Electric, Dielectric, and Phonon Properties of Cu2OCl2.

Investigating the multiferroic properties of Cu2OCl2$\left(\text{Cu}\right)_{2} \left(\text{OCl}\right)_{2}$, their temperature and magnetic‐field dependencies around the magnetic and ferroelectric phase transition temperatures TN$T_{N}$ and TE$T_{E}$ are analyzed using a microscopic model and Green's function technique. Near the Neel temperature TN$T_{N}$, a kink in the specific heat Cp(T)$C_{p} \left(\right. T \left.\right)$ and also in the phonon energy ω(T)$\omega \left(\right. T \left.\right)$ and damping γ(T)$\gamma \left(\right. T \left.\right)$ due to strong anharmonic spin–phonon interaction is observed. The kink in Cp(T)$C_{p} \left(\right. T \left.\right)$ disappears with increasing magnetic field h. The polarization P(T)$P \left(\right. T \left.\right)$ shows also a small anomaly at TN$T_{N}$ and decreases with increasing magnetic field h. This behavior strongly suggests that Cu2OCl2$\left(\text{Cu}\right)_{2} \left(\text{OCl}\right)_{2}$ exhibits multiferroic characteristics. A kink at TN$T_{N}$ can be seen in the real part of the dielectric constant ε′(T)$\left(\epsilon\right)^{&aposx;} \left(\right. T \left.\right)$, too. It should be noted that ε′$\left(\epsilon\right)^{&aposx;}$ demonstrates a significant increase with increasing field strength h below TN$T_{N}$, which is a pronounced magneto‐dielectric effect. These findings qualitatively agree with the experimental data. [ABSTRACT FROM AUTHOR]