X.C. Liu

Effect of annealing ambient on the ferromagnetism of Mn-doped anatase TiO2 films

The magnetic properties of anatase Ti1?xMnxO2 (0 < x < 0.06) films prepared by sol?gel spin coating annealed in air and vacuum have been investigated. Room temperature ferromagnetism was observed in all the films. Enhancement of ferromagnetism is revealed in the films annealed in vacuum. The magnetic moment of the films annealed in vacuum, at 300?K, is 0.285 ? 0.004 ?B/Mn for Ti0.9618Mn0.0382 O2 and 0.366 ? 0.005 ?B/Mn for Ti0.9409 Mn0.0591O2. It is believed that the enhanced ferromagnetism could be due to the formation of oxygen vacancies and/or defects.

Hole-mediated ferromagnetism in polycrystalline Si1−xMnx:B films

Polycrystalline Si1−xMnx thin films codoped with boron have been fabricated by sputtering technique followed by postcrystallization processes. Structural, magnetic, and transport properties of the films were investigated. Magnetic property investigation indicated that the films consist of two ferromagnetic phases. The low Curie temperature ferromagnetic phase (TC∼50K) is due to the Mn4Si7 phase in the films as detected by x-ray diffraction, while the high temperature one (TC∼250K) is resulted from the incorporation of Mn into silicon. It has been found that, with carriers confirmed as p type, for the same effective concentration of Mn the saturation magnetization of the films with higher carrier concentration is higher than that of those with lower carrier concentration, which suggests a mechanism of hole-mediated ferromagnetism for Si-based diluted ferromagnetic semiconductors.

Large low field magnetoresistance in ultrathin nanocrystalline magnetite Fe3O4 films at room temperature

Ultrathin (15nm) Fe3O4 nanocrystalline films with (111) spinel texture have been prepared by rapid annealing of amorphous ion oxide films. Large low field magnetoresistance (LFMR), with the values of about −6.3% at 300K and −10% at 200K under a field of 0.5T, has been observed in the films. The LFMR is mainly attributed to the boundary tunneling of high spin-polarized electrons in Fe3O4 grains of the films and nearly follows a simple relationship between MR and polarization for intergranular tunneling. The fabricating method here seems to be a good approach to prepare high quality Fe3O4 nanocrystalline films with a large LFMR at room temperature.

Effect of hydrogenation on the ferromagnetism in polycrystalline Si1−xMnx:B thin films

Polycrystalline Si1−xMnx films codoped with boron have been prepared by radio-frequency magnetron sputtering deposition followed by post-thermal processing for crystallization. The polycrystalline thin films were treated by hydrogen plasma excited with approach of radio-frequency plasma-enhanced chemical vapor deposition. It has been found that the saturation magnetization decreases after hydrogenation while the structural properties of the films do not show any change. At the same time, it is observed that after hydrogenation the hole concentration in the films is lower than that before the treatment, believed to be due to a combination between hydrogen and boron. The obvious correlation between the magnetic properties and the transport properties of the polycrystalline Si1−xMnx films suggests that there be a mechanism of hole-mediated ferromagnetism for Si-based diluted magnetic semiconductors.

Anomalous Hall effect and magnetoresistance of (FexSn1?x)1?y(SiO2)y films

Structural, magnetic and transport properties were investigated for heterogeneous (FexSn1?x)1?y(SiO2)y films deposited on oxidized silicon substrates at room temperature with RF magnetron sputtering. X-ray diffraction indicated that the films consist of a nanocrystalline phase of FeSn2 embedded into an amorphous background. For (FexSn1?x)92.33(SiO2)7.67, it was demonstrated that with the increase in the Fe component an evolution from negative isotropic magnetoresistance (MR) behaviour to one with a mixture of anisotropic magnetoresistance and isotropic negative MR occurs. On fixing the SiO2 percentage and decreasing the Fe?Sn ratio, the negative transverse MR first increases and then decreases. For samples having a fixed Fe?Sn ratio, the negative transverse MR increases with the increase in SiO2. Compared with the Fe?Sn system, the addition of 7.67?at.% SiO2 enhances the saturated Hall resistivity. Further increase in SiO2 introduces a complicated saturated Hall resistivity dependence on the concentration of SiO2.

Room-temperature ferromagnetism in p-type (Mn, N)-codoped ZnO thin films achieved by thermal oxidation of sputtered Zn3N2:Mn films

P-type (Mn, N)-codoped ZnO films have been fabricated by oxidative annealing of sputtered Zn2N3 : Mn films on silicon substrates at 550 °C in flowing O2 ambient. X-ray diffraction and x-ray photoelectron spectroscopy studies reveal that the Mn and N ions incorporated into the ZnO lattice are divalent Mn2+ and trivalent N3− ions, respectively. Ferromagnetism with Curie temperature above 300 K was observed in p-type (Mn, N)-codoped ZnO films. The results indicate that holes are favourable for ferromagnetic ordering in doped Mn2+ ions in ZnO, in agreement with recent theoretical studies.