Quantum Monte-Carlo and Series-Expansion Analysis of Spin-Models for Molecular Magnets

• Applicant: Professor Dr. Wolfram Brenig
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2006 to 2009
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 25514662

This project is devoted to thermodynamic, time-dependent, and zero temperature properties of molecular magnets. First, we will analyze the susceptibility and magnetization, of unfrustrated single-molecule magnets (SMM)s which are too large to be handled with present days exact diagonalization (ED) methods. This will be done using the stochastic series expansion (SSE), which is a novel Quantum Monte-Carlo (QMC) simulation method. We intend to improve and adopt the SSE for this purpose. In particular we will apply the SSE to the SMM [Mn9(2POAP-2H)2]6+. Second, we will study the role of dimer-coupling, local anisotropies, and magnetic fields in dimer-ladders as eg. the oxalate systems Na2Me2(C2O4)3(H2O)2, with Me = Mn, Fe, Co, Ni and spin S = (5, 4, 3, 2)/2. This study will be based on the SSE, complemented by an analytic bond-operator theory (BOT). Finally, using a high order series expansion at zero temperature, which is based on an operator renormalization group (ORG) method we will study inter-cluster exchange and spin-frustration in weakly coupled tetra-nuclear molecular magnets. In collaboration with experimental groups the role of inter-tetrahedral exchange on the spin-dynamics of eg. [L2Ni4(N3)(O2CAda)4](CIO4) will be considered.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1137: Molecular Magnetism
• Participating Person: Dr. Marcelo Arlego