Influences of Co on structural and magnetic properties of R3(Fe1-xCox)29-yMy (R = rare earth metal, M = transition metal) intermetallic compounds

Orestis Kalogirou 1Charalambos Sarafidis 1Konstantinos G. Efthimiadis 1Margaritis Gjoka 2

1. Dept. of Physics, Aristotle University of Thessaloniki, 54 124 Thessaloniki, Greece, Thessaloniki 54 124, Greece
2. Institute of Materials Science, NCSR “Demokritos”, 153 10 Ag. Paraskevi, Attiki, Greece, Athens 153 10, Greece

Abstract

The Nd3(Fe,Ti)29-type intermetallic compounds (3:29) crystallise in the A2/m space group and consist of 2:17R-type and 1:12-type segments in a ratio 1:1. The study of the effect of Co substitution on the structural and magnetic properties of R3(Fe1-xCox)29-yMy (R = Y, Nd, Tb, Dy; M = Ti, V, Cr, Mn; 0≤x≤1; y=0.9-7.0) is presented. For the compounds with low Co content (0≤x≤0.4) the unit cell volume is decreasing as the Co content increases. 57Fe Mössbauer spectroscopy has shown that the Co atoms avoid those Fe sites shared with the Ti atoms, i.e., the dumb-bell sites. The Curie temperature values, TC, increase monotonically with x. For the compounds with high Co content (0.6≤x≤1) the situation is rather different. Starting with the 3:29 stoichiometry [Tb3(Fe1-xCox)27.4V1.6 and Dy3(Fe1-xCox)27.8V1.2; x= 0.6, 0.8, 1.0] a disordered variant of the hexagonal Th2Ni17-type structure is formed. In Y3(Fe1-xCox)29-yCry the monoclinic 3:29 structure is retained if the amount of the stabilizing element is increased. The lattice parameters are changing in a constant manner with the increase of Co showing that the replacement of Co for Fe is a continuous procedure. The change in the monoclinic angle shows an interesting difference compared to the compounds with x<0.3; it increases with Co indicating that high Co concentration (x>0.3) is pushing the structure to its limit. The TC values of the compounds are reduced; this should be attributed to the larger Cr content. The same behavior was observed in the case of Nd based products with 0.6≤x≤1. The TC values present a considerable difference (more than 100 K for x=0.6). Preliminary studies show that in the Nd3(Fe1-xCox)29-yCry samples the main phase is a rhombohedral Th2Zn17-type structure. In all cases the considerable effect of Co substitution on the magnetocrystalline anisotropy will be discussed.

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Presentation: invited oral at E-MRS Fall Meeting 2005, Symposium B, by Orestis Kalogirou
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-05-04 08:12
Revised:   2009-06-07 00:44
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