  The ability to break Kirchhoff s law is of fundamental importance in thermal
radiation. Various nonreciprocal emitters have been proposed to break the
balance between absorption and emission. However, the thicknesses of the
nonreciprocal materials are usually larger than 1/10 times of the wavelength.
Besides, the previous proposed nonreciprocal emitters are complex, thus they
can hardly be fabricated in experiment to verify the Kirchhoff s law for
nonreciprocal materials. In this paper, we investigate the nonreciprocal
thermal radiation of the magnetic Weyl semimetal (MWSM) film atop of the metal
substrate. It is found that the strong nonreciprocal radiation at the
wavelength of 9.15 {\mu}m can be achieved when the thickness of the MWSM film
is 100 nm. The enhanced nonreciprocity is attributed to the Fabry-Perot
resonances. The results indicate that the MWSM film is the promising candidate
to engineer the ultrathin and simple nonreciprocal thermal emitters. What is
perhaps most intriguing here is that the proposed structure can be more easily
fabricated in experiment to verify the Kirchhoff s law for nonreciprocal
materials.
