Monte Carlo simulations of core/shell nanoparticles containing interfacial defects: Role of disordered ferromagnetic spins

Ho, Le Bin; Lan, Tran Nguyen; Hải, Trương Nam

doi:10.1016/j.physb.2013.08.020

Cited by 7 publications

(4 citation statements)

References 19 publications

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“…The role of the F(i)M/AFM interface in mediating exchange bias has been widely studied as a function of the core size, 15,16 shell structure, 17−21 strains and distortion, 11,17 or spin disorder. 22,23,15 Inverted AFM/F(i)M structures such as FeO/Fe 3 O 4 24−26 or MnO/Mn 3 O 4 27 NPs have also been reported. Recently, the formation of interfacial layer produced by intermixing of F(i)M and AFM phases has also been demonstrated to have some strong effect on the overall magnetic properties of nanoparticles.…”

Section: ■ Introductionmentioning

confidence: 96%

“…Metal oxides have been widely investigated for many reasons among which is the epitaxial growth relationship which warrants high crystallinity of the interface between F(i)M and AFM phases. The role of the F(i)M/AFM interface in mediating exchange bias has been widely studied as a function of the core size, , shell structure, − strains and distortion, , or spin disorder. ,, Inverted AFM/F(i)M structures such as FeO/Fe 3 O 4 − or MnO/Mn 3 O 4 NPs have also been reported. Recently, the formation of interfacial layer produced by intermixing of F(i)M and AFM phases has also been demonstrated to have some strong effect on the overall magnetic properties of nanoparticles. − Although the exchange bias coupling has been widely investigated, the effect of the AFM shell structure on magnetic properties has rarely been systematically investigated.…”

Section: Introductionmentioning

confidence: 99%

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Systematic Study of Exchange Coupling in Core–Shell Fe_3−δO₄@CoO Nanoparticles

et al. 2015

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Although single magnetic domain nanoparticles are very promising for many applications, size reduction usually results in low magnetic anisotropy and unblocked domain at room temperature, e.g., superparamagnetism. An alternative approach is core–shell nanoparticles featured by exchange bias coupling between ferro(i)magnetic [F(i)M] and antiferromagnetic (AFM) phases. Although exchange bias coupling has been reported for very diverse core–shell nanoparticles, it is difficult to compare these studies to rationalize the effect of many structural parameters on the magnetic properties. Herein, we report on a systematic study which consists of the modulation of the shell structure and its influence on the exchange bias coupling. A series of Fe3−δO4@CoO core–shell nanoparticles has been synthesized by seed-mediated growth based on the thermal decomposition technique. The variation of Co reactant concentration resulted in the modulation of the shell structure for which thickness, crystallinity, and interface with the iron oxide core strongly affect the magnetic properties. The thickest CoO shell and the largest F(i)M/AFM interface led to the largest exchange bias coupling. Very high values of coercive field (19 000 Oe) and M R/M S ratio (0.86) were obtained. The most stricking results consist of the increase of the coercive field while exchange field vanishes when the CoO thickness decreases: it is ascribed to the diffusion of Co species in the surface layer of iron oxide which generates to some extent cobalt ferrite and induces hard/soft exchange coupling between ferrimagnetic phases.

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Section: ■ Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Systematic Study of Exchange Coupling in Core–Shell Fe_3−δO₄@CoO Nanoparticles

et al. 2015

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“…From this point of view, experimental systems showing exchange bias may contain statistical distributions due to the presence of randomly located defects in the system [25,26]. Recently, Ho and co-workers have attempted to address the magnetic properties of a ferromagnetic/antiferromagnetic core-shell nanospherical particle including the vacancies at the antiferromagnetic interface, based on Monte-Carlo simulation method [27]. It is found that the frustrated spins at the ferromagnetic interface is another pinning-source generating exchange bias phenomenon, in addition to the antiferromagnetic shell spins.…”

Section: Introductionmentioning

confidence: 99%

Nonmagnetic impurities and roughness effects on the finite temperature magnetic properties of core–shell spherical nanoparticles with antiferromagnetic interface coupling

Vatansever

Yüksel

2017

Journal of Magnetism and Magnetic Materials

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Being inspired by a recent study [V. Dimitriadis et al. Phys. Rev. B 92, 064420 (2015)], we study the finite temperature magnetic properties of the spherical nanoparticles with core-shell structure including quenched (i) surface and (ii) interface nonmagnetic impurities (static holes) as well as (iii) roughened interface effects. The particle core is composed of ferromagnetic spins, and it is surrounded by a ferromagnetic shell. By means of Monte Carlo simulation based on an improved Metropolis algorithm, we implement the nanoparticles using classical Heisenberg Hamiltonians. Particular attention has also been devoted to elucidate the effects of the particle size on the thermal and magnetic phase transition features of these systems. For nanoparticles with imperfect surface layers, it is found that bigger particles exhibit lower compensation point which decreases gradually with increasing amount of vacancies, and vanishes at a critical value. In view of nanoparticles with diluted interface, our Monte Carlo simulation results suggest that there exists a region in the disorder spectrum where compensation temperature linearly decreases with decreasing dilution parameter. For nanoparticles with roughened interface, it is observed that the degree of roughness does not play any significant role on the variation of both the compensation point and critical temperature. However, the low temperature saturation magnetizations of the core and shell interface regions sensitively depend on the roughness parameter.

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“…Com este tipo de representação das nanopartículas também podemos observar efeitos do tamanho nas propriedades magnéticas, como redução do campo coercivo, da temperatura de ordenamento e magnetização espontânea para partículas menores [12,36,37]. Outra possibilidade é representar as nanopartículas com uma estrutura coreshell, mudando o sinal da constante de troca J que é positiva para amostras ferromagnéticas e negativa para antiferromagnéticas [38]. Neste tipo de sistemas, os autores puderam observar que o aparecimento de um campo de exchange bias é dependente do surgimento de um momento magnético não nulo na interface antiferromagnética [39,40].…”

Section: Contribuições De Simulações Utilizando O Método De Monte Carunclassified

Sistemas de nanopartículas magnéticas: estudos experimentais e simulações Monte Carlo

Arantes¹

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Fapesp pela bolsa de doutorado concedida. Ao meu orientador, Daniel Reinaldo Cornejo, que me orientou desde a iniciação científica até o doutorado, e que foi a pessoa mais importante para a minha formação acadêmica. Ao professor Stefan Odenbach, da Technische Universität Dresden, pela sua supervisão durante o período em que usufrui da bolsa BEPE da Fapesp. Ao professor Antônio Martins Figueiredo Neto pelas discussões e suporte na preparação das amostras. Ao professor Carlos Alberto Ramos, do Centro Atómico de Bariloche, pelas medidas de ressonância ferromagnética. Ao professor Luiz Nagamine pela ajuda com os ajustes dos espectros Mössbauer. À professora Sylvia Carneiro, do Instituto Butantan, pelas imagens de microcopia eletrônica de transmissão. Ao Tarsis, do Laboratório de Cristalografia, pelas medidas de raios X. Aos funcionários do LMM, Sergio, Renato e Marcelo, por toda ajuda com os equipamentos, confecção dos porta-amostras e amizade. Aos demais colegas do LMM, professores Antonio Domingues e Carmen Partiti, e todos os alunos que tive a oportunidade de conhecer durante todos esses anos. Aos funcionários da oficina mecânica e criogenia, Paulo, Marcão, Vagner, Gilberto e Luciano. À Rita, técnica do grupo de Fluidos Complexos, por ter me orientado no preparo das amostras de cristais líquidos. Aos colegas da Technische Universität Dresden, Lisa Sprenger, Johannes Nowak, Julia Linke e Dmitry Borin. Ao Renato por todo companheirismo, apoio, paciência e ajuda com problemas computacionais. À minha família, em especial ao meu irmão Juliano, à minha mãe Irany e meu pai Paulo (in memoriam) que sempre me apoiaram e me incentivaram em todas as minhas escolhas. ix S U M Á R I O introdução 1 magnetismo de nanopartículas 5 2.1 Efeitos de superfície em nanopartículas 10 2.2 Interações entre partículas magnéticas 14 2.3 Contribuições de simulações utilizando o método de Monte Carlo na compreensão do magnetismo de nanopartículas 16 2.4 Fluidos magnéticos 17 2.4.1 Cristais líquidos dopados com nanopartículas magnéticas 21 2.4.2 Efeito magnetoviscoso 24 métodos experimentais 27 3.1 Caracterização estrutural das amostras 27 3.1.1 Difratometria de raios X 27 3.1.2 Determinação do tamanho de nanopartículas utilizando um microscópio eletrônico de transmissão 30 3.1.3 Espectroscopia Mössbauer 31 3.2 Caracterização magnética das amostras 33 3.2.1 Magnetometria SQUID 33 3.2.2 Curvas Zero Field Cooling-Field Cooling (ZFC-FC) 35 3.2.3 Curvas de remanência e ∆m 37 3.2.4 Curvas de inversão de primeira ordem (FORCs) 39 3.2.5 Medidas de suscetibilidade AC 44 3.2.6 Ressonância ferromagnética 45 3.3 Caracterização magnetoreológica de fluidos magnéticos 53 3.4 Algoritmo de Metropolis 56 estudos experimentais 59 4.1 Caracterização estrutural dos ferrofluidos comerciais 59 4.1.1 Microscopia de transmissão de ferrofluidos 59 4.1.2 Difratometria de raios X 63 4.1.3 Espectroscopia Mössbauer 64 4.2 Caracterização magnética de ferrofluidos congelados 67 4.3 Curvas ZFC-FC e transição de fase do estado sólido para o líquido em ferrofluidos 80 4.3.1 Obs...

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Monte Carlo simulations of core/shell nanoparticles containing interfacial defects: Role of disordered ferromagnetic spins

Cited by 7 publications

References 19 publications

Systematic Study of Exchange Coupling in Core–Shell Fe_3−δO₄@CoO Nanoparticles

Systematic Study of Exchange Coupling in Core–Shell Fe_3−δO₄@CoO Nanoparticles

Nonmagnetic impurities and roughness effects on the finite temperature magnetic properties of core–shell spherical nanoparticles with antiferromagnetic interface coupling

Sistemas de nanopartículas magnéticas: estudos experimentais e simulações Monte Carlo

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Monte Carlo simulations of core/shell nanoparticles containing interfacial defects: Role of disordered ferromagnetic spins

Cited by 7 publications

References 19 publications

Systematic Study of Exchange Coupling in Core–Shell Fe3−δO4@CoO Nanoparticles

Systematic Study of Exchange Coupling in Core–Shell Fe3−δO4@CoO Nanoparticles

Nonmagnetic impurities and roughness effects on the finite temperature magnetic properties of core–shell spherical nanoparticles with antiferromagnetic interface coupling

Sistemas de nanopartículas magnéticas: estudos experimentais e simulações Monte Carlo

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Systematic Study of Exchange Coupling in Core–Shell Fe_3−δO₄@CoO Nanoparticles

Systematic Study of Exchange Coupling in Core–Shell Fe_3−δO₄@CoO Nanoparticles