2003-5

Experimental ESR Investigations of Quantum Molecular Magnet V15 below 1K
低次元量子スピン系磁性体V15の極低温におけるESR

Low-temperature magnetism of molecular magnet V15 was studied using by ESR experiments. A new ESR apparatus combined with a Helium-3 cryostat and a Vector Network Analyzer has been developed. This system enabled ESR investigations at low temperatures down to 0.5 K. At 4.2 K, a resonant peak was observed clearly between 45 GHz and 110 GHz. We found that the magnetic moments of V15 clusters drastically decrease with lowering temperature. This result indicates that the ground state of spins for V15 ions is doublet with S = 1/2. The ESR line width increases with lowering temperature, which suggests that the molecular magnet V15 reveals the quantum characteristics in contrast with usual magnets.

Fac. of Eng., Akita University: T. Sakon
IMR, Tohoku University: K. Koyama, M. Motokawa
Grad. School of Sci., Kyushuu University: Y. Ajiro
Universitat Bielefeld: A. Muller
CRNS: B. Barbara
Reference: T. Sakon, K. Koyama, M. Motokawa, Y. Ajiro, A. Muller, B. Barbara, "ESR Experiments of molecular magnet V15 at ultra-low temperatures" Physica B 346-347 (2004) pp.206-210.

ヘリウム3冷凍機を用いた超低温ESR実験装置を作製し，量子スピン系の分子磁性体V15の超低温ESR実験を行なった．その結果，ESRスペクトルに大きな温度依存性及び磁場依存性が観測された.　これらの結果は，基底状態がスピン1/2であり，また，通常の磁性体とは異なる特徴的な量子磁性体であることを示している.

秋田大学　工学資源学部：左近拓男
東北大学　金属材料研究所：小山佳一，本河光博
Universitat Bielefeld : A. ミューラー