Exchange interactions and spin dynamics in a [CuNd2(C4O4)4(H2O)16]·2H2O crystal

Abstract

Crystalline [CuNd2(C4O4)4(H2O)16]·2H2O constructed of complexes of trivalent neodymium and divalent copper, has been synthesized and studied by EPR. The square anion groups (C4O4) enter as bridge ligands, forming chains of neodymium ions interconnected by (C4O4)Cu(C4O4) fragments. It is found that the relaxation rate of the neodymium subsystem at room temperature significantly exceeds the exchange interaction rate between copper and neodymium ions. Under these conditions the magnetic properties of the crystal are determined by two magnetically nonequivalent chains of copper ions, which do not interact. The intrachain exchange interaction via hydrogen bonds is estimated to be ∼0.1 cm−1. As one proceeds from the high-temperature (250<T<300 K) to the low-temperature region (T<40 K), a substantial change in the nature of the interaction is revealed. An unusual magnetic structure given in a crystal is observed at low temperatures, which is determined by the presence of two magnetically nonequivalent “ribbons,” formed by the interacting copper and neodymium ions: chains of copper ions are framed on two sides by chains of neodymium ions. The magnitude of the parameter of the exchange interaction between the copper and neodymium ions is estimated as JCu-Nd⩾0.2 cm−1. An exchange interaction between magnetically nonequivalent neodymium ions is not revealed in the EPR spectra.