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

Abstract

We present a study of the spin dynamics of the magnetic dimer $[\mathrm{Fe}(\mathrm{OMe})(\mathrm{dpm}{)}_{2}{]}_{2},$ using M\ossbauer 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 ${\mathrm{DS}}_{z}^{2}$ 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 ${J}_{z}$ of the hyperfine-field correlation function versus the temperature was obtained from the spectrum fittings. The trend of ${J}_{z}$ 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 ${J}_{z}(T):$ $D(1)\ensuremath{\approx}8.1\mathrm{K},$ $E/D(1)\ensuremath{\approx}8.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4},$ and ${w=w}_{0}\mathrm{exp}(\ensuremath{-}{2T}_{0}/T)$ with ${w}_{0}\ensuremath{\approx}9.2\ifmmode\times\else\texttimes\fi{}{10}^{8}{\mathrm{s}}^{\ensuremath{-}1}$ and ${T}_{0}\ensuremath{\approx}732\mathrm{K}.$ Lastly, similarities in spin dynamics between the dimer and the ring shaped clusters were discussed.