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Phases with spontaneous time-reversal (T ) symmetry breaking are sought after for their anomalous physical properties, low-dissipation electronic and spin responses, and information-technology applications. Recently predicted altermagnetic phase features an unconventional and attractive combination of a strong T -symmetry breaking in the electronic structure and a zero or only weak-relativistic magnetization. In this work, we experimentally observe the anomalous Hall effect, a prominent representative of the T -symmetry breaking responses, in the absence of an external magnetic field in epitaxial thin-film Mn5Si3 with a vanishingly small net magnetic moment. By symmetry analysis and first-principles calculations we demonstrate that the unconventional d-wave altermagnetic phase is consistent with the experimental structural and magnetic characterization of the Mn5Si3 epilayers, and that the theoretical anomalous Hall conductivity generated by the phase is sizable, in agreement with experiment. An analogy with unconventional d-wave superconductivity suggests that our identification of a candidate of unconventional d-wave altermagnetism points towards a new chapter of research and applications of magnetic phases. The classification of magnets now includes altermagnets which possess opposite-spin sublattices connected by rotation and share some features with ferro- and antiferromagnets. Here the authors report the anomalous Hall effect in Mn5Si3 and interpret the results in terms of a d-wave altermagnetic phase. [ABSTRACT FROM AUTHOR]

Phases with spontaneous time-reversal ( T ) symmetry breaking are sought after for their anomalous physical properties, low-dissipation electronic and spin responses, and information-technology applications. Recently predicted altermagnetic phase features an unconventional and attractive combination of a strong T -symmetry breaking in the electronic structure and a zero or only weak-relativistic magnetization. In this work, we experimentally observe the anomalous Hall effect, a prominent representative of the T -symmetry breaking responses, in the absence of an external magnetic field in epitaxial thin-film Mn 5 Si 3 with a vanishingly small net magnetic moment. By symmetry analysis and first-principles calculations we demonstrate that the unconventional d-wave altermagnetic phase is consistent with the experimental structural and magnetic characterization of the Mn 5 Si 3 epilayers, and that the theoretical anomalous Hall conductivity generated by the phase is sizable, in agreement with experiment. An analogy with unconventional d-wave superconductivity suggests that our identification of a candidate of unconventional d-wave altermagnetism points towards a new chapter of research and applications of magnetic phases., (© 2024. The Author(s).)

The structure and stoichiometry of a new metal-free and ammonium-free compound [dabcoH 2 ] 2+ H 3 O + Br - 3 (where [dabcoH 2 ] 2+ = 1,4-di-aza-bicyclo-[2.2.2]octane dication) correspond to the general formula ABX 3 characteristic of perovskites. In enantiomorphic trigonal polymorph α of [dabcoH 2 ] 2+ H 3 O + Br - 3 , the corner-sharing [H 3 O]Br 6 octahedra combine into a 3D framework embedding [dabcoH 2 ] 2+ dications in pseudo-cubic cages. In the more dense polymorph β, the face-sharing [H 3 O]Br 6 octahedra form 1D polyanionic columns separated by [dabcoH 2 ] 2+ dications. These different topologies correlate with different crystal fields around the cations and their different disorder types: orientational disorders of [dabcoH 2 ] 2+ dications and H 3 O + cations in polymorph α and positional disorder of [H 3 O] + cations in polymorph β. The orientational disorder increases the lengths of OH⋯Br hydrogen bonds in polymorph α, but NH⋯Br distances of ordered dabcoH 2 dications are longer in polymorph β. The presence of polar [H 3 O] + cations in [dabcoH 2 ] 2+ H 3 O + Br - 3 polymorphs offers additional polarizability of the centres compared with analogous metal-free [dabcoH 2 ] 2+ [NH 4 ] + Br - 3 perovskite., (© Budzianowski et al. 2022.)