The effect of nano-diamond additives on the enhancement of critical current density and related performance of bulk MgB₂

We report the synthesis, high-resolution micro-structure, magneto-transport and magnetization of nano-diamond doped MgB₂-nD_x with x ≤ 0.0-0.1. The superconducting transition temperature (T_c) is not affected by x up to x ≤ 0.05, indicating that the added nano-diamond (1) does not decompose to C and (2) does not partially substitute for B in MgB ₂. R(T) versus H measurements show higher T_c values under the same applied magnetic field for the nano-diamond added samples, resulting in higher estimated H_c2 values. Isothermal magnetization measurements show that above 2T, the critical current density (j_c) is of the order of 10⁵Acm^-2 for the pristine sample. j_c is further increased to three times for 3% nano-diamond doped samples. High-resolution transmission electron microscopy (HRTEM) observations clearly show the dispersion of nano-diamond particles, with an average particle size of 8-10nm, in the MgB₂ matrix. It seems likely that the dispersed nano-diamond particles of below 10 nm in size are acting as effective pinning centres responsible for improving the superconducting performance of the parent MgB₂.