Diagonal magnetoelectric susceptibility and effect of Fe-doping in a polar ferrimagnet Mn2Mo3O8

TL;DR

This study explores how Fe-doping in Mn2Mo3O8 significantly alters its magnetoelectric susceptibility, revealing a large, tunable effect driven by changes in magnetic ion composition and site preference.

Contribution

It demonstrates the large, composition-dependent tunability of the magnetoelectric effect in Mn2Mo3O8 through Fe substitution, highlighting the interplay of exchange striction and relativistic mechanisms.

Findings

ME susceptibility increases fourfold with 50% Fe doping

Negative shift of ME coefficient with increased Fe content

ME coefficient becomes negative across all temperatures at high Fe doping

Abstract

We investigate a large variation in a diagonal component of the linear magnetoelectric (ME) susceptibility in a polar ferrimagnet Mn2Mo3O8 while changing the magnetic-ion site from orbital-quenched Mn2+ to Fe2+ with strong uniaxial anisotropy. In Mn2Mo3O8, the linear ME susceptibility is dominated by the non-relativistic exchange striction mechanism, showing a positive value at low temperature and a critical behavior toward negative divergence around the transition temperature. This negative peak value becomes four times larger when 50% of Mn2+ ions are replaced with Fe2+ ion, highlighting the beneficial perspective of the compositionally-tunable ME effect. As the doped Fe increases in fraction, gradual negative shift of the ME coefficient is observed around the lowest temperature, which manifests relativistic single-site origin of the ME susceptibility. Further doping with x >= 75% in (Mn1-xFex)2Mo3O8, the ME coefficient becomes negative in the entire temperature region. Such a composition dependence can be explained in terms of the chemical preference for the two types of magnetic sites of Mn/Fe ions. The present study demonstrates the large tunability of ME effect by substituting the magnetic ion with the primary structural/magnetic characters kept intact.