Magnetoresistance (MR) measurements up to 50 T have been performed in the half-metallic polycrystalline ${\left({\mathrm{Ba}}_{0.8}{\mathrm{Sr}}_{0.2}\right)}_2{\mathrm{FeMoO}}_6$ double perovskite in the temperature range 4.2 K–350 K. At temperatures far below $T_C(=345\mathrm{K})$ the MR is only due to intergrain MR and has allowed us to extract useful information on the spin-dependent transport process as well as the magnetic nature of the grain boundaries. In sharp contrast with the linear behavior of the intergrain magnetoconductance up to 50 T reported on half-metallic manganites and magnetite, the intergrain magnetoconductance of ${\left({\mathrm{Ba}}_{0.8}{\mathrm{Sr}}_{0.2}\right)}_2{\mathrm{FeMoO}}_6$ tends to saturate at high fields. Our experimental results can be understood within the framework of the Inoue and Maekawa model for intergranular MR but using the magnetic state of the grain boundary as the relevant parameter instead of the bulk magnetic state. Detailed analysis of the field dependence of the MR points to a spin-glass magnetic state of the grain boundary.

• Received 21 October 2004

DOI:https://doi.org/10.1103/PhysRevB.71.104409