The influence of Fe3+ ions at tetrahedral sites on the magnetic properties of nanocrystalline ZnFe2O4

A systematic study on the variation of Mössbauer hyperfine parameters with grain size in nanocrystalline zinc ferrite is lacking. In the present study, nanocrystalline ZnFe2O4 ferrites with different grain sizes were prepared by ball-milling technique and characterised by X-ray, EDAX, magnetisation and Mössbauer studies. The grain size decreases with increasing milling time and lattice parameter is found to be slightly higher than the bulk value. Magnetisation at room temperature (RT) and at 77 K could not be saturated with a magnetic field of 7 kOe and the observed magnetisation at these temperatures can be explained on the basis of deviation of cation distribution from normal spinel structure. The Mössbauer spectra were recorded at different temperatures between RT and 16 K. The values of quadrupole splitting at RT are higher for the milled samples indicating the disordering of ZnFe2O4 on milling. The strength of the magnetic hyperfine interactions increases with grain size reduction and this can be explained on the basis of the distribution of Fe3+ ions at both tetrahedral and octahedral sites

Magnetic properties of mechanically alloyed nanocrystalline Ni3Fe

Disordered nanocrystalline Ni3Fe alloy was prepared by mechanical alloying of elemental powders. X-ray diffractograms show the formation of Ni3Fe single phase. The chemical composition and morphology of the powder have been obtained by using EDAX and SEM analysis respectively. While the saturation magnetisation decreases with milling time, the coercivity increases. The width of the hyperfine field distributions obtained from Mossbauer studies shows that the alloy is highly disordered Atomic ordering is found to take place at a faster rate compared to that in the bulk alloy. (C) 1999 Acta Metallurgica Inc

Order–disorder studies and magnetic properties of mechanically alloyed nanocrystalline Ni3Fe alloy

Ni3Fe alloy with different grain sizes has been formed by mechanical alloying technique using a high energy ball mill. Fe-57 Mossbauer studies have been carried out at room temperature and hyperfine field distributions have been obtained for various milling durations. The influence of surface atoms on magnetic hyperfine fields and the effect of grain size an Fe magnetic moment have been investigated. The atomic ordering is found to be faster in the nanocrystalline form of Ni3Fe than in the bulk Ni3Fe

Ferrimagnetic Ordering In Nanostructured Zinc Ferrite

Recent investigations of nanocrystalline ZnFe2O4 have suggested that the cation distribution in this material is partially inverted and this gives rise to scope for potential technological applications [1. T. Sato, K. Haneda, M. Seki and T. Iijima. Appl. Phys. A. 50 (1990), p. 13. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (96)1]. In view of this a considerable amount of research has been done to investigate the effect of grain size on the cation distribution and magnetic properties of nanocrystalline ZnFe2O4. All these studies agree in one aspect that ZnFe2O4 is magnetically ordered with high ordering temperature and large magnetic moment. But they differ in predicting the type of magnetic ordering [2, 3, 4, 5 and 6]. In order to confirm the type of magnetic ordering and to study the effect of grain boundary and surface spins on the magnetic properties of nanostructured ZnFe2O4, we have carried out Mössbauer and magnetisation studies on nanostructured ZnFe2O4 with various grain sizes prepared by ball milling technique

Magnetic properties of nanostructured ferrimagnetic zinc ferrite

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

Grain size effect on the Neel temperature and magnetic properties of nanocrystalline NiFe2O4NiFe{_2}O{_4} spinel

Nanocrystalline NiFe2O4 spinel ferrites with various grain sizes have been synthesized by ball milling the bulk NiFe2O4. The average grain sizes were estimated from the X-ray line broadening of the (3 1 1) reflection. The Neel temperatures of NiFe2O4 for various grain sizes were determined by magneto thermogravimetric method. The magnetic behaviour has been explained by combining the effects of changes in cation distribution on milling and finite size scaling. The shift in B-H loops has been correlated to the surface spin effects. The high coercivities observed here may be due to high anisotropies of the milled samples. The Hopkinson peak observed just below the Neel temperature has been explained by the mathematical formalism given by the Stoner Wohlfarth model

Low-temperature magnetic properties and the crystallization behavior of FINEMET alloy

We have synthesized FINEMET alloy by a melt spinning technique and studied in detail its crystallization behavior and low-temperature magnetic properties. The crystallization behavior is characterized by transmission electron microscopy and Mossbauer spectroscopy. At early stages bcc solid solution precipitates from the amorphous matrix. At later stages, they order to yield DO3 ordered Fe3Si coexisting with a small amount of Fe2B. The analysis of Mossbauer spectra supports this observation. The temperature dependence of the magnetization in the temperature range 10-300 K of the FINEMET alloy in its as-quenched state follows the relation M(T) = M-0(T) (1-B T-3/2-C T-5/2-...), which is indicative of the presence of spin wave excitations in the alloy. The value of the C/B ratio and the mean-square value of the range of exchange interaction [r(2]) are found to be characteristic of the noncrystalline ferromagnets. The small value obtained for the exchange stiffness constant D is an indication of the softening of the exchange interaction