title: Room-Temperature Magneto-dielectric Effect in LaGa0.7Fe0.3O3+γ; Origin and Impact of Excess Oxygen.
abstract: We report an observation of room-temperature magneto-dielectric (RTMD) effect in LaGa0.7Fe0.3O3+γcompound. 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 × 106Hz for present sample), the observed MD phenomenon is MR-free/intrinsic, whereas at lower probing frequencies (<1 × 106Hz), 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+γwas 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 LaGaO3can be a candidate for RTMD applications.
authors.forename: Hari Mohan
authors.initials: HM
authors.lastname: Rai
authors.forename: Preetam
authors.initials: P
authors.lastname: Singh
authors.forename: Shailendra K
authors.initials: SK
authors.lastname: Saxena
authors.forename: Vikash
authors.initials: V
authors.lastname: Mishra
authors.forename: M Kamal
authors.initials: MK
authors.lastname: Warshi
authors.forename: Rajesh
authors.identifier: http://orcid.org/0000-0001-7977-986X
authors.initials: R
authors.lastname: Kumar
authors.affiliation: Atomic & Molecular Physics Division, Bhabha Atomic research Centre , Mumbai 400085, India.
authors.forename: Parasmani
authors.initials: P
authors.lastname: Rajput
authors.affiliation: Raja Ramanna Center for Advance Technology , Indore, M.P. 452013, India.
authors.forename: Archna
authors.initials: A
authors.lastname: Sagdeo
authors.forename: Indrani
authors.initials: I
authors.lastname: Choudhuri
authors.forename: Biswarup
authors.identifier: http://orcid.org/0000-0002-9972-9947
authors.initials: B
authors.lastname: Pathak
authors.forename: Pankaj R
authors.identifier: http://orcid.org/0000-0002-2475-6676
authors.initials: PR
authors.lastname: Sagdeo