  We show that in some trigonal and hexagonal crystals the Zeeman coupling of
band electrons with an external magnetic field is strongly anisotropic and
necessarily vanishes along the main symmetry axis. This leads to qualitative
changes in the temperature dependence of the electron spin susceptibility in
the superconducting state. In particular, the power-law exponents at low
temperatures due to the contribution of the nodal quasiparticles are
considerably modified compared to their textbook values.
