Nuclear magnetic resonance studies of magnetic properties of antiferromagnetic triangular spin system isolated in nano-meter region

我们已经carried out nuclear magnetic resonance (NMR) measurements at very low temperatures down to0.05K using a He^3- He^4 dilution refrigerator in order to investigate the magnetic properties of annanoscale molecular magnet k_6 [v_< 15> as_6o_< 42> h_2ho] 8 h_2o (in short V15). The V15 cluster is knowto be一个典型的Heisenberg triangular antifenomagnet and一个理想和简单系统toinvestigate the effects of spin chirality on the magnetism. the cluster is comprised of fifteenV^<4+> ions with S=1/2which arranged in a quasi-spherical layered structure with a triangle sandwiched betweenhexagons. All the exchange interactions between V <4+> spins are antiferromagnetic. Each hexagon ofthe cluster consists of三个pans of strongly coupled spins with J-800Kresulting in spin singlet state at low temperatures. Only threes V^<4+> spins on the triangletherefore play an important role on the magnetic properties at low temperatures. the exchangeinteractions between V^<4+> spins oMore n the triangle is known to be J =2.44K Followings are summary of main results.(1) Energylevel structure of V15 cluster is determined by NMR and μSR measurements. (Paper No.1 and 2)(2) Aspin singlet state of V <4+> spin on the hexagons at low temperature was directly revealed by theobservation of <51> VNMR signal from the V ions on the hexagons. (Paper No.3)(3)We have succeededto observe on-site <51>V-NMR signal from magnetic ions on the triangle at very low temperaturesbelow 0.1K. In the total spin s_t =3/2 ground state (non frustrated state)，each V <4+> spin on the triangle has been revealed to have almost full spin moment of 1μ _b and spinof three V ions on the triangle directs along to external fieldresulting in total spin s_t =3/2. in the case of s_t =1/2 frustrated state，a pure chiral state expected in an s=1/2 Heisenberg triangular antiferromagnet is found to be brokendown in the V15 cluster. Instead，the two s_t =1/2 states are found to be expressed by the mixed chiral states. (paper No.5) Less

We have carried out nuclear magnetic resonance (NMR) measurements at very low temperatures down to 0.05K using a He^3- He^4 dilution refrigerator in order to investigate the magnetic properties of an nanoscale molecular magnet K_6[V_<15>As_6O_<42>H_2HO]・8H_2O (in short V15). The V15 cluster is know to be an typical Heisenberg triangular antifenomagnet and an ideal and simplest system to investigate the effects of spin chirality on the magnetism. The cluster is comprised of fifteen V^<4+> ions with S=1/2, which are arranged in a quasi-spherical layered structure with a triangle sandwiched between hexagons. All the exchange interactions between V^<4+> spins are antiferromagnetic. Each hexagon of the cluster consists of three pans of strongly coupled spins with J-800K, resulting in spin singlet state at low temperatures. Only threes V^<4+> spins on the triangle therefore play an important role on the magnetic properties at low temperatures. The exchange interactions between V^<4+> spins o … More n the triangle is known to be J =2.44K Followings are summary of main results.(1) Energy level structure of V15 cluster is determined by NMR and μSR measurements. (Paper No.1 and 2)(2) A spin singlet state of V^<4+> spin on the hexagons at low temperature was directly revealed by the observation of ^<51> VNMR signal from the V ions on the hexagons. (Paper No.3)(3)We have succeeded to observe on-site ^<51>V-NMR signal from magnetic ions on the triangle at very low temperatures below 0.1K. In the total spin S_T=3/2 ground state (non frustrated state), each V^<4+> spin on the triangle has been revealed to have almost full spin moment of 1μ_B and spin of three V ions on the triangle directs along to external field, resulting in total spin S_T=3/2. In the case of S_T=1/2 frustrated state, a pure chiral state expected in an s=1/2 Heisenberg triangular antiferromagnet is found to be broken down in the V15 cluster. Instead, the two S_T=1/2 states are found to be expressed by the mixed chiral states. (paper No.5) Less