ESR experiments of molecular magnet V15 at ultra-low temperatures

Abstract The low-temperature magnetism of fascinating molecular magnet V15 is studied using by ESR technique. A new ESR apparatus for use a Helium-3 cryostat and a Vector Network Analyzer has been developed. Using this system, ESR investigations were performed at low temperatures down to 0.5 K . At 4.2 K , a resonant peak was observed clearly. Both the width and height increase with lowering temperature, which indicates the intensity of the absorption signal increases steadily. Nevertheless, from the analysis of temperature dependence of the signal intensity, we found that the magnetic moments of V15 clusters drastically decrease with lowering temperature. This result indicates the ground state of spins of V15 ions is doublet with S= 1 2 .