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Monday, 23. September 2013 13:41 Age: 9 yrs

Room-temperature spin-spiral multiferroicity in high-pressure cupric oxide

Category: Scientific Highlights

Published in Nature Communications

ABSTRACT:

Multiferroic materials, 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. Unfortunately, CuO is only ferroelectric in a temperature range of 20 K, from 210 to 230 K. Here, by using a combination of density functional theory and Monte Carlo calculations, we establish 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.

 

Figure: High-pressure evolution of the structural and magnetic properties of CuO. (a) Schematic view of the tetrahedral environment of oxygen atoms
in CuO and definition of the largest (Jz) and smaller magnetic superexchange couplings (Jx, Ja and Jb). The super-superexchange magnetic coupling, J2a,
corresponds to the second-neighbour interaction of the edge-sharing chains, defined by the first-neighbour interaction, Ja. Oxygen atoms are represented
by small red dots, and the Cu2þ sites are depicted as filled and open dots, representing up-spin and down-spin, respectively. (b) Pressure dependence of
the volume of CuO. The experimental values, deduced from a Birch–Murnaghan equation of state fitted to data of nanocrystalline CuO up to a pressure of
17 GPa (ref. 21), are compared with those calculated by DFT. (c) Pressure dependence of the magnetic exchange couplings of CuO. Positive and negative
values represent antiferromagnetic and ferromagnetic interactions, respectively. The J’s in the grey area are ferromagnetic. The uncertainty in the DFT Jij
values is between 1.2 and 2.5meV (that is, smaller than the symbols).

Rocquefelte X., Schwarz K., Blaha P., Kumar S., van den Brink J. (2013), Room-temperature spin-spiral multiferroicity in high-pressure cupric oxide, Nat. Commun. 4DOI:10.1038/ncomms3511

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