Equilibrium magnetization in heavy-ion-irradiatedBi2Sr2CaCu2

Entropy, vortex interactions, and the phase diagram of heavy-ion-irradiatedBi2Sr2CaCuBeek1, Kończykowski2, Drost3 et al. 2000Phys. Rev. BSelf Cite403290View full textAdd to dashboardCite

“…Reversible magnetization Figure 1 shows the reversible magnetization for an optimally doped Bi 2 Sr 2 CaCu 2 O 8+δ single crystal (T c = 88.8 K), 38 irradiated with 10 11 Pb ions cm −2 , which corresponds to a matching field B φ = 2 T. This value of B φ is comparable to that used in previous studies, [13][14][15][16][17] and the reversible magnetization shows all the features discussed there. Recapitulating, at low fields H irr < H a ≪ B φ , the absolute value of the magnetization |M rev | decreases more or less proportionally to ln(1/H a ), in rev (corrected for the reduction in superfluid density expressed bỹ λ −2 (T ) = (1 − 2πc 2 0 n d )λ −2 ).…”

“…For the crystal with B φ = 0.5 T, the low-and high field limits of ∂M rev /∂ ln B are nearly equal, implying that at this temperature, the entropy contribution to ∂M rev /∂ ln B lies within the error bar of 0.1k B T /Φ 0 s found in Section III A 2 (see also Ref. 17, Fig. 3).…”

“…The nonmonotonic field dependence of the reversible magnetization has a straightforward explanation in terms of the lowering of the vortex free energy by pinning onto the columnar defects. 15,17 The magnetization…”

“…At low B φ , T S remains small in comparison with other terms contributing to the free energy. This can also be inferred directly from the near-equality of the low-and high field limits of the logarithmic slope of the reversible magnetization for B φ < ∼ 0.5 T. 17,18 At high matching field, T S follows a logarithmic dependence on ion dose. We interpret this behavior as follows.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] The effect of the ion tracks is twofold. First, the destruction of superconductivity within the columnar defect core, the radius of which is comparable to the superconducting coherence length ξ, leads to a large reduction of the mixed state free energy [14][15][16][17][18] arising from the pinning of the two-dimensional pancake vortices in the superconducting layers 19,20 by the columns. The reduction in free energy due to pinning is readily measurable because it entails a significant reduction of the reversible magnetization M rev at fields well below the matching field B φ = Φ 0 n d , and a nonmonotonicity of ∂M rev /∂ ln B as function of B (Φ 0 = h/2e is the flux quantum and n d is the density of column intersections with the layers).…”