Volume 83, Number 3, August 2008
Article Number 37006
Number of page(s) 6
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
Published online 18 July 2008
EPL, 83 (2008) 37006
DOI: 10.1209/0295-5075/83/37006

Magnetization relaxation in the single-molecule magnet Ni4 under continuous microwave irradiation

G. de Loubens1, D. A. Garanin2, C. C. Beedle3, D. N. Hendrickson3 and A. D. Kent1

1  Department of Physics, New York University - 4 Washington Place, New York, NY 10003, USA
2  Department of Physics and Astronomy, City University of New York - 250 Bedford Park Boulevard West Bronx, NY 10468-1589, USA
3  Department of Chemistry and Biochemistry, University of California San Diego - La Jolla, CA 92093, USA

received 22 April 2008; accepted in final form 16 June 2008; published August 2008
published online 18 July 2008

Spin relaxation between the two lowest-lying spin-states has been studied in the S=4 single-molecule magnet Ni4 under steady-state conditions of low amplitude and continuous microwave irradiation. The relaxation rate was determined as a function of temperature at two frequencies, 10 and 27.8 GHz, by simultaneously measuring the magnetization and the absorbed microwave power. A strong temperature dependence is observed below 1.5 K, which is not consistent with a direct single-spin-phonon relaxation process. The data instead suggest that the spin relaxation is dominated by a phonon bottleneck at low temperatures and occurs by an Orbach mechanism involving excited spin-levels at higher temperatures. Experimental results are compared with detailed calculations of the relaxation rate using the universal density matrix equation.

75.45.+j - Macroscopic quantum phenomena in magnetic systems.
75.50.Xx - Molecular magnets.
76.30.-v - Electron paramagnetic resonance and relaxation.

© EPLA 2008