Posters

III Joint European Magnetic Symposia, San
Sebastian, Spain, 26-30 June 2006.

QUANTUM MAGNETIC DEFLAGRATION USING LiNbO3/Mn12 HYBRIDS

A. Hernández-Mínguez, J. M. Hernandez, F. Macià, A. García-Santiago, J. Tejada
P. V. Santos

Recently it has been demonstrated that magnetic avalanches in Mn12-acetate, which are fast magnetization reversals produced at low temperatures (below 3 K), consist in the propagation of a narrow magnetic reversal front (the deflagration front) at constant velocity along the crystal (Y. Suzuki et. al., Phys. Rev. Lett. 95, 147201 (2005)). We demonstrate in our work that the ignition of this deflagration process can be controlled in a deterministic way using surface acoustic waves (SAWs). In the super-paramagnetic regime (above 3 K), the magnetization shows pronounced changes when the IDT is excited at its resonant frequencies. At low temperatures (below 3 K), we demonstrate that both the ignition rate and the velocity of the deflagration front present peaks for the values of the magnetic fields that bring the spin levels on both sides of the tunnelling barrier into resonance, thus demonstrating the occurrence of both quantum magnetic ignition and quantum magnetic deflagration.

International Conference on Low
Energy Electrodynamics in Solids", Kloster Banz, Germany, 18-23 July 2004

LOW TEMPERATURE MICROWAVE EMISSION FROM
MOLECULAR CLUSTERS

A. Hernández-Mínguez, M. Jordi, R. Amigó,
A. García-Santiago, J.M. Hernández and J. Tejada

The experimental detection of the electromagnetic radiation generated in the avalanches of magnetization reversal in Mn12-acetate has been investigated. Related to the magnetization inversion a short radiation burst was observed.
The rate of spontaneous decay from an energy level to a lower one due to phonons is much greater than for photons. A possible explanation for these results is that the detected electromagnetic radiation could be superradiance as suggested by P.H. Dicke.

MAGNETIZATION REVERSAL IN MOLECULAR NANO NANOMAGNETS
UNDER PULSED MAGNETIC FIELDS

M.Jordi, J.Tejada, R.Amigó
J.Vanacken, S.Stroobants, M.Malfait, V.V.Moshalkov
E.M.Chudnovsky, D.A.Garanin

We report experimental results of the magnetization measurements on Mn12 and Fe8 single crystals at T = 0.6 K, using fast magnetic field pulses up to 4 kT/s. We see that at such high sweep rates, the position of the steps in the magnetic relaxation, M(t), shifts to higher fields as the sweep rate goes up. Our explanation to this experiment is the collective magnetization reversal expected at very sweep rates, due to superradiance, at fields larger than the ressonant field. In this case, all the magnetization curves should scale on a single curve.