed from Mn-pyz-Mn chains, linked with dca anions to form two interpenetrating three-dimensional (3D) networks. Antiferromagnetic ordering in this compound is seen as a rapid change in the measured asymmetry around TN=2.5K. Fe(NCS)2(pyz)2 is a two-dimensional (2D) sheet-like polymer with the sheets consisting of Fe atoms bridged by pyz ligands. μ+SR measurements display both the 3D and 2D nature of the material in the measured relaxation spectra. We observe the transition into the LRO state below TN along with an excitation of E=1.09(5)meV above TN associated with fluctuations within the correlated 2D layers.