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The synthesis and crystallographic and physical properties of polycrystalline EuNiGe3 are reported. EuNiGe3 crystallizes in the noncentrosymmetric body-centered tetragonal BaNiSn3-type structure (space group I4mm), in agreement with previous reports, with the Eu atoms at the corners and body center of the unit cell. The physical property data consistently demonstrate that this is a metallic system in which Eu spins S = 7/2 order antiferromagnetically at a temperature TN = 13.6 K. Magnetic susceptibility χ data for T > TN indicate that the Eu atoms have spin 7/2 with g = 2, that the Ni atoms are nonmagnetic, and that the dominant interactions between the Eu spins are ferromagnetic. Thus we propose that EuNiGe3 has a collinear A-type antiferromagnetic structure, with the Eu ordered moments in the ab-plane aligned ferromagnetically and with the moments in adjacent planes along the c-axis aligned antiferromagnetically. A fit of χ(T ≤ TN) by our molecular field theory is consistent with a collinear magnetic structure. Electrical resistivity ρ data from TN to 350 K are fitted by the Bloch-Grüneisen model for electron-phonon scattering, yielding a Debye temperature of 265(2) K. A strong decrease in ρ occurs below TN due to loss of spin-disorder scattering. Heat capacity data at 25 K ≤ T ≤ 300 K are fitted by the Debye model, yielding the same Debye temperature 268(2) K as found from ρ(T ). The extracted magnetic heat capacity is consistent with S = 7/2 and shows that significant short-range dynamical spin correlations occur above TN. The magnetic entropy at TN = 13.6 K is 83% of the expected asymptotic high-T value, with the remainder recovered by 30 K.

Polycrystalline samples of Lu1−xScxMnSi (x = 0, 0.25, 0.5) are studied using powder x-ray diffraction, heat capacity Cp, magnetization, magnetic susceptibility χ, and electrical resistivity ρ 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 ρ(T ) data indicate metallic behavior. The Cp(T ), χ(T ), and ρ(T ) measurements consistently indicate longrange antiferromagnetic (AF) transitions with AF ordering temperatures TN = 246, 215 and 188 K for x = 0, 0.25 and 0.5, respectively. A second transition is observed at somewhat lower T for each sample from the χ(T ) and ρ(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 γ = 24-29 mJ/mol K 2 . The χ(T ) measurements up to 1000 K were fitted by local-moment Curie-Weiss behaviors which indicate a low Mn spin S ∼ 1. The χ data below TN are analyzed using the Weiss molecular field theory for a planar noncollinear cycloidal 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 ordered moments along the cycloid axis of ∼ 100• or ∼ 145• , either of which indicate dominant AF interactions between the Mn spins in the Lu1−xScxMnSi series of compounds.

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