The spin glass delafossite CuFe0.5V0.5O2: a dipolar glass?

The ferroelectric and spin glass properties of CuFe(0.5)V(0.5)O(2) have been studied. Magnetization, ac magnetic susceptibility and specific heat measurements reveal a spin glass behavior (T(f) = 20.5 K) for this delafossite. In CuFeO(2), substitution of trivalent diamagnetic cations for Fe(3 + ) is known to change the antiferromagnetic state and induce ferroelectricity. But partial occupation of the Fe(3 + ) site by V(3 + ) is responsible for disordered magnetism in CuFe(0.5)V(0.5)O(2). The dielectric permittivity shows a frequency dependence reminiscent of relaxor ferroelectrics in which different cations occupy the same crystallographic site. Polarization measurements show the existence of a ferroelectric state below T(f) with P(5 K)≈1.3 µC m( - 2). These results point towards a relaxor-type ferroelectricity originating from a disordered array of magnetic cations. A clear coupling between electronic charges and spins is evidenced by the magnetodielectric effect.