title: Butterfly hysteresis loop at nonzero bias field in antiferromagnetic molecular rings: cooling by adiabatic magnetization.
abstract: At low temperatures, the magnetization of the molecular ferric wheel NaFe6 exhibits a step at a critical field B(c) due to a field-induced level crossing. By means of high-field torque magnetometry we observed a hysteretic behavior at the level crossing with a characteristic butterfly shape which is analyzed in terms of a dissipative two-level model. Several unusual features were found. The nonzero bias field of the level crossing suggests the possibility of cooling by adiabatic magnetization.
authors.affiliation: Physikalisches Institut III, Universität Erlangen-Nürnberg, Germany. waldmann@physik.uni-erlangen.de
authors.forename: O
authors.initials: O
authors.lastname: Waldmann
authors.forename: R
authors.initials: R
authors.lastname: Koch
authors.forename: S
authors.initials: S
authors.lastname: Schromm
authors.forename: P
authors.initials: P
authors.lastname: Müller
authors.forename: I
authors.initials: I
authors.lastname: Bernt
authors.forename: R W
authors.initials: RW
authors.lastname: Saalfrank