  Recently, a new class of magnetic phenomenon, called altermagnetism, was
proposed where the underlying spin configuration resembles antiferromagnetic
structure, but the system violates \textbf{PT} (PT: Parity times Time reversal)
symmetry due to the alternation of crystalline symmetry across magnetic ions.
Although the original idea was proposed for the collinear spin structure, a
recent report by Cheong et al. has suggested that antiferromagnetic materials
with non-collinear spin structure and local alternation of crystalline
arrangement can also manifest altermagnetism. Besides breaking the \textbf{PT}
symmetry, altermagnetic compounds are also expected to exhibit anomalous Hall
effects of odd orders. Here, we discuss possible candidates in this regard. One
example is nickel monosilicide, which was recently shown to exhibit high
temperature antiferromagnetism with non-collinear spin structure. It fulfills
both criteria of breaking the \textbf{PT} symmetry and manifesting nonlinear
anomalous Hall effect. In addition to NiSi, we also discuss other potential
antiferromagnetic materials with non-collinear spin configuration for the
exploration of altermagnetic states.
