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Helical Antiferromagnetic Ordering in Lu{1-x}Sc{x}MnSi (x = 0, 0.25, 0.50)

Polycrystalline samples of Lu{1-x}Sc{x}MnSi (x= 0, 0.25, 0.50) are studied using powder x-ray diffraction (XRD), heat capacity Cp, magnetization M, magnetic susceptibility chi, and electrical resistivity rho measurements versus temperature T and magnetic field H. This system crystallizes in the primitive orthorhombic TiNiSi-type structure (space group Pnma) as previously reported. The rho(T) data indicate metallic behavior. The Cp(T), chi(T), and rho(T) measurements consistently indicate long-range antiferromagnetic (AF) transitions with AF ordering temperatures TN = 246, 215 and 188 K for x = 0, 0.025 and 0.50, respectively. A second transition is observed at somewhat lower T for each sample from the chi(T) and rho(T) measurements, which we speculate are due to spin reorientation transitions; these second transitions are completely suppressed in H = 5.5 T. The Cp data below 10 K for each composition indicate an enhanced Sommerfeld electronic heat capacity coefficient for the series in the range gamma = 24 to 29 mJ/mol K^2. The chi(T) measurements up to 1000 K were fitted by local-moment Curie-Weiss behaviors which indicate a low Mn spin S ~ 1. The chi data below TN are analyzed using the Weiss molecular field theory for a planar noncollinear helical AF structure with a composition-dependent pitch, following the previous neutron diffraction work of Venturini et al. [J. Alloys Compd. 256, 65 (1997)]. Within this model, the fits indicate a turn angle between Mn moments along the helix axis of ~100 degrees or ~145 degrees, either of which indicate dominant AF interactions between the Mn spins in the Lu{1-x}Sc{x}MnSi series of compounds.