Effect of Ar ion irradiation on the room temperature ferromagnetism of undoped and Cu-doped rutile TiO_2 single crystals

Remarkable room-temperature ferromagnetism was observed both in undoped and Cu-doped rutile TiO_2 single crystals(SCs).To tune their magnetism,Ar ion irradiation was quantitatively performed on the two crystals in which the saturation magnetizations for the samples were enhanced distinctively.The post-irradiation led to a spongelike layer in the near surface of the Cu-doped TiO_2.Meanwhile,a new CuO-like species present in the sample was found to be dissolved after the post-irradiation.Analyzing the magnetization data unambiguously reveals that the experimentally observed ferromagnetism is related to the intrinsic defects rather than the exotic Cu ions,while these ions are directly involved in boosting the absorption in the visible region.     

室温铁磁Sr3YCo4O10.5+δ多晶的制备及其性能研究

采用传统简便的固相烧结法制备了四方相的室温铁磁Sr3YCo4O10.5+δ多晶.热分析、X射线衍射和扫描电镜结果表明Sr3 YCo4 O10.5+δ多晶最终烧结温度应在963℃以上,较佳的烧结温度为1180℃.Sr3YCo4O10.5+δ多晶在80～300K为半导体电输运行为,较佳烧结温度多晶的室温电阻率～78.8 mΩ·cm;多晶热电势在317～1018 K随温度增加而减小,317 K时为70.74 μV/K.磁化强度-温度曲线、磁滞回线结果表明,多晶在受外加磁场、温度及晶体场的影响下,内部Co3+自旋态及磁畴壁、磁矩方向发生改变,导致多晶磁化强度变化及多晶磁性的改变.外磁场(0.1 T)下的ZFC曲线在320 K出现磁化强度最大为0.46 emu/g的Hopkinson峰,居里温度(Tc) =323 K,而FC曲线在奈尔温度(TN)=264 K时磁化强度达到最大为1.1 emu/g,TC=320 K.ZFC、FC方式下多晶均表现为室温铁磁性.     

Electronic structure and magnetic properties of(Cu,N)-codoped3C-SiC studied by first-principles calculations

The electronic structures and magnetic properties of the Cu and N codoped 3C-Si C system have been investigated by the first-principles calculation.The results show that the Cu doped Si C system prefers the anti-ferromagnetic(AFM) state.Compared to the Cu doped system,the ionicities of C–Cu and C–Si in Cu and N codoped Si C are respectively enhanced and weakened.Especially,the Cu and N codoped Si C systems favor the ferromagnetic(FM) coupling.The FM interactions can be explained by virtual hopping.However,higher N concentration will weaken the ferromagnetism.In order to keep the FM interaction,the N concentration should be restricted within 9.3% according to our analysis.     

Quantum Hall ferromagnetism in a two-valley strained Si quantum well

Tilted field magnetotransport study was performed in a two-valley strained Si quantum well and hysteretic diagonal resistance spikes were observed near the coincidence angles. The spike around filling factor ν=3 develops into a giant feature when it moves to the high-field edge of the quantum Hall (QH) state and quenches for higher tilt angles. When the spike is most prominent, its peak resistance is temperature independent from T20 mK up to 0.3 K, which is different from the critical behavior previously reported near the Curie temperature of the QH ferromagnet in AlAs quantum wells. Our data suggest a strong interplay between spins and valleys near the coincidence.     

Temperature dependent carrier induced ferromagnetism in Zn(Fe)O and Zn(FeAl)O thin films

Epitaxial films of ZnO doped with magnetic ion Fe and, in some cases, with 1% Al show clear evidence of room temperature ferromagnetic ordering but containing huge amount of paramagnetic moment in it. The total ferromagnetic and paramagnetic contributions have been extracted from the low temperature SQUID measurements. A clear correlation between the magnetization per transition metal ion and the ratio of the number of carriers and number of donors have been found in these films and established the theory of carrier induced ferromagnetism. The experimental data has been best explained through the modification of electronic structure of oxide semiconductors with impurity states.     

The magnetic mechanism of Zn<Subscript>0.93</Subscript>Co<Subscript>0.07</Subscript>O thin films

Zn_0.93Co_0.07O thin films infiltrated with nitrogen and aluminum were prepared by means of magneton sputtering. The structural and magnetic properties of the films were studied systematically. The materials were single phase (wurtzite structure) with surfaces showing signs of homogeneous growth. The films were ferromagnetic at room temperature, and magnetic domains could be clearly observed on the surfaces. In the case of Al infiltration, saturated magnetization increased with Al concentration increasing; whereas in the case of N infiltration, saturated magnetization decreased with the increase in N concentration. The results show that ferromagnetic interactions in Co-doped ZnO diluted magnetic semiconductor may be transferred by electrons. Supported by the National Natural Science Foundation of China (Grant No. 10674059) and the Major Project of National Basic Research Program of China (Grant No. 2005CB623605)     

Role of oxygen vacancies in the origin of ferromagnetism in Mn‐doped ZnO

The relationship between the oxygen vacancy and ferromagnetism in Mn‐doped ZnO has been studied based on the first‐principles calculations. Three possible charge states of oxygen vacancies, i.e., neutral (V_O⁰), 1+ (V_O¹⁺) and 2+ (V_O²⁺) are considered. Results show that the lattice relaxations around oxygen vacancies are large difference under different charge states. It is found that V_O¹⁺ and V_O²⁺ oxygen vacancies induce ferromagnetism. However, Mn‐doped ZnO system shows ferromagnetism with V_O⁰ oxygen vacancies in hydrogenated environment, the ferromagnetism is attributed to the interstitial H, which forms a bridge bond and mediates d ‐d coupling and stabilizes the ferromagnetic state. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electronic structures and magnetic properties of Zn-and Cd-doped AlN nanosheets:A first-principles study

In this paper, the magnetic properties, electronic structures and the stabilities of Zn/Cd incorporated two-dimensional Al N nanosheets are investigated by the first-principles method. Numerical results indicate that Zn and Cd substituting Al atom in Al N nanosheets introduce some holes into the 2p orbitals of the N atoms, and the holes mainly come from spindown 2p orbitals of the N atoms. The magnetic moment of 1.0 μBis produced by Zn/Cd doping Al N nanosheets, and the main component of the magnetic moment of the system is contributed by the partially filled 2p states of the N atoms around the dopant. In particular, when Zn/Cd substituting Al atoms, the magnetic coupling is found to be ferromagnetic. We attribute the hole-mediated p–d interaction to the created ferromagnetic coupling. More importantly, the result of formation energy indicates that Al atom is more inclined to be replaced by Zn atom rather than Cd. This finding is beneficial to developing the spin electronic devices.     

Ferromagnetism in Eu-doped ZnO films deposited by radio-frequency magnetic sputtering

This paper reports that Eu-doped ZnO films were successfully deposited on silicon (100) by radio-frequency magnetic sputtering. The x-ray diffraction patterns indicate that Eu substitutes for Zn in the lattice. Ferromagnetic loops were obtained by using superconducting quantum interference device at 10 K and room temperature. No discontinuous change was found in both of the zero-field-cooled and field-cooled curves. The observed ferromagnetism in Eu-doped ZnO can be attributed to a single magnetic phase. The saturation magnetisation decreased remarkably for the Eu-doped ZnO prepared by introducing 5% of oxygen in the sputtering gas or by the post annealing in O2, suggesting that the defects play key roles in the development of ferromagnetism in Eu-doped ZnO films.     

Mn、Cu共掺ZnO磁性的研究

本文采用水热法,分别以ZnO、Zn(OH)2为前驱物,添加一定量的MnCl4.4H2O和CuSO4.2H2O, 3mol/LKOH作矿化剂,温度430℃,填充度35%,反应24h,制备了Mn、Cu共掺ZnO晶体。当前驱物为Zn(OH)2时,所得晶体大部分为短柱状晶体,显露正负极面{0001}、{0001-}、负锥面-p{101-1-}和柱面m{1-010},长度约为30 ～50μm。少部分晶体为单锥六棱柱状,显露正锥面p{101-1},柱面m{1-010},负极面-c{0001-},晶体的长度约为100μm,长径比为5:1。当ZnO用作前驱物时,短柱状晶体长度大约为10 ～30μm,晶体的六棱对称性都出现较大的偏差。X射线荧光能谱分析表明,前驱物为ZnO、Zn(OH)2时,Mn离子含量在分别为3.19%和1.62%原子分数,没有检测到Cu离子。虽然Mn、Cu离子的掺入会明显影响晶体形态,磁性测量显示掺杂Mn、Cu的ZnO仍为反铁磁。