Synthesis, structure and magnetic properties of nanosized manganites Ca0.7La0.3MnO3 i Ca0.7La0.3Mn0.8Ce0.2O3

Abstract

Nanosized mixed valent perovskite manganites Ca0.7La0.3MnO3 and Ca0.7La0.3Mn0.8Ce0.2O3 were synthesized by the modified glycine-nitrate procedure. Based on the analysis of the x-ray diffraction data and TEM microscopy findings, the average crystallite size of Ca0.7La0.3MnO3 and Ca0.7La0.3Mn0.8Ce0.2O3 are found to be 36 nm and 32 nm, respectively. Their magnetic properties were investigated by M(T) measurements in both ZFC and FC regimes in several applied DC magnetic fields, as well as by M(H) measurements. Obtained M(T) magnetization curves display the irreversibility of ZFC and FC curves, and field dependence of the magnetization maximum in ZFC branches which is typical behavior for magnetic nanoparticle systems. Below the phase transition temperature, M(H) measurements show the existence of hysteresis without saturation in the magnetic fields up to 5 T, which points to the presence of AF interaction. Investigation of the magnetic properties of bulk counterparts shows that nanosizing suppresses G-AFM and C-AFM phases that exist in bulk compounds. Phase transitions temperatures for these phases as well as for charge ordering transition TCO are in accordance with estimated temperatures found in literature phase diagrams. Presence of cerium ions in both nanosized and bulk samples leeds to the increase of the ireversibility and blocking temperatures.

Nanočestični manganiti Ca0.7La0.3MnO3 i Ca0.7La0.3Mn0.8Ce0.2O3 sintetisani su modifikovanim glicin-nitratnim postupkom. Kristalna struktura je utačnjena na osnovu difraktograma dobijenih rendgenskom difrakcijom korišćenjem Rietveld-ove profilne metode u okviru prostorne grupe Pnma. Analizom rezultata rendgenskih merenja i TEM mikroskopije određeni su srednji dijametri čestica od 36 nm i 32 nm za Ca0.7La0.3MnO3 i Ca0.7La0.3Mn0.8Ce0.2O3 respektivno. Temperature ireverzibilnosti u krivama ZFC i FC magnetizacije, kao i temperature blokiranja TB koja zavisi od jačine primenjenog magnetnog polja, ukazuju na tipično ponašanje nanočestičnih sistema. Merenja magnetizacije u zavisnosti od jačine DC magnetnog polja, na temperaturama ispod tačke faznog prelaza, pokazuju postojanje histerezisa bez saturacije do jačine magnetnog polja od 5T, što je posledica postojanja AF interakcije između magnetnih jona. Uzorci dobijeni naknadnim sinterovanjem nanočestičnih manganita Ca0.7La0.3MnO3 i Ca0.7La0.3Mn0.8Ce0.2O3, pokazuju postojanje G-AFM i C-AFM faza, čije se temperature prelaza slažu sa literaturnim podacima. Prisustvo cerijumovog jona dovodi do porasta temperatura ireverzibilnosti i blokiranja kako kod nanočestičnih tako i kod sintenovanih ("bulk") uzoraka.