N空位对Cu掺杂AlN电磁性质的影响的第一性原理研究

利用基于密度泛函理论的平面波超软赝势法研究了N空位对Cu掺杂AlN的电子结构和磁学性质的影响。结果表明,与Cu最近邻的N原子更易失去形成N空位。N空位的引入减小了Cu掺杂AlN体系的半金属能隙;减弱了Cu及其近邻N原子的自旋极化的强度以及Cu3d与N2p轨道间的杂化,因而减小了体系的半金属铁磁性。因此,制备Cu掺杂AlN稀磁半导体时应尽可能地避免产生N空位。     

Ge纳米结构的形貌与铁磁性研究

利用等离子体增强化学气相沉积技术制备了厚度不同的Ge薄膜, 随着样品厚度的减小, 样品表现出了室温铁磁性. 厚度为12 nm样品经过300 ℃退火后, 由于颗粒细化, 颗粒之间的界面增加, 界面缺陷增加, 样品表现出最大的铁磁性 (50 emu/cm³). 场冷却和零场冷却曲线测试表明居里温度约为350 K. 进行600 ℃退火后, 颗粒团聚, 样品的铁磁性最小. 当样品厚度进一步减小为6 nm时, 沉积态样品表现出铁磁性和顺磁性共存. 对6 nm厚的样品进行300 ℃退火后, 样品只具有铁磁性. 进行600 ℃退火后, 样品却只具有顺磁性. 12 nm 和6 nm 厚的Ge纳米结构薄膜随退火温度变化表现出不同的磁性规律, 我们认为是由于样品的颗粒大小和颗粒分布不同造成的. 样品越薄, Si基底与Ge薄膜之间的界面缺陷越明显, 界面缺陷以及Ge颗粒之间的界面缺陷为样品提供了未配对电子, 未配对电子的铁磁性耦合强度与样品颗粒的分布以及颗粒之间的结合有一定的关系. 颗粒之间分散或颗粒之间的融合程度大都将会降低样品的铁磁性.     

Angle-resolved photoemission spectroscopy study on iron-based superconductors

Angle-resolved photoemission spectroscopy （ARPES） has played an important role in determining the band structure and the superconducting gap structure of iron-based superconductors. In this paper, from the ARPES perspective, we briefly review the main results from our group in recent years on the iron-based superconductors and their parent compounds, and depict our current understanding on the antiferromagnetism and superconductivity in these materials.     

Doping effects on structural and magnetic evolutions of orthoferrite SmFe（1-x） Alx O3

The structural and magnetic properties of SmFeO3 with B site substitution of non-magnetic atom A1 are investigated. The x-ray diffraction patterns show that SmFe（1-x）AlxO3 remains an orthorhombic structure within the whole doping range, and the unit-cell volume decreases monotonically with the increase of doped A1 concentration. Besides, the octa- hedral tilting distortions of FeO6 are found to be alleviated while the tolerance factor increases. However, the relationship between the lattice parameters and Al concentration is observed to deviate from Vegard＇s rule, and this may be caused by magnetostriction effects. For the doping content values in a range 0 〈 x 〈 0.6, the ferromagnetism, antiferromagnetism, and paramagnetism are observed to occur continuously. Moreover, the magnetization and the spin reorientation temperature （Tk） decrease monotonically as Al content value increases. With the doping content values being x = 0.8 and 1.0, these compounds only show paramagnetic behavior.     

钙钛矿型纳米BaFeO3的制备、结构表征及铁磁性研究

采用溶胶-凝胶法制备出钙钛矿型纳米BaFeO3粉末,利用X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)分析研究了其微观结构及形貌,结果表明:胶体试样经800℃退火处理后,形成了20nm左右的钙钛矿型BaFeO3粉末,其(110)面晶面间距为0.280nm左右,(100)面晶面间距为0.401nm左右.利用振动样品磁强计(VSM)研究了纳米BaFeO3粉末的室温铁磁性能,测量结果表明:在室温条件下,纳米BaFeO3粉末具有完整闭合的磁滞回线,具有较小的矫顽力和较低的饱和磁化强度,呈现出明显的弱铁磁性,且铁磁性随退火温度的变化明显.钙钛矿型纳米BaFeO3的铁磁性主要归因于Fe3 _O_Fe4 之间的氧空位.     

Additional Y3+ Doping Effect on Ferromagnetism of Ce0.97Co0.03O2-δ Compounds

Y^3＋ doping effect on magnetic properties of Ce0.97Co0.03O2-δ are examined. Vibrating sample magnetometer （VSM） measurements indicate that Ce0.97Co0.03O2-δ is ferromagnetic at room temperature. The saturated magnetization Ms is altered by additional Y^3＋ doping, i.e., with the increase of the amount of Y^3＋ doping concentration in Ce0.97-yYyCo0.03O2-δ（y = 0.01, 0.05 and 0.10）, Ms increases persistently, Raman spectra measurements indicate that additional oxygen vacancies are introduced with the amount of Y^3＋ doping content. The results can be well elucidated by the F-centre exchange coupling （FCE） mechanism proposed recently, thus they are important for understanding the ferromagnetism origination in transitional metal-doped insulating oxides.     

Ferromagnetic Antiresonance and Giant Microwave Magneto-Impedance in Polycrystalline La0.49Sr0.51MnO3

The ferromagnetic antiresonance （FMAR） phenomenon, i.e., the minimum of the microwave absorption, in polycrystalline La0.49Sr0.51MnO3 is observed near Curie temperature TC = 282 K. Temperature-dependences of magnetization μ0M are obtained from the FMAR. The results show that as μ0H = 0, by fitting the scaling law M ∝ （TC -T）^β to temperature-dependences of μ0M at the different microwave frequencies, it yields TC=281.2 K and β = 0.47. However, temperature-dependences of μ0M under different μ0H are not in agreement with the scaling law. Due to FMAR, about 40% giant microwave magneto-impedance at 11.9 GHz can occur under a low field μ0H = 0.03 T.     

Room-Temperature Anisotropic Ferromagnetism in Fe-Doped In2O3 Heteroepitaxial Films

Fe-doped In2O3 films are grown epitaxially on YSZ （100） substrates by pulsed laser deposition. The in-situ reflection high-energy electron diffraction, the atomic force microscopy, and the x-ray diffraction patterns show that the films have a well defined cubic structure epitaxially oriented in the （100） direction. Room temperature ferromagnetism is observed by an alternating gradient magnetometer. Strong perpendicular magnetic anisotropy with a remnant magnetization ratio of 0.83 and a coercivity of 2,5 kOe is revealed. Both the structural and the magnetic measurements suggest that this ferromagnetism is an intrinsic property deriving from the spin-orbit coupling between the diluted Fe atoms.     

LaOFeAs的反铁磁能带结构

基于密度泛函理论（DFT）,采用线性缀加平面波展式结合改进的局域轨道方法（APW+lo）,对新型超导材料LaOFeAs的结构进行了计算和分析。反铁磁计算的结果表明,由于巡游电子的贡献,系统具有负的磁矩。费米面附近两种自旋电子的能带在Г点附近具有显著差异,自旋向下的一条空带在此形成了与自旋向上未满填充导带局域相似的结构。而在其他K点,这两种自旋能带的结构基本相同。     

LaOFeAs的反铁磁能带结构

基于密度泛函理论(DFT),采用线性缀加平面波展式结合改进的局域轨道方法(APW+lo),对新型超导材料LaOFeAs的结构进行了计算和分析.反铁磁计算的结果表明,由于巡游电子的贡献,系统具有负的磁矩.费米面附近两种自旋电子的能带在Г点附近具有显著差异,自旋向下的一条空带在此形成了与自旋向上未满填充导带局域相似的结构.而在其他K点,这两种自旋能带的结构基本相同.