Hydrogen ordering and magnetic transitions in YyTb1-yH(D)(x) (y = 0.9 and 0.2)

We have measured the electrical resistivity in the range 1.5-300 K of the h ydrogenated alloy system YyTb1-yH(D)(x), for y = 0.9 and 0.2, and for hydro gen concentrations 0 less than or equal to x less than or equal to 0.25. It is found that, in the case y = 0.9, hydrogen forms alpha*-solid solutions up to concentrations x(max)(alpha)*=0.21(1). Like in binary alpha*-YHx, one observes ordering in the H sublattice near 170 K; a correlation between th e periodicity of the helical antiferromagnetic (AF) structure in this alloy and that of the modulated chainlike H-H pair configuration in the ordered H sublattice is noted. For y = 0.2, hydrogen precipitates at once as dihydr ide, which is, e.g., seen through the emergence of an H-dependent peak at 1 0 K due to the AF transition of beta-TbH2; the same is also noted, for x>x( max)(alpha)* in the case y = 0.9. Hydrogen influences the various magnetic structures present by generally weakening the Ruderman-Kittel-Kasuya-Yosida polarization interaction. Thus, H addition results in a decrease of the sp in-disorder scattering and of the magnetic manifestations at T-N(Tb) and T- C(Tb). The low-T intrinsic resistivities are analyzed in terms of various t ypes of spin-wave spectra for the two alloys and their interaction with hyd rogen. [S0163-1829(99)10513-7].