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Title: Review of NMR studies of nanoscale molecular magnets composed of geometrically frustrated antiferromagnetic triangles

This paper presents a comprehensive review of nuclear magnetic resonance (NMR) studies performed on three nanoscale molecular magnets with different novel configurations of geometrically frustrated antiferromagnetic (AFM) triangles: (1) the isolated single AFM triangle K 6[V 15As 6O 42(H 2O)]·8H 2O (in short V15), (2) the spin ball [Mo 72Fe 30O 252(Mo 2O 7(H 2O)) 2(Mo 2O 8H 2(H 2O)) (CH 3COO) 12(H 2O) 91]·150H 2O (in short Fe30 spin ball), and (3) the twisted triangular spin tube [(CuCl 2tachH) 3Cl]Cl 2 (in short Cu3 spin tube). In V15t, from 51V NMR spectra, the local spin configurations were directly determined in both the nonfrustrated total spin S T = 3/2 state at higher magnetic fields (H ge; 2.7 T) and the two nearly degenerate S T = 1/2 ground states at lower magnetic fields (H ≤ 2.7 T). The dynamical magnetic properties of V15 were investigated by proton spin-lattice relaxation rate (1/T 1) measurements. In the S T = 3/2 state, 1/T 1 shows thermally activated behaviour as a function of temperature. On the other hand, the temperature independent behaviour of 1/T 1 at very low temperatures is observed in the frustrated S T = 1/2 ground state. Possible originsmore » for the peculiar behaviour of 1/T 1 will be discussed in terms of magnetic fluctuations due to spin frustrations. In Fe30, static and dynamical properties of Fe 3+ (s = 5/2) have been investigated by proton NMR spectra and 1/T 1 measurements. From the temperature dependence of 1/T 1, the fluctuation frequency of the Fe 3+ spins is found to decrease with decreasing temperature, indicating spin freezing at low temperatures. The spin freezing is also evidenced by the observation of a sudden broadening of 1H NMR spectra below 0.6 K. Finally, 1H NMR data in Cu3 will be described. An observation of magnetic broadening of 1H NMR spectra at low temperatures below 1 K directly revealed a gapless ground state. The 1/T 1 measurements revealed a usual slow spin dynamics in the Cu3 spin tube.« less
  1. Ames Lab. and Iowa State Univ., Ames, IA (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 1475-7435
Grant/Contract Number:
Accepted Manuscript
Journal Name:
International Journal of Nanotechnology
Additional Journal Information:
Journal Volume: 13; Journal Issue: 10/11/12; Journal ID: ISSN 1475-7435
Research Org:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org:
Country of Publication:
United States
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; frustrated spin systems; antiferromagnetic triangles; nanomagnets; nuclear magnetic resonance; NMR; nuclear spin lattice relaxation rates; spin dynamics; nanotechnology; review; nanoscale molecular magnets; temperature dependence; spin freezing; magnetic fluctuations
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