The effect of rare-earth Gd-substitution on the structural, magnetic and specific heat properties in orthorhombic DyMnO3 ceramics

Abstract

The acrylamide polymer gel template method has been adopted to synthesize single phase Dy1–xGdxMnO3 (DGMO, x= 0, 0.05, 0.1, 0.15, 0.2) ceramics. The Rietveld refinement of x-ray diffraction patterns recorded at room temperature suggests that DGMO ceramics are stabilized in an orthorhombic crystal structure with a Pnma space group. Gd3+ cations play an important role in stabilizing the orthorhombic phase and the unit cell volume increases with x. We report the phonon spectra of pure and Gd-substituted DyMnO3 (DMO) and their mode assignments. Raman modes are softened with x due to the relaxation in the stiffness constants upon the increase in the volume of the unit cell. The magnetic transition temperatures corresponding to TN(Dy) and Tlock decrease with the increase in Gd concentration as inferred from the temperature dependent magnetization data (M–T curve). The magnetization value increases below TN(Dy) with the increase in the Gd concentration as observed from the M–T plot. The magnetic hysteresis loop is fitted to extract ferromagnetic and antiferromagnetic/paramagnetic contributions for each composition x. Fittings of M–H loops indicate the increase in the magnetic contribution below TN(Dy) upon increasing the Gd dopant concentrations, while that decreases above TN(Dy). The temperature dependent specific heat data identifies these magnetic transition temperatures TN(Dy), Tlock and TN(Mn). Furthermore, magnetic field dependencies on TN(Dy), Tlock and TN(Mn) are studied in an elaborate manner. Both DMO and DGMO samples are found to be viable candidates for magnetic refrigeration applications in cryogenic temperature region.