Structural, magnetic, magnetocaloric, and critical behavior of selected Ti-doped manganites

Abstract In this article we report the effect of Ti doping on the magnetic properties and structural characteristics of La0.67Ba0.22Sr0.11Mn1−xTixO3 (x=0, 0.1, 0.2 and 0.3) nanopowder samples. The samples were prepared by a sol–gel method. X-ray diffraction revealed that these manganites crystallized in the orthorhombic structure with space group Pnma. Measurements of the magnetization as a function of temperature and applied magnetic field indicated that Ti doping weakens the double exchange ferromagnetic–paramagnetic transition and lowers the transition temperature to around room temperature. The maximum of the magnetic entropy change decreased with Ti-substitution from 2.75 J/kg K for the sample with x=0.0–1.33 J/kg K for the sample with x=0.1. However, the peak profile of the magnetic entropy change for the sample with x=0.1 broadened significantly, resulting in a relatively high relative cooling power (RCP) of 255 J/kg. These characteristics, together with the critical transition temperature being near room temperature, indicate that this sample is promising as an efficient magnetic refrigerant in a wide temperature range around room temperature. The refined values of the critical exponents β, γ, and δ obtained from the modified Arrott plots and Kouvel–Fisher method indicated that the behavior of the parent sample (x=0.0) is consistent with a 3D-Heisenberg-likeferromagnet with short-range exchange coupling. However, the critical exponent β for the sample with x=0.1 is characteristic of mean-field behavior (with β=0.50), while the critical exponent γ decreased to 1.21, approaching the mean-field value of 1.0.