ИСТИНА

Mössbauer measurements of lanthanum manganite La1-xCaxMn0.98Fe0.02O3+δ (where x = 0.05, 0.10, 0.20) of nonstoichiometric (δ ≠ 0) and stoichiometric (δ = 0) composition were carried out at 80 K and 300 K temperature. Magnetic investigations were done at temperatures from 100 K to 300 K in fields up to 16 kOe. According to the Mössbauer spectroscopy methods samples of doped non-stoichiometric La1-xCaxMn0.98Fe0.02O3+δ oxides (x = 0.05, 0.10, 0.20) are single-phase and have the rhombohedral structure (space group R3-c) for x = 0.05; 0.1 and the orthorhombic structure (space group PnmaI) for x=0.20. Interstitial oxygen strongly distorts the lattice in samples with rhombohedral structure. All the samples demonstrated superparamagnetic behavior. The relaxation type of the spectra can be due to the presence of small ferromagnetic clusters (domains) of different sizes, which behave like superparamagnetic particles. With an increase in Ca concentration, a distortion of the nearest environment of iron atoms decreases. The presence of ferromagnetic clusters in the structure observed. Mössbauer studies of the lanthanum manganite La1-xCaxMn0.98Fe0.02O3 (x = 0.05, 0.10, 0.20) of the stoichiometric composition identified phase separation, which is the coexistence in a mixture of three orthorhombic PnmaI, PnmaII and PnmaII* phases. PnmaI phase becomes into the ferromagnetic state, and the PnmaII and PnmaII* phases  become antiferromagnetic when the temperature is lowered. With an increase in Ca concentration, the relative content of the ferromagnetic phase increases and the temperature of its magnetic transition also increases. To confirm the results obtained by Mössbauer spectroscopy, magnetic measurements were additionally performed: for each sample, hysteresis loops and the temperature behavior of ZFC-FC were obtained. With increasing calcium concentration, the coercive force, magnetization, and blocking temperature increase.