Eur. Phys. J. B 17, 69-83 (2000)
https://doi.org/10.1007/s100510070161

Magnetic tunneling told to ignorants by two ignorants

¹ Centre de Recherches sur les Très basses températures, CNRS, BP 166, 38042 Grenoble Cedex 9, France
² Département de Recherche Fondamentale sur la Matière Condensée, Commissariat à l'Énergie Atomique, 17 avenue des Martyrs, 38054 Grenoble Cedex 9, France
³ Dipartimento di fisica, Università di Firenze, Istituto Nazionale di Fisica della Materia, Unità di Firenze, Largo Enrico Fermi 2, 50125 Firenze, Italy

Received: 17 May 2000
Published online: 15 September 2000

Abstract

Magnetic tunneling of a large spin subject to the Hamiltonian is investigated by elementary methods for weak fields . In zero field () the tunnel frequency in the ground state is found to be equal to multiplied by a quantity whose variation with s is slower than exponential. This result coincides with that of path integral methods [CITE]. For the values of the longitudinal field which allow tunneling, the tunnel frequency is shown to vanish when H_y=0 for certain "diabolic" values of , in qualitative agreement with experiments by Wernsdorfer and Sessoli. The particular case H_z=0 was already obtained by Garg by means of path integrals. The diabolic values of are in agreement with numerical results but, as already noticed by Wernsdorfer and Sessoli, they disagree with the experimental ones. This may be an effect of higher order anisotropy terms, which is briefly addressed in the conclusion.