Magnetization in molecular iron rings - art. no. 184409

The organometallic ring molecules Fe-6 and Fe-10 are leading examples of a class of nanoscopic molecular magnets which have been of intense recent int erest both for their intrinsic magnetic properties and as candidates for th e observation of macroscopic quantum coherent phenomena. Torque magnetometr y experiments have been performed to measure the magnetization in single cr ystals of both systems. We provide a detailed interpretation of these resul ts, with a view to full characterization of the material parameters. We pre sent both the most accurate numerical simulations performed to date for rin g molecules, using exact diagonalization and density-matrix renormalization -group techniques, and a semiclassical description for purposes of comparis on. The results permit quantitative analysis of the variation of critical f ields with angle, of the nature and height of magnetization and torque step s, and of the width and rounding of the plateau regions in both quantities.