In this work we present electrical resistivity, magnetic susceptibility, and electron spin resonance data at high temperature of the ${\mathrm{Sr}}_2{\mathrm{FeMoO}}_6$ double perovskite. We found between 300 K and 900 K two metal-insulator transition temperatures at $T_c\approx 405$ K and $\approx 590$ K respectively. Below the first transition, the material is metallic and magnetically ordered. Above 590 K, $\rho$ shows a metallic behavior again, while in the range $405\mathrm{K}<~T<~590\mathrm{K}$ we observed a weak localization. The magnetic susceptibility can be described taking into account localized and itinerant electrons. The paramagnetic resonance of ${\mathrm{Fe}}^{3+}$ ions with $g=2.009\mathrm{}\left(5\right)\mathrm{}$ can be studied in temperature. Above $T_c$ the linewidth data present similar behavior to that of manganese perovskites, with a relaxation mechanism related to spin-spin interactions. The intensity of the resonance line decreases with T faster than a Curie law expected, due to a reduction in the number of localized spins of the ${\mathrm{Fe}}^{3+}$ ions. At high temperatures $(T>~520$ K) we observe a second paramagnetic resonance line with $g=1.995\mathrm{}\left(1\right)\mathrm{}$ associated with a small amount of ${\mathrm{Mo}}^{5+}$ ions.

• Received 29 December 1999

DOI:https://doi.org/10.1103/PhysRevB.62.3340