We have prepared pyrolytic carbon samples from triethylamine and investigated their yields and magnetic properties. Ferromagnetic samples were obtained from the pyrolysis products even at room temperature. The yield of the ferromagnetic sample was increased by setting a magnetic circuit on the pyrolysis chamber. The magnetic field seemed to affect the triethylamine vapor and then increased the yield and the magnetization. Also, the synchrotron X-ray diffraction experiments were performed for these pyrolytic carbon samples. Diffraction peaks of iron or iron oxides were not observed for the ferromagnetic samples, whereas the major diffraction peaks of the intermediate graphite-diamond (IGD) structure were observed for the ferromagnetic samples. The best magnetization sample also showed the diffraction peaks of the diamond-like-carbon structure. Therefore, the magnetic field may help to form a three-dimentional ferromagnetic structure in pyrolytic carbon.