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Séminaire Magnétisme non conventionnel

Jeudi 17 octobre à 14h00,
Salle Remy Lemaire, K223

Orateur : Edward RIORDAN (University of Cardiff, UK)
"Coexisting Relaxation Mechanisms in Spinel Spin Ice Measured Using New MHz Range AC-Susceptibility Capability"

Abstract

Spin ice materials exhibit novel magnetic behaviour because of their atomic interactions and geometric constraints of the crystal lattice. Dominant dipole-dipole interactions and crystal field induced ising-like behaviour lead to emergent quasi-particles that behave as magnetic monopoles [1] as well as a finite residual ground state entropy [2]. The pyrochlore spin ice materials are well studied, but spin ices with a spinel structure are a more recent discovery [3,4]. We have studied the spin ice materials CdEr2Se4 and CdEr2S4 with ac susceptibilty up to MHz frequencies using a bespoke ac-susceptometer developed in Cardiff [5]. These ac susceptibility measurements have uncovered novel behaviour when in the presence of applied DC fields, in the form of two coexisting relaxation channels with differing time scales and temperature dependence.
[1] Castelnovo, Claudio, Roderich Moessner, and Shivaji L. Sondhi. "Magnetic monopoles in spin ice." Nature 451.7174 (2008) : 42.
[2] Ramirez, Arthur P., et al. "Zero-point entropy in ‘spin ice’." Nature 399.6734 (1999) : 333.
[3] Lago, Jorge, et al. "CdEr 2 Se 4 : A New Erbium Spin Ice System in a Spinel Structure." Physical review letters 104.24 (2010) : 247203.
[4] Gao, Shang, et al. "Dipolar Spin Ice States with a Fast Monopole Hopping Rate in CdEr 2 X 4 (X= Se, S)." Physical review letters 120.13 (2018) : 137201.
[5] Riordan, E., et al. "Design and implementation of a low temperature, inductance based high frequency alternating current susceptometer." Review of Scientific Instruments 90.7 (2019) : 073908.

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