1 research outputs found
Room-Temperature Magneto-dielectric Effect in LaGa<sub>0.7</sub>Fe<sub>0.3</sub>O<sub>3+Îł</sub>; Origin and Impact of Excess Oxygen
We report an observation of room-temperature
magneto-dielectric (RTMD) effect in LaGa<sub>0.7</sub>Fe<sub>0.3</sub>O<sub>3+Îł</sub> compound. The contribution of intrinsic/resistive
sources in the presently observed RTMD effect was analyzed by measuring
direct-current (dc) magnetoresistance (MR) in four-probe geometry
and frequency-dependent MR via impedance spectroscopy (MRIS). Present
MRIS analysis reveals that at frequencies corresponding to grain contribution
(≥1 × 10<sup>6</sup> Hz for present sample), the observed
MD phenomenon is MR-free/intrinsic, whereas at lower probing frequencies
(<1 Ă— 10<sup>6</sup> Hz), the observed MD coupling appears
to be MR-dominated possibly due to oxygen excess, that is, due to
coexistence of Fe<sup>3+</sup> and Fe<sup>4+</sup>. The magnetostriction
is anticipated as a mechanism responsible for MR-free/intrinsic MD
coupling, whereas the MR-dominated part is attributed to hopping charge
transport along with Maxwell–Wagner and space charge polarization.
The multivalence of Fe ions in LaGa<sub>0.7</sub>Fe<sub>0.3</sub>O<sub>3+Îł</sub> was validated through iodometric titration and Fe
K-edge X-ray absorption near-edge structure measurements. The excess
of oxygen, that is, coexistence of Fe<sup>3+</sup> and Fe<sup>4+</sup>, was understood in terms of stability of Fe<sup>4+</sup> by means
of “bond-valence-sum” analysis and density functional
theory-based first-principles calculations. The cation vacancies at
La/Ga site (or at La and Ga both) were proposed as the possible origin
of excess oxygen in presently studied compound. Present investigation
suggests that, to justify the intrinsic/resistive origin of MD phenomenon,
frequency-dependent MR measurements are more useful than measuring
only dc MR or comparing the trends of magnetic-field-dependent change
in dielectric constant and tan δ. Presently studied Fe-doped
LaGaO<sub>3</sub> can be a candidate for RTMD applications