Ga-substitution-induced single ferroelectric phase in multiferroicCuFeO2

Abstract

We have succeeded in realizing a single ferroelectric phase in ${\text{CuFe}}_{0.963}{\text{Ga}}_{0.037}{\text{O}}_{2}$ by substituting nonmagnetic ${\text{Ga}}^{3+}$ for ${\text{Fe}}^{3+}$ sites in ${\text{CuFeO}}_{2}$. Ferroelectric polarization $P$ in ${\text{CuFe}}_{0.963}{\text{Ga}}_{0.037}{\text{O}}_{2}$ is observed below 7.5 K, and has the relatively large value of $\ensuremath{\sim}250\text{ }\ensuremath{\mu}\text{C}/{\text{m}}^{2}$, which is comparable to $P=300\ensuremath{\sim}400\text{ }\ensuremath{\mu}\text{C}/{\text{m}}^{2}$ in the magnetic-field-induced ferroelectric phase of ${\text{CuFeO}}_{2}$. In neutron-diffraction measurements, a single magnetic diffraction peak with an incommensurate wave number was observed below 7.5 K in ${\text{CuFe}}_{0.963}{\text{Ga}}_{0.037}{\text{O}}_{2}$, indicating that the ferroelectric-incommensurate (FEIC) phase is realized as a single phase. Therefore, ${\text{CuFe}}_{0.963}{\text{Ga}}_{0.037}{\text{O}}_{2}$ with a single FEIC phase is strongly expected to provide the best opportunity to investigate unresolved problems regarding the ferroelectric mechanism in ${\text{CuFeO}}_{2}$. In this paper, we report measurements of magnetic susceptibility, specific heat, pyroelectric, dielectric constant, and neutron diffraction of a single crystal of ${\text{CuFe}}_{0.963}{\text{Ga}}_{0.037}{\text{O}}_{2}$.