  We study the magnetic susceptibility in various three-dimensional gapless
systems, including Dirac and Weyl semimetals and a line-node semimetal. The
susceptibility is decomposed into the orbital term, the spin term and also the
spin-orbit cross term which is caused by the spin-orbit interaction. We show
that the orbital susceptibility logarithmically diverges at the band touching
energy in the point-node case, while it exhibits a stronger delta-function
singularity in the line node case. The spin-orbit cross term is shown to be
paramagnetic in the electron side while diamagnetic in the hole side, in
contrast with other two terms which are both even functions in Fermi energy.
The spin-orbit cross term in the nodal semimetal is found to be directly
related to the chiral surface current induced by the topological surface modes.
