  In this letter, we report the discovery of a new class of spintronic
materials, namely spin semi-metals (SSM), employing both theoretical and
experimental tools. The band structure of this class of materials is such that
one of the spin bands resembles that of a semi-metal, while the other is
similar to that of an insulator/semiconductor. This report is the experimental
verification of the first SSM, FeRhCrGe, a quaternary Heusler alloy with a
magnetic moment 3 $\mu_B$ and a Curie temperature of 550 K. The measurement
below 300 K shows nearly temperature independent conductivity and a relatively
moderate Hall effect. SSM behavior for FeRhCrGe is also confirmed by rigorous
first principles calculations. Band structure calculations also reveal that the
spin up (semi metallic) band has combined features of type II Weyl and nodal
line semimetal. As such, this study opens up the possibility of a new class of
material with combined spintronic and topological properties, which is
important both from fundamental and applied point of view.

Materials Science