[Wien] PhD position in Rennes, France with X. Rocquefelte

[Peter Blaha]

PhD proposal in France (University of Rennes)

Modelling Magnetic and Multiferroic Properties of Copper Oxides

Keywords: DFT modelling and programming, magnetism, highly correlated materials, multiferroism

Multiferroic materials [1], in which ferroelectric and magnetic ordering coexist, are of fundamental interest for the development of multi-state memory devices that allow 
for electrical writing and non-destructive magnetic readout operation. The great challenge is to create multiferroic materials that operate at room temperature and have a 
large ferroelectric polarization P. Cupric oxide, CuO, is promising because it exhibits a significant polarization, that is, P~0.1 μC cm−2, for a spin-spiral multiferroic 
[2]. Unfortunately, CuO is only ferroelectric in a temperature range of 20 K, from 210 to 230 K. In 2013, by using a combination of density functional theory and Monte 
Carlo calculations, we have established that pressure-driven phase competition induces a giant stabilization of the multiferroic phase of CuO, which at 20–40 GPa becomes 
stable in a domain larger than 300 K, from 0 to T>300 K. Thus, under high pressure, CuO is predicted to be a room-temperature multiferroic with large polarization [3-7].

The PhD project will consist to enlarge the scope by considering a wide variety of copper oxides in order to estimate theoretically their related magnetic and multiferroic 
properties. In particular, the tetragonal form of CuO created using an epitaxial thin-film deposition approach [8] will be considered. Indeed, this nanosized material 
exhibits 180° Cu-O-Cu superexchange paths. Such an arrangement cannot be obtained at ambient pressure CuO bulk samples and would correspond to very high pressure bulk CuO 
(larger than 200 GPa). Unusual properties are thus expected in this epitaxially deposited tetragonal form of CuO. This PhD project will be then divided in two main parts: 
(1) the DFT modelling of the magnetic and multiferroic properties of tetragonal CuO and other copper oxides; (2) the participation of the development of the AIMPRO code, 
which allows to do both fast and accurate DFT calculations.



References

[1] Cheong, S. W. & Mostovoy, M. Multiferroics: a magnetic twist for ferroelectricity, Nature Mater. 6, 13-20 (2007).

[2] Kimura, T., Sekio, Y., Nakamura, H., Siegrist, T., Ramirez, A. P. Cupric oxide as an induced-multiferroic with high-TC, Nature Mater. 7, 291-294 (2008).

[3] Giovannetti, G. et al. High-TC Ferroelectricity Emerging from Magnetic Degeneracy in Cupric Oxide, Phys. Rev. Lett. 106, 026401 (2011).

[4] Rocquefelte, X., Schwarz, K. & Blaha, P. Comment on “High-TC Ferroelectricity Emerging from Magnetic Degeneracy in Cupric Oxide”, Phys. Rev. Lett. 107, 239701 (2011).

[5] Rocquefelte, X. et al. Short-range magnetic order and temperature-dependent properties of cupric oxide, J. Phys. Condens. Matter 21, 045502 (2010).

[6] Rocquefelte, X., Schwarz, K. & Blaha, P. Theoretical Investigation of the Magnetic Exchange Interactions in Copper(II) Oxides under Chemical and Physical Pressures, 
Scientific Reports 2, 759 (2012).

[7] Rocquefelte, X. et al. Room-temperature spin-spiral multiferroicity in high-pressure cupric oxide, Nature Communications 4, 2511 (2013).

[8] Samal D. et al.  Direct structural and spectroscopic investigation of ultrathin films of tetragonal CuO: Six-fold coordinated copper, Eur. Phys. Lett. 105, 17003 (2014).

Research method – This project is at the frontier between materials science and computer modelling in chemistry and physics. To fulfil this project, a background in 
physical chemistry, solid-state physics & chemistry and/or inorganic chemistry is mandatory. In this context, the main goal is to characterize the electronic structure of 
solid-state magnetic materials, copper oxide compounds by means of density functional theory (DFT). All DFT calculations will be performed with periodic DFT codes, such as 
VASP, WIEN2k and AIMPRO.

European network – The PhD student will be involved in a European network involving research groups from UK, Austria and Croatia. He will have to interact with 
experimentalists (synthesis and magnetic characterization) and theoreticians (code development).

Contact – Pr. Xavier Rocquefelte, xavier.rocquefelte at univ-rennes1.fr

Université de Rennes 1 – Bâtiment 10 – 263 avenue du Général Leclerc – 35042 RENNES Cedex - Tél.: +33 (0)2 23 23 62 69


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Peter Blaha
Inst. Materials Chemistry, TU Vienna
Getreidemarkt 9, A-1060 Vienna, Austria
Tel: +43-1-5880115671
Fax: +43-1-5880115698
email: pblaha at theochem.tuwien.ac.at
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