Determination of a zero-field splitting parameter D in Mn12Ac below 20 K

Molecular magnet Mn12Ac has a large molecular spin S = 10. The uniaxial cry stalline anisotropy splits the energy levels in zero magnetic field into 10 doublets and one singlet. The simplest Hamiltonian in magnetic field H-z f or this symmetry is H = - DSz2 - y mu(B)mu(0)HS(z). The zero-field splittin g parameter D has been determined from measured hl(H) in weak magnetic fiel d at different temperatures. The approximate value is D = 0.7 K. (C) 2000 E lsevier Science B.V. All rights reserved.