Journal of Alloys and Compounds 437 (2007) 16–21 Study on the existence and properties of Y 3 (Fe 1-x Co x ) 29-y Cr y (x = 0.6–1.0; y = 5–7) intermetallic compounds C. Sarafidis a,∗ , M. Gjoka b , K.G. Efthimiadis a , O. Kalogirou a a Department of Physics, Aristotle University of Thessaloniki, 54 124 Thessaloniki, Greece b Institute for Materials Science, NCSR “Demokritos”, 15310 Ag. Paraskevi, Attiki, Greece Received 28 February 2006; received in revised form 20 July 2006; accepted 21 July 2006 Available online 1 September 2006 Abstract The structural and magnetic properties of compounds with nominal composition Y 3 (Fe 1-x Co x ) 29-y Cr y (x = 0.6–1.0 and y = 5–7) have been investigated. The main phase formed was that of Nd 3 (Fe,Ti) 29 -type structure (3:29) with a significant amount of a disordered variant of the hexagonal Th 2 Ni 17 -type structure (2:17H) as a secondary phase (25–50 wt.%), especially for higher Co (80% and above) content. The unit cell volume is decreasing with the increase of the Co and Cr content, as well as all the cell parameters. The Curie temperature of both phases decreases monotonically with x and y. The x = 1.0 compound is paramagnetic at room temperature. The x = 0.6, 0.8 compounds present uniaxial anisotropy along the [2 0 4] direction of the monoclinic Nd 3 (Fe,Ti) 29 -type structure, which should be attributed to the transition metal sublattice. The saturation magnetization and the anisotropy field are lower in the sample with x = 0.8 compared to the one with x = 0.6. This reduction is also observed in the M¨ ossbauer spectra of the materials at room temperature which are also presented. © 2006 Elsevier B.V. All rights reserved. Keywords: Intermetallics; Magnetically ordered materials; X-ray diffraction; Magnetic measurements; M¨ ossbauer spectroscopy 1. Introduction The substitution of Co for Fe in R 3 (Fe,TM) 29 intermetal- lic compounds (3:29) has a remarkable effect on the magnetic properties of these rare-earth transition metal materials. In order to improve the understanding of the behavior of Co and Fe in R 3 (Fe,TM) 29 (3:29) substituted alloys, several groups have stud- ied the replacement of Fe by Co in this system synthesized with various rare earths [1–9]. Generally, there has been successful attempts to synthesize the 3:29 phase with up to 40% replace- ment of Fe atoms for Co for almost all the rare earth atoms (R = Pr; M = Ti [3], R=Gd; M=Ti, Cr [4], R=Sm; M=Mo [5], R = Ce; M = Mo [6], R = Nd; M = Ti [7], R = Tb, Dy; M = V [8]; R=Y; M=V [9]). Many attempts to synthesize the 3:29 phase with higher Co content were unsuccessful. Recently, the formation of 3:29-type compounds with 100% Co has been ∗ Corresponding author at. Third Laboratory of Physics, Department of Physics, Aristotle University of Thessaloniki, 54 124 Thessaloniki, Greece. Tel.: +30 2310 998003; fax: +30 2310 998003. E-mail address: hsara@physics.auth.gr (C. Sarafidis). reported [6,10]. The formation of the 3:29 phase for more than 40% substitution of Fe by Co atom demands a large amount of stabilizing atom such as R = Gd, M = Cr with y = 4–7 [6] and R = Sm, M = Cr [10] with y = 4.5–7. For more than 40% Co for Fe substitution when the amount of the stabilizing atom is low (f.e. y = 1.5) a disordered variant of the hexagonal Th 2 Ni 17 -type structure is formed [11]. The structural and magnetic properties of these compounds are strongly affected by the Co content. The concentration dependence of the magnetocrystalline anisotropy in rare earth intermetallic compounds results from the differ- ent contributions to the magnetocrystalline anisotropy from the various transition-metal sites and the preferential occupation of Co atoms. The presence of a large amount of stabilizing atom, results to the magnetic dilution of the transition metal sublattice. However, in the case of high Co content substituted 3:29 compounds with R = Gd, M = Cr with y = 4–7 and R = Sm, M = Cr with y = 4.5–7 the desired change from planar to uniax- ial anisotropy has been observed [6,10]. The Nd 3 (Fe,Ti) 29 -type compounds crystallize in the monoclinic system with the A2/m space group [12]. In that structure the rare earth ion occupies two and the Fe atoms eleven crystallographic sites. In the case of Co atoms, neutron diffraction on Pr 3 (Fe 1-x Co x ) 27.5 Ti 1.5 (x = 0.1 0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.07.099