The observation and suppression of an unusual equilibrium in the molecular
nanomagnet Fe8
Carley Paulsena , Vincent Villara , Elsa Lhotela , and Claudio Sangregoriob
a
CRTBT, laboratoire associé à l’Université Joseph Fourier, CNRS, BP 166, 38042 Grenoble cedex 9,
France
b
Dipartimento di Chimica, Università degli Studi di Firenze
Low temperature susceptibility and magnetic relaxation measurements show that an unusual equilibrium
phase occurs below 0.9 K in the spin S = 10 molecular nanomagnet Fe8 . A plateau in the susceptibility
results from a competition between ordering of spins governed by thermodynamics and quantum tunnelling of the spins which tends to disorder the system. Very unusual dynamic behaviour is observed
along the plateau and the relaxation is non-monotonic. The giant spins do not freeze even at very low
temperature due to tunnelling and as a result the spin entropy remains very large. If the tunnelling is
”turned off” by the application of an appropriate transverse field the above effects are suppressed, and
the system behaves as a normal super paramagnet.
Sorting category: Ce Magnetism and properties of solids
Keywords: magnetism, quantum tunneling, equilibrium, entropy
LT2071