Observation of room temperature magnetodielectric effect in Mn-doped lanthanum gallate and study of its magnetic properties

Abstract

Polycrystalline samples of Mn-doped LaGa_1−xMn_xO₃ (LGMO) with 0 ≤ x ≤ 0.2 have been prepared via solid-state reaction method. The structural phase purity of all these samples was confirmed by powder X-ray diffraction experiments carried out at the BL-12 beamline of the Indus-2 synchrotron radiation source. Room-temperature (RT) dielectric measurements were performed in the absence and presence of a magnetic field. A noticeable magnetodielectric (MD) effect, i.e., a change in the value of the dielectric constant owing to the application of a low magnetic field, was observed in the LGMO sample with x = 0.2 (LG8M2O). In order to separate the intrinsic and resistive contributions present in the observed RT MD effect, magnetoresistance impedance spectroscopy (MRIS) was performed at RT. The present MRIS analysis suggests that at frequencies corresponding to the grain contribution (≥10⁵ Hz for the present samples), the observed MD phenomenon appears to be an intrinsic property of the presently studied samples, whereas at lower probing frequencies (<10⁵ Hz) the observed change appears to be dominated by MR (considering frequency-dependent resistance), which was possibly due to the coexistence of Mn³⁺ and Mn⁴⁺. The coexistence of Mn³⁺ and Mn⁴⁺ was revealed by XANES (Mn K-edge) spectroscopy. Moreover, RT and low-temperature magnetization–magnetic field (M–H) measurements, along with M–T measurements in FC and ZFC modes, were performed to investigate the state of magnetic ordering. The appearance of a narrow M–H loop indicates the presence of some magnetic ordering at RT. Furthermore, a ferromagnetic (FM) transition observed around 36 K and a normal M–H loop with saturated magnetization recorded at 5 K confirm FM ordering at low temperatures, whereas a bifurcation in FC-ZFC curves indicates competing FM and antiferromagnetic (AFM) interactions at low temperatures.