ZnFe2O4 Nanocrystals: Synthesis and Magnetic Properties
02 Aug 2007-Journal of Physical Chemistry C (American Chemical Society)-Vol. 111, Iss: 33, pp 12274-12278
TL;DR: In this paper, as-synthesized ZnFe2O4 nanocrystals were synthesized via the thermal decomposition of metal−surfactant complexes, and the results demonstrate that magnetic properties of magnetic particles can be largely modified by just changing p...
Abstract: Ferromagnetic zinc ferrite nanocrystals at ambient temperature were synthesized via the thermal decomposition of metal−surfactant complexes. Characterization measurements including transmission electron microscopy and X-ray diffraction were performed for as-synthesized ZnFe2O4 particles. The sample has a relatively narrow size distribution with an average particle size of 9.8 ± 0.2 nm and standard deviation of 30%. The as-synthesized zinc ferrite nanocrystals are superparamagnetic at room temperature with a blocking temperature TB = 68 ± 2 K and a saturation magnetization MS = 65.4 emu·g-1 at T = 10 K, which are caused by the change in the inversion degree of the spinel structure. A coercive field of HC = 102 ± 5 Oe in the blocked state indicates small particle anisotropy, although evidence of surface spin canting was inferred from magnetization data in the as-synthesized ZnFe2O4 nanocrystals. Our results demonstrate that magnetic properties of magnetic particles can be largely modified by just changing p...
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TL;DR: In this paper, a model of the magnetization within these particles consisting of ferrimagnetically aligned core spins and a spin-glass-like surface layer is proposed, and the qualitative features of this model are reproduced by a numerical calculation of the spin distribution.
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703 citations
TL;DR: In this paper, the average grain size and the root mean square strain were estimated from the x-ray diffraction line broadening, and the lattice parameter initially decreases slightly with milling and it increases with further milling.
Abstract: Nanostructured ZnFe2O4 ferrites with different grain sizes were prepared by high energy ball milling for various milling times. Both the average grain size and the root mean square strain were estimated from the x-ray diffraction line broadening. The lattice parameter initially decreases slightly with milling and it increases with further milling. The magnetization is found to increase as the grain size decreases and its large value is attributed to the cation inversion associated with grain size reduction. The Fe-57 Mossbauer spectra were recorded at 300 K and 77 K for the samples with grain sizes of 22 and 11 nm. There is no evidence for the presence of the Fe2+ charge state. At 77 K the Mossbauer spectra consist of a magnetically ordered component along with a doublet due to the superparamagnetic behaviour of small crystalline grains with the superparamagnetic component decreasing with grain size reduction. At 4.2 K the sample with 11 nm grain size displays a magnetically blocked state as revealed by the Mossbauer spectrum. The Mossbauer spectrum of this sample recorded at 10 K in an external magnetic field of 6 T applied parallel to the direction of gamma rays clearly shows ferrimagnetic ordering of the sample. Also, the sample exhibits spin canting with a large canting angle, maybe due to a spin-glass-like surface layer or grain boundary anisotropies in the material.
339 citations