# Synopsis: How to make CuO sit up straight

$\text{CuO}$ 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 ($\sim 100\phantom{\rule{0.333em}{0ex}}\text{meV}$ or $>1000\phantom{\rule{0.333em}{0ex}}\text{K}$). 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, $\text{CuO}$ is the last member of the transition metal rock-salt series that includes $\text{MnO}$, $\text{FeO}$, $\text{CoO}$, and $\text{NiO}$. Except for $\text{CuO}$, each of these oxides has a cubic structure, like salt, where the transition metal ion is surrounded by six oxygen ions. From $\text{MnO}$ to $\text{NiO}$, the antiferromagnetic (Néel) transition temperature, which scales with the magnetic interaction between the spins on the transition metal sites, increases from $100$ to $500\phantom{\rule{0.333em}{0ex}}\text{K}$. Following this trend, $\text{CuO}$ should have a Néel temperature as high as $900\phantom{\rule{0.333em}{0ex}}\text{K}$, but in bulk form, $\text{CuO}$ has a low-symmetry, distorted rock-salt structure and a transition temperature of only $200\phantom{\rule{0.333em}{0ex}}\text{K}$.

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 $\text{CuO}$ 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 $\text{CuO}$ compare with those of the high-temperature superconducting oxides. – Jessica Thomas

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## Subject Areas

Materials Science

## Previous Synopsis

Superconductivity

Optics

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