Spin dynamics of the magnetic dimer [Fe(OMe)(dpm)(2)](2) studied using Mossbauer spectroscopy

We present a study of the spin dynamics of the magnetic dimer [Fe(OMe)(dpm)2]2, using Mössbauer spectroscopy. In this cluster, the two iron(III) ions are antiferromagnetically coupled so that the dimer presents a S=0 spin ground state. Spin multiplets with values of S ranging from 1 to 5 follow in order of increasing energy. Axial anisotropy DSz2 is also present with D of the order of a few kelvin. Spectra were collected over a range from 6.5 K to room temperature. They consist of doublets in which any magnetic structure is lacking, but the line widths of which increase with the temperature, due to relaxation effects. We performed their fits by assuming a fast-fluctuating hyperfine field which stochastically inverts its direction along the anisotropy axis. The zero-frequency Fourier transform Jz of the hyperfine-field correlation function versus the temperature was obtained from the spectrum fittings. The trend of Jz suggests that the basic mechanisms of the spin dynamics consist of a tunnel effect due to magnetic-anisotropy transversal terms, as well as of spin-thermal bath interactions. By assuming this, the following parameters were estimated from the fitting of Jz(T): D(1)?8.1K, E/D(1)?8.5×10-4, and w=w0exp(-2T0/T) with w0?9.2×108s-1 and T0?732K. Lastly, similarities in spin dynamics between the dimer and the ring shaped clusters were discussed.