Study of the local field distribution on a single-molecule magnet by a single paramagnetic crystal: A DPPH crystal on the surface of an Mn_(12)-acetate crystal

摘要

The local magnetic field distribution on the surface of a single-molecule magnet crystal (SMM) above blocking temperature (T 》T_b) detected for a very short time interval (～10~(10)s), has been investigated. Electron paramagnetic resonance (EPR) spectroscopy, using a local paramagnetic probe, was employed as a simple alternative detection method. An SMM crystal of [Mn_(12)O_(12)(CH_3COO)_(16)(H_2O)_4]-2CH_3COOH_4H_2O (Mn_(12)-acetate) and a crystal of 2,2-diphenyl-l-picrylhydrazyl (DPPH), as the paramagnetic probe, were chosen for this study. The EPR spectra of DPPH deposited on Mn_(12)-acetate show additional broadening and shifting in the magnetic field in comparison to the spectra of the DPPH in the absence of the SMM crystal. The additional broadening of the DPPH linewidth was considered in terms of the two dominant electron spin interactions (dipolar and exchange) and the local magnetic field distribution on the crystal surface. The temperature dependence of the linewidth of the Gaussian distribution of local fields at the SMM surface was extrapolated for the low-temperature interval (70-5K).