Magnetic structure of R2CoGa8 (R = Gd, Tb, and Dy): Structural tuning of magnetic properties in layered Ga-based intermetallic compounds

In this work we have determined the magnetic structure of R2CoGa8 (R = Gd, Tb, and Dy) intermetallic compounds using x-ray resonant magnetic scattering in order to study the evolution of the anisotropic magnetic properties along the series for R = Gd-Tm. The three compounds have a commensurate antiferromagnetic spin structure with a magnetic propagation vector (tau) over right arrow = (1/2, 1/2, 1/2) and a Neel temperature of approximately 20, 28.5, and 15.2 K for R = Gd, Tb, and Dy, respectively. The critical exponent beta obtained from the temperature dependence of the magnetic peaks suggest a three-dimensional universality class for the three compounds. Comparing the simulated and integrated intensities we conclude that the magnetic moment direction is in the ab plane for the Gd2CoGa8 compound and parallel to the c axis for the Tb2CoGa8 and Dy2CoGa8 compounds. The evolution of the magnetic properties of the R2CoGa8 series for R = Gd-Tm is discussed taking into account the indirect Ruderman-Kittel-Kasuya-Yoshida interaction and crystalline-electric field effects. The comparison between the reported magnetic properties of the Ga-based compounds with those for the In-based isostructural family reveals differences in their exchange couplings that contribute to the understanding of the role of the f-electronmagnetism in these classes of materials. (AU)