Synopsis

# How to make CuO sit up straight

Physics 2, s56
$\text{CuO}$ in thin-film form could be a prototype material for exploring magnetism that is similar to what is found in high-temperature superconductors.

The parent compounds of cuprate high-temperature superconductors are typically antiferromagnets where the magnetic interaction between the spins on the copper sites is unusually large ( $∼100meV$ or $>1000K$). Since they may play a role in the superconducting mechanism, researchers have explored similarly large magnetic interactions in other copper-oxide compounds.

Moving from left to right on the periodic table, $CuO$ is the last member of the transition metal rock-salt series that includes $MnO$, $FeO$, $CoO$, and $NiO$. Except for $CuO$, each of these oxides has a cubic structure, like salt, where the transition metal ion is surrounded by six oxygen ions. From $MnO$ to $NiO$, the antiferromagnetic (Néel) transition temperature, which scales with the magnetic interaction between the spins on the transition metal sites, increases from $100$ to $500K$. Following this trend, $CuO$ should have a Néel temperature as high as $900K$, but in bulk form, $CuO$ has a low-symmetry, distorted rock-salt structure and a transition temperature of only $200K$.

Wolter Siemons and colleagues at the University of Twente in The Netherlands and collaborators at Stanford University in the US report in Physical Review B that they have succeeded in using pulsed laser deposition to grow thin films of $CuO$ with a structure that is an elongated (tetragonal) version of its rock-salt cousins.

While Siemons et al. have determined the structure with extensive crystallography, magnetic measurements will be necessary to determine if the magnetic interactions in this tetragonal form of $CuO$ compare with those of the high-temperature superconducting oxides. – Jessica Thomas

## Subject Areas

Materials Science

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