The spin glass delafossite CuFe 0.5 V 0.5 O 2 : a dipolar glass?
Résumé
The ferroelectric and spin glass properties of CuFe0.5V0.5O2 have been studied. Magnetization, ac magnetic susceptibility and specific heat measurements reveal a spin glass behavior (Tf = 20.5 K) for this delafossite. In CuFeO2, substitution of trivalent diamagnetic cations for Fe3 + is known to change the antiferromagnetic state and induce ferroelectricity. But partial occupation of the Fe3 + site by V3 + is responsible for disordered magnetism in CuFe0.5V0.5O2. 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 Tf with P5 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.