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 y FeMoO6 (y = 0.1, 0.2, 0.3) and Sr(2-y)Na y Fe(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 y FeMoO6 (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 y Fe(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 y FeMoO6 (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 y Fe(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 y Fe(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 y FeMoO6. 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.
ABSTRACT
The spin-phonon coupling and the effects of strain on the ground-state phases of artificial SrMnO3/BaMnO3 superlattices were systematically investigated using first-principles calculations. The results confirm that this system has antiferromagnetic order and an intrinsic ferroelectric polarisation with the P4mm space group. A tensile epitaxial strain can drive the ground state to another antiferromagnetic-ferroelectric phase and then to a ferromagnetic-ferroelectric phase with the Amm2 space group, accompanied by a change in the ferroelectric polarisation from an out-of-plane direction to an in-plane direction. In contrast, a compressive strain could induce a transition from the antiferromagnetic insulator phase to the ferromagnetic metal phase.
