This article presents the annealing effect on the structural, elastic, thermodynamic, optical, magnetic, and electric properties of Ni _0.6 Zn _0.4 Fe _1.5 Al _0.5 O ₄ (NZFAO) nanoparticles (NPs).

Phases with spontaneous time-reversal ( $${{{{{{{\mathcal{T}}}}}}}}$$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 $${{{{{{{\mathcal{T}}}}}}}}$$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 $${{{{{{{\mathcal{T}}}}}}}}$$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.

A scheelite crystal with residual concentration of erbium is cooled down to 10 mK, yielding a record spin coherence time of 23 ms.