The spin dynamics of a cluster of four iron(III) ions characterized by a total spin ground state S T=5 and Ising anisotropy have been investigated by the 1H nuclear magnetic resonance (NMR) linewidth and 1H NMR spin-lattice relaxation rate 1/T 1 as a function of the temperature (0.5-295 K) and external magnetic field (0.3-7.2 T). At very low T (0.5 K) the spectrum becomes very broad indicating freezing of the Fe 3+ moments in a superparamagnetic state. The temperature dependence of T 1 -1 and T 2 -1 shows strong field dependent enhancement below 50 K which must be related to the spin dynamics of the Fe 3+ moment freezing process, although no quantitative theory of this is currently available.
ASJC Scopus subject areas
- Physics and Astronomy(all)