Low temperature magnetic hysteresis in Mn${}_{12}$ acetate single crystals

Abstract

Precise magnetic hysteresis measurements of small single crystals of Mn${}_{12}$ acetate of spin 10 have been conducted down to 0.4 K using a high sensitivity Hall magnetometer. At higher temperature (>1.6K) step-like changes in magnetization are observed at regularly spaced magnetic field intervals, as previously reported. However, on lowering the temperature the steps in magnetization shift to higher magnetic fields, initially gradually. These results are consistent with the presence of a second order uniaxial magnetic anisotropy, first observed by EPR spectroscopy, and thermally assisted tunnelling with tunnelling relaxation occurring from levels of progressively lower energy as the temperature is reduced. At lower temperature an abrupt shift in step positions is found. We suggest that this shift may be the first evidence of an abrupt, or first-order, transition between thermally assisted and pure quantum tunnelling, suggested by recent theory.

8 pages, 4 figures, submitted to Europhys. Lett

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• Dislocation-induced spin tunneling in Mn-12 acetate
• Phonon-assisted tunneling in the quantum regime of Mn12-ac
• Single-Molecule Magnets: Jahn-Teller Isomerism and the Origin of Two Magnetization Relaxation Processes in Mn12 Complexes
• Spin dynamics of Mn12-acetate in the thermally-activated tunneling regime: ac-susceptibility and magnetization relaxation
• Dipolar ordering in Fe8?
• Macroscopic quantum tunneling and quantum-classical phase transitions of the escape rate in large spin systems
• Hall cross size scaling and its application to measurements on nanometer-size iron particle arrays
• Tunneling with dissipation and decoherence for a large spin
• Quantum statistical metastability for a finite spin
• 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
• Abrupt Transition between Thermally-Activated Relaxation and Quantum Tunneling in a Molecular Magnet
• Escape-Rate Crossover between Quantum and Classical Regimes in Molecular Magnets: A Diagonalization Approach
• Macroscopic quantum effects generated by the acoustic wave in a molecular magnet
• On Ground State Tunneling in Mn${}_{12}$-Acetate
• Collective electromagnetic relaxation in crystals of molecular magnets
• The effect of uniaxial pressure on the magnetic anisotropy of the Mn_{12}-Ac single-molecule magnet
• More Evidence for a Distribution of Tunnel Splittings in Mn${}_{12}$-acetate