Hyperfine Interactions 156/157: 123–127, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands. 123 Mössbauer Studies of Fe 0.7−x Si 0.3 Mn x Alloys I. A. AL-OMARI ∗ , A. GISMELSEED, A. RAIS, H. M. WIDATALLAH, A. AL RAWAS, M. ELZAIN and A. A. YOUSIF Department of Physics, P.O. Box 36, Sultan Qaboos University, PC 123, Muscat, Sultanate of Oman; e-mail: ialomari@yahoo.com Abstract. In this work we present Fe 57 Mössbauer study for the alloy system Fe 0.7−x Si 0.3 Mn x , where 0  x  0.3. Mössbauer spectroscopic results show that all the samples studied are mag- netically ordered at 77 K, and at room temperature, except for x = 0.3 at 300 K where it shows paramagnetic behavior. The average magnetic hyperfine field is found to decrease with increasing the manganese concentration at 77 K and 300 K. The average magnetic hyperfine field is found to increase with decreasing the temperature from 300 K to 77 K for all samples under investigation. The average isomer shift is found to decrease with increasing the manganese concentration. Key words: Mössbauer effect, hyperfine field, isomer shift. 1. Introduction Materials based on Fe 3 Si and Fe 3 Al alloy systems are of great interest, because of their high temperature strength, excellent oxidation and corrosion resistance. Substitution of Fe by transition metal element affect the magnetic properties, the lattice parameter, and the structural ordering of these compounds [1–3]. Neutron diffraction study for Fe 3−x Mn x Si by Yoon and Booth [2] showed that Mn pref- erentially occupies the B site of the DO 3 -type structure for x< 0.75, and then starts to occupy the A and C sites for higher Mn concentrations. They also found that this system exhibits ferromagnetic behavior for x< 0.75 and a complex magnetic behavior evolves for x> 0.75. Substituting Fe by Mn was found to decrease the magnetic moment, interaction energy, and Curie temperature with increasing the Mn concentration. Waliszewski et al. [3] studied the Fe 3−x Cr x Si system and found that Curie temperature decreases from 840 K for x = 0 to 712 K for x = 0.4, and the magnetic moment of iron at the B site to be 2.44 μ B , and about 1.18 μ B for (A, C) sites, while the magnetic moments of Cr were determined to be (2.03 ± 1.3)μ B for Cr at the B site and (0.41 ± 0.63) μ B for the (A, C) sites with orientation antiparallel to the magnetic moments of Fe. The structural and magnetic properties of the intermetallic Fe–Si alloys depend on the Si concentration. FeSi 2 was found to form the tetragonal type structure, FeSi forms the B 2 O type structure, while Fe 3 Si forms the DO 3 type cubic structure. * Author for correspondence.