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Séminaire Magnétisme frustré

Jeudi 19 Décembre, 14h00,
Salle Nevill Mott, D420

Orateur : Carley Paulsen (Institut Néel, équipe SFCE)
"Far From Equilibrium Monopole Dynamics in Spin ice"


Avalanches of the magnetization, that is to say abrupt reversal of the magnetization at a given -eld, have been reported in the spin-ice compound Dy2Ti2O7 at very low temperature (below 500 mK) [1]. This out-of-equilibrium process results in a heating of the whole sample up to a temperature of about 900 mK. Based on this mechanism of avalanches which induces a fast internal heating and cooling of the sample, we have developed a simple and robust technique, the `magnetothermal avalanche quench’, which results in the creation of nonequilibrium populations of magnetic monopoles in spin ice at millikelvin temperatures. Indeed, this technique forces thermal excitations out of equilibrium by a rapid temperature quench, and thus allows to prepare the spin-ice sample with a high density of monopoles.

We have performed measurements of the relaxation of the magnetization in Dy2Ti2O7 at very low temperature as a function of the applied -eld in various cooling conditions, including the `avalanche quench’ condition. We show that the dynamics strongly depend on the cooling rate, and thus on the density of magnetic monopoles. In particular, in the case of the `avalanche quench’ protocol, which corresponds to the fastest cooling rate and to the highest density of monopoles, the relaxation is found to exhibit spontaneous dynamical e-ects that typify far-from-equilibrium systems, yet are captured by simple models.

[1] D. Slobinsky et al., Phys. Rev. Lett. 105, 267205 (2010).

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