Magnetic behavior of La-doped Fe3O4 studied by perturbed angular correlation spectroscopy with 111Cd and 140Ce

Abstract

In this paper, the local magnetic properties of La-doped Fe3O4 (5% and 10%) bulk and Nanoparticles (NPs) samples were studied by measuring hyperfine interactions in a wide range of temperature from 10 to 900 K with perturbed γ-γ angular correlation spectroscopy using 111In(111Cd) and 140La(140Ce) as probe nuclei. Results for the temperature dependence of the magnetic hyperfine field (Bhf) for bulk and NP samples, pure and doped with La show that its behavior follows a second order Brillouin-like transition from which the Curie temperature (TC) was determined (TC ∼ 855 K). Results also show two different regions in NP samples: the core where a minor fraction of probe nuclei with well defined magnetic dipole frequency was observed and the shell where a major fraction with broad distributed electric quadrupolar frequency (surface effect in NP) was observed. The Verwey transition TV ∼ 120 K, due the order disorder phase, was also observed in all samples. The results are discussed in terms of the magnetic exchange interaction between Fe2+ and Fe3+ ions in the two regions of NP.

Caracterização em escala atômica de nanopartículas magnéticas de magnetita e ferrita do tipo TMFe₂O₄ (TM = Co, Ni) para uso em biomedicina pela espectroscopia de correlação angular gama-gama perturbada

“…região saturada (figura 4.24) e a dependência de temperatura de B hf indicam que a temperatura de transição é de cerca de 900 K. O valor de saturação de B hf é ligeiramente superior ao de 12,2 (1) observado para as nanopartículas Fe 3 O 4(Matos, Bosch-Santos, Cabrera-Pasca, & Cabonari, 2015). Curiosamente, a frequência quadrupolar de cerca de 160 (10) MHz atribuída à região shell é semelhante à observada para as nanopartículas Fe 3 O 4(Matos, Bosch-Santos, Cabrera- Pasca, & Cabonari, 2015), o que indica que a estrutura local distorcida na região shell de ambos os compostos é bastante semelhante. Os espectros de PAC em todas as temperaturas não mostram evidências de interações dinâmicas como esperado para técnicas de interação hiperfinas(Jr, Brandl, A., & G., 2006) quando a temperatura se aproxima da temperatura de bloqueio.…”