Magnetization studied on spin alignments in organic molecule-based ferrimagnetics

A physics picture of spin alignments in molecule-based ferrimagnets is presented from studying the temperature dependence of the effective sublattice magnetic moments and the total reduced magnetization by means of Green's function theory combined with the Jordan-Wigner transformation. The ferrimagnetic chain includes an S = I biradical and an S = 1/2 monoradical with antiferromagnetic alternating interactions, and the S = I site in the chain is composed of two S = 1/2 spins coupled by a finite ferromagnetic interaction. From the calculations of the sublattice magnetic moments, the magnetic moment of the S = I biradical is negative, while that of the S = 1/2 monoradical is positive, leading to a ferrimagnetic ground state. With the different kinds of the elementary excitations and the competition between the magnetic interactions and thermal fluctuations, the temperature dependence of the magnetization displays rich thermodynamic properties. Meanwhile, the external magnetic field dependence of the magnetization has a clear plateau at one third of the saturation magnetization, which can be compared with the possible experimental findings. (c) 2006 Elsevier Ltd. All rights reserved.