Anisotropic magnetization properties of an NdBa₂Cu₃O_7-δ single crystal

The magnetization properties of a flux-grown NdBa₂Cu₃O_7-δ (Nd123) single crystal were investigated by measuring DC magnetization hysteresis (M-H) loops in a wide temperature range (10-92 K) and for applied fields parallel (H ∥ c) and perpendicular (H ∥ a-b) to the c-axis of the sample. For both field directions, temperature-dependent fishtail peaks in the M-H loops are clearly observed at high temperatures above 70 K, and all the data could be scaled to a single master curve with the hysteresis loop width ΔM versus H plot when they are normalized with the peak field H_pk and its magnetization value ΔM_pk, respectively. This indicates that the origins of the peak effect and the pinning are identical for this temperature range. We have also found that H_pk and the irreversibility field H_irr scale with the reduced temperature, t = T/T_c (T_c: critical temperature), and follow the relationship H_irr ∝ (1 - t)ⁿ with a power n of 1.1-1.3. The anisotropy parameters γ_pk of H_pk (≅ 6.8) and γ_irr of H_irr (≅ 4.7) were deduced from the angular dependence of H_pk and H_irr at 88 K. We emphasize that all the present results support our proposal that the peak effect in the Nd123 originates from the localized Nd-Ba substituted regions with depressed T_c.