Room-temperature structural phase transition in the quasi-2D spin-1/2 Heisenberg antiferromagnet Cu(pz)&lt;sub&gt;2&lt;/sub&gt;(ClO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;

Barbero, N.; Medarde, M.; Shang, T.; Sheptyakov, D.; Landee, C.P.; Mesot, J.; Ott, H.-R.; Shiroka, T.

doi:10.1103/PhysRevMaterials.3.053602

Room-temperature structural phase transition in the quasi-2D spin-1/2 Heisenberg antiferromagnet Cu(pz)₂(ClO₄)₂

Barbero N, Medarde M, Shang T, Sheptyakov D, Landee CP, Mesot J, Ott H-R & Shiroka T

Citation

Barbero, N., Medarde, M., Shang, T., Sheptyakov, D., Landee, C. P., Mesot, J., … Shiroka, T. (2019). Room-temperature structural phase transition in the quasi-2D spin-1/2 Heisenberg antiferromagnet Cu(pz)₂(ClO₄)₂. Physical Review Materials, 3(5), 053602 (10 pp.). https://doi.org/10.1103/PhysRevMaterials.3.053602

Persistent URL https://www.dora.lib4ri.ch/psi/islandora/object/psi:22133

Cu(pz)₂(ClO₄)₂ (with pz denoting pyrazine, C⁴H⁴N²) is a two-dimensional spin-1/2 square-lattice antiferromagnet with T_N = 4.24 K. Due to a persisting focus on the low-temperature magnetic properties, its room-temperature structural and physical properties caught no attention up to now. Here we report a study of the structural features of Cu(pz)₂(ClO₄)₂ in the paramagnetic phase, up to 330 K. By employing magnetization, specific heat, ³⁵Cl nuclear magnetic resonance, and neutron diffraction measurements, we provide evidence of a second-order phase transition at T^★ = 294 K, not reported before. The absence of a magnetic ordering across T^★ in the magnetization data, yet the presence of a sizable anomaly in the specific heat, suggests a structural order-to-disorder-type transition. NMR and neutron-diffraction data corroborate our conjecture by revealing subtle angular distortions of the pyrazine rings and of ClO⁻₄ counteranion tetrahedra, shown to adopt a configuration of higher symmetry above the transition temperature.