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Magnetic properties of europium chromites (EuCrO3)

Rare earth chromites exhibit a diversity of interesting chemical and physical properties depending on the rare earth ion. EuCrO3 shows a weak spontaneous magnetic moment below a Néel temperature of 181 K; attributed to a slight canting of the Cr3+ magnetic moments that are otherwise antiferromagneti...

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Main Author: MARÍN RAMIREZ, Juan Marcos
Other Authors: MACHADO, Fernando Luis de Araujo
Format: masterThesis
Language: eng
Published: Universidade Federal de Pernambuco 2017
Subjects:
Rareearthchromites. Combustionreactionmethod. Magnetism.
Cromitadeterrasraras. Reação porcombustão. Magnetismo.
Online Access: https://repositorio.ufpe.br/handle/123456789/19481
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spelling ir-123456789-194812018-10-03T18:46:26Z Magnetic properties of europium chromites (EuCrO3) MARÍN RAMIREZ, Juan Marcos MACHADO, Fernando Luis de Araujo FRANCO JÚNIOR, Adolfo http://lattes.cnpq.br/7437161779132978 http://lattes.cnpq.br/4572625669922885 Rareearthchromites. Combustionreactionmethod. Magnetism. Cromitadeterrasraras. Reação porcombustão. Magnetismo. Rare earth chromites exhibit a diversity of interesting chemical and physical properties depending on the rare earth ion. EuCrO3 shows a weak spontaneous magnetic moment below a Néel temperature of 181 K; attributed to a slight canting of the Cr3+ magnetic moments that are otherwise antiferromagnetically aligned. We have synthesized chromites by using a combustion reaction method applying urea as fuel. X-ray diffraction (XRD), Fourier transformed Infrared Spectroscopy (FT-IR), Scanning and Transmission Electron Microscopy (SEM and TEM), Thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) were used to study the samples. The magnetization was measured by using a vibrating sample magnetometer (VSM) and a Physical Properties Measurement System (PPMS) at a wide range of temperature (5 K to 300 K). Rietveld analysis of the XRD data yielded to an orthorhombic structure (Pnma) for EuCrO3, with an average crystallite size about 65 nm. Then, EuCrO3 was doped with iron forming a mixed chromite Eu1−xFexCrO3 (0 ≤ x ≤ 1.0). The presence of iron proved to be a source of microstrain in the system, due to the substitution of Eu3+ ions by Fe3+ in the perovskite structure. In fact, single phase EuCrO3 is paramagnetic at room temperature. However, above x>0.2, an enhance in the exchange interaction among the magnetic ions. The magnetic properties of Eu1−xFexCrO3 is accounted for by taking into consideration the lattice distortion introduced by the iron substitution in the EuCrO3 perovskite structure mainly due to the large difference in the ionic radius of Eu3+ and Fe3+ and in their magnetic moments. One of the most important contributions of our work has been focus on the relation between the bond angle of Cr3+-O2−-Cr3+ and the Néel temperature. This angle is responsible for the weak magnetic behavior of the rare earth chromites. We have found that as a product of the induced stress the Néel temperature is modified, so does the bonding angle. This behavior has been also found analyzing the shift towards higher values of the Hopkinson peak. To conclude, a termal treatment at 800°C for the Eu1−xFexCrO3 made at different times, shown a reduction in the microstrain of the system accompanied by an inhibition of the ferromagnetic-like character of the as-prepared samples. FACEPE As cromitas, à base de terras raras, exibem várias propriedades químicas e físicas interessantes dependendo do íon de terra rara. EuCrO3 mostra um momento magnético espontâneo fraco abaixo da temperatura de Néel (181 K); atribuída a uma ligeira inclinação dos momentos magnéticos do Cr3+ que são, de outra forma, antiferromagneticamente alinhados. Sintetizamos cromita de európio utilizando a técnica de reação por combustão. Difração de raiosX (XRD), espectroscopia de infravermelho por transformada de Fourier (FT-IR), microscopia electrónica de varredura e de transmissão (SEM e TEM), análises térmicas como termogravimetria e a calorimetria diferencial de varredura (TGA-DSC) foram utilizados para estudar nossas amostras. A magnetização foi medida usando um magnetómetro de amostra vibrante (VSM) e um PPMS (Physical Properties Measurement System) numa vasta região de temperatura (5 K até 300 K). O analises Rietveld dos difratogramas de XRD mostrou uma estrutura ortorrômbica (Pnma) para o EuCrO3, com um tamanho médio de cristalito de 65 nm. Depois, o sistema foi dopado com ferro formando cromitas mistas do tipo Eu1−xFex CrO3 (0≤ x ≤ 1,0). A presença de Fe provou ser uma fonte de “micro-strain” no sistema, devido à substituição dos íons de Eu3+ por aqueles de Fe3+. Na realidade, a fase pura de EuCrO3 é paramagnética à temperatura ambiente. No entanto, acima de x > 0,2, uma melhora na interação de troca entre os íons magnéticos é encontrada. As propriedades magnéticas de Eu1−xFexCrO3 são contabilizadas tendo em conta a distorção da estrutura introduzida pela substituição de ferro, principalmente devido à diferença no raio iónico de Eu3+ e Fe 3+ e dos seus momentos magnéticos. A relação entre o ângulo de ligação de Cr3+-O2−-Cr3+ (responsável pelo magnétismo fraco das cromitas de terras raras em baixa temperatura) e seu efeito na temperatura de Néel é estudada. Verificou-se que como produto do “strain” induzido, a temperatura de Néel é modificada e o mesmo acontece com o ângulo de ligação. Esse comportamento foi também encontrado analisando a mudança para valores mais elevados no pico de Hopkinson. Para concluir, um tratamento térmico feito a 800 °C para Eu1−xFexCrO3 durante tempos diferentes, mostraram que existe uma redução no “micro-strain” do sistema acompanhado por uma inibição do caráter ferromagnético das amostras (x > 0,2). 2017-07-10T18:32:41Z 2017-07-10T18:32:41Z 2016-03-10 masterThesis https://repositorio.ufpe.br/handle/123456789/19481 eng Attribution-NonCommercial-NoDerivs 3.0 Brazil http://creativecommons.org/licenses/by-nc-nd/3.0/br/ Universidade Federal de Pernambuco UFPE Brasil Programa de Pos Graduacao em Fisica
institution REPOSITORIO UFPE
collection REPOSITORIO UFPE
language eng
topic Rareearthchromites. Combustionreactionmethod. Magnetism.
Cromitadeterrasraras. Reação porcombustão. Magnetismo.
spellingShingle Rareearthchromites. Combustionreactionmethod. Magnetism.
Cromitadeterrasraras. Reação porcombustão. Magnetismo.
MARÍN RAMIREZ, Juan Marcos
Magnetic properties of europium chromites (EuCrO3)
description Rare earth chromites exhibit a diversity of interesting chemical and physical properties depending on the rare earth ion. EuCrO3 shows a weak spontaneous magnetic moment below a Néel temperature of 181 K; attributed to a slight canting of the Cr3+ magnetic moments that are otherwise antiferromagnetically aligned. We have synthesized chromites by using a combustion reaction method applying urea as fuel. X-ray diffraction (XRD), Fourier transformed Infrared Spectroscopy (FT-IR), Scanning and Transmission Electron Microscopy (SEM and TEM), Thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) were used to study the samples. The magnetization was measured by using a vibrating sample magnetometer (VSM) and a Physical Properties Measurement System (PPMS) at a wide range of temperature (5 K to 300 K). Rietveld analysis of the XRD data yielded to an orthorhombic structure (Pnma) for EuCrO3, with an average crystallite size about 65 nm. Then, EuCrO3 was doped with iron forming a mixed chromite Eu1−xFexCrO3 (0 ≤ x ≤ 1.0). The presence of iron proved to be a source of microstrain in the system, due to the substitution of Eu3+ ions by Fe3+ in the perovskite structure. In fact, single phase EuCrO3 is paramagnetic at room temperature. However, above x>0.2, an enhance in the exchange interaction among the magnetic ions. The magnetic properties of Eu1−xFexCrO3 is accounted for by taking into consideration the lattice distortion introduced by the iron substitution in the EuCrO3 perovskite structure mainly due to the large difference in the ionic radius of Eu3+ and Fe3+ and in their magnetic moments. One of the most important contributions of our work has been focus on the relation between the bond angle of Cr3+-O2−-Cr3+ and the Néel temperature. This angle is responsible for the weak magnetic behavior of the rare earth chromites. We have found that as a product of the induced stress the Néel temperature is modified, so does the bonding angle. This behavior has been also found analyzing the shift towards higher values of the Hopkinson peak. To conclude, a termal treatment at 800°C for the Eu1−xFexCrO3 made at different times, shown a reduction in the microstrain of the system accompanied by an inhibition of the ferromagnetic-like character of the as-prepared samples.
author2 MACHADO, Fernando Luis de Araujo
format masterThesis
author MARÍN RAMIREZ, Juan Marcos
author_sort MARÍN RAMIREZ, Juan Marcos
title Magnetic properties of europium chromites (EuCrO3)
title_short Magnetic properties of europium chromites (EuCrO3)
title_full Magnetic properties of europium chromites (EuCrO3)
title_fullStr Magnetic properties of europium chromites (EuCrO3)
title_full_unstemmed Magnetic properties of europium chromites (EuCrO3)
title_sort magnetic properties of europium chromites (eucro3)
publisher Universidade Federal de Pernambuco
publishDate 2017
url https://repositorio.ufpe.br/handle/123456789/19481
_version_ 1641987043224453120
score 13.657419

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