Ac susceptibility and magnetic interaction in Mg–Ni–Fe–O system Mazhar U. Rana * , Tahir Abbas Department of Physics and Materials Science, Bahauddin Zakariya University, Multan 60800, Pakistan Received 23 November 2001; received in revised form 18 April 2002; accepted 29 April 2002 Abstract A series of Mg 1  x Ni x Fe 2 O 4 spinel ferrites with x = 0, 0.25, 0.50, 0.75 and 1.0 have been prepared using standard ceramic method. Lande-g factor ( g), effective magnetic moments ( P eff ), Curie temperature (T c ), paramagnetic Curie temperature (h(K)) and exchange integral ( J/k) were calculated from ac susceptibility measurements using mutual inductance technique. With the addition of Ni ions g-values, P eff and h(K) show increasing trend up to x = 0.75 while T c continues to decrease. For x>0.75 decreasing trend in magnetic moments (n B ) and h(K) is exhibited, which could be correlated to the redistribution of cations on A and B sites. The dominant interaction in all the samples is A – B interaction, which is due to the negative values of h(K), showing the magnetic ordering is antiferromagnetic. The Y – K angle increases gradually with increasing Ni contents and extrapolates to 60j for NiFe 2 O 4 . From the computation of Y–K angles for Mg 1  x Ni x Fe 2 O 4 , it can be concluded that mixed nickel ferrites exhibit a non-colinearity of the Y – K type while MgFe 2 O 4 show a Neel type of ordering. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Magnesium ferrites; Susceptibility; Magnetic moments; Interaction; Y – K angles 1. Introduction Magnesium ferrites belong to a class of compounds having the general formula M 2+ Fe 2 3+ O 4 and crys- tallizing with the spinel structure, a mixed spinel, have been the subject of study for a long time [1,2].A number of investigators have studied the influence of divalent Zn [3], trivalent In [4] and tetravalent Ti [5– 7] substitution in its various properties. The effect of Ge substitution in Mg–ferrites have been also studied [2]. The basic magnetic properties of ferrites are very sensitive function of the distribution of the metallic ions among the available A and B sites [8]. In the present study, the influence of addition of Ni in MgFe 2 O 4 ferrite system has been investigated. The low field ac susceptibility (v) method reported earlier [9] was used for these investigations. 1/v vs. T plots have been drawn and the exchange integral for each sample have been calculated using paramagnetic temperature h obtained from these curves. Such calculations have been carried out by Neel [10] and Srivastava et al. [11]. In these calculations, sponta- neous magnetization and susceptibility data in para- 0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0167-577X(02)00897-2 * Corresponding author. Tel.: +92-61-220-089; fax: +92-61- 220-091. E-mail address: mazharranapk@yahoo.com (M.U. Rana). www.elsevier.com/locate/matlet December 2002 Materials Letters 57 (2002) 925 – 928