  Employing the state-of-the-art Density Functional Theory with both GGA and
hybrid HSE06 functional along with the incorporation of spin-orbit coupling, we
have engineered stable room temperature ferromagnetism in non-magnetic LaH$_3$
through C substitution at octahedral and tetrahedral H sites where the induced
magnetic moment is mostly contributed by 2p orbital of C atom. It is
interesting that the magnetic signature is switched on with an impurity
concentration as low as 1.04 at% with a magnetic moment of $\approx$ 1.0
$\mu_B$ per impurity, where the localized behavior of the 2p states of C along
with significant exchange splitting energy can be attributed as the origin of
the induced magnetic moment. The verification of the Stoner criterion in the
material further confirmed the onset of ferromagnetism in the system, and the
computed Curie temperature is found to be well above room temperature. Reduced
formation energy and requirement of lower impurity concentration ensure
practical feasibility towards a spintronic device where room temperature
ferromagnetism is established from the non-magnetic host and the dopant.
