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Séminaire MCBT : mardi 14 juin 2022 à 11h00 [Annulé]

Sergio Garcia Magalhaes (Federal University of Rio Grande do Sul, Brazil)

Titre : Spin liquid and infinitesimal-disorder-driven cluster spin glass in geometric frustrated lattices: a possible route to increase the magnetocaloric effect


Institut Néel, Salle D420
Résumé : The interplay between geometric frustration (GF) and bond disorder is studied in the Ising kagome lattice within a cluster approach. The model considers antiferromagnetic (AF) short-range couplings and long-range intercluster disordered interactions. The replica formalism is used to obtain an effective single cluster model from where the thermodynamics is analyzed by exact diagonalization.
We found that the presence of GF can introduce cluster freezing at very low levels of disorder. The system exhibits an entropy plateau followed by a large entropy drop close to the freezing temperature. In this scenario, a classical spin-liquid  (SL) behavior prevents conventional long-range order, but an infinitesimal disorder picks out uncompensated cluster states from the multi degenerate SL regime, potentializing the intercluster disordered coupling and bringing the cluster spin-glass state.  We propose that this physical mechanism could be present in several geometrically frustrated materials. In particular, we discuss our results in connection to to experimental investigations of the Ising kagome compound Co3Mg(OH)6Cl2.  We also show that a strong increase in the Magnetocaloric Effect (MCE)  can be achieved just above the freezing temperature Tf for low levels of disorder.  Moreover, this increase depends only on the proper interplay between geometric frustration and disorder.