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

Journal Article · Sat Oct 01 00:00:00 EDT 2016 · International Journal of Nanotechnology

DOI:https://doi.org/10.1504/ijnt.2016.080351· OSTI ID:1347415

Furukawa, Yuji ^[1]

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1. Ames Lab. and Iowa State Univ., Ames, IA (United States)

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 K₆[V₁₅As₆O₄₂(H₂O)]·8H₂O (in short V15), (2) the spin ball [Mo₇₂Fe₃₀O₂₅₂(Mo₂O₇(H₂O))₂(Mo₂O₈H₂(H₂O)) (CH₃COO)₁₂(H₂O)₉₁]·150H₂O (in short Fe30 spin ball), and (3) the twisted triangular spin tube [(CuCl₂tachH)₃Cl]Cl₂ (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/T₁) measurements. In the S_T = 3/2 state, 1/T₁ shows thermally activated behaviour as a function of temperature. On the other hand, the temperature independent behaviour of 1/T₁ at very low temperatures is observed in the frustrated S_T = 1/2 ground state. Possible origins for the peculiar behaviour of 1/T₁ will be discussed in terms of magnetic fluctuations due to spin frustrations. In Fe30, static and dynamical properties of Fe³⁺ (s = 5/2) have been investigated by proton NMR spectra and 1/T₁ measurements. From the temperature dependence of 1/T₁, the fluctuation frequency of the Fe³⁺ 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/T₁ measurements revealed a usual slow spin dynamics in the Cu3 spin tube.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-07CH11358
• OSTI ID: 1347415
• Report Number(s): IS-J-9199
• Journal Information: International Journal of Nanotechnology, Vol. 13, Issue 10/11/12; ISSN 1475-7435
• Country of Publication: United States
• Language: English

Related Subjects

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