The paramagnetic photon. Absence of perpendicular component and decay in large fields

Previous results from the authors concerning the arising a tiny photon anomalous paramagnetic moment $\mu_{\gamma}$ due to its interaction with a magnetized virtual electron-positron background are complemented and discussed. It is argued that such magnetic moment it cannot be a linear function of the angular momentum and that there is no room for the existence of an hypothetical perpendicular component, as recently claimed in the literature. It is discussed that in the region beyond the first threshold, where photons may decay in electron-positron pairs, the photon magnetic moment cannot be defined independently of the magnetic moment of the created pairs. It is shown that for magnetic fields large enough, the vacuum becomes unstable and decays also in electron-positron pairs.