Elastic coupling and anelastic relaxation associated with multiple phase transitions in para-chloroanilinium tetrachlorocuprate, [p-ClC6H4NH3]2CuCl4

Thomson, Richard I. and Rawson, Jeremy M. and Goeta, Andrés and Probert, Michael R. and Coome, Jonathan A. and Tuan, Hoang K.A. and Carpenter, Michael A. (2013) Elastic coupling and anelastic relaxation associated with multiple phase transitions in para-chloroanilinium tetrachlorocuprate, [p-ClC6H4NH3]2CuCl4. Materials Chemistry and Physics, 139 (1). pp. 34-46. ISSN 0254-0584 DOI 10.1016/j.matchemphys.2012.11.031

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Abstract

The perovskite-like salt [p-ClC6H4NH3]2CuCl4 1 exhibits a wealth of magnetic and structural phase transitions which have been probed by variable temperature single crystal X-ray diffraction, SQUID magnetometry, resonant ultrasound spectroscopy (RUS), EPR spectroscopy, DSC measurements and DFT calculations. Single crystal X-ray diffraction studies between room temperature and 3 K reveal a rich tapestry of structural changes; at 298 K the structure conforms to a monoclinic setting but undergoes a first order phase transition upon cooling below ∼275 K to a higher symmetry orthorhombic cell. This is facilitated by a transition to an intermediate phase at ∼277 K. Whilst the intermediate phase has a limited stability window (∼2 K) and has not been structurally determined, the two discrete phase transitions at 275.5 K and 277 K have been clearly detected by differential scanning calorimetry, EPR spectroscopy and RUS studies. On further cooling a dynamic relaxation process is observed in RUS measurements, evidenced by a Debye-like peak in the dissipation at ∼140 K. Residual electron density maps from single crystal X-ray diffraction studies reveal that this may be associated with a freezing out of the NH3⋯Cl hydrogen-bonding between cation and anion frameworks upon cooling. The activation barrier for this order/disorder process was estimated to be at least 27 kJ mol−1 from the RUS data. Variable temperature dc SQUID data reveal that 1 is a 2D ferromagnet with antiferromagnetic interactions between layers below 9 K. Analysis of the temperature dependence of the magnetic susceptibility for T > 40 K reveals that 1 exhibits Curie–Weiss behaviour with θ = +22.8 K indicative of dominant ferromagnetic interactions. Good agreement is observed between the strength of the ferromagnetic interaction extracted from the Weiss constant (J/k = +22.8 K) and that calculated by DFT (J/k = +25 to +28 K) and from EPR studies (J/k = +17 K). The presence of short range ferromagnetic interactions is reflected in a marked temperature dependence of the g-factors determined from EPR spectroscopy below 20 K and possibly a small elastic anomaly in the RUS data. RUS studies indicate a very small elastic anomaly associated with the transition to long range order, implying weak or no magnetoelastic effect. At fields above ∼15 G a spin flip transition is induced and 1 displays metamagnetic behaviour, with a saturation magnetization of 0.96 μB.

Item Type: Article
Uncontrolled Keywords: 2012AREP; IA65;
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: Materials Chemistry and Physics
Volume: 139
Page Range: pp. 34-46
Identification Number: 10.1016/j.matchemphys.2012.11.031
Depositing User: Sarah Humbert
Date Deposited: 26 Jan 2013 10:34
Last Modified: 23 Jul 2013 10:05
URI: http://eprints.esc.cam.ac.uk/id/eprint/2665

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