Magnetic and ferroelectric properties of exchange-frustrated multiferroics (Ni1-x T x )3V2O8 (T = Co, Mn, Zn)

The effect of the substitution of Co2+, Mn2+, and Zn2+ ions for Ni2+ ions on the magnetic, dielectric, and ferroelectric properties of vanadate single crystals (Ni1 - x T (x) )(3)V2O8 has been analyzed. It has been found that the low-level (x a parts per thousand currency sign 0.1) substitution of both magnetic and nonmagnetic ions stabilizes the ferroelectric state with a cycloidal magnetic structure. The existence region of this state is expanded to low temperatures down to 3 K for Zn2+ and below 1.8 K for Co2+ and Mn2+ owing to the suppression of a low-temperature weak ferromagnetic phase. At the same time, the ferroelectric phase disappears completely at large concentrations of Co and Mn. The effect of magnetic fields on the magnetic and ferroelectric states has been analyzed. It has been shown that the magnetic field along the c axis suppresses the ferroelectric state, whereas the magnetization along the antiferromagnetism axis (a axis) induces the reentrant phase transition from a paraelectric weak ferromagnetic structure to a ferroelectric structure. The corresponding H-T phase diagrams have been drawn.