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81.
The optical and magnetic properties of ZnS:Mn2+ nanowires are tuned by Mn2+ concentration. The magnetic variation is ascribed to the competition between antiferromagnetic and ferromagnetic exchange interactions. 相似文献
82.
Aloysius Soon Joel Wallman Bernard Delley Catherine Stampfl 《Current Applied Physics》2013,13(8):1707-1712
We present a trend study of a large variety of dopants at the cation site in Cu2O (i.e. substituting Cu), focussing largely on the early 3d-, 4d-, and 5d-transition metals (TMs) in which many of them are known to be non-magnetic. We also include s-, sp- and d10-metals for comparison. We find that doping with sp-elements results in zero spin moment while dopants with a partially filled d-band show a stronger tendency to magnetize and 3d-TM dopants exhibit a larger magnetic moment than most of the 4d- and 5d-TM dopants. From this trend study, we also find a correlation between their substitution enthalpy and associated interatomic relaxations. In particular, Ti-doped Cu2O appears to be an interesting system, given its “peculiar” ability to exhibit a spin moment when doped with a non-magnetic substituent like Ti. We also find that the interaction between two doped Ti atoms in Ti2:Cu2O is predominantly antiferromagnetic, and interestingly (and unexpectedly), this interaction rapidly declines as a function of inter-dopant distance, as in the case for the magnetic late-TM dopants like Co2:Cu2O. 相似文献
83.
Recently, many studies have been started in search for materials which show a photoinduced phase transition (PIPT). In this work, we review two systems as typical examples of PIPT accompanied with changes in magnetic characteristics; (1) organo-metal complex [Fe(2-pic)3]Cl2 EtOH (2-pic = 2-amino-methyl-pyridine) and (2) III-V based magnetic semiconductors (In1-x , Mn x )As. In the former case, we show several nonlinear characteristics in dynamical process of photoinduced spin state transition from low-spin to high-spin states. In the latter one, photocarrier-induced ferromagnetic order has been observed by both magnetic and transport measurements. 相似文献
84.
Time-resolved magneto photoluminescence in a diluted magnetic semiconductor Cd 0.9 Mn 0.1 Te has been carried out with varying exciton density from 10 14 to 10 19 cm m 3 . The reduction of the Zeeman shift and that of the magnetic polaron energy was found under strong photoexcitation. The spectral feature is interpreted in terms of the heating of the manganese spin subsystem. Polarization dependence of the spin heating is observed for the first time, revealing the contribution of the spin flip between excitons and magnetic ions to the heating process. 相似文献
85.
Liu-Niu Tong Yi-Chao Wang Xian-Mei He Huai-Bin Han Ai-Lin Xia Jin-Lian Hu 《Journal of magnetism and magnetic materials》2012
We explore the effects of hydrogen annealing on the room temperature ferromagnetism and optical properties of Cr-doped ZnO nanoparticles synthesized by the sol-gel method. X-ray diffraction and x-ray photoelectron spectroscopy data show evidence that Cr has been incorporated into the wurtzite ZnO lattice as Cr2+ ions substituting for Zn2+ ions without any detectable secondary phase in as-synthesized Zn0.97Cr0.03O nanopowders. The room temperature magnetization measurements reveal a large enhancement of saturation magnetization Ms as well as an increase of coercivity of H2-annealed Zn0.97Cr0.03O:H samples. It is found that the field-cooled magnetization curves as a function of temperature from 40 to 400 K can be well fitted by a combination of a standard Bloch spin-wave model and Curie–Weiss law. The values of the fitted parameters of the ferromagnetic exchange interaction constant a and the Curie constant C of H2-annealed Zn0.97Cr0.03O:H nanoparticles are almost doubled upon H2-annealing. Photoluminescence measurements show evidence that the shallow donor defect or/and defect complexes such as hydrogen occupying an oxygen vacancy Ho may play an important role in the origin of H2-annealing induced enhancement of ferromagnetism in Cr-H codoped ZnO nanoparticles. 相似文献
86.
In this paper we investigate the role of magneto-crystalline anisotropy on the domain wall (DW) properties of tubular magnetic nanostructures. Based on a theoretical model and micromagnetic simulations, we show that either cubic or uniaxial magneto-crystalline anisotropies have some influence on the domain wall properties (wall size, propagation velocity and energy barrier) and then on the overall magnetization reversal mechanism. Besides the characterization of the transverse and vortex domain wall sizes for different anisotropies, we predict an anisotropy dependent transition between the occurrence of transverse and vortex domain walls in tubular nanowires. We also discuss the dynamics of the vortex DW propagation gradually increasing the uniaxial anisotropy constant and we found that the average velocity is considerably reduced. Our results show that different anisotropies can be considered in real samples in order to manipulate the domain wall behavior and the magnetization reversal process. 相似文献
87.
The high-pressure induced phase transitions initiated by electronic transition in 3d ions from the high-spin (HS) to the low-spin (LS) state (HS-LS spin-crossover) are considered. Behavior of the system with d6 electronic configuration is investigated in the ground state of zero temperature and critical pressure Pc. Magnetic properties of the Mott–Hubbard insulator (Mg1−xFex)O are studied in the vicinity of the quantum critical point (T=0, Pc). At the critical pressure of spin crossover Pc, the spin gap energy εS between HS and LS states is zero. The quantum spins fluctuations HS⇔LS do not require any energy, and the antiferromagnetism is destroyed in the quantum critical point by the first order transition. 相似文献
88.
R. Lavín C. Gallardo J.L. Palma J. Escrig J.C. Denardin 《Journal of magnetism and magnetic materials》2012
The angular dependence of the coercivity and remanence of ordered hexagonal arrays of Co nanowires prepared using anodic aluminum oxide templates was investigated. The experimental evolution of coercivity as a function of the angle, in which the external field is applied, is interpreted considering micromagnetic simulations. Depending on the angle between the axis of the wire and the applied magnetic field direction our results show that the magnetization reversal mode changes from vortex to a transverse domain wall. Besides, we observed that the dipolar interactions cause a reduction in coercive fields, mainly in the direction of easy magnetization of the nanowires. Good agreement between numerical and experimental data is obtained. 相似文献
89.
In this paper we study the asymmetric voltage behavior (AVB) of the tunnel magnetoresistance (TMR) for single and double barrier magnetic tunnel junctions (MTJs) in range of a quasi-classical free electron model. Numerical calculations of the TMR–V curves, output voltages and I–V characteristics for negative and positive values of applied voltages were carried out using MTJs with CoFeB/MgO interfaces as an example. Asymmetry of the experimental TMR–V curves is explained by different values of the minority and majority Fermi wave vectors for the left and right sides of the tunnel barrier, which arises due to different annealing regimes. Electron tunneling in DMTJs was simulated in two ways: (i) Coherent tunneling, where the DMTJ is modeled as one tunnel system and (ii) consecutive tunneling, where the DMTJ is modeled by two single barrier junctions connected in series. 相似文献
90.