Determination of the magnetic anisotropy axes of single-molecule magnets

Simple methods are presented allowing the determination of the magnetic anisotropy axes of a crystal of a single-molecule magnet (SMM). These methods are used to determine an upper bound of the easy axis tilts in a standard Mn12-Ac crystal. The values obtained in the present study are significately smaller than those reported in recent high frequency electron paramagnetic resonance (HF-EPR) studies which suggest distributions of hard-axes tilts.Comment: 10 pages, 6 figure

Magnetic relaxation studies on a single-molecule magnet by time-resolved inelastic neutron scattering

Time-resolved inelastic neutron scattering measurements on an array of single-crystals of the single-molecule magnet Mn12ac are presented. The data facilitate a spectroscopic investigation of the slow relaxation of the magnetization in this compound in the time domain.Comment: 3 pages, 4 figures, REVTEX4, to appear in Appl. Phys. Lett., for an animation see also http://www.dcb.unibe.ch/groups/guedel/members/ow2/trins.ht

Quantum phase interference and spin parity in Mn12 single-molecule magnets

Magnetization measurements of Mn12 molecular nanomagnets with spin ground states of S = 10 and S = 19/2 showresonance tunneling at avoided energy level crossings. The observed oscillations of the tunnel probability as a function of the magnetic field applied along the hard anisotropy axis are due to topological quantum phase interference of two tunnel paths of opposite windings. Spin-parity dependent tunneling is established by comparing the quantum phase interference of integer and half-integer spin systems.Comment: 5 pages, 5 figure

Propagation of Avalanches in Mn12_{12}-acetate: Magnetic Deflagration

Local time-resolved measurements of fast reversal of the magnetization of single crystals of Mn12-acetate indicate that the magnetization avalanche spreads as a narrow interface that propagates through the crystal at a constant velocity that is roughly two orders of magnitude smaller than the speed of sound. We argue that this phenomenon is closely analogous to the propagation of a flame front (deflagration) through a flammable chemical substance.Comment: 5 pages, 5 figure

Crystal Lattice Desolvation Effects On The Magnetic Quantum Tunneling Of Single-Molecule Magnets

High-frequency electron paramagnetic resonance (HFEPR) and alternating current (ac) susceptibility measurements are reported for a new high-symmetry Mn12 complex, [Mn12O12(O2CCH3)16(CH3OH)4]⋅CH3OH. The results are compared to those of other high-symmetry spin S=10 Mn12 single-molecule magnets (SMMs), including the original acetate, [Mn12(O2CCH3)16(H2O)4]⋅2CH3CO2H⋅4H2O, and the [Mn12O12(O2CCH2Br)16(H2O)4]⋅4CH2Cl2 and [Mn12O12(O2CCH2But)16(CH3OH)4]⋅CH3OH complexes. These comparisons reveal important insights into the factors that influence the values of the effective barrier to magnetization reversal, Ueff, deduced on the basis of ac susceptibility measurements. In particular, we find that variations in Ueff can be correlated with the degree of disorder in a crystal which can be controlled by desolvating (drying) samples. This highlights the importance of careful sample handling when making measurements on SMM crystals containing volatile lattice solvents. The HFEPR data additionally provide spectroscopic evidence suggesting that the relatively weak disorder induced by desolvation influences the quantum tunneling interactions and that it is under-barrier tunneling that is responsible for a consistent reduction in Ueff that is found upon drying samples. Meanwhile, the axial anisotropy deduced from HFEPR is found to be virtually identical for all four Mn12 complexes, with no measurable reduction upon desolvation

Observation of a Distribution of Internal Transverse Magnetic Fields in a Mn12-Based Single Molecule Magnet

A distribution of internal transverse magnetic fields has been observed in single molecule magnet (SMM) Mn12-BrAc in the pure magnetic quantum tunneling (MQT) regime. Magnetic relaxation experiments at 0.4 K are used to produce a hole in the distribution of transverse fields whose angle and depth depend on the orientation and amplitude of an applied transverse ``digging field.'' The presence of such transverse magnetic fields can explain the main features of resonant MQT in this material, including the tunneling rates, the form of the relaxation and the absence of tunneling selection rules. We propose a model in which the transverse fields originate from a distribution of tilts of the molecular magnetic easy axes.Comment: 4 page