Zhigao Chen

A novel spin modulation of work function for C adsorbed Cr/Fe(001) metal gate

Work functions and magnetic moments of C adsorbed Cr/Fe(001) surfaces with different C coverages θ and magnetic alignments (parallel or antiparallel) between Cr and Fe atom moments are investigated using first-principles methods based on density functional theory. The calculated results reveal that the spin configuration plays a significant role in determining the work function of the systems. The work functions of the systems with parallel states are evidently larger than those with antiparallel states. Moreover, for θ≤0.5 ML, with increasing value of θ, the work function increases from 4.23 eV to 5.13 eV for antiparallel states and from 4.47 eV to 5.44 eV for parallel states. While for θ>0.5 ML, the work function decreases with increasing value of θ. It can be also found that, for θ≤0.5 ML, the smaller the Cr and Fe magnetic moments are, the lower the Fermi energy EF is and the larger the work functions of the systems are. Based on analysis and discussion, we conclude that the changes of the work functi...

Surface and size effects of magnetic properties in ferromagnetic nanoparticles

The oscillatory behavior of the average magnetic moment as a function of the cluster size and shape is studied. Based on Monte Carlo simulation, the temperature dependence of magnetic moment with different cluster size is studied for free and embedded Co clusters. It is found that the oscillations superimposed on the moment decrease are associated with not only the geometrical structure effects but also the thermal fluctuation roles. The fitting results on the temperature dependence of moment for both free and embedded clusters by using Bloch exponent law reveal that differences between them exist. At the same time, the simulated results are compared with the experimental facts.

Numerical calculation of magnetization behavior for Co nanowire array

Based on Monte Carlo method, the hysteresis loops for both individual Co nanowires and their array were simulated, and the influence of the strength of the dipolar interaction on the macroscopical magnetic properties of Co nanowire array was investigated. The simulated results indicate that the coercivity approximately increases linearly with the increase of the strength coefficient of the dipolar interaction. The interwire dipole interaction between wires tends to develop a magnetic easy axis perpendicular to the wire axis. In the magnetic reversal process, competition between the interwire dipolar interaction and the shape anisotropy of individual wires which forces the moments to orient along the axis makes the magnetic reversal of the array different from that of individual wire. For applied field parallel to wire axis, the coercivity of nanowire array increases rapidly with the increase of the nearest-neighbor interwire distance, and approximately increases linearly with the increase of the strength coefficient of the dipolar interaction for the fixed diameter and the nearest-neighbor interwire distance. While for applied field perpendicular to wire axis, in contrast, the coercivity decreases with increasing the nearest-neighbor interwire distance, and nearly remains a constant with the increase of the strength coefficient of the dipolar interaction.

Magnetism and work function of Ni-Cu alloys as metal gates

The magnetism and work function of pure Ni(001) and Ni-Cu slab alloys were investigated using first-principles methods based on density functional theory. The calculated results reveal that both magnetic moments and work functions of the alloys depend strongly on the surface orientation, but hardly on the distribution of doped Cu atoms for a given surface orientation. It is found that the doped Cu atoms have evident influence on the magnetic moment of Ni-Cu slabs, and the average magnetic moment of Ni atoms for Ni-Cu alloys decreases with increasing concentration of Cu atoms. Moreover, it is observed that the work function of Ni(001) is insensitive to the supercell thickness and the inner concentration of Cu atoms. In the meantime, the spin polarization is found to have an obvious role on the work function of the Ni-Cu alloys, which may give a new way to modulate the work function of the metal gate.

Spin and surface orientation effects of work function for Cr/Ni(111), Cr/Ni(100) and Cr/Ni(110) metal gates

Work functions of Cr/Ni(111), Cr/Ni(100) and Cr/Ni(110) surfaces with different magnetic configurations for Cr atoms in the topmost Cr monolayer are investigated using first-principles methods based on density functional theory. The calculated results reveal that work functions vary with crystal orientations and magnetic configurations. The magnitude of the Cr magnetic moments for the three (111), (100) and (110) surfaces follows a change trend with MCr, Cr/Ni(111) < MCr, Cr/Ni(100) < MCr, Cr/Ni(110). Altering the magnetic configurations of the systems from an original ground state to an excited one will have the total energy and the Fermi level increase. Consequently, it will give rise to the reduction of the work function for the system. Moreover, the quite favorable variation range (4.92–4.41 eV) of the calculated work functions for Cr/Ni(100) system modulated by spin effect implies that the Cr/Ni(100) system may be a more promising candidate. Our work suggests that changing magnetic configurations can modulate the work functions of magnetic metal gates well.

Ferromagnetism of Cu doped ZnO: First-principles calculation and Monte Carlo simulation

In this work, the electronic structure and the stability ferromagnetism of Cu-doped ZnO are studied by first-principles calculations and Monte Carlo simulation. The calculated results from first principles indicate that the ferromagnetic ground state is stabilized by its half-metallic electronic structure which originates from the strong hybridization between Cu-3d and O-2p electrons. Meanwhile, through the coupling strength from first-principles calculations, the Monte Carlo simulated results predict that the Curie temperatures of Zn1-xCuxO (x = 5.55%, 833%,12.5%) are 140, 480, 530 K, respectively, which is generally consistent with some theroetical and experimental results.

Effect of process conditions and NiO on magnetoresistance of La-(Ca,Ba)-Mn-O composites

La2/3(Ca0.6Ba0.4)1/3MnO3/XNiO heterogenous composites have been synthesized by modified sol-gel method. Resistivity versus temperature in difference magnetic fields for the samples, as well as magnetoresistance (MR) versus magnetic in room temperature, have been measured. It is indicated that the addition of NiO results to the increase in resistivity and the weakeness in magnetization. Enhanced MR has been obtained in NiO-doped composites. The temperature dependence of magenetoresistance for NiO-doped composites in low magnetic field may be explained by the model of spin-polarized tunneling. The vary trend of MR in MR-T curve is similar to the result obtained by Monte Carlo simulation. MR in high magnetic field may be explained by spin polarization inside ferromagnetic grains.

The size effects of the magnetic properties for the 200-nm Co nanorings: Monte Carlo simulation

In this work, using Monte Carlo simulation, we study the magnetic properties of individual Co nanorings with the outer diameter of 200 nm, the thickness of 10 nm, 20 nm, 30 nm and the varying width from 10 nm to 90 nm, obtaining various spin configurations. The simulated results indicate that, there exist evident size effects on the magnetic states and magnetization processes of the nanorings; in the magnetization reversal process there exist the onion-type state for the narrow rings, and the vortex-type state and onion-type state for the wide rings, respectively. The vortex-type spin configuration is responded for the step of hysteresis loops, which is named as the second stable state. At the same time, it is found that the stability of the second stable state has evident size effect. Moreover, the simulated results are consistent with experimental facts.