Xiaobo Xue

Exchange bias in BiFeO3/La0.67Sr0.33MnO3 bilayers

The exchange bias in BiFeO3/La0.67Sr0.33MnO3 (BFO/LSMO) bilayers has been investigated. Exchange bias field with blocking temperature of about 150 K and enhanced coercivity at room temperature has been observed in (001) BFO/LSMO bilayers. The blocking temperature coincides well with the emerging temperature of the vertical magnetization shift due to the blocking of the possible interfacial spin glass. Only enhanced coercivity without exchange bias field down to 10 K has been observed in (111) BFO/LSMO bilayers. The piezoelectric force microscopy images show that the domain size of (111) BFO is 2 orders larger than that of the (001) BFO, indicating the much higher domain wall density in (001) BFO. Our results demonstrate that the exchange coupling with interfacial spin glass at the domain walls contributes to the exchange bias field with blocking temperature of about 150 K, while the exchange coupling with the domains contributes to the enhanced coercivity up to room temperature.

Search for ferromagnetism in Mn-doped LaAlO 3 single crystals

In recent years, because of the intriguing prospect of their applications in the next generation of spintronic devices, diluted magnetic semiconductors (DMSs) have stimulated intense interest, typically III-V or II-VI semiconductors exhibiting magnetic order upon doping with a few percent of magnetic elements, like Fe, Co or Mn. Search for intrinsic high Curie temperature DMSs has become a fascinating endeavor in transition metal doped wide-banded semiconducting oxides such as TiCh, CuO, ZnO, and SnO2. On the other hand, ABO3 perovskite oxides can show both metallic and semiconducting behavior at different temperatures. However, very little work searching for ferromagnetism has been carried out on ABO3 perovskite oxides. In this work, LaAlO3 single crystals were dilutely doped with magnetic transition element Mn for investigation of ferromagnetism. Mn doped LaAlO3 single crystals were prepared by a thermal diffuse technique, which is commonly used as a flexible method by easily doping impurity into host material. In our experiments, two pieces of commercial LaAlO3 single crystals were closely surrounded by MnO2 powders in two crucibles. Then these two crucibles containing LaAlO3 crystal and MnO2 powders were annealed in air at 750°C and 1300°C respectively for 24 hours. The temperature dependence of magnetization of Mn-doped LaAlO3 was measured using a commercial vibrating sample magnetometer (VSM) in the temperature range between 60 K and 300 K with an applied field of 500 Oe. The corresponding magnetic hysteresis (M-H) loops at different temperatures were also measured by VSM.