Effect of Sm3+ and Yb3+ doping on the structural and magnetic properties of La2−xRExNiMnO6 (x = 0.1–0.7) double perovskites

The doping effect of samarium (Sm) and ytterbium (Yb) at the La sites of La2NiMnO6 (LMNO) double perovskite on the structural and magnetic properties was studied. The rare-earth (RE = Sm, Yb) ion-doped La2-x RExNiMnO6 (x = 0.1–0.7) double perovskites were synthesized using sol-gel auto combustion route. The X-ray diffraction patterns of the Sm- and Yb-doped samples indicated single-phase monoclinic symmetry (P21/n space group). The Raman spectra provided complementary information of structural phase stability. The antisymmetric (∼528 cm−1) and symmetric (∼670 cm−1) stretching modes of vibration and a shoulder at wavenumber ∼250 cm−1 of the Raman spectra were consistent with a monoclinic phase. The X-ray photoelectron spectroscopy revealed the presence of La3+, Sm3+, Yb3+, Ni3+, Ni2+, Mn3+, and Mn4+ ions and improvement of the ordering of Ni2+ and Mn4+ ions in monoclinic structure of the Sm- and Yb-doped double perovskite structure. The temperature and magnetic field dependent magnetization studies revealed ferromagnetic nature with Curie temperature (TC) in the range of 205–265 K. The increase of Sm and Yb doping at the La sites of LMNO decreased TC and the presence of an additional weak magnetic transition at low-temperature range (∼100–150 K). The downturn feature of magnetization curves for a low-temperature regime (≤50 K) indicated a decrease of ferromagnetic exchange interactions and was a signature of spin freezing behavior in Sm- and Yb-doped LNMO samples.