Quantum dynamic simulations for single molecular magnets using anisotropic spin models

We performed quantum spin dynamics in anisotropic electron-spin systems to clarify the mechanism in single molecular magnets (SMM) theoretically. Usually. SMMs have large negative anisotropic D value and the large total spin angular moment (S-total). The splitting ground spin states in one SMM molecule are usually caused by the anisotropic terms (D and E), which become more important as well as isotropic term (J). In order to examine the effects of such anisotropic magnetic terms, model systems with large spin multiplicity of the ground state (S-total = 5 and 2) were treated. First, energy diagram in external magnetic field is shown, since negative D terms are responsible to the zero-field magnetic moment. Next, the quantum Liouvile approach is used for our spin dynamics simulation involving the relaxation processes of the system. Our simulations in S-total = 5 system successfully reproduced magnetic quantum tunneling (MQT) behavior in DC-external magnetic field. Moreover, in S-total = 2 system under AC-external magnetic field, frequency dependence of real (chi') and imaginary (chi '') parts of chi can be shown with Fourier transformation. Our theoretically drawn half circles in Cole-Cole plot (chi' versus chi '') will give information to many experimental studies. (c) 2009 Elsevier Ltd. All rights reserved.