Helical antiferromagnetic ordering inLu1−xScxMnSi

Abstract

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.

Unified molecular field theory for collinear and noncollinear Heisenberg antiferromagnets

“…and B ′ S (y) is given in Eq. (11). Equation (188b) is applicable to the entire PM region of the (h, t) phase diagram in Fig.…”

“…1 of Ref. 11. Like Van Vleck's theory, Yoshimori's predictions were very restrictive and have been little used by experimentalists to fit their χ(T ≤ T N ) data for helical or cycloidal AFs.…”

EuCo2P2: A model molecular-field helical Heisenberg antiferromagnet

“…Parameters γ and β obtained by fitting the zerofield Cp(T ) data of EuCo2P2 and BaCo2P2 in the temperature range 1.8 to 5 K by Eq (6)…”

Molecular-field-theory fits to magnetic susceptibilities of antiferromagnetic GdCu2Si2, CuO, LiCrO2, and alpha-CaCr2O4 single crystals below their Neel temperatures

“…[1], in addition to the coplanar noncollinear antiferromagnet GdB 4 noted above, the anisotropy in χ(T ≤ T N ) of the collinear antiferromagnets GdNiGe 3 and MnF 2 and of the coplanar noncollinear triangular 120 • antiferromagnets YMnO 3 and RbCuCl 3 were fitted within the unified MFT. Comparisons were also carried out of the powder-averaged MFT predictions with measured χ(T < T N ) data for polycrystalline samples with inferred collinear and noncollinear AF structures [9][10][11][12][13][14]. More recently, the anisotropic susceptibilities below T N of single crystals of the helical antiferromagnets EuCo 2 P 2 [15], EuCo 2 As 2 [16], EuNi 2 As 2 [17], and EuMg 2 Bi 2 [18] were successfully modeled by the MFT.…”