Peak Effects in 2H-NbSe2 Single Crystals Induced by Particle Irradiations

Effects of three kinds of columnar defects in NbSe2 single crystals introduced by 320 MeV Au irradiation with a dose equivalent matching field B-Phi up to 4 T were studied. Through the magnetization measurement using a SQUID magnetometer, two pronounced peak effects in the external field dependence of critical current density (J(c)) were observed in crystals introduced with splayed and tilted columnar defects. In crystals with splayed columnar defects, J(c) at the peak field reaches the maximum for splay angle theta(CD) = +/- 10 degrees, which is a little different from that found in YBa2Cu3O7 and iron-based superconductors, where optimal. theta(CD) is equal to +/- 5 degrees.