Preface

This book aims to provide a coherent and pedagogical collection of articles on the physics and applications of molecular magnets. All contributors have played a major role in either (1) discovering or elucidating the physics that underlies molecular magnets, or in (2) the present exploration of avenues toward their applications. Issues that are by now well understood as well as open questions are covered. Inevitably, overlaps among some chapters do occur, but we are sure that the reader will find them complementary rather than repetitious. Molecular magnets are made up of chemically identical molecules with high– spin cores. The cornerstone for the rise of present day interest in molecular magnetism was the discovery of magnetic quantum tunneling in Mn12-acetate molecules. There was before 1996 some indirect evidence for quantum tunneling of large spins. In 1993, magnetic hysteresis (and thus magnetic memory) at liquid Helium temperatures was shown to come from single molecular clusters of Mn12-acetate. However, a clear imprint of magnetic quantum tunneling was only observed in 1996. Then, experiments revealed that magnetic hysteresis in Mn12-acetate is rather unconventional, in that the magnetization jumps at equally spaced values of the applied magnetic field. The gist of this effect is that spins can tunnel between different magnetic states as they are brought on and off resonance by an external magnetic field. Mn12-acetate molecules thus behave as “single molecule magnets” (SMMs). “Resonant spin tunneling” in molecular magnets illustrates beautifully quantum physics at the mesoscopic scale, that is, in the crossover region between the macroscopic and microscopic worlds, where quantum and classical physics meet. Finally, SMMs are a variant of magnetic nanoparticles, which are at the basis of magnetic recording. Much interest in SMMs arises from this fact. The field has expanded considerably in the last two decades, owing to the creativity of molecular chemists (who have crafted high and low spin clusters and single chain magnets), to the observation and elucidation of interesting phenomena (e.g., hole burning, spin avalanches and deflagration, as well as dipolar long-range ordering), and to the development of experimental techniques (e.g., single molecule manipulation on substrates). Finally, there is the vibrant ongoing work on applications. Most of it has to do with the fact that single molecule magnets are potential