Magnetic Order in GaMnAs Layers

MBE grown Ga_1–x Mn _x As layers were investigated by means of magnetic resonance techniques. Two phases can be distinguished: an almost isotropic ferromagnetic phase in insulating layers and an anisotropic ferromagnetic phase in the metallic Ga_1–x Mn _x As. Under a strong magnetic field the field-induced insulator-to-metal transition is accompanied by the change from the ferromagnetic to the ferrimagnetic phase.     

Magnetic Properties of (Ga,Fe)N

Wurtzite (Ga,Fe)N bulk crystals were, for the first time, successfully grown by AMMONO and chemical transport methods. The magnetization measurements of (Ga,Fe)N crystals revealed the coexistence of paramagnetic and ferromagnetic contributions. The paramagnetic component was shown to be growth condition dependent. The Brillouin-type behavior was observed in the samples obtained by both methods. Some (Ga,Fe)N samples (especially those codoped with Si) grown by the chemical transport method show a Van Vleck–type paramagnetic behavior.     

Curie Temperatures of III–V Diluted Magnetic Semiconductors Calculated from First-Principles in Mean Field Approximation

Electronic structure and ferromagnetism in III–V compound-based diluted magnetic semiconductors (DMS) are investigated based on first-principles calculations by using the Korringa-Kohn-Rostoker method combined with the coherent-potential-approximation. The stability of the ferromagnetic phase in GaN-, GaAs-, GaP-, GaSb-based DMS is investigated systematically. The calculations show that 3d-impurities from the first-half of the transition metal series favor the ferromagnetic state, while impurities from the latter-half of the series exhibit spin-glass behavior. This chemical trend in the magnetism is explained by the double exchange mechanism taking the local symmetry at the impurity gap states into account. Curie temperatures of GaAs- and GaN-based DMS are estimated by using the Heisenberg model in a mean field approximation with the parameters calculated from first-principles. It is suggested that room-temperature ferromagnetism can be realized in these systems.     

Fe掺杂量和退火氛围对TiO2薄膜晶体结构和磁性能的影响

采用直流磁控溅射方法在玻璃基片上制备了不同Fe掺杂量的TiO2薄膜,并对薄膜分别在空气和真空氛围下500℃进行30min退火处理。研究了Fe掺杂量和退火氛围对TiO2薄膜的结晶状态、表面形貌和磁性能的影响。结果表明,真空中500℃下退火的Fe掺杂的TiO2薄膜表现为非晶态结构,没有观察到室温铁磁性能的出现,而空气中500℃退火的样品显示出良好的结晶状态,且所有掺杂的样品均显示出室温铁磁性,并且随着Fe掺杂量的增加,TiO2薄膜的晶体结构逐渐由锐钛矿相向金红石相转变。     

Mn、Li共掺ZnO稀磁半导体的制备与铁磁性研究

采用固相陶瓷烧结法制备了Mn、Li共掺的ZnO稀磁半导体材料,实现了室温铁磁性。分别用XRD、XPS和VSM对各样品进行了结构测量和磁性能测量,分析了Mn、Li掺杂浓度对ZnO基稀磁半导体的影响。结果表明,在相同的外磁场下,随着Mn掺杂浓度的增加,陶瓷的磁化强度增大。但较高的Li掺杂浓度可能会形成更多填隙离子,减少空穴浓度,最终使材料的室温铁磁性变差。     

Magnetic Properties of Chalcopyrite-Based Diluted Magnetic Semiconductors

We calculated the chemical trends of transition metal-doped chalcopyrite DMS (diluted magnetic semiconductors) by the use of KKR–CPA–LDA method. The ferromagnetism was stable in V- and Cr-doped chalcopyrite DMS. In the case of Fe and Co doping, however, the spinglass-like state was realized. On the other hand, in the cases of Mn doped I-III-VI₂ and II-IV-V₂ type DMS, the ground state was ferromagnetic and spinglass-like, respectively.     

低能离子束方法制备磁性Fe-Si合金薄膜

利用质量分离的低能离子束技术．获得了磁性Fe-Si合金薄膜。利用俄歇电子能谱法(AES)、X射线衍射法(XRD)以及交变梯度样品磁强计(AGM)测试了样品的组分、结构以及磁特性。测试结果表明在室温下制备的Fe-Si合金是Fe组分渐变的非晶薄膜,具有室温铁磁性。当衬底温度为300℃时制备的非晶Fe-Si薄膜中有Fe硅化物FeSi相产生．样品的铁磁性被抑制。     

Room Temperature Ferromagnetism in III–V-Based Diluted Magnetic Semiconductor GaCrN Grown by ECR Molecular-Beam Epitaxy

A new III–V nitride-based diluted magnetic semiconductor GaCrN has been successfully synthesized for the first time. X-ray diffraction measurement showed no existence of secondary phase in the GaCrN layers. They showed a ferromagnetic behavior with the Curie temperature of higher than 400 K, and clear saturation and hysteresis were observed in the magnetization versus magnetic field curves at all measuring temperatures (10–400 K). Specially, GaCrN magnetization data show no paramagnetic component at low temperature, which are superior characteristics over GaMnN. Photoluminescence emission from GaCrN layer was observed at around 3.29 eV at 10–300 K.     

Cu掺杂ZnO纳米粒子的光学性能及铁磁性

利用溶胶凝胶法制备了纳米结构的Cu掺杂ZnO基稀磁半导体,通过X射线衍射分析表明,样品为纯相ZnO纤锌矿结构,磁性测量表明样品在室温下呈室温铁磁性,铁磁性来源为氧化锌晶格中的缺陷与Cu2＋离子之间的交换作用。室温光致发光（PL）谱观察到紫外带边和可见光区两个发射峰,且随着Cu掺杂量增加,紫外峰淬灭,可见峰发射增强。