  The response in capacitance to low external magnetic fields (up to 0.1 T) of
suspensions of spherical magnetic nanoparticles, single-wall carbon nanotubes
(SWCNT), SWCNT functionalized with carboxyl group (SWCNT-COOH) and SWCNT
functionalized with Fe$_3$O$_4$ nanoparticles in a nematic liquid crystal has
been studied experimentally. The volume concentration of nanoparticles was
$\phi_1$ = 10$^{-4}$ and $\phi_2$ = 10$^{-3}$. Independent of the type and the
volume concentration of the nanoparticles, a linear response to low magnetic
fields (far below the magnetic Fr\'eederiksz transition threshold) has been
observed, which is not present in the undoped nematic.
