title: Magnetic-field-dependent heat capacity of the single-molecule magnet [Mn(12)O(12)(O(2)CEt)(16)(H(2)O)(3)].
abstract: Accurate heat capacities of the single-molecule magnet [Mn(12)O(12)(O(2)CEt)(16)(H(2)O)(3)] were measured from 0.3 to 311 K by adiabatic calorimetry without an external magnetic field. Heat-capacity anomalies were separated by assuming several contributions including lattice vibration, magnetic anisotropy, and hyperfine splitting. Among them, a tiny thermal anomaly between 1 and 2 K is attributable to the presence of Jahn-Teller isomers. The heat capacities of the polycrystalline sample were also measured with applied magnetic fields from 0 to 9 T in the 2-20 K temperature region by the relaxation method. With an applied magnetic field of up to 2 T, a steplike heat-capacity anomaly was observed around the blocking temperature T(B) approximately 3.5 K. The magnitude of the anomaly reached a maximum at 0.7 T. With a further increase in the magnetic field, the step was decreasing, and finally it disappeared above 3 T. The step at T(B) under 0.7 T can be roughly accounted for by assuming that a conversion between the up-spin and down-spin states is allowed above T(B) by phonon-assisted quantum tunneling, while it is less effective below T(B). Excess heat capacity under a magnetic field revealed a large heat-capacity hump around 14 K and 2 T, which would be attributed to a thermal excitation from the S = 9 ground state to the spin manifold with different S values, where S is the total spin quantum number.
authors.affiliation: Research Center for Molecular Thermodynamics, Graduate School of Science, and Department of Molecular Chemistry, Graduate School of Engineering, Osaka University, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Miyazaki
authors.forename: A
authors.initials: A
authors.lastname: Bhattacharjee
authors.forename: M
authors.initials: M
authors.lastname: Nakano
authors.forename: K
authors.initials: K
authors.lastname: Saito
authors.forename: S M
authors.initials: SM
authors.lastname: Aubin
authors.forename: H J
authors.initials: HJ
authors.lastname: Eppley
authors.forename: G
authors.initials: G
authors.lastname: Christou
authors.forename: D N
authors.initials: DN
authors.lastname: Hendrickson
authors.forename: M
authors.initials: M
authors.lastname: Sorai