Room-Temperature Magneto-dielectric Effect in LaGa_0.7Fe_0.3O_3+γ; Origin and Impact of Excess Oxygen

Abstract

We report an observation of room-temperature magneto-dielectric (RTMD) effect in LaGaFeO 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 Hz for present sample), the observed MD phenomenon is MR-free/intrinsic, whereas at lower probing frequencies (<1 × 10 Hz), the observed MD coupling appears to be MR-dominated possibly due to oxygen excess, that is, due to coexistence of Fe and Fe. 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 LaGaFeO 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 and Fe, was understood in terms of stability of Fe 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 can be a candidate for RTMD applications.

Design and development of a fully automated experimental setup for in situ temperature dependent magneto-dielectric measurements

“…GaFeO 3 is a well-known multiferroic as well as MD material and these properties have been studied earlier in details by Shireen et al [24]. It is clear from the figure 5 that with the application of magnetic field dielectric constant changes significantly even at room temperature in MHz frequency range which is well consistent with the earlier report [23,24]. The MD coupling is observed in this oxide around 100 kHz and at this frequency, GaFeO 3 shows approximately 25% magnetocapacitance measured at 2 T calculated by using equation (1).…”

“…Keeping this in view, an economical and automated in situ nondestructive temperature dependent MD technique has been designed. More importantly, present results are in good conformance with results reported earlier by Ajmala Shireen et al [24] and Rai et al [23], which ensures/proves the performance of the designed set up.…”

“…At this point, it should be noted that the materials under consideration are GaFeO 3 and LaGa 0.7 Fe 0.3 O 3 are well known MD materials showing strong MD coupling even at room temperature [23,24]. The choice of GaFeO 3 sample is due to it's MD properties as well as multiferroic behaviour [24] which has been well established and can be used as a reference data for comparison with the present economical experimental setup.…”

Methodology to Probe Disorder Contribution in Raman Linewidth via Optical Absorption Spectroscopy in Orthoferrite EuFeO3

“…In this study, orthoferrite EuFeO 3 (hereafter, EFO) has been considered for investigating the disorder-coupling parameter via RS and OAS techniques. The perovskite oxides possess intriguing physical properties that make them potential candidates for various technological applications. − Especially, the rare earth orthoferrite (RFeO 3 ) family of such materials has been of much interest in spintronics, multiferroics, magneto-optics, photovoltaics and even in manipulating the electromagnetic waves due to its tunable electronic, optical, and magnetoelastic behavior. − Being correlated systems, these materials are also of interest for fundamental studies. − In addition, the band gap of this family lies in the visible region, which may also provoke the resonant scattering. Such processes could certainly affect the EPIs existing in the system .…”

Strain induced disordered phonon modes in Cr doped PrFeO3

“…The structural phase purity of the prepared samples has been investigated by SXRD technique using angle-dispersive x-ray diffraction beamline BL-12, at Indus-2, the Indian synchrotron source. All the experiments were performed in angledispersive mode using a Huber 5020 diffractometer and with beam energy of 15 keV [19,44].…”