The ( to ) samples were prepared by solution route technique. These samples were characterized by XRD and EPR spectra at X-band frequency (~9.2？GHz). The XRD spectra of these ferrites confirm the formation of spinel structure. The average particle size calculated by using Scherrer’s formula was found to be of the order of 24.7？nm. The EPR spectra of these ferrites are mainly due to Fe3+ ions. Fe2+ ions have very short spin-lattice relaxation time and therefore EPR spectra of Fe2+ could be observed only at very low temperature. This fact is also supported by the isomer shift values of these ferrites obtained from M？ssbauer spectroscopy. The variation of and with Sn4+ concentration is attributed to the variation of superexchange interaction. Moreover in this system the dominant process of relaxation is the spin lattice relaxation rather than the spin-spin interaction. 1. Introduction Ferrites are certain double oxides of iron and another metal taken as the most important ferromagnetic substances. The magnetic ferrites fall mainly into two groups with different crystal structures. One is cubic ferrites having the general formula MO·Fe2O3 where M is a divalent metal ion, like Mn, Ni, Fe, Co, and Mg. Second one is hexagonal ferrites. The most important member in this group is barium-ferrites BaO·6Fe2O3. The ferrites are ionic compounds, and their magnetic properties are due to the magnetic ions they contain. The commercial value lies in the fact that they have higher values of saturation magnetization and Curie temperature, which are imperative for use as core materials. They are more suitable for high power application in addition to the applications, such as multilayer chip inductor and electromagnetic interference (EMI) suppression; recent studies suggest their applications in biomedical applications such as molecular imaging and drug delivery [1–4]. There are two main classes of materials containing zinc ferrites, that is, Mn-Zn ferrites and Ni-Zn ferrites. Out of them Ni-Zn ferrites are designed for very high frequency operation, to more than 100？MHz as well as very high resistivity, about 105？ohm？cm. The effect of TiO2 addition on saturation magnetization and magnetic spectrum of Ni0.3Zn0.7Fe2O4 has been studied [4]. An unexpected dip was reported in the saturation magnetization curve at a particular Ti4+ concentration in Ti4+-substituted Ni-Zn ferrite [5]. It has also been concluded that lattice parameter decreased with the increase of Ti4+ up to a certain concentration and subsequently it increased monotonically. The variation of lattice parameter
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