Co₄(OH)₂(C₁₀H₁₆O₄)₃ Metal–Organic Framework: Slow Magnetic Relaxation in the Ordered Phase of Magnetic Chains

Abstract

Reported here are the synthesis and structural and topological analysis as well as a magnetic investigation of the new Co₄(OH)₂(C₁₀H₁₆O₄)₃ metal–organic framework. The structural analysis reveals a one-dimensional inorganic subnetwork based on complex chains of cobalt­(II) ions in two different oxygen environments. Long alkane dioic acid molecules bridge these inorganic chains together to afford large distances and poor magnetic media between dense spin chains. The thermal dependence of the χ<i>T</i> product provides evidence for uncompensated antiferromagnetic interactions within the cobaltous chains. In zero-field, dynamic magnetic susceptibility measurements show slow magnetic relaxation below 5.4 K while both neutron diffraction and heat capacity measurements give evidence of long-range order (LRO) below this temperature. The slow dynamics may originate from the motion of broad domain walls and is characterized by an Arrhenius law with a single energy barrier Δ_τ/k_B = 67(1) K for the [10–5000 Hz] frequency range. Moreover, in nonzero dc fields the ac susceptibility signal splits into a low-temperature frequency-dependent peak and a high-temperature frequency-independent peak which strongly shifts to higher temperature upon increasing the bias dc field. Heat capacity measurements have been carried out for various applied field values, and the recorded <i>C</i>_P(<i>T</i>) data are used for the calculation of the thermal variations of both the adiabatic temperature change Δ<i>T</i>_ad and magnetic entropy change Δ<i>S</i>_m. The deduced data show a modest magnetocaloric effect at low temperature. Its maximum moves up to higher temperature upon increasing the field variation, in relation with the field-sensibility of the intrachain magnetic correlation length