We report an observation of room-temperature magneto-dielectric (RTMD) effect in LaGa0.7Fe0.3O3+γ 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 × 106 Hz for present sample), the observed MD phenomenon is MR-free/intrinsic, whereas at lower probing frequencies (<1 × 106 Hz), the observed MD coupling appears to be MR-dominated possibly due to oxygen excess, that is, due to coexistence of Fe3+ and Fe4+. 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 LaGa0.7Fe0.3O3+γ was validated through iodometric titration and Fe K-edge X-ray absorption near-edge structure measurements. The excess of oxygen, that is, coexistence of Fe3+ and Fe4+, was understood in terms of stability of Fe4+ 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 LaGaO3 can be a candidate for RTMD applications.
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Authors sincerely thank Prof. P. Mathur, Director of IIT Indore, for his encouragement. Dr. A. Shahee is acknowledged for extending help in determining oxygen stoichiometry through the titration method. The authors thank Prof. Sujeet Chaudhary (IIT Delhi, India) for providing experimental facility. CSIR, New Delhi, is acknowledged for funding high-temperature furnace under the Project 03(1274)/13/EMR-II used for the sample preparations. DAEBRNS is acknowledged for funding Impedance Analyzer used for the present measurements under the Grant No. 2013/37P/31/BRNS. One of the authors (H.M.R.) acknowledges the Ministry of Human Resource Development, government of India, for providing financial support as Teaching Assistantship.
© 2017 American Chemical Society.