Dislocation-induced spin tunneling in Mn-12 acetate

Abstract

Comprehensive theory of quantum spin relaxation in Mn-12 acetate crystals is developed, that takes into account imperfections of the crystal structure and is based upon the generalization of the Landau-Zener effect for incoherent tunneling from excited energy levels. It is shown that linear dislocations at plausible concentrations provide the transverse anisotropy which is the main source of tunneling in Mn-12. Local rotations of the easy axis due to dislocations result in a transverse magnetic field generated by the field applied along the c-axis of the crystal, which explains the presence of odd tunneling resonances. Long-range deformations due to dislocations produce a broad distribution of tunnel splittings. The theory predicts that at subkelvin temperatures the relaxation curves for different tunneling resonances can be scaled onto a single master curve. The magnetic relaxation in the thermally activated regime follows the stretched-exponential law with the exponent depending on the field, temperature, and concentration of defects.

17 pages, 14 figures, 1 table, submitted to PRB

References in corpus (3)

• Spin tunneling via dislocations in Mn-12 acetate crystals
• Crossover between Thermally Assisted and Pure Quantum Tunneling in Molecular Magnet Mn12-Acetate
• A Distribution of Tunnel Splittings in Mn${}_{12}$-Acetate

Cited by in corpus (34)

• Detailed single crystal EPR lineshape measurements for the single molecule magnets Fe8Br and Mn12-ac
• Definitive spectroscopic determination of the transverse interactions responsible for the magnetic quantum tunneling in Mn12-acetate
• Resonant Tunneling in Truly Axial Symmetry Mn12 Single-Molecule Magnets: Sharp Crossover between Thermally Assisted and Pure Quantum Tunneling
• Electronic Transport in Single-Molecule Magnets on Metallic Surfaces
• Superradiance from crystals of molecular nanomagnets
• Fast noise in the Landau-Zener theory
• Role of dipolar and exchange interactions in the positions and widths of EPR transitions for the single-molecule magnets Fe8 and Mn12
• Effect of extra electrons on the exchange and magnetic anisotropy in the anionic single-molecule magnet Mn12
• Theory of magnetic deflagration
• Evidence for the S=9 excited state in Mn12-bromoacetate measured by electron paramagnetic resonance
• Magnetization Process of Single Molecule Magnets at Low Temperatures
• Tunneling Splittings in Mn12-Acetate Single Crystals
• Second-order transverse magnetic anisotropy induced by disorders in the single-molecule magnet Mn12
• Macroscopic quantum tunneling and quantum-classical phase transitions of the escape rate in large spin systems
• Tunneling with dissipation and decoherence for a large spin
• Semiconductive and Photoconductive Properties of the Single Molecule Magnets Mn${}_{12}$-Acetate and Fe${}_8$Br${}_8$
• Quadratic transverse anisotropy term due to dislocations in Mn12-Ac directly obtained by EPR spectroscopy
• Self-organized patterns of macroscopic quantum tunneling in molecular magnets
• Asymmetric Lineshape due to Inhomogeneous Broadening of the Crystal-Field Transitions in Mn12ac Single Crystals
• Crystal defects and spin tunneling in single crystals of Mn12 clusters
• Pulsed field studies of the magnetization reversal in molecular nanomagnets
• Level splittings in exchange-biased spin tunneling
• How systems of single-molecule magnets magnetize at low temperatures
• On Ground State Tunneling in Mn${}_{12}$-Acetate
• Phonon bottleneck in the low-excitation limit
• Collective electromagnetic relaxation in crystals of molecular magnets
• Non-exponential relaxation and quantum tunnel splitting in molecular magnet Fe8
• Instanton versus traditional WKB approach to Landau - Zener problem
• Quantum dynamics of crystals of molecular nanomagnets inside a resonant cavity
• Suppression of Quantum Phase Interference in Molecular Magnets Fe₈ with Dipolar-Dipolar Interaction
• Lattice effects on the spin dynamics in antiferromagnetic molecular rings
• Effect of Defects on the Line shape of Electron Paramagnetic Resonance Signals from the Single-Molecule Magnet Mn12: A Theoretical Study
• More Evidence for a Distribution of Tunnel Splittings in Mn${}_{12}$-acetate
• Experimental evidence of the dependence of spin tunnelling on the concentration of dislocations in Mn12 crystals