Forum DQMP

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Date(s) - 26/01/2016
13 h 00 min - 14 h 00 min

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Tuesday, January 26th 2016 – 13h00

Grand Auditoire – Ecole de physique

Coffee and tea will be available from
12h50 at the entrance of the Auditoire

 

Exchange bias and interlayer coupling in
LaNiO3/LaMnO3 superlattices
Marta Gibert (group of Prof. Triscone)
In recent years, complex-oxide heterostructures have garnered much attention due to the many routes
they offer for the engineering of novel functionalities and the discovery of fascinating and often
unexpected phenomena. The emergence of new phases due to reduced dimensionality or at interfaces
between chemically distinct compounds have led to some of the most interesting findings.
In this presentation, we show how interface engineering can be used not only to induce a new
magnetic phase in an otherwise non-magnetic material but also to generate rich and complex magnetic
behaviour in (111)-oriented LaNiO3/LaMnO3 heterostructures. For 7-monolayer-thick LaNiO3/LaMnO3
superlattices, the emergence of negative and positive exchange bias is observed at low temperature
before the stabilization of an antiferromagnetically coupled state between the LaMnO3 layers above the
blocking temperature. This behaviour is explained by the onset of an antiferromagnetic spiral of
(1/4,1/4,1/4) wave vector in the ultrathin LaNiO3 layer.

 

Soft X-ray ARPES investigation of the nickelate Fermi surface in
LaNiO3-LaMnO3 superlattices
Flavio Y. Bruno (group of Prof. Baumberger)

Recent advances in the growth of oxide heterostructures have produced a surge in the efforts to
manipulate phenomena such as magnetism, superconductivity and metal-insulator transitions at oxide
interfaces. Many transition metal oxides possess a (distorted) perovskite crystallographic structure,
which facilitates their combination in epitaxial heterostructures. However, the vast majority of
experiments have been performed by stacking different oxides along the (001)-direction [1]. In this talk
I will discuss our efforts to characterize the electronic structure of oxide heterostructures grown along
the (111)-direction by means of angle resolved photoemission spectroscopy (ARPES). While ARPES is
an ideal tool for characterizing the electronic structure of materials, its application to interfaces is much
more difficult due to the intrinsic surface sensitivity of the technique. We investigate (111)-oriented
superlattices consisting of paramagnetic metallic LaNiO3 (LNO) and ferromagnetic insulating LaMnO3
(LMO). These superlattices display various unexpected properties as the relative thickness of LNO and
LMO is varied. I will discuss the implications of two of them, namely exchange bias and a metalinsulator
transition, on the electronic structure [2]. I will first describe our measurements of the Fermi
surface of a thin film of LNO and show that even when that layer is buried below LMO we are able to
resolve the Fermi surface. I will then proceed to show that as the thickness of the LNO layer is
reduced, the spectral weight at the Fermi level is lost and a small gap is opened explaining the
insulating behavior observed in transport measurements. Finally, I will discuss our measurements in
the context of the magnetic signatures observed in SQUID and X-ray magnetic reflectivity
measurements.
[1] Nature Mat. 11, 103 (2012)
[2] Nature Mat. 11, 195 (2012)

Forum Committee : L. Foini, C. Lichtensteiger, N. Ubrig (19.01.2016)

Réalisation : Sur Mesure concept