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Séminaire Magnétisme Frustré

Jeudi 8 Octobre à 14h00,
Salle Remy Lemaire, K223

Orateur : Emilie Lefrançois (ILL-Institut Néel)
"Anisotropy tuned magnetic order in pyrochlore iridates"

Attention of the condensed matter community was recently attracted by the pyrochlore iridates R2Ir2O7 (R = rare-earth ion) where magnetic frustration, strong spin-orbit coupling associated to the Ir4+ ions, and magnetocrystalline anisotropy associated to the rare earth ions coexist and may lead to exotic magnetic phases and unprecedented electronic transport properties. These compounds exhibit a spin-orbit driven metal-insulator transition at the temperature corresponding to the onset of the Ir4+ magnetic ordering, which is very difficult to determine due to the small magnetic moment of the Ir [1]. An alternative way to access the Ir magnetism is through the magnetic configuration of the rare-earth sub-lattice.
We have chosen to study Er2Ir2O7 and Tb2Ir2O7 by means of magnetization measurement and neutron diffraction on polycrystalline samples. Both compounds undergo a magnetic transition around 130 K, associated with an ordering of the Ir sublattice. In Tb2Ir2O7, we show that the Ir molecular field leads the Tb magnetic moments to order below 40 K in the allin/ all-out magnetic arrangement. No sign of magnetic long-range order on the Er sublattice is evidenced in Er2Ir2O7 down to 0.6 K where a spin freezing is detected. These contrasting behaviors result from the competition between the Ir molecular field and the different singleion anisotropy of the rare-earth elements on which it is acting. Additionally, this strongly supports the all-in/all-out iridium magnetic order [2].

[1] Matsuhira et al., JPSJ 80 (2011) 094701
[2] Lefrançois et al, PRL 144 (2015) 247202

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