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Hole-doped double perovskite compounds (Sr,Na)2FeMoO6 with the Na content of x=0,0.02,0.03,0.07 and 0.17 have been synthesized by sol–gel method. Effects of hole doping on the crystal structure and magnetic properties of Sr2FeMoO6 have been investigated by means of X-ray powder diffraction (XRD) and magnetic measurements. The XRD pattern indicates that all the samples are of single phase and belong to the space group I4/m. Due to the smaller ionic radius of Na+ than that of Sr2+ ions, the lattice constants and unit cell volume of the compound decrease slightly with x. The degree of cation ordering in the Na-doped Sr2FeMoO6 compounds shows a non-monotonic variation with the doping level, increasing from x=0 to x=0.03 and decreasing slightly with further increase of the doping. In contrast to the composition dependence of the degree of ordering, the Curie temperature of the compound decreases at low doping level and increases at high doping level. The saturation magnetization of the compound increases with x for x<0.17. Similar to the electron-doped Sr2FeMoO6, provided that the doped hole enters selectively the spin-down band, the variation of the saturation magnetization can be explained in light of the ferrimagnetic model (FIM). [ABSTRACT FROM AUTHOR]

Abstract: In contrast to the substitution of exotic elements such as Mn, Cu for Fe or W for Mo in Sr2FeMoO6, the degree of ordering of Fe and Mo in Sr2Fe x Mo2−x O6 shows a maximum at x C=0.95 and decreases as x deviates from x C. Saturation magnetization depends upon composition in a similar way. It is shown that the entropy due to antisite defects or substitutional disorder can stabilize the double perovskite structure. It is proposed that the stability of the double perovskite structure of Sr2Fe x Mo2−x O6 is essentially determined by the combined contribution to free energy of configuration entropy and differences in ionic charge and in ionic radius. A plausible charge distribution of Fe and Mo cations in Sr2Fe x Mo2−x O6 is proposed to elucidate the observed composition-dependence of magnetization. [Copyright &y& Elsevier]

Abstract: The crystal structure and magnetic properties of Nd2−x Tb x Fe17 and NdTbFe17−y Al y compounds were studied by means of X-ray diffraction and magnetization measurements. All the samples show the rhombohedral Th2Zn17-type structure with space group . For Nd2−x Tb x Fe17 compounds, the lattice parameters decrease with increasing Tb concentration, and the Curie temperature increases with the Tb content while the saturation magnetization decreases linearly at a rate of 10.54μ B/f.u. per Tb atom. For NdTbFe17−y Al y compounds, the substitution of Al for Fe leads to an increase in lattice parameters a, c and unit-cell volume V. The Al atoms preferentially occupy 18h site at low Al concentration whereas prefer to occupy 6c and 18f sites at high Al concentration. The Curie temperature increases with Al content up to y =3 then decreases for 3≤ y ≤8. X-ray diffraction of magnetically pre-aligned samples indicates that the easy magnetization direction of the samples changes from planar to c-axial with increasing aluminum concentration. The saturation magnetization of compounds decreases with increasing Al concentration. [Copyright &y& Elsevier]

Abstract: TbFe12− x Mo x compounds (x=0.5–3.0) with the tetragonal ThMn12-type structure have been synthesized. The structural and the magnetic properties of the compounds have been investigated by means of X-ray diffraction and magnetic measurements. The lattice parameters a, c and the unit-cell volume V increase with increasing Mo content. Both the Curie temperature T C and the saturation magnetization M S at 5K decrease monotonically with increasing Mo content. The molecular field coefficients n FeFe and n RFe have been estimated from a mean-field analysis of the Curie temperature of the compounds. The easy magnetization direction at room temperature changes with increasing Mo content from planar to probably cone and finally to uniaxial. The decrease of saturation magnetization with increasing Mo content may be caused by the reduction of the due to hybridization of the Fe and Mo d-bands. [Copyright &y& Elsevier]

Abstract: We have investigated the crystal structure, magnetization and magnetoresistance of the double perovskite compounds Sr2(Fe1-xVx)MoO6 (0≤x≤0.1). The lattice constants and the cation ordering decrease monotonously with the V content. The Curie temperature, saturation magnetization and low field magnetoresistance of the compounds decrease with increasing x due to the reduced degree of ordering. The resistivity of Sr2FeMoO6 and lightly doped samples shows semiconductive behavior, while the samples with higher doping levels exhibit a semiconductor-metal transition around 80K. [Copyright &y& Elsevier]