Reduction in the electron density-of-states in superconducting MgB$_2$ disordered by $n^1$-irradiation: the $^{11}$B and $^{25}$Mg NMR estimates

NMR line shift and nuclear spin-lattice relaxation rate T − 1 1 of 11 B and 25 Mg were measured in superconducting MgB 2 ( T onsc =38K) structurally disordered by nuclear reactor neutrons up to the fluence of thermal neutrons Φ = 1 · 10 19 cm − 2 . The temperature of superconducting transition was shifted down to T onsc,irrad =7K under irradiation. The change due irradiation in the partial electron density of states (DOS) at the Fermi energy of boron and magnesium were traced by taking into account that T − 1 1 of 11 B and 25 Mg are determined by hyperfine magnetic interactions with carriers. It was revealed that electronic states near E F of Mg are influenced negligibly by irradiation whereas partial DOS of the B 2 p x,y states reduces greatly in irradiated MgB 2 . Acording to the Mc Millan formula, NMR data show that critical temperature decreases in irradiated MgB 2 mainly due to reduction in the partial DOS of p states of boron.