Eur. Phys. J. B 49, 135-140 (2006)
https://doi.org/10.1140/epjb/e2006-00043-y

Lower critical field and intragrain critical current density in the ruthenate-cuprate RuSr₂Gd_1.5Ce_0.5Cu₂O₁₀

¹ Instituto de Física, Universidade Federal do Rio de Janeiro, C.P. 68528, RJ, 21941-972, Brazil
² Instituto de Física, Universidade Federal Fluminense, Niterói, RJ, 24210-340, Brazil
³ Laboratorio de Superconductividad, Facultad de Física-IMRE, Universidad de La Habana, San Lázaro y L, Ciudad de La Habana, 10400, Cuba

Corresponding author: ^a sgg@if.ufrj.br

Received: 19 August 2005
Revised: 16 November 2005
Published online: 17 February 2006

Abstract

The lower critical field of the grains, H_c1, and the intragrain critical current density, J_c, were determined for the superconducting ruthenate-cuprate RuSr₂Gd_1.5Ce_0.5Cu₂O_10-δ [Ru-1222(Gd)] through a systematic study of the hysteresis in magnetoresistance loops. A reliable method, based on the effects of the magnetization of the grains on the net local field at the intergranular junctions is provided, circumventing the problem of the strong masking of the superconducting diamagnetic signal by the ferromagnetic background. The temperature dependency of H_c1 and J_c both exhibit a smooth increase on cooling without saturation down to . The obtained H_c1 values vary between 150 and 1500 Oe in the 0.2 ≤ T/T_SC ≤0.4 interval, for samples annealed in an oxygen flow; oxygenation under high pressure (50 atm) leads to a further increase. These values are much larger than the previously reported rough assessments (25–50 Oe), using conventional magnetization measurements. High J_c values of ~10⁷ A/cm², comparable to the high-T_c cuprates, were obtained. The H_c1(T) and J_c(T) dependencies are explained in the context of a magnetic phase separation scenario.