X.F. Han

Temperature dependent magnetic properties of Co nanowires and nanotubes prepared by electrodeposition method

Co nanowires (NWs) and nanotubes (NTs) with same length and different diameter have been deposited in anodized aluminum oxide templates by electrodeposition method at the room temperature. The Co NWs show hcp structure while Co NTs show poor crystalline with no strong texture. The spontaneous magnetization of the Co NWs was found to be parallel to the nanowires, while Co NTs have a transverse spontaneous magnetization. Magnetization reversal occurs by curling mode in Co nanotubes while nucleation mode in Co nanowires. Temperature dependent magnetic properties show that the thermal energy decreases at low temperature causing an increase in coercivity and saturation magnetization. The dominance of shape anisotropy in case of Co NWs is manifested by the weak temperature dependence of the enhanced coercive field. Magnetostatic interactions and magnetocrystalline anisotropy is found dominant in case of Co NTs due to their distinct geometry.

Structural characterization of the ternary phase R3(Fe,Mo)29 (R=rare earth)

In this paper, the structural characterization of the ternary phase Y-3(Fe,Mo)(29) compound has been investigated in great detail by refinement of the X-ray diffraction pattern. The structural relationship of the 3 : 29 phase with 2 : 17 and 1 : 12 phases has been studied according to theoretical calculations and experimental results. The results show that the 3 : 29 compound belongs to A(2/m) space group and the 3 : 29 compound is a kind of mixed structure of 2 : 17 and 1 : 12 structures

Large magnetoresistance of paracyclophane-based molecular tunnel junctions: A first-principles study

We report a theoretical study of magnetoresistance and spin-polarized transport of a series of paracyclophane-based molecular tunnel junctions. We predict that the molecular tunnel junction using [2.2]-paracyclophane barrier has the desired low resistance area product in combination with high magnetoresistance ratio. In addition, we find the spin-polarized conductance decreases exponentially with increasing the molecular length, indicating a nonresonant tunneling mechanism. In particular, the characteristic decay constant can be theoretically evaluated from the complex band structure of periodic paracyclophane molecule. The spin-polarized transport mechanism is systematically analyzed.

Post magnetic field annealing effect on magnetic and structural properties of Co80Pt20 nanowires and nanotubes fabricated by electrochemical method

Highly ordered Co80Pt20 nanowires (NWs) and nanotubes (NTs) have been synthesized by low cost DC electrochemical deposition method with constant stirring during the fabrication process in anodic aluminum oxide nano-templates with average pore diameter of about 200 nm. The structural and magnetic properties of nanostructures have been investigated before and after simple and magnetic field annealing. Magnetic field of 1 T has been applied during annealing process in the direction perpendicular to NWs and NTs axis. X-Ray Diffraction analysis shows face centered cubic (fcc) as the dominant phase for Co80Pt20 NWs and post annealing led to better crystallinity with retained fcc phase. Furthermore, magnetic properties, including saturation magnetization (Ms), squareness ratio (Mr/Ms), and coercivity (Hc), have been investigated as a function of annealing temperature by Vibrating Sample Magnetometer.

Fabrication and magnetic properties of La-X (X = Co, Ni, and Fe) nanotube arrays prepared by electrodeposition methods

Well-ordered La-X (X = Co, Ni and Fe) nanotubes, with the average diameter of ∼200 nm, wall thicknesses of ∼40 nm, have been fabricated into anodized aluminum oxide template by potentiostatic electrodeposition method. Various composition of La-X nanotubes were obtained by tuning the applied deposition potential. Magnetization measurements reveal that doped La could enhance the coercivity (Hc) of La-X nanotubes and their easy axis is perpendicular to the nanotube axis. There is a transition from the curling to transverse mode with increase of angle. Temperature dependent magnetization indicates the existence of superparamagnetic nanoparticles and that the surface effect results in the increase of saturation magnetization (Ms) at low temperature. Abnormal behavior of temperature dependent Hc may result from thermal excitation, magnetoelastic anisotropy, as well as oxide layer of nanotube inner surface induced coupling. These one-dimensional rare-earth transition metal nanostructures could have potential applications in novel spintronics device, ultra-small magnetic media, drug delivery, or other nanodevice.Well-ordered La-X (X = Co, Ni and Fe) nanotubes, with the average diameter of ∼200 nm, wall thicknesses of ∼40 nm, have been fabricated into anodized aluminum oxide template by potentiostatic electrodeposition method. Various composition of La-X nanotubes were obtained by tuning the applied deposition potential. Magnetization measurements reveal that doped La could enhance the coercivity (Hc) of La-X nanotubes and their easy axis is perpendicular to the nanotube axis. There is a transition from the curling to transverse mode with increase of angle. Temperature dependent magnetization indicates the existence of superparamagnetic nanoparticles and that the surface effect results in the increase of saturation magnetization (Ms) at low temperature. Abnormal behavior of temperature dependent Hc may result from thermal excitation, magnetoelastic anisotropy, as well as oxide layer of nanotube inner surface induced coupling. These one-dimensional rare-earth transition metal nanostructures could have potential app...

Nanotube wall thickness dependent magnetization reversal properties of NiFe nanotubes

Nanotube wall thickness dependent magnetization properties of NiFe nanotube arrays electrodeposited in polycarbonate membranes are investigated. A systematic variation of nanotube wall thickness (tw) has been investigated. The magnetization reversal properties are strongly influenced by the variation of tw keeping length and external radius constant.

Tunneling processes in asymmetric double barrier magnetic tunnel junctions with a thin top MgO layer

Dynamic conductance dI/dV and inelastic electron tunneling spectroscopy (IETS) d 2I/dV 2 have been measured at different temperatures for double barrier magnetic tunnel junctions with a thin top MgO layer. The resistance in the antiparallel state exhibits a normal tunnel-like behavior, while the resistance in the parallel state shows metallic-like transport, indicating the presence of pinholes in the thin top MgO layer. Three IETS peaks are the zero-bias anomaly, interface magnons, and barrier phonons in both the parallel and antiparallel states. The zero-bias anomaly is the strongest peak in the parallel state and its intensity decreases with temperature. The magnon has the largest intensity in the antiparallel state and its intensity also decreases with temperature. The origins of the dips and peaks in the dI/dV-V curve are also discussed.

Structural and magnetic properties of R2(Fe,Si)17 compounds with R=Tb and Er

The structural and magnetic properties of R2F17-xSix compounds have been investigated by means of X-ray diffraction and magnetization measurements. Substitution of Si for Fe leads to a clear reduction of the unit-cell volume. With increasing Si content, a phase transition from the Th2Ni17- to the Th2Zn17-type of structure has been observed for R=Tb, while all compounds crystallize in the Th2Ni17-type of structure for R=Er. A clear decrease of the saturation moment and an increase of the Curie temperature have been found upon Si substitution. The exchange-interaction constant J(TbFe) between the Tb and the Fe moments has been obtained from a mean-field analysis of the Curie temperature T-c. The X-ray diffraction patterns of magnetically-aligned powder samples show that the easy magnetization direction is in the plane for all compounds investigated

External electric field effects on electronic and magnetic properties at molecule-metal interfaces: Cu-phthalocyanine adsorbed on Fe(001) surface

We report the first-principles studies of adsorption of Cu-phthalocyanine (CuPc) molecules on Fe(001) surfaces using density functional theory with generalized gradient approximation. The van der Walls interaction between CuPc molecules and Fe surfaces was included with Grimme approximation. The detailed structural and electronic and magnetic properties at the interface between the CuPc and Fe(001) were obtained. More importantly, based on the understanding of adsorption configurations, we further studied the interfacial properties with considering the effect of external electric field. The results demonstrate that both the transferred charge and localized magnetic moments of adsorbed molecules can be tuned by external applied electric field.

Magnetic properties of Y(Co1−xFex)10Si2 compounds

The magnetic properties of Y(Co1-xFex)(10)Si-2 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) compounds have been studied. All compounds crystallize in ThMn12 type structures. The lattice parameters a and c increase with increasing iron content, while the Curie temperature has a maximum at about x = 0.6. The easy magnetization direction at room temperature changes from basal plane to the c-axis at about x = 0.2. The anisotropy field obtained by the SPD technique reaches a maximum at x = 1.0, with values of 2.1 T at room temperature and 2.6 T at 77 K respectively.