Anomalous magnetic behaviour of zinc and chromium ferrites without any hyperfine splitting
Two groups of ferrite namely zinc ferrite and chromium ferrite were synthesized by citrate precursor route in the size range of 8 to 35 nm. We have studied the structural and magnetic behaviour of these ferrites using X-ray diffraction (XRD), vibrating sa
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Originally published in the journal Hyperfine Interactions, Volume 183, Nos 1–3, 189–196. DOI: 10.1007/s10751-008-9730-9 © Springer Science + Business Media B.V. 2008
Abstract Two groups of ferrite namely zinc ferrite and chromium ferrite were synthesized by citrate precursor route in the size range of 8 to 35 nm. We have studied the structural and magnetic behaviour of these ferrites using X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Mössbauer spectroscopic techniques. Our studies show that the nanocrystalline ferrites interact with the hand magnet strongly and give large magnetization in the VSM measurement. The maximum magnetization in the samples sensitively depends on the particle size of synthesized ferrites. We observed as large as 28 Am2 /kg of magnetization in the zinc ferrite nanoparticles while that in chromium ferrite is around 11 Am2 /kg. In spite of the large magnetization in the zinc ferrite nanoparticles we did not observe any hyperfine splitting even down to 12 K of temperature. Similar behaviour is also observed for chromium ferrite down to 16 K. Keywords Mössbauer spectroscopy · Ferrites · Nanophase iron · Magnetic nanoparticles
1 Introduction Nanosize zinc ferrites prepared by a variety of methods have been studied by large number of researchers in the past decade [1–7]. The most interesting aspect of the nanosize zinc ferrite is the cation distribution where increasing degree of inversion is found conclusively with decreasing particle size. This leads to enhanced magnetization in the otherwise paramagnetic system. Recently Upadhyay [8] reported nanosize zinc ferrite with particle size 6 nm having magnetization as large as 38 Am2 /kg at 6 and 60 K, but showing no hyperfine splitting down to 12 K. With this particle size
B. Pandey · H. C. Verma (B) Department of Physics, I.I.T. Kanpur, Kanpur 208016, India e-mail: [email protected]
N. S. Gajbhiye and S. K. Date, ICAME 2007. DOI: 10.1007/978-3-540-78696-2_19
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B. Pandey, H.C. Verma
one does not expect the blocking temperature to be so low that no trace of magnetic splitting is seen up to 12 K. Hyperfine magnetic field at the site of 57 Fe nucleus is supposed to come from the exchange coupled magnetic ions and this itself is responsible to magnetic ordering in the crystalline system and gives rise to magnetization. Thus, magnetization Ms and hyperfine magnetic field Bhf go hand in hand and it is often assumed that Bhf is proportional to Ms . ZnFe2 O4 prepared by Upadhyay [8] using citrate precursor route does not confirm to this expectation. In order to check the reproducibility we prepared nanosize ZnFe2 O4 using the same method [8] and found that at 13 nm average size, the magnetization is 28 Am2 /kg at room temperature which is comparable to that obtained by Upadhyay [8]. This sample too did not give any splitting at least at 15 K. Iron, chromium and oxygen form a stable oxide FeCr2 O4 known as iron chromite. This system too is paramagnetic and gives a single line in Mössbauer spectrum corresponding to Fe2+ sta
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