Definitive spectroscopic determination of the transverse interactions responsible for the magnetic quantum tunneling in Mn12-acetate -: art. no. 217204

We present detailed angle-dependent single crystal electron paramagnetic resonance (EPR) data for field rotations in the hard plane of the S=10 single molecule magnet Mn-12-acetate. A clear fourfold variation in the resonance positions may be attributed to an intrinsic fourth-order transverse anisotropy ((O) over cap (4)(4)). Meanwhile, a fourfold variation of the EPR line shapes confirms a recently proposed model wherein disorder associated with the acetic acid of crystallization induces a locally varying quadratic (rhombic) transverse anisotropy [(O) over cap (2)(2)equivalent toE((S) over cap (2)(x)-(S) over cap (2)(y))]. These findings explain most aspects of the magnetic quantum tunneling observed in Mn-12-acetate.