Ferromagnetic long range ordering in copper(II) maleate monohydrate

Summary The magnetic properties of copper(II) maleate monohydrate, Cu(C₄H₂O₄)·H₂O, have been measured in the 1.8–66 K range. Magnetic susceptibility and isothermal magnetization measurements on powdered samples reveal a transition to a ferromagnetic state in this layered compound. The transition to the ordered state occurs at T_c=4.0 K. The positive value of 8.0 K for the Weiss constant in the paramagnetic region confirms the ferromagnetic nature of the interactions. The magnetic susceptibility data above 3T_c may be fitted with a Heisenberg quadratic layer expression with the best-fit parameters J=+4.3 cm^–1, g=2.0, and zJ=+0.42 cm^–1. The e.p.r. spectrum at room temperature indicates orthorhombic symmetry. A complex containing the isomeric form of the ligand, copper(II) fumarate dihydrate, has also been prepared and its magnetic properties determined in the 80–300 K range. The data may be accomodated by two-dimensional theory with J=+1.05 cm^–1, g=2.09, and zJ=+0.10 cm^–1.