Nd₃(Fe,Ti)₂₉-type structure, widely studied during the last years, consists of a combination of Th₂Zn₁₇ (2:17) rhombohedral and ThMn₁₂ (1:12) tetragonal segments in a ratio of 1:1. The existence of this composition indicates that more intermediate phases should be possible: e.g. a ratio 1:2 resulting to a 4:41 phase. The synthesis of a new phase with nominal composition Tb₄(Fe,Si)₄₁ has been recently reported [1]. In a previous work we have investigated the alloys with starting nominal composition R₄(Fe,Ti)₄₁ (R=Nd, Er; T=Ti, V) [2]. In this work we extend the previous study for the R₄(Co,Ti)₄₁ alloys (R=Gd, Pr, Sm). Alloys with starting composition R₄(Co1-xTix)₄₁ (x=0.037, 0.051, 0.061) were prepared and annealed in the temperature interval of 1133-1438 K. Thermomagnetic analysis (TMA) for the samples annealed at 1133 K showed one magnetic transition at 1025 K and 1058 K respectively for Gd (x=0.051) and Pr (x=0.037) which, according to the X-ray spectra, correspond to the disordered CaCu₅-type structure. The saturation magnetization, MS, of the first samples is 77.3 Am²/kg at room temperature and both exhibit uniaxial anisotropy. The Gd₄(Co,Ti)₄₁ (x=0.051) alloy annealed at 1438 K crystallizes into the disordered 2:17 hexagonal phase with cell parameters a=8.350(1) and c=8.224(1) angstrom. In contrary, the Pr₄(Fe,Ti)₄₁ samples annealed at 1438 K crystallize into the rhombohedral 2:17R-type structure. The study of the magnetic properties and of the microstructure of this series is in progress and will be reported.

1. Ivanova, G.M. Makarova, Ye.V. Shcherbakova and Ye.V. Belozerov, J. Alloys Compounds 309 (2000) 141.

2. M. Gjoka, D. Niarchos, C. Sarafidis and O. Kalogirou, Proceedings of 17th International Workshop on Rare-Earth Magnets and their Applications, pp. 216-220 (2002).

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