Abstract
Structural and magnetic properties of La
0.6
Ca
0.4−
x
Sr
x
MnO
3
manganites have been investigated for
x
= 0.0, 0.1 and 0.4. The Rietveld analysis of X-ray diffraction data indicates that, with increasing Sr content, a structural phase transition from rhombohedral to orthorhombic is occurred. Structural parameters are calculated and found to be dependent upon the composition. The nanometric size of our samples estimated using Debye–Scherrer equation is confirmed by SEM images. Magnetic measurements according to the zero-field cooled and field cooled procedures are performed. The observed irreversibility between the two modes is assigned to the presence of magnetic anisotropy which has been explained as arising from the surface effects. The blocking temperature (
T
B
) is estimated and found to increase as the particle size increases. Above
T
B
, the materials show a superparamagnetic (SPM) behavior where the coercivity and remanence magnetizations are almost zero that favors their application in the biomedical field. Studying the thermal variation of
dc
susceptibility confirms the SPM nature of the studied compounds. The good fit of the magnetization vs. magnetic field curves with Langevin function supports our findings. From this simulation, the saturation magnetization is calculated and found to increase as particle size increases which is explained in terms of Core–shell model. With the reduction of particle size to the nanometric scale, single domain structure and SPM regime structure are detected.