Structural and magnetic phase transitions in Ti-doped Nd0.7Ba0.3MnO3 perovskite manganites

Effect of Ti-doping on structural and magnetic phase transitions in Nd_0.7Ba_0.3Mn_1-xTi_xO₃ (NBMTO) manganites at Mn-site has been studied for the first time. The NBMTO perovskites with 0 ≤ x ≤ 0.3 have been synthesized by using auto-combustion method, which is a most facile and commercial synthesis method. The Rietveld structure refinement using X-ray diffraction data reveals a structural phase transition from orthorhombic to tetragonal structure at the composition x = 0.3. The NBMTO manganites with x < 0.3 exhibit the orthorhombic crystal structure with Imma space group and the sample with x = 0.3, crystallizes into two coexisting tetragonal structures having I4/mcm and P4mm space groups. Lattice parameters and unit cell volume enhance as the content of Ti⁴⁺-ions increases, which confirms that Ti⁴⁺-ions replace Mn⁴⁺-ions. The average values of lattice strain and the crystallite size of the NBMTO manganites have been calculated using the Williamson-Hall plot technique for nanocrystalline samples. The temperature dependence of magnetic measurement shows that all compositions of NBMTO exhibit paramagnetic to ferromagnetic transition at Curie-temperature (T_C). It has been found that the values of T_C reduces exponentially with enhancing the concentration of Ti⁴⁺-ion from 140 K for x = 0 to 28 K for x = 0.3. Analysis of field-dependent magnetizations at a low temperature of 10 K clearly shows antiferromagnetic ordering within the ferromagnetic order. Investigation of Arrott’s plots reveals that all the samples exhibit second-order magnetic transition in the high-field region and first-order magnetic transition in the low-field region.