Discrete easy-axis tilting in Mn12-acetate, as determined by EPR: implications for the magnetic quantum tunneling mechanism

摘要: The variation with microwave frequency and temperature of previously reported anomalous peaks in the EPR spectra Mn12-acetate, under large transverse fields, reveals that molecular easy magnetization axes are tilted respect to global symmetry direction. More importantly, on basis angle-dependence fine structures observed we infer tilt distribution must be discrete, as was suspected from studies which demonstrated presence a locally varying rhombic anisotropy [S. Hill et al., Phys. Rev. Lett. 90, 217204 (2003)]. tilts confined two orthogonal planes, extends up ∼ 1.7◦ degrees away (z-) axis. We ascribe tilting hydrogen-bonding effect associated disordered acetic acid solvent molecules. is considerably larger than deduced x-ray diffraction analyses. These data constitute sought-after evidence for fields provide possible explanation lack selection rules resonant quantum tunneling behavior seen low-temperature hysteresis experiments this S = 10 system. PACS numbers: 75.50.Xx, 75.60.Jk, 75.75.+a, 76.30.-v