Rare Earth-transition Metal Alloy Films Research Articles

Keynote Speakers

Keynote 1Prof. Ke Wang, East China University of Technology, Nanchang, ChinaSpeech Title:Magnetic and Perpendicular Exchange Coupling Properties of Rare-earth Transition Metal Alloy Films:In this talk, we will present some work we are carrying out on perpendicularly magnetized rare-earth transition metal alloy films (e.g., TbFeCo or Gd FeCo), which are currently attracting more attention for applications in low-power spintronic devices, ultrafast switching and logic memories. The perpendicular exchange coupling properties of TbFeCo/GdFeCo hard/soft bilayers are systematically investigated and some new results will be presented.Keynote 2Prof. Rangsu Liu, Hunan University, ChinaSpeech Title:Visualizing Study for Formation, Evolution and Hereditary Mechanisms of Nano-Clusters during Solidification Processes of Liquid Alloy under High Pressures:In recent years, we have deeply investigated the solidification processes of liquid metals of Al, Ag, Cu, Mg Na, Pb, Zn and alloys of Mg-Zn, Mg-Y, Al-Mg, Al-Zn, Ca-Zn by molecular dynamics simulation for the systems with different sizes of 100,000, 1,000,000 and 10.000,000 atoms, respectively. By using the visualizing method, the formation, evolution and hereditary mechanisms of nano-clusters, especially, under high pressures the large-scale microstructurel evolution, the crystallization and the hereditary mechanisms during their solidification processes have been clearly analyzed and described by the cluster type index method (CTIM) proposed by authors. Recently, many important results obtained. Highly interesting, for liquid alloy Mg-Y, it is found that all the simulation systems are directly solidified into crystal structures, and the crystallization temperature Tc is enhanced almost linearly with the increase of pressure. Highly interesting, there is an important phase transformation point from FCC to BCC structures between 15 ~ 20GPa during the solidification processes. And the structures formed at 20GPa possess the admirable microstructure configurations and excellent mechanical properties of materials.Keynote 3Prof. Chen Hsu, Lungwha University of Science and Technology, TaiwanSpeech Title:Small Molecular Sensing with Graphene, Zinc oxide, and Zinc Oxalate:Small molecules such as hydrogen and methane are able to be sensible using graphene, zinc oxide (ZnO), and zinc oxalate (ZnC2O4) via Van der Waals force. First of all, graphene is generally regarded as to have the function of adsorbing hydrogen molecules, but in really the adsorbing effect is not fit the demand. Graphene does not have the function of attracting hydrogen molecules. Graphene does not have the function of bullying hydrogen molecules. The main reason is that its plane is fully occupied by functional group. The graphene reduction exhibits many defect structures and residual oxidized groups, so even if many reduction methods are proposed, it is impossible to obtain a structure close to the perfect lattice of graphene. The basal plane and the edge of the reduced graphene oxide will contain a large number of oxygen functional groups; epoxy (C=O) and hydroxyl (hydroxyl, C)-OH is formed on the base surface, and carboxyl groups (COOH) and carbonyl groups (CO, CO) are distributed at the boundary.Keynote 4Prof. Chen-Kuei Chung, Department of Mechanical Engineering, National Cheng Kung University, TaiwanSpeech Title:Fabrication and Characteristics of Nanoporous Anodic Aluminum Oxide at High Temperature:The nanoporous anodic aluminum oxide (AAO) is one important nano-template used for synthesis of nanocomposite materials or as an etching mask for pattern transfer in a variety of applications. Conventional AAO templates were synthesized using two-step potentiostatic method of direct current anodization (DCA) at low temperature (0-10°C) to avoid dissolution effect. In this talk, an effective method of hybrid pulse anodization (HPA) with normal-positive and small-negative voltages has been proposed for AAO synthesis at relatively high temperature of 15-25°C for enhancing performance of AAO structure for both the cheap low-purity (99%) and costly high-purity (99.997%) aluminum foils. The pore size distribution and circularity of AAO by HPA is much better than DCA due to its effective cooling at relatively high temperature. The HPA not only merits manufacturing convenience and cost reduction but also promotes pore characteristics of AAO at severe conditions of cheap low-purity Al foils and high temperature. Moreover, the pore diameter can be enlarged by wet etching. A new finding of AAO pore diameter highly linked to the electrolyte anions contaminated AAO prepared by HPA at low-to-high concentrations (0.3~0.9 M) of oxalic acid at 25°C. The increase of widened diameter decreased with concentration due to AAO walls containing more anions high oxalic acid concentration to decrease etching rate during widening. Some application in humidity sensing and SERS will be presented.

Determination of Crystallographic Phase and Estimation of Order Degree for Rare Earth-Transition Metal Alloy Films with Hexagonal Structures

Determination of Crystallographic Phase and Estimation of Order Degree for Rare Earth-Transition Metal Alloy Films with Hexagonal Structures

Effect of crystalline orientation and lattice distortion of FeCo spin polarization enhancement layer in perpendicular magnetic tunnel junction with RE-TM alloy films

Relationship between FeCo crystalline orientation and magnetic properties of TbFeCo/FeCo/Ta trilayer films was investigated. FeCo crystalline orientation could be controlled by changing FeCo deposition rate. Ferromagnetic Hall effect observation clarified that perpendicular component of magnetization in FeCo layer of TbFeCo/FeCo(001)/Ta were better than that of TbFeCo/FeCo(110)/Ta. Lattice spacing of both FeCo(001) films and FeCo(110) ones in the TbFeCo(50 nm)/FeCo (X nm) was also observed. Expansion ratios of FeCo(001) toward film normal direction were higher than that of FeCo(110) as increasing FeCo film thickness, and this indicated that FeCo(001) films were more favorable for magnetic coupling with rare-earth transition metal (RE-TM) alloy films than FeCo(110) ones when FeCo films become thick. However investigation of relationship between FeCo expansion ratios and magnetic properties of TbFeCo/FeCo(001) or (110) (X nm)/Ta trilayer films showed that squareness ratios of specimens with FeCo(001) were worse than that with FeCo(110).

Large spontaneous Hall angle in [Co, CoFe/Pt] multilayer

We have quantitatively investigated the Hall effect in [Co, CoFe/Pt] multilayer films. The [Co, CoFe/Pt] multilayers exhibit large spontaneous Hall resistivity ( ρ H) and Hall angle ( ρ H/ ρ). Even though the Hall resistivity in [Co, CoFe/Pt] multilayer films (2.7–4 × 10 −7 Ω cm) is smaller than that of amorphous RE–TM alloy films which show large spontaneous Hall resistivity (<2 × 10 −6 Ω cm), the Hall angle of multilayer (6–8%) is almost twice than that in amorphous rare earth–transition metal alloy films (∼3%). The Hall angle provides evidence of the effects of the exchange interaction of the Hall scattering. The exchange is between conduction electron spins and the localized spins of the transition metal. The large Hall angle of [Co, CoFe/Pt] multilayer can be considered due to the high spin polarization and high Curie temperature of Co and CoFe transition metal layers. Even though the role of interfaces and surfaces in the magnetic properties of multilayer films may dominate that of the bulk, the Hall effects in [Co, CoFe/Pt] multilayer may be mainly dominated by the bulk effect.

Evaluation of Anisotropic Film Structure of Amorphous Alloy by Computer Simulation

ABSTRACTA film growth of a virtual GdCo amorphous binary alloy was studied with a molecular dynamics simulation. A deviation of the atomic environment δ and an atomic pair distribution index η were calculated to evaluate the atomic structure of the prepared film. It was found that an anisotropic atomic distribution is induced in the film. The value of δ for a Gd atom environment is of the order of 10−4 and is almost in quantitatively agreement with the experimental value. The anelastic deformation is affected by the roughness of the substrate and becomes large in the film deposited on a smooth substrate. The value of η shows that the atomic pairs preferentially orient toward a horizontal film plane. The obtained results strongly support a single ion model as a main origin of a perpendicular magnetic anisotropy experimentally observed in amorphous rare earth-transition metal alloy films.

Magnetic and magnetostrictive properties of amorphous rare earth-transition metal alloy films

The magnetic and magnetostrictive properties of amorphous binary TbxFe100-x and DyxFe100-x and amorphous ternary (TbxDy1-x)20Fe80, (TbxDy1-x)33Fe67 and (TbxDy1-x)43Fe57 thin films are presented. The films were prepared by sputter deposition from composite targets onto nominally room temperature substrates. Magnetization, coercivity and magnetostriction measurements reflect the compositional dependence of the easy direction of magnetization in the films. In-plane magnetostrictions of over 300*10-6 were measured for some of the TbxFe100-x and (TbxDy1-x)43Fe57 films.

RELIABILITY OF Pt/Co MAGNETO-OPTICAL DISK WITH A SIMPLE STRUCTURE

The reliability of a Pt/Co Magneto-Optical disk with a simplified structure (poly-carbonate/ZnO/PtCo/UV resin) was examined with accelerated tests. After aging for 2000 hours at 80°C with 85% RH, Carrier to noise ratio was scarcely lowered, while the value of block error rate increased because of extra noise which was produced by local defects. The defects did not seem to be pin-holes as seen in the case of rare earth-transition metal alloy films. According to the Arrhenius plots of accelerated tests, the life time of the disk is estimated to be more than 10 years at room temperature.

Ellipsometric comparisons of rare earth-transition metal alloy films in connection with magneto-optical recording

The results of a comprehensive set of ellipsometric observations of 17 rare earth-transition metal amorphous alloy films are presented in terms of the optical and magneto-optical constants of the film materials. The films were prepared independently in two American and two European laboratories, one academic and the other industrial in each case. The measurements are used to emphasize the sensitivity of ellipsometry and the ability of this technique of observation to provide insight into structural features of thin films, as well as to assess the potential of the given thin film materials for the magneto-optical read-out of magnetically stored information. The advantages of measuring basic constants are also stressed.

Magnetic properties of rare-earth transition-metal alloy films prepared by oblique incidence method

Ferromagnetic thin films of Sm-Co and Sm-Fe system were prepared by the oblique incidence method. The saturation flux density of both systems decreases rapidly with the increase of Sm concentration. Coercive force of 2.0 kOe in Sm-Co and 1.0 kOe in Sm-Fe films were obtained at an incident angle of 45°. These films were magnetically anisotropic and the magnetic easy direction was always aligned for perpendicular direction of the incident plane. The structure of the film in the present work seemd to be amorphous in which microdomains were orientated by the oblique incidence, in contrast to the columnar grane structure found in Fe and Co films prepared by the oblique incidence.