Role of trivalent bismuth ion substitution at Dy site on the physical properties of DyMnO3

Abstract

Polycrystalline compounds of Dy1−xBixMnO3 (x = 0 & 0.1) synthesized by ceramic method were characterized by X-ray diffraction technique and their vibrational, transport and magnetic properties studied. Refinement of powder X-ray diffraction data showed that both materials exhibit orthorhombic structure with Pnma space group. Although Bismuth substitution retains the crystal structure, bond angles and bond lengths within MnO6 octahedra are altered as compared to the pristine compound, DyMnO3. While bond angle between manganese ions along the b-axis reduces slightly (1°), axial bond angle increased by ∼3° in the substituted compound. Raman bands arising from the atomic vibrations of rare earth dysprosium and oxygen ions have been identified from room temperature Raman spectra. For 10 at.% substitution of Bi3+, these modes are hardened. Transport measurement studies indicated that the materials are semiconducting in nature with small polaron hopping type of conduction. Hopping energy is decreased to 98.52 meV for Bi3+ substituted DyMnO3 (Dy0.9Bi0.1MnO3) from 103.85 meV for DyMnO3. Temperature dependence of dc magnetization studies revealed anomalies around 39 K, 12 K and 3.62 K corresponding to antiferromagnetic ordering involving Mn3+ and Dy3+ ions respectively. Temperature and frequency variation of ac susceptibility data corroborated the dc magnetization results. In both compounds, magnetization versus applied magnetic field curves measured at several temperatures from room temperature down to 10 K showed linear behavior revealing paramagnetic nature. This behavior indicates the absence of magnetic correlations which is in accordance with MT data. On the other hand, hysteresis loops were observed in M-H data registered ∼2 K with coercive fields of 1520 Oe and 1365 Oe for DMO and DBMO respectively. However, magnetization does not saturate even at 7 × 104 Oe field. The origin for the ferromagnetic coupling could be ascribed to the correlations between Dy3+ and Mn3+ ions through apical oxygen ions in the unit cell favoring superexchange interactions.