Colossal magnetoresistive and ferroelectric thin films deposited by excimer laser induced plasma

We prepared the colossal magnetoresistive La_0.8Sr_0.2MnO₃ thin films on single crystal MgO, SrTiO₃ and LaAlO₃ substrates by KrF excimer pulsed laser deposition technique. The thickness dependence of the structural, electric and magnetic properties of the LSMO films on different substrates is reported. The integration of the ferroelectrics with the colossal magnetoresistance thin film was achieved. The plasma plume ablated from target was investigated by intensified charge coupled device and optical emission spectroscopy.     

Electro- and magneto-transport properties of amorphous carbon films doped with iron

Electro- and magneto-transport properties of amorphous carbon films doped with iron element have been systematically studied. The electro-transport mechanism of the films is dominated by thermal activation at T > 200 K, Mott-type variable range hopping (VRH) at 200 K > T > 60 K and Efros-Shklovskii type (ES-) VRH at T < 60 K. An anomalous giant positive magnetoresistance (MR) 6.40% is found at the ES-VRH range, which is attributed to the spin blockage effect. At high temperatures, an anomalous Hall effect (AHE) is also found with a large AHE coefficiency 49.6 μΩcm/T. Electron energy loss spectroscopy (EELS) reveals that iron atoms chemically bond with carbon matrix. These iron carbides exist as amorphous nanoparticles with a diameter of 6-12 nm, which is regarded as the origin of the MR and AHE. Besides, the films are p-type conductive at high temperature, which might be related with the iron doping. These properties make iron doped amorphous carbon films applicable in carbon-based solar cells, magnetic sensors or some other multifunctional devices.     

Tunable insulator-quantum Hall transition in a weakly interacting two-dimensional electron system

We have performed low-temperature measurements on a gated two-dimensional electron system in which electron–electron (e-e) interactions are insignificant. At low magnetic fields, disorder-driven movement of the crossing of longitudinal and Hall resistivities (ρ_xx and ρ_xy) can be observed. Interestingly, by applying different gate voltages, we demonstrate that such a crossing at ρ_xx ~ ρ_xy can occur at a magnetic field higher, lower, or equal to the temperature-independent point in ρ_xx which corresponds to the direct insulator-quantum Hall transition. We explicitly show that ρ_xx ~ ρ_xy occurs at the inverse of the classical Drude mobility 1/μ_D rather than the crossing field corresponding to the insulator-quantum Hall transition. Moreover, we show that the background magnetoresistance can affect the transport properties of our device significantly. Thus, we suggest that great care must be taken when calculating the renormalized mobility caused by e-e interactions.     

序列分段算法在磁阻效应数据处理中的应用

对磁阻效应作用原理和磁阻元件的应用进行了介绍,并利用序列分段算法对磁阻效应实验数据分析处理的方法进行了设计和验证。     

可判向磁敏电阻转速传感器

简要介绍了磁敏电阻转速传感器的敏感元件——InSb磁敏电阻的工作原理。设计了一种可以判别齿轮转向的判向测速电路，并给出了对应于判向与倍频功能的时序图。测速时对传感器输出信号进行了四倍频，提高了测速精度。采用高性能的可编辑逻辑器件（PID）GAL16V8代替了通常的分立器件，实现判向倍频的功能，简化了外围电路，提高了判向测速电路的稳定性和可靠性。     

Large magnetocaloric and magnetoresistance effects in metamagnetic Sm0.55(Sr0.5Ca0.5)0.45MnO3 manganite

The metamagnetic transition, magnetocaloric and magnetoresistance effects are investigated in polycrystalline Sm_0.55(Sr_0.5Ca_0.5)_0.45MnO₃ (SSCMO) manganite. A sharp magnetization jump at Curie temperature (T_C) 73.5 K with large thermal hysteresis is observed. Magnetic measurements and Arrott plots analysis indicate that the transition is first order in nature. Under a low magnetic field change of 1 T, the magnetic entropy change exhibits a peak value of $-\Delta S_M^{\max }(T)$=4.01 J/kg K with relative cooling power (RCP) value of 44.1 J/kg in the vicinity of T_C. The mechanism of charge conduction in insulator phase is polaron transport. Large negative magnetoresistance ratio with value of ~99% is obtained within a broad temperature range below metal insulator transition temperature under 1 T magnetic field. These results indicate the potential applications of SSCMO in magnetic refrigeration and spintronics devices.     

短切纤维炭/炭复合材料磁电阻特性研究

研究了经不同温度下热处理后短切纤维模压预制体炭／炭复合材料样品的磁电阻特性。研究结果表明C／C复合材料的磁电阻一位向关系曲线的形状与C／C预制体结构有关，不同预制体结构的材料，磁电阻一位向关系曲线形状不同。C／C复合材料出现磁电阻恒为0的起始温度与材料的石墨化特性有很大关系。石墨化程度越高，材料的磁电阻越大，磁电阻达到0时的测量温度越高。研究发现，磁电阻一测量温度曲线回归方程的斜率随热处理温度的增加而降低，且斜率-热处理温度的变化曲线与材料d002随热处理温度的变化曲线形状类似。