Relaxor ferroelectricity and colossal magnetocapacitive coupling in ferromagnetic CdCr2S4

TL;DR

This study reports on a cubic spinel material, CdCr2S4, exhibiting both ferromagnetism and relaxor ferroelectricity, with a colossal magneto-capacitive effect near the magnetic transition, driven by geometric frustration.

Contribution

It demonstrates the coexistence of ferromagnetism and relaxor ferroelectricity with strong magneto-capacitive coupling in CdCr2S4, a simple cubic spinel, revealing new multiferroic properties.

Findings

Colossal magneto-capacitive effect of nearly 500% near the ferromagnetic transition.

Coexistence of ferromagnetic order and relaxor ferroelectricity in CdCr2S4.

Relaxor properties attributed to geometric frustration impeding long-range structural order.

Abstract

Multiferroic materials, which reveal magnetic and electric order, are in the focus of recent solid state research. Especially the simultaneous occurrence of ferroelectricity and ferromagnetism, combined with an intimate coupling of magnetization and polarization via magneto-capacitive effects, could pave the way for a new generation of electronic devices. Here we present measurements on a simple cubic spinel with unusual properties: It shows ferromagnetic order and simultaneously relaxor ferroelectricity, i.e. a ferroelectric cluster state, reached by a smeared-out phase transition, both with sizable ordering temperatures and moments. Close to the ferromagnetic ordering temperature the magneto-capacitive coupling, characterized by a variation of the dielectric constant in an external magnetic field, reaches colossal values of nearly 500%. We attribute the relaxor properties to geometric frustration, which is well known for magnetic moments, but here is found to impede long-range order of the structural degrees of freedom.