Temperature dependencies of dielectric permittivity and loss tangent (at frequencies 0.1–200 kHz) together with thermally stimulated depolarization currents, magnetization, and Mössbauer spectra of ceramic solid solutions Co${}_{1-x}$Ni${}_x$Cr${}_2$O${}_4$ ($x$ $=$ 0, 0.2, 0.4, 0.6, 1.0) are studied at temperatures from 80 to 350 K. We find evidence of two reversible phase transitions located at $T_1$ and $T_2$ (220 and 245 K, respectively, for $x$ $=$ 0.2), of occurrence of pyroelectric properties below $T_2$, as well as of a phase transition to magnetically ordered state of ferrimagnetic type (below 86 K for $x$ $=$ 0.2). The obtained results evidence that the compounds possess, additionally to magnetic, ferroelectric properties and are thus new members in the family of multiferroics.

• Received 13 February 2012

DOI:https://doi.org/10.1103/PhysRevB.85.214112