Unusual field dependence of the reversible magnetization in heavy ions irradiated thallium-based single crystals

Entropy, vortex interactions, and the phase diagram of heavy-ion-irradiatedBi2Sr2CaCuBeek1, Kończykowski2, Drost3 et al. 2000Phys. Rev. B403290View 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 ).…”

“…This extra contribution can be comparable to or larger than the pinning energy. Previously presented values of the pinning energy extracted from the reversible magnetization of crystals with relatively high matching fields [14][15][16]32 should thus be considered with reserve. More accurate measurements of the pinning energy for crystals with lower B φ were recently presented in Ref.…”

“…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). [14][15][16] The coincidence of the radius of the columnar defect core with that of the vortex core implies a large pinning force 21 and concommittantly large values of the critical current density, 5 as well as a large increase of the field H irr (T ) below which irreversible magnetic response is measured. 5 Second, the linear geometry of the ion tracks results in the effective alignment of the pancake vortices along the tracks, and the re-establishment of interlayer superconducting phase coherence at temperatures and fields where the unirradiated material behaves as a stack of nearly decoupled superconducting layers.…”

“…30 The importance of intralayer pancake repulsion is often downplayed, even though it has been shown to be important in determining the pancake arrangement, 31 reversible magnetization, 14,31 and transport properties. 31 It is the purpose of this paper to investigate the importance of the contributions of intra-and interlayer pancake vortex interaction energy, entropy, and pinning energy to the Gibbs free energy G, and the impact of each on the phase diagram of heavy-ion irradiated Bi 2 Sr 2 CaCu 2 O 8+δ .…”

“…[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).…”