Magnetic scattering effects in two-band superconductor : the ferromagnetic dopants in MgB2

This paper demonstrates the magnetic scattering effects on the electron–phonon interaction in two-band superconductors based on the transition-metal-doped MgB2 to clarify the effects of magnetic dopants on multi-band superconductivity. The phonon properties of polycrystalline Mg1−xMxB2 (M = Fe, Ni and Co), with x up to 0.05, were studied, with the investigation based on the normal state Raman spectra, especially the variation of the E2g mode. The magnetic scattering effect of Fe is much weaker than that of Mn in MgB2, while it is stronger than that of Ni. The weak magnetic scattering effects are responsible for the superconducting behaviors of Mg1−xFexB2 and Mg1−xNixB2. Co shows almost no magnetic scattering effects on the superconductivity, while the depression of the critical temperature, Tc, in Mg1−xCoxB2 is attributed to the phonon behavior and is independent of the ferromagnetic nature of cobalt.