Propriedades magnéticas de ortoferritas de lantânio dopadas com estrôncio
Samples of lanthanum Ortoferrites doped with strontium were synthesized in a single phase by the sol-gel method. Two samples were prepared, one by varying the concentration of strontium in lanthanum ortoferrites La1−xSrxFeO3−δ with (0 ≤ x ≤ 0.5), and another batch of samples of type, La1/3Sr2/3Fe...
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| Formato: | Dissertação |
| Idioma: | por |
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Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/18603 |
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| Resumo: | Samples of lanthanum Ortoferrites doped with strontium were synthesized in a single
phase by the sol-gel method. Two samples were prepared, one by varying the concentration of
strontium in lanthanum ortoferrites La1−xSrxFeO3−δ with (0 ≤ x ≤ 0.5), and another batch
of samples of type, La1/3Sr2/3FeO3−δ, now varying only the temperature of calcination. Our
samples were obtained by Pechini method and sintered in air and oxygen atmospheric. Their
crystal structures were determined by x-ray diraction (XRD), scanning electron microscopy
(SEM), where we observed that the samples (0 ≤ x ≤ 0.3) have orthorhombic symmetry and
the volume of the single cell decreases with the increasing of concentration of strontium. For
x = 0.5 it is only observed the simple phase when that is sintered in O2 atmospheric. Their
magnetic characteristics were obtained by the Mössbauer spectroscopy and magnetic measurements.
The magnetization measurements for samples La1−xSrxFeO3−δ with (0 ≤ x ≤ 0.5)
revealed that the magnetization decreases with increasing concentration of strontium, but
for the sample x = 0.4 the magnetization shows a high coercive field and a ferrimagnetic
behavior, which is attributed to a small amount of strontium hexaferrite. As for the samples
La1/3Sr2/3FeO3−δ calcined between 800 oC e 1200 oC. The hysteresis curves revealed
two distinct behaviors: an declined antiferromagnetic behavior (Canted) for samples calcined
between 800 oC and 1000 oC and a paramagnetic behavior for the samples calcined at
1100 oC e 1200 o C. Thermal hysteresis and sharp peaks around the Néel temperature (TN),
over the curves of specific heat as a function of temperature was only observed in calcined
samples with 1100 oC and 1200 oC. This eect is attributed to the charge ordering. These
results indicate that the charge ordering occurs only in the samples without oxygen deficiency.
Magnetic measurements as a function of temperature are also in agreement with this
interpretation |
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