Magnetodielectric coupling and multi-blocking effect in the Ising-chain magnet Sr2Ca2CoMn2O9

TL;DR

This study demonstrates magnetodielectric coupling in Sr2Ca2CoMn2O9, revealing how magnetic order influences dielectric properties and uncovering a multi-blocking effect related to spin-dipole interactions in an Ising-chain magnet.

Contribution

It provides the first detailed investigation of magnetodielectric coupling and multi-blocking effects in Sr2Ca2CoMn2O9, linking spin-chain structure to dielectric behavior.

Findings

Magnetodielectric coupling observed at TN ~ 28 K under magnetic field.

Dielectric constant peaks at TN only with external magnetic field.

Identification of a multi-blocking effect related to spin-dipole dynamics.

Abstract

We have demonstrated magnetodielectric (MD) coupling in an Ising-chain magnet Sr2Ca2CoMn2O9, via detailed investigation of ac susceptibility and dielectric constant as a function of temperature, magnetic field and frequency. Sr2Ca2CoMn2O9 consists of spin-chains, made of the regular stacking of one CoO6 trigonal prism with two MnO6 octahedra. The (Co2+ Mn4+ Mn4+) unit stabilizes a (up-down-up) spin-state along the chains which are distributed on a triangular lattice. This compound undergoes a partially disordered antiferromagnetic transition at TN ~ 28 K. The dielectric constant exhibits a clear peak at TN only in presence of an external magnetic field (above 5 kOe), evidencing the presence of MD coupling, which is further confirmed by field-dependent dielectric measurements. We argue that spatial inversion symmetry can be broken as a result of exchange-striction along each spin chain, inducing uncompensated local dipoles. At low temperatures, a dipolar relaxation phenomenon is observed, bearing strong similarities with the blocking effect typical of the spin dynamics in this compound. Such a spin-dipole relationship is referred to as a multi-blocking effect, in relation with the concept of magnetodielectric multiglass previously introduced for related materials.