Possible percolation and magnetoresistance in ordered double perovskite alloys Sr2Fe(W1-xMox)O6

Electronic properties including magnetoresistance have been investigated for polycrystals of ordered double perovskite alloy, (SrFe)-Fe-2(W1-xMox)O-6. Tn this system, the ground state changes from an antiferromagnetic insulator to a ferromagnetic metal with increasing x. The magnetization in Sr2Fe(W1-xMox)O-6 develops by the minimal substitution of W by Mo, and then the conductivity as well as the density of states at the Fermi level grows rapidly with x above 0.25. The present alloy also shows a variety of magnetoresistance behaviors. For example, Sr2Fe(W0.4Mo0.6)O-6 (x = 0.6) exhibits a magnetoresistance (MR) at 4.2 and 300K as large as 69 and 10%, respectively. Furthermore, Sr2Fe(W0(.85)Mo(0.15))O-6 (x = 0.15), located near the insulator-metal phase boundary, shows an extremely large magnetoresistance as large as 195% at 16 K. The low-field MR can be ascribed to a held suppression of the spin-dependent scattering at the grain or domain boundaries. (C) 2000 Elsevier Science B.V. All rights reserved.