Reference: T. Sau, P. Yadav, S. Sharma, R. Raghunathan, P. Manuel, V. Petricek, U. P. Deshpande, N. P. Lalla, PHYSICAL REVIEW B (2021) 103 144418 DOI: 10.1103/PhysRevB.103.144418 Atomic positions from: same reference
Other magnetic phase at higher temperatures, between 192K and 37K (see #0.696).
Non-standard parent setting Pbnm
This structure was refined and reported under the MSG P2_1'2_1'2_1 in its standard setting related according to: b,c,a;1/2,0,0, with respect to the Pbnm parent setting. All small parameters with very large errors in a first fit were constrained to zero.
The structure has in fact a larger symmetry described by the MSG Pn'm'a (Pbn'm' in the parent setting), the same MSG as in the structure reported at 25K (see #0.697). Therefore the claim of a symmetry breaking transition between this temperature and 1.5K is not supported by the structure being reported.
Here we describe the structure under its correct MSG, keeping the parent setting.
FM along a (Pbnm setting)
Contrary to the statement in the paper, this structure is NOT polar
A second model under the MSG Pn'a2_1' (standard setting: -b,a,c;0,0,0 with respect to the Pbnm seeting) is reported to fit the data nearly equally well. This second model however suffers the same defect: its actual symmetry is given again by the higher MSG Pn'm'a (Pbn'm' in the parent setting), as the only degree of freedom breaking this symmetry is constrained to zero, after showing a negligible value in an unconstrained fit. This assumedly alternative second model is in fact essentially equivalent to the first one described here, except for the small non-zero my component of the Cr moment, which was constrained to zero in the supposedly alternative model.
See #0.478 for a different structure at 2K, which has been proposed for the same phase. This alternative model has a different MSG not allowing FM.