Effects of Dstrain, gstrain, and dipolar interactions on EPR linewidths of the molecular.pdf

Effects of D-strain, g-strain, and dipolar interactions on EPR linewidths of the molecular magnets Fe8 and Mn12 1,∗ 1,† 2 3,‡ 1,4 Kyungwha Park , M. A. Novotny , N. S. Dalal , S. Hill , and P. A. Rikvold 1School of Computational Science and Information Technology, Florida State University, 3 Tallahassee, FL 32306 0 0 2Department of Chemistry, Florida State University, Tallahassee, FL 32306 2 b 3Department of Physics, Montana State University, Bozeman, MT 59717 e F 4 Center for Materials Research and Technology and Department of Physics, Florida State 4 2 University, Tallahassee, FL 32306 3 v (February 1, 2008) 6 7 2 6 0 1 Abstract 0 / t a Electron paramagnetic resonance (EPR) measurements on single crystals of m - d the molecular magnets Fe8 and Mn12 reveal complex nonlinearities in the n o linewidths as functions of energy eigenstate, frequency, and temperature. Us- c : v ing a density-matrix equation with distributions of the uniaxial anisotropy pa- i X rameter D, the Land´e g factor, and dipolar interactions, we obtain linewidths r a in good agreement with experiments. Our study shows that the distribution in D is common to the examined molecular magnets Fe8 and Mn12 regardless of the qualities of the samples. This could provide the basis for a proposed tunneling mechanism due to lattice defects. The distribution in g