Volume 49, Number 4, February II 2000
|Page(s)||521 - 527|
|Section||Condensed matter: electronic structure, electrical, magnetic, and optical properties|
|Published online||01 September 2002|
Low-temperature magnetic hysteresis in acetate single crystals
Department of Physics, New York University 4 Washington Place,
New York, NY 10003 USA
2 Physics Department, City College of the City University of New York New York, NY 10031 USA
3 Department of Chemistry and Biochemistry, University of California at San Diego La Jolla, CA 92093 USA
Corresponding author: email@example.com
Accepted: 5 December 1999
Precise magnetic-hysteresis measurements of small single crystals of Mn12 acetate of spin 10 have been conducted down to 0.4 K using a high-sensitivity Hall magnetometer. At higher temperature (> 1.6 K) 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 higher-order uniaxial magnetic anisotropy (fourth order in Sz), 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.
PACS: 75.45.+j – Macroscopic quantum phenomena in magnetic systems / 75.60.Ej – Magnetisation curves, hysteresis, Barkhausen and related effects / 75.50.Tt – Fine-particle systems
© EDP Sciences, 2000
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