Busca avançada
Ano de início
(Referência obtida automaticamente do Web of Science, por meio da informação sobre o financiamento pela FAPESP e o número do processo correspondente, incluída na publicação pelos autores.)

Blocking and remanence properties of weakly and highly interactive cobalt ferrite based nanoparticles

Texto completo
Vieira, C. A. M. [1] ; Gomes, R. Cabreira [1, 2] ; Silva, F. G. [1, 2] ; Dias, A. L. [1] ; Aquino, R. [2] ; Campos, A. F. C. [2] ; Depeyrot, J. [1]
Número total de Autores: 7
Afiliação do(s) autor(es):
[1] Univ Brasilia, Inst Fis, Complex Fluids Grp, Caixa Postal 04455, BR-70919970 Brasilia, DF - Brazil
[2] Univ Brasilia, Fac UnB Planaltina, LNAA, BR-73345010 Brasilia, DF - Brazil
Número total de Afiliações: 2
Tipo de documento: Artigo Científico
Citações Web of Science: 0

We compare both magnetic blocking properties and remanence curves for dilute ferrofluid and powder samples of ferrite magnetic nanoparticles. Low field DC magnetization, AC susceptibility, isothermal remanent magnetization and DC demagnetization techniques are employed to investigate the role of interparticle magnetic interactions on the superparamagnetic relaxation, the magnetic anisotropy and on the super-spin-glass state in closely packed particles. The samples used herein are 3 nm sized spinel-type nanocrystals made of a cobalt ferrite core covered by a layer of maghemite on its outermost surface and can be obtained as aqueous colloidal dispersions thanks to this core-shell strategy. They show large anisotropy attributed to an enhanced surface contribution and the blocking temperature is shifted towards higher values as interparticle distance decreases. For all investigated diluted liquids and powder samples the frequency dependency of the peak temperature is well accounted by a Vogel-Fulcher law, with the insertion of a phenomenological temperature associated to the magnitude of interparticle dipolar interactions. The fractional change of the peak temperature per decade of frequency enlights the presence of interactions between particles in dilute liquids and of a spin-glass-like state in powder samples. The remanence curves always show global demagnetizing behavior, attributed to the combination of both spin surface disorder and interparticle dipolar interactions, the former being predominant in isolated nanoparticles and the latter in powder samples. However, in the most compacted powder, exchange interaction between surface ions of different particles becomes more pronounced and promotes an additive magnetizing effect. (AU)

Processo FAPESP: 14/50983-3 - INCT 2014: fluidos complexos
Beneficiário:Antonio Martins Figueiredo Neto
Linha de fomento: Auxílio à Pesquisa - Temático