Zero- and longitudinal-field muon-spin-rotation (μSR) and H1 NMR measurements on the S= 1 2 molecular nanomagnet K6 [V15IV As6 O42 (H2 O)] •8 H2 O are presented. In LF experiments, the muon asymmetry P (t) was fitted by the sum of three different exponential components with fixed weights. The different muon relaxation rates λi (i=1,2,3) and the low-field H=0.23 T H1 NMR spin-lattice relaxation rate 1 T1 show a similar behavior for T>50 K: starting from room temperature they increase as the temperature is decreased. The increase of λi and 1 T1 can be attributed to the "condensation" of the system toward the lowest-lying energy levels. The gap Δ∼550 K between the first and second S= 3 2 excited states was determined experimentally. For T<2 K, the muon relaxation rates λi stay constant, independently of the field value H≤0.15 T. The behavior for T<2 K strongly suggests that, at low T, the spin fluctuations are not thermally driven but rather originate from quasielastic intramolecular or intermolecular magnetic interactions. We suggest that the very-low-temperature relaxation rates could be driven by energy exchanges between two almost degenerate S= 1 2 ground states and/or by quantum effects.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - May 22 2006|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics