Exchange bias of MnFe2O4@γFe2O3 and CoFe2O4@γFe2O3 core/shell nanoparticles

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS

卷:368

Article; Proceedings Paper

Cabreira-Gomes, R.^1,2,3  Silva, F. G.^1,2,3  Aquino, R.^1,4  Bonville, P.⁵  Tourinho, F. A.⁶  Perzynski, R.^2,3  Depeyrot, J.¹ 

[1] Univ Brasilia, Inst Fis, Complex Fluids Grp, BR-70919970 Brasilia, DF, Brazil

[2] UPMC, Univ Paris 04, PHENIX, UMR 8234, F-75005 Paris, France

[3] CNRS, PHENIX, UMR 8234, F-75005 Paris, France

[4] Univ Brasilia, Fac UnB Planaltina, LNAA, BR-73300000 Brasilia, DF, Brazil

[5] CEA Saclay, DSM IRAMIS, SPEC URA CNRS 2464, F-91191 Gif Sur Yvette, France

[6] Univ Brasilia, Inst Quim, Complex Fluids Grp, BR-70910900 Brasilia, DF, Brazil

关键词: Coprecipitation method;    Ferrite nanoparticle;    Magnetic property;    Exchange bias effect;    Spin glass like;   

DOI  :  10.1016/j.jmmm.2014.03.003

来源: Elsevier

【 摘 要 】

We compare here exchange bias (EB) properties of chemically synthesized core-shell nanoparticles (NPs), based either on a core of soft ferrite (MnFe2O4) or hard ferrite (CoFe2O4) protected by a maghemite shell (gamma-Fe2O3). These NPs dispersed in acidic solutions are electrostatically stabilized, yielding to stable colloidal dispersions with a strong interparticle repulsion and negligible dipolar interactions in the probed range of temperatures. Field cooled (FC) magnetic hysteresis loops of non-textured frozen dispersions (with magnetic anisotropy axis of NPs distributed at random) and those of a powder based on the same NPs present a shift along the H-axis, expressing the coupling between the spin-ordered cores and the disordered surface layer of the NPs. The bias field is found to present a maximum, larger for NPs based on harder ferrite core. It is obtained for a cooling field of the order of one half of the anisotropy field, which is much larger for the CoFe2O4 cores than for MnFe2O4 ones. In powders, particles are in contact leading to an interparticle exchange which is not present in the dilute solutions where exchange bias properties are only due to an intraparticle exchange between core and surface. The thermal dependence of the bias field is well described by a reduced exponential behavior with a characteristic freezing temperature of about 8 K. (C) 2014 Elsevier B.V. All rights reserved

【 授权许可】

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