Collinear antiferromagnetism in trigonal SrMn₂As₂revealed by single-crystal neutron diffraction

Abstract

Iron pnictides and related materials have been a topic of intense research for understanding the complex interplay between magnetism and superconductivity. Here we report on the magnetic structure of SrMnAs that crystallizes in a trigonal structure ([Formula: see text]) and undergoes an antiferromagnetic (AFM) transition at [Formula: see text] K. The magnetic susceptibility remains nearly constant at temperatures [Formula: see text] with [Formula: see text] whereas it decreases significantly with [Formula: see text]. This shows that the ordered Mn moments lie in the [Formula: see text] plane instead of aligning along the [Formula: see text]-axis as in tetragonal BaMnAs. Single-crystal neutron diffraction measurements on SrMnAs demonstrate that the Mn moments are ordered in a collinear Néel AFM phase with [Formula: see text] AFM alignment between a moment and all nearest neighbor moments in the basal plane and also perpendicular to it. Moreover, quasi-two-dimensional AFM order is manifested in SrMnAs as evident from the temperature dependence of the order parameter.

Antiferromagnetism in semiconductingSrMn2Sb2andBaMn2Sb2single crystals

“…Single-crystal neutron diffraction measurements on trigonal SrMn 2 As 2 showed that the Mn moments are ordered in the ab plane in a collinear Néel AFM structure below T N = 118(2) K [51] and magnetic susceptibility data exhibited quasi-2D behavior at T T N [30], as does ThCr 2 Si 2 -type BaMn 2 As 2 as noted above. SrMn 2 P 2 exhibits a novel pressure-induced structural transition from the trigonal CaAl 2 Si 2 -type to the body-centered-tetragonal ThCr 2 Si 2 -type structure [58].…”

Metallic behavior induced by potassium doping of the trigonal antiferromagnetic insulatorEuMn2As2

“…The χ(T ) and M (H) data suggest that the AFM structure of the Eu spins is a noncollinear, noncoplanar structure. AFM ordering of the Mn spins in EuMn 2 As 2 is inferred from the high-T χ(T ) and C p (T ) data which indicate that the Mn Néel temperature is T N = 142 K. Although our measurements yield no information on the AFM structure of the Mn spins below their T N , we note that the Mn spins in the very similar SrMn 2 As 2 compound have a collinear AFM structure with the easy axis aligned within the ab plane [50]. We see no clear evidence from M (H) isotherms between 2 and 20 K of metamagnetic transitions in EuMn 2 As 2 in fields up to 14 T.…”

“…Both compounds are AFM semiconductors with T N = 62 K and 120 K, respectively [49,50]. A previous study of SrMn 2 As 2 single crystals found T N = 125 K [51].…”

“…The anisotropic magnetic susceptibility versus temperature χ(T ) data for both compounds indicate that the easy plane for AFM ordering of the Mn +2 spins S = 5/2 is the hexagonal ab plane [49]. Neutron diffraction measurements of SrMn 2 As 2 revealed that the Mn spins exhibit collinear AFM ordering in the ab plane with propagation vector k = (0, 0, 0), i.e., the AFM and chemical unit cells are the same [50]. The χ(T ) and neutron diffraction studies together indicate that the magnetism is quasi-twodimensional with strong AFM correlations surviving to at least 900 K.…”

Itinerant G-type antiferromagnetic order inSrCr2As2

“…These results are qualitatively similar to those in BaCr 2 As 2 [22] but distinctly different from those of other SrT 2 As 2 (T = Mn, Fe, Co) compounds. Specifically, SrMn 2 As 2 does not crystallize in a tetragonal I4/mmm space group but forms a trigonal lattice with collinear AFM structure [18], SrFe 2 As 2 undergoes a first order structural transition from tetragonal to an orthorhombic AFM phase at low temperatures [38] and SrCo 2 As 2 is non-magnetic with I4/mmm crystal symmetry but undergoes a pressure-induced cT phase [28]. Figure 5 shows the temperature dependence of the integrated intensity (I M ) of the (1 0 1) Bragg peak, which is a measure of the magnetic moment.…”