Magnetic and magnetotransport properties in the n-type (Ga,Mn)N thin films

We present the magnetic and magnetotransport properties of epitaxial (Ga,Mn)N films with nominal Mn concentration (x=0.1–0.73%) grown by plasma-enhanced molecular beam epitaxy (PEMBE). X-ray diffraction (XRD) reveals that (Ga,Mn)N has the single-phase wurtzite structure without secondary phases. The epitaxial (Ga,Mn)N films were found to exhibit n-type conductivity, ferromagnetic ordering with Curie temperature in the range 550–700 K, and in-plane magnetic anisotropy. The negative magnetoresistance (MR) was observed at temperatures below 50 K and was found to gradually increase with decreasing temperature.     

Ferromagnetism of Ni-Doped ZnO Powders Prepared by Sol-Gel Method above Room Temperature

The magnetic and structural properties of 2% Ni-doped ZnO powers prepared by sol-gel method were studied. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) of the sample do not show existence of any signal of second phase. The X-photoelectron spectroscopy (XPS) of the sample shows the chemical valence of Ni is 2 and the real Ni concentration is 2.19% determined by X-ray fluorescence spectra (XRFS). The magnetic property performed with superconducting quantum interference device (SQUID) shows that the sample exhibits ferromagnetism above room temperature and the Curie temperature (TC) is about 600 K.     

Alloying (In,Mn)As and (Ga,Mn)As: Ferromagnetic (In,Ga,Mn)As Lattice-Matched to InP

An effect of alloying two ferromagnetic semiconductors (In,Mn)As and (Ga,Mn)As on the ferromagnetic properties of resultant (In,Ga,Mn)As alloys is reported. For conditions close to lattice-matching to InP substrates, y = 0.53 in (In _y Ga_1–y )_1–x Mn _x As, ferromagnetism up to Curie temperatures T _C = 100–110 K could be achieved for a Mn composition x = 0.13. Trends in the Curie temperature in (In,Ga,Mn)As are compared with (Ga,Mn)As and (In,Mn)As as a function of Mn content. Hole concentrations determined from magnetotransport, taking into account the anomalous Hall contribution to Hall resistance, gives p/Mn = 0.03 ratio to Mn composition in metallic case for x = 0.13. We mention the possible role of chemical ordering (short range) of Mn impurity atoms on hole concentration and, consequently, for the ferromagnetic properties.     

具有宽过冷液相区的Fe63Co7NbxZr10-xB20非晶态合金的热稳定性和磁性研究

利用单辊急冷法制备出厚约35μm宽5mm的 Fe63Co7NbxZr10-xB20条带,并研究了合金的热稳定性、非晶结构和磁性能.结果表明,含4at%Nb的Fe63Co7Nb4Zr6B20合金过冷液相区Δ Tx最宽,达到79K.合金系的饱和比磁化强度σs随着Nb含量的增加而线性减小.合金系经973K退火900s,由于α\|Fe等相的析出,使得合金的σs和Hc均迅速升高.     

La_(1-x)Na_xMnO_3室温巨磁电阻增强效应

采用固相反应法制备了一系Ｌａ_(１－ｘ)Ｎａ_ｘＭｎＯ_３多晶样品。研究了样品的微结构、磁电阻、磁化强度以及居里温度等性质。发现随着Ａ位平均离子半径＜ｒ_Ａ＞的减小,样品的居里温度下降,磁电阻增大。另外,实验还发现了磁电阻与磁化强度之间有着密切的联系。     

Fine Strontium Ferrite Powders from an Ethanol-Based Microemulsion

A fine strontium ferrite powder with high coercivity was successfully prepared by forming hydroxide precursor particles in the continuous ethanol-based phase of a microemulsion consisting of iso-octane, NP9, and an ethanol solution containing Sr²⁺ and Fe³⁺ cations at a molar ratio of 1:12. The microemulsion-derived hydroxide precursor was calcined at various temperatures, ranging from 600° to 1100°C, to develop the hexagonal strontium ferrite phase. X-ray diffractometry and infrared characterizations revealed that the formation mechanisms of strontium ferrite in the microemulsion-derived precursor differed from those of the precursor derived by conventional coprecipitation. The microemulsion resulted in a strontium ferrite of finer particle size and better magnetic properties than those of the conventionally coprecipitated strontium ferrite. The microemulsion-derived strontium ferrite exhibited an intrinsic coercivity of 6195 Oe and a saturation magnetization of 58.28 emu/g when calcined at 900^oC. The saturation magnetization increased further, to 69.75 emu/g, when the microemulsion-derived precursor was calcined at 1100^oC.     

Cu掺杂对ZnO纳米薄膜结构及物性的影响

利用溶胶-凝胶法制备了Cu掺杂Zn O纳米晶体薄膜,通过XRD、TEM、AFM、UV-VLS和VSM对其晶体结构、表面形貌、透光性、禁带宽度和磁性进行了表征和分析。结果表明,所有样品都具有c轴择优生长取向,Cu掺杂没有改变Zn O晶体的纤锌矿结构,即没有检测到任何非晶态产物以及各种第二相的存在,表明Cu2+已经取代Zn2+融入了晶体。但是,Cu的掺杂浓度以及煅烧温度的变化,改善了薄膜的粗糙度、晶粒度、透光率、禁带宽度及室温铁磁性。在所有样品中,掺杂浓度为2%、煅烧温度为500℃的薄膜粗糙度、晶粒度最小而透光性和室温铁磁性最强。样品的能隙则是随着Cu掺杂浓度和煅烧温度的提高而变小。     

Tunable optical,electronic and magnetic properties of semiconductor nanoparticles induced by magnetic and nonmagnetic dopants: A comparative experimental and theoretical study

While combining semiconductor and magnetic properties at the nanoscale provides dilute magnetic semiconductor (DMS) nanomaterials with a wide range of applications in next-generation electronic devices, tuning DMS properties still presents a challenge. Here, the synthesis of pure ZnO and transition metal (TM)-doped ZnO nanoparticles (NPs) with different magnetic (Fe and Co) and nonmagnetic (Mn) dopant concentrations (ranging from 2% to 10%) is reported using a co-precipitation method. Introducing the TM-dopants into ZnO NPs with 35?nm wurtzite structure causes crystallite and mean NP sizes to decrease, as characterized by X-ray diffraction and field-emission scanning electron microscopic analyses. Room-temperature magnetic measurements indicate coexistence of paramagnetic and ferromagnetic phases with tunability in the resulting TM-doped NPs. The maximum ferromagnetic coercivity and saturation magnetization are found to be 89?Oe and 0.074?emu/g for 10% Fe-doped ZnO NPs. UV–visible spectra showed a blue shift with increasing the dopant concentration, being in agreement with increasing trend in band gap energy calculated from band structure and density of state of TM-doped ZnO nanocrystal systems.     

铁磁性构件缺陷的脉冲涡流检测传感机理研究

铁磁性构件的脉冲涡流检测法是一种融合了漏磁检测与涡流检测的新的复合磁传感检测法。建立了脉冲涡流复合传感有限元仿真模型,仿真分析了铁磁性构件电导率、磁导率和导入直流电流激励大小对脉冲涡流响应信号的影响规律。实验结果表明:随着导入直流电流激励增加,铁磁性构件表面缺陷漏磁场和电流密度引起扰动磁场的复合场对脉冲涡流响应信号的影响更显著,而铁磁构件亚表面埋藏缺陷随着缺陷深度的增大而增大,缺陷漏磁及电流扰动磁场的复合场对脉冲涡流响应信号的影响变小,涡流响应信号占主导地位,为脉冲涡流传感器设计奠定理论基础。