The magnetostriction of the off-stoichiometric R2Fe17-type intermetallic compounds based on R2Fe14−xCoxSi2 (R=Y, Er, Tm and x=0, 4) was measured, using the strain gauge method in the temperature range 77–460 K under applied magnetic fields up to 1.5 T. All compounds show sign change and reduction in magnetostriction values compared to the R2Fe17 compounds by Si substitution. For Y2Fe14Si2 and Er2Fe14Si2, saturation behaviour is observed near magnetic ordering temperature (TC), whereas for Tm2Fe14Si2, saturation starts from T>143 K. Also, Co substitution has different effects on the magnetostriction of R2Fe14Si2 compounds. In Er2Fe10Co4Si2 and Tm2Fe10Co4Si2, saturation occurs below the spin reorientation temperature (TSR). In addition, in Er2Fe14Si2, a sign change occurs in the anisotropic magnetostriction (Δλ) as well as the volume magnetostriction (ΔV/V) at their TSR values. The volume magnetostrictions of the Tm-containing compounds show an anomaly around their TSR. In R2Fe14Si2 compounds, parastrictive behaviour is also observed in ΔV/V near their TC values. In addition, the magnetostriction of the sublattices is investigated. Results show that in R2Fe14Si2 compounds, the rare-earth sublattice contribution to magnetostriction is negative and comparable to the iron sublattice, whereas, in R2Fe10Co4Si2 compounds, the rare-earth sublattice contribution is positive and larger than Fe sublattice. These results are discussed based on the effect of Si and Co substitutions on the anisotropy field of these compounds. Influence of the spin reorientation transition on the magnetostriction of these compounds is discussed in terms of the anisotropic sublattice interactions.

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