Magnetic studies of quasi one-dimensional systems

Background

The quasi-one dimensional systems this group has been studying are electron transfer salts consisting of linear chains of alternating metallocenium or metalloporphyrin electron donors (D) and spin 1/2 cyanocarbon acceptors (A), ... D+A-D+A-D+A- .... The family of metalloporphyrin-based magnets provides an unusual opportunity for the study of magnetic ordering [1] because it offers a wide range of controlling factors. For instance, the cyanocarbon bridge connecting the adjacent porphyrins can be varied (TCNE = tetracyanoethylene, HCBD = hexacyanobutadiene) to influence the intrachain interaction; different organic constituents can be added at the periphery of the porphyrin (TPP = meso-tetraphenylporphyrinato, OEP = octaethylporphyrinato) to affect the interchain interaction and, thereby, build up or reduce three-dimensional magnetic order; various solvents (toluene, xylene, dichlorobenzene) that may induce glassy behavior can be incorporated into the structure.

Figure 1 [MnTPP][TCNE]

Recent Advances

Recent progress made in understanding the role of the building blocks forming these materials revealed interesting magnetic properties (one-dimensional ferrimagnetic behavior at high temperatures, three dimensional canted antiferromagnetic or weak ferromagnetic behavior at low temperatures) [1,2], and phenomena (spin- and/or lattice-dimensionality crossovers) [3,4]. The presence of disorder leads in some of these materials to cluster glass-like behavior [5].

For instance while [MnOEP][HCBD] has transitions from a one-dimensional Heisenberg ferrimagnet to a two-dimensional Ising antiferromagnet at 20 K [3] and to a canted three-dimensional antiferromagnet below 5K [4], [MnTPP][TCNE][solvent] has a transition from a one-dimensional ferrimagnet to a three-dimensional weak ferromagnet in the range 9-13 K, depending on the solvent [1]. In this last case, the intercalated solvent and the various possible configurations of the bridging TCNE molecule lead to disorder and glassy behavior [5].

In all these materials, the role of the strong intrachain exchange, single-ion anisotropy and weak dipole-dipole interchain interactions have been examined. Based on the correlations between structural and magnetic data a new way to design quasi-1D molecule-based magnets has been proposed [1].

Publications

C.M. Wynn, M. Girtu, W.B. Brinckerhoff, K-I. Sugiura, Joel S. Miller, and A.J. Epstein, Magnetic Dipole-Dipole Interactions and Single Ion Anisotropy:  Revisiting a Classical Approach to Magnets, Chemistry of Materials 9, 2156-2163 (1997).

A.J. Epstein, C.M. Wynn, M.A. Girtu, W.B. Brinckerhoff, K.I. Sugiura, and J.S. Miller, Magnetic Ground State and Its Control in Porphyrin-Based Magnets, Molecular Crystals, Liquid Crystals 305, 321-332 (1997).

C.M. Wynn, M.A. Girtu, Joel S. Miller, and A.J. Epstein, Lattice- and Spin-Dimensionality Crossovers in a Linear Chain Molecule-Based Ferrimagnet with Weak Spin Anisotropy, Physical Review B 56, 315-320 (1997).

C.M. Wynn, M.A. Girtu, J.S. Miller, and A.J. Epstein, Magnetic Phase Diagram of of a Molecule-Based Ferrimagnet:  Weak Ferromagnetism and Multiple Dimensionality Crossovers, Physical Review B 56, 14050-14057 (1997).

M.A. Girtu, C.M. Wynn, K-I. Sugiura, J.S. Miller, and A.J. Epstein, The Effect of Disorder on the Linear and Nonlinear Magnetic Susceptibilities of Two Manganeseporphyrin-Based Magnets, Journal of Applied Physics 81, 4410-4412 (1997).

Created by Darren Gebler and Mihai Gîrtu. Maintained by John Rohrbacher. Last updated 6/1/00.