Effect of the itinerant electron density on the magnetization and Curie temperature of Sr2FeMoO6 ceramics

Abstract

The itinerant electron density (n) near the Fermi level has a close correlation with the physical properties of Sr₂FeMoO₆. Two series of single-phase Sr_(2−y)Na_yFeMoO₆ (y = 0.1, 0.2, 0.3) and Sr_(2−y)Na_yFe_(1−x)Mo_(1+x)O₆ (y = 2x; y = 0.1, 0.2, 0.3) ceramics were specially designed and the itinerant electron density (n) of them can be artificially controlled to be: n = 1 − y and n = 1 − y + 3x = 1 + 0.5y, respectively. The corresponding crystal structure, magnetization and the ferromagnetic Curie temperature (T_C) of two subjects were investigated systematically. The X-ray diffraction analysis indicates that Sr_(2−y)Na_yFeMoO₆ (y = 0.1, 0.2, 0.3) have comparable Fe/Mo anti-site defect (ASD) content in spite of decreased n. However, a drastically improved Fe/Mo ASD can be observed in Sr_(2−y)Na_yFe_(1−x)Mo_(1+x)O₆ (y = 2x; y = 0.1, 0.2, 0.3) caused by the intrinsic wrong occupation of normal Fe sites with excess Mo. Magnetization–magnetic field (M–H) behavior confirms that it is the Fe/Mo ASD not n that dominantly determines the magnetization properties. Interestingly, approximately when n ≤ 0.9, T_C of Sr_(2−y)Na_yFeMoO₆ (y = 0.1, 0.2, 0.3) exhibits an overall increase with decreasing n, which is contrary to the T_C response in electron-doped SFMO. Such abnormal T_C is supposed to relate with the ratio variation of n(Mo)/n(Fe). Moreover, when n ≥ 1, T_C of Sr_(2−y)Na_yFe_(1−x)Mo_(1+x)O₆ (y = 2x; y = 0.3) exhibits a considerable rise of about 75 K over that of Sr_(2−y)Na_yFe_(1−x)Mo_(1+x)O₆ (y = 2x; y = 0.1), resulting from improved n caused by introducing excess Mo into Sr_(2−y)Na_yFeMoO₆. Maybe, our work can provide an effective strategy to artificially control n and ferromagnetic T_C accordingly, and provoke further investigation on the FeMo-baseddouble perovskites.