Magnetic transitions in CaMn7O12 : a Raman observation of spin-phonon couplings

TL;DR

This study uses Raman spectroscopy to investigate spin-phonon couplings in CaMn7O12, revealing magnetic transition effects on phonon modes and low-energy excitations related to magnetoelectric properties.

Contribution

It provides the first detailed Raman analysis of spin-phonon interactions and low-energy excitations in CaMn7O12, highlighting their temperature dependence and magnetic coupling.

Findings

Phonon mode at 432 cm-1 shows spin-phonon coupling at 50 K.

Low-energy excitations at 25 and 47 cm-1 are associated with electro-magneto-active modes.

Magnetic transitions significantly influence phonon and low-energy excitation behaviors.

Abstract

The quadruple Calcium manganite (CaMn7O12) is a multiferroic material that exhibits a giant magnetically-induced ferroelectric polarization which makes it very interesting for magnetoelectric applications. Here, we report the Raman spectroscopy study on this compound of both the phonon modes and the low energy excitations from 4 K to room temperature. A detailed study of the Raman active phonon excitations shows that three phonon modes evidence a spin-phonon coupling at TN2 = 50 K. In particular, we show that the mode at 432 cm-1 associated to Mn(B)O6 (B position of the perovskite) rotations around the [111] cubic diagonal is impacted by the magnetic transition at 50 K and its coupling to the new modulation of the Mn spin in the (a,b) plane. At low energies, two large low energy excitations are observed at 25 and 47 cm-1. The first one disappears at 50 K and the second one at 90 K. We have associated these excitations to electro-magneto-active modes.