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Классификация： 核科学技术 >> 辐射物理与技术 Время подачи： 2024-04-07
Аннотация： Room-temperature ferromagnetism is observed in the O+-implanted AlN films with O+ doses of 5 × 1016 cm-2 (AlN:O5×1016) and 2 × 1017 cm-2 (AlN:O2×1017). The observed magnetic anisotropy indicate that the ferromagnetism is attributed to the intrinsic properties of O+-implanted AlN films. The out-of-plane saturation magnetization (𝑀S) of the AlN:O5×1016 is about 0.68 emu/g, much higher than that of AlN:O2×1017, 0.09 emu/g, which is due to the excessively high O+ dose made more O+ ions occupy adjacent Al3+ positions in forms of antiferromagnetic coupling. Doppler broadening of positron annihilation radiation measurements demonstrate the existence of Al vacancies in the O+-implanted AlN films. The first-principles calculations suggest that the ferromagnetism originates mainly from the Al vacancies.
Классификация： 物理学 >> 凝聚态:电子结构、电、磁和光学性质 Время подачи： 2017-11-27
Аннотация： Critical phenomenon of the noncentrosymmetric Cr11Ge19, which exhibits an itinerant ferromagnetic ground state, is investigated by scaling of the magnetic entropy change [ΔSM(T;H)]. It is found that parameters #14;FWHM (the full width at half maximum), ΔSmax M (the maximum of the magnetic entropy change), and RCP (the relative cooling power) of ΔSM(T) are governed by the power law of critical exponents. With the critical exponents, ΔSM(T;H) curves are scaled into a universal curve independent of temperature and field, which suggests that the magnetic transition is of a second order type. The universal collapse of ΔSM(T;H) indicates that the critical behavior of Cr11Ge19 can be well described by the scaling laws for the critical phenomenon. Moreover, the ΔSM follows the power law of Hn with n(T;H) = dlnjΔSMj=dln(H). The temperature dependence of n values reach minimum at #24; 71.5 K. Based on the magnetic specific change ΔCp(T;H), the actual magnetic transition temperature is strictly determined as TC = 71:3 #6; 0:2 K for the single crystal Cr11Ge19.
Классификация： 物理学 >> 凝聚态:电子结构、电、磁和光学性质 Время подачи： 2017-11-27
Аннотация： In this work, we successfully synthesize the single crystal Cr11Ge19. The magnetism of the noncentrosymmetric Cr11Ge19 with itinerant ferromagnetic ground state is thoroughly investigated on the single crystal. Based on the variation measurements including the angular rotation, temperature, and magnetic field dependence of magnetization, we find that this material exhibits strong magnetic anisotropy along the c-axis. To clearly reveal the magnetic interactions, the critical behavior is studied using the modified Arrott plot, the Kouvel-Fisher method, and the critical isotherm technique. Combining these different methods, three main critical exponents (β, γ, and δ) are obtained. The critical exponent β is close to the theoretical prediction of a three-dimensional XY model with spin-dimensionality n = 2, indicating two-dimensional magnetic coupling. Meanwhile, the critical exponent γ suggests that the magnetic interaction is of long-range type with magnetic exchange distance decaying as J(r) #25; r−4:61. We propose that the ferromagnetic ground state of Cr11Ge19 is formed by the polarized magnetic moments along the c-axis, while the long-range magnetic coupling is established within the ab plane.
Классификация： 物理学 >> 凝聚态:结构、力学和热性能 Время подачи： 2017-03-26
Аннотация： Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when magnetic field is applied parallel to the sample plane. By combining X-ray absorption near edge structure spectrum and positron annihilation lifetime spectroscopy, Ti3+-VO defect complexes (or clusters) have been identified in annealed crystals at high vacuum. We elucidate that the unpaired 3d electrons in Ti3+ ions provide the observed room-temperature ferromagnetism. Besides, excess oxygen ions in TiO2 lattice could induce a number of Ti vacancies which increase magnetic moments obviously.
Классификация： 物理学 >> 凝聚态:结构、力学和热性能 Время подачи： 2017-03-26
Peng Zhan
Weipeng Wang
Can Liu
Yang Hu
Zhengcao Li
Zhengjun Zhang
Peng Zhang
Baoyi Wang
Xingzhong Cao
Аннотация： ZnO films became ferromagnetic when defects were introduced by thermal annealing in flowing argon. This ferromagnetism, as shown by the photoluminescence measurement and positron annihilation analysis, was induced by the singly occupied oxygen vacancy, with a saturated magnetization dependent positively on the amount of this vacancy. This study clarified the origin of the ferromagnetism of un-doped ZnO thin films, and provides possibly an alternative way to prepare ferromagnetic ZnO films.
Классификация： 物理学 >> 基本粒子与场物理学 Время подачи： 2016-05-08
Аннотация： In this paper we build a holographic model of paramagnetism/antiferromagnetism phase transition, which is realized by introducing two real antisymmetric tensor fields coupling to the background gauge field strength and interacting with each other in a dyonic black brane background. In the case without an external magnetic field and in low temperatures, the magnetic moments condense spontaneously in an antiparallel manner with the same magnitude and the time reversal symmetry is also broken spontaneously (if the boundary spatial dimension is more than 2, spatial rotational symmetry is broken spontaneously as well), which leads to an antiferromagnetic phase. In the case with the weak external magnetic field, the magnetic susceptibility density has a peak at the critical temperature and satisfies the Curie-Weiss law in the paramagnetic phase of antiferromagnetism. In the strong external magnetic field case, there is a critical magnetic field B-c in the antiferromagnetic phase: when the magnetic field reaches Bc, the system will return into the paramagnetic phase by a second order phase transition.
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