L Journal of Alloys and Compounds 282 (1999) 268–273 Magnetic and microstructural properties of Sn / Nb substituted Mn–Zn ferrites a, b c b * A.D.P. Rao , B. Ramesh , P.R.M. Rao , S.B. Raju a Department of Nuclear Physics, Andhra University, Visakhapatnam 530 003, India b Department of Physics Andhra University, Visakhapatnam 530 003, India c Department of Inorganic and Analytical Chemistry, Andhra University, Visakhapatnam 530 003, India Received 5 June 1998; received in revised form 28 August 1998 Abstract Saturation magnetisation, Curie temperature and initial permeability of Sn / Nb substituted Mn–Zn ferrites have been studied at room temperature. The influence of high valency cations on the microstructure has been studied. Grains of monodomain form are obtained and the variation of initial permeability with grain size is discussed in the light of recent studies on Mn–Zn ferrites, where initial permeability variation with grain size was explained on the basis of the Pankert model. The variation of saturation magnetisation and Curie temperature with dopant cation concentration is explained.  1999 Elsevier Science S.A. All rights reserved. Keywords: Ferrites; Magnetic properties; Microstructure; Grain size; Permeability 1. Introduction that Sn was soluble in the ferrite and altered the micro- 41 structure. Contrary to this, Sn was found to lead to Magnetic and microstructural properties play a vital role additional phase formation due to unreacted material in in the field of ferrites for application in industry. At low other mixed ferrites like Ni–Zn ferrite [4,5]. The effect of 41 51 frequencies, Mn–Zn ferrites are superior over other ferrites Sn / Nb substitution on the magnetic and micro- because of high initial permeability ( m ), low losses, high structural properties of Mn–Zn ferrites is reported in the i saturation magnetisation ( M ) and relatively high Curie present study. s Temperature ( T ). Ferrite properties are very sensitive to c the preparative conditions like sintering temperature, at- mosphere in the furnace, rate of heating and cooling. To 2. Preparation of samples achieve desired values of the properties, a well known method [1] is to replace some of the cations in the The basic composition of the ferrite in which Sn / Nb composition of the ferrite. substituted is Mn Zn Fe O . Ferrites with the com- It was found that by replacing with high valency cations 0.58 0.37 2.05 4 51 41 41 41 position Mn Zn M Fe O were prepared, like Nb , Sn , Ti and Ge the properties of ferrites 0.582x /2 0.372x /2 x 2.05 4 41 51 would change significantly [2,3]. Earlier studies [4–6] on where M5Sn /Nb and ‘x’ varied from 0.00 to 0.50 in mixed ferrites indicated that the high valency cations like steps of 0.05. Calcination was done in air atmosphere for 3 41 Sn occupied octahedral sites (B sites). Recent studies [3] h at 10008C. The sintering was done at 13808C for 1 h, and showed that these cations occupied non-preferential (A) later temperature was lowered to 12808C and kept for 1 h sites at lower concentrations and B sites at higher con- in air. For Nb concentrations from x50.35 to 0.50, the centrations. Studies [2,7] on substitution of high valence initial sintering was done at 10508C in air for 1 h and then cations in Mn–Zn ferrite found that, initially the cation had lowered to 9508C and kept for 1 h, since it is known [1] a strong tendency to occupy B sites and under certain that bulk diffusion of niobium occurs at high sintering conditions it was also occupying A sites. A previous study temperatures and increases the vacancy concentration. 41 of the substitution [2] of Sn in Mn–Zn ferrite indicated After completion of preparation of these ferrites the presence of the quoted concentration(s) of dopant(s) in the * Corresponding author samples was checked by using Atomic Absorption Spec- 0925-8388 / 99 / $ – see front matter  1999 Elsevier Science S.A. All rights reserved. PII: S0925-8388(98)00823-8