Exposé de Benjamin Verlhac postdoctorant à l’Université Radboud à Nijmegen (Pays-Bas)

Benjamin fera un exposé sur ses travaux en cours (microscopie champ proche sous champ magnétique) :

“Thermally-induced magnetic order from glassiness in elemental neodymium”

Le vendredi 26/11 à 11h
IEMN – Laboratoire central LCI – Villeneuve d’Ascq – Salle du Conseil


Thermally-induced magnetic order from glassiness in elemental neodymium
In common thermodynamic systems, disorder can be induced by temperature which leads to phase transitions from order to disorder, exemplified by the well-known ferromagnetic-paramagnetic phase transition. However, disorder can also be induced by the existence of numerous metastable states due to frustration. This was recently exemplified by elemental neodymium for which a self-induced spin glass phase was reported between 30 mK and 4 K[1]. It was shown that this phase is solely caused by magnetic frustration within the dhcp lattice of neodymium and possesses the aging dynamics of a spin glass.
In this talk, I will show that neodymium undergoes an unusual magnetic transition, where long range multi-Q order emerges from this spin-Q glass phase as temperature is increased from 5 K to 15 K[2]. By means of a temperature study using spin-polarized scanning tunneling microscopy, we characterize the very local order of the spin-Q glass phase and the long-range nature of the multi-Q order phase present at higher temperatures. From the measured magnetization maps, we quantify the phase transition and determine its critical temperature using two distinct analyses. These findings are supported by atomistic spin dynamics simulations, in which the phase transition is qualitatively reproduced and explained by a weakened frustration in the multi-Q order phase compared to the spin-Q glass phase.

[1] Kamber, U. et al. Self-induced spin glass state in elemental and crystalline neodymium. Science 368, eaay6757, (2020).
[2] Verlhac, B. et al. Thermally-induced magnetic order from glassiness in elemental neodymium. arXiv:2109.04815 [cond-mat], (2021).

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