In vitro osteoblast response to ferritic stainless steel fiber networks for magneto-active layers on implants

The use of a porous coating on prosthetic components to encourage bone ingrowth is an important way of improving uncemented implant fixation. Enhanced fixation may be achieved by the use of porous magneto-active layers on the surface of prosthetic implants, which would deform elastically on application of a magnetic field, generating internal stresses within the in-growing bone. This approach requires a ferromagnetic material able to support osteoblast attachment, proliferation, differentiation, and mineralization. In this study, the human osteoblast responses to ferromagnetic 444 stainless steel networks were considered alongside those to nonmagnetic 316L (medical grade) stainless steel networks. While both networks had similar porosities, 444 networks were made from coarser fibers, resulting in larger inter-fiber spaces. The networks were analyzed for cell morphology, distribution, proliferation, and differentiation, extracellular matrix production and the formation of mineralized nodules. Cell culture was performed in both the presence of osteogenic supplements, to encourage cell differentiation, and in their absence. It was found that fiber size affected osteoblast morphology, cytoskeleton organization and proliferation at the early stages of culture. The larger inter-fiber spaces in the 444 networks resulted in better spatial distribution of the extracellular matrix. The addition of osteogenic supplements enhanced cell differentiation and reduced cell proliferation thereby preventing the differences in proliferation observed in the absence of osteogenic supplements. The results demonstrated that 444 networks elicited favorable responses from human osteoblasts, and thus show potential for use as magnetically active porous coatings for advanced bone implant applications. © 2012 Wiley Periodicals, Inc.

Magneto-Optical Imaging of Superconductors for Liquid Hydrogen Applications

Restricted deposits of fossil fuels and ecological problems created by their extensive use require a transition to renewable energy resources and clean fuel free from emissions of CO2. This fuel is likely to be liquid hydrogen. An important feature of liquid hydrogen is that it allows wide use of superconductivity. Superconductors provide compactness, high efficiency, savings in energy and a range of new applications not possible with other materials. The benefits of superconductivity justify use of low temperatures and facilitate development of fossil-free energy economy. The widespread use of superconductors requires a simple and reliable technique to monitor their properties. Magneto-optical imaging (MOI) is currently the only direct technique allowing visualization of the superconducting properties of materials. We report the application of this technique to key superconducting materials suitable for the hydrogen economy: MgB2 and high temperature superconductors (HTS) in bulk and thin-film form. The study shows that the MOI technique is well suited to the study of these materials. It demonstrates the advantage of HTS at liquid hydrogen temperatures and emphasizes the benefits of MgB2, in particular. © 2012 Springer Science+Business Media New York.

Magneto transport characterization of the Sn-doped TbMnO3 manganites

The structural, magnetic and electrical transport properties of the Sn-doped TbMnO3 manganites are studied by X-ray diffraction, ac susceptibility, dc magnetization and electrical resistivity measurements. The Sn doping into the Tb and Mn sites of TbMnO3 compresses the unit cell and changes parameters of the antiferromagnetic phase whereas the magnetic moment of Mn are only weakly affected. The electrical resistivity of doped manganites is reduced and the activation energy EA is determined for the thermally activated conduction. © 2007 Elsevier B.V. All rights reserved.

Magneto-transport study of Nb-doped Bi/Pb2223 superconductor

The magneto-transport properties of Bi1.5Pb0.4Nb0.1Sr2Ca2Cu 3O10-x polycrystalline, superconducting ceramic are reported. The material was found to be chemically homogeneous and partially textured. The mixed state properties were investigated by measuring the electrical resistivity, longitudinal and transverse (Nernst effect) thermoelectric power, and thermal conductivity. The magnetization and AC susceptibility measurements were also performed. The variation of these characteristics for magnetic fields up to 5 T are discussed and compared to those of the zero field case. The transport entropy and thermal Hall angle are extracted and quantitatively compared to previously reported data of closely related systems. © 2003 Elsevier Science B.V. All rights reserved.

Dynamics of photo-enhanced magneto-crystalline anisotropy in diluted ferromagnetic GaMnAs

By chopping a pump beam in conventional time-resolved Kerr rotation (TRKR) experiments and measuring the time evolution of M-shaped "major" hysteresis loops of magnetic linear dichroism (Delta MLD = MLDpump-on MLDpump-off), the differential MLD signal in the presence and the absence of the pump beam, we studied the dynamics of photo-enhanced magneto-crystalline anisotropy, and found that its very long recovering time (much longer than 13 ns) might reflect the nature of the coherent coupling between photo-excited holes and localized spins in the d shell of manganese.

Easy axis reorientation and magneto-crystalline anisotropic resistance of tensile strained (Ga,Mn)As films

We present a study of magnetic anisotropy by using magneto-transport and direct magnetization measurements on tensile strained (Ga,Mn)As films. The magnetic easy axis of the films is in-plane at low temperatures, while the easy axis flips to out-of-plane when temperature is raised or hole concentration is increased. This easy axis reorientation is explained qualitatively in a simple physical picture by Zeners pd model. In addition, the magneto-crystalline anisotropic resistance was also investigated experimentally and theoretically based on the single magnetic domain model. The dependence of sheet resistance on the angle between the magnetic field and [1 0 0] direction was measured. It is found that the magnetization vector M in the single-domain state deviates from the external magnetic field H direction at low magnetic field, while for high magnetic field, M continuously moves following the field direction, which leads to different resistivity function behaviors.

Electric-tunable magneto resistance effect in a two-dimensional electron gas modulated by hybrid magnetic-electric barrier nanostructure

The electric-tunable spin-independent magneto resistance effect has been theoretically investigated in ballistic regime within a two-dimensional electron gas modulated by magnetic-electric barrier nanostructure. By including the omitted stray field in previous investigations oil analogous structures, it is demonstrated based on this improved approximation that the magnetoresistance ratio for the considered structure can be efficiently enhanced by a proper electric barrier up to the maximum value depending on the specific magnetic suppression. Besides, it is also shown the introduction of positive electrostatic modulation can effectively overcome the degradation of magnetoresistance ratio for asymmetric configuration and enhance the visibility of periodic pattern induced by the size effect, while for an opposite modulation the system magnetoresistance ratio concerned may change its sign. (C) 2009 Elsevier B.V. All rights reserved.

Magneto - Transport of electron symmetric and antisymmrtric states in highly doped InGaAs/InAlAs single quantum well

Beating patterns in longitudinal resistance caused by the symmetric and antisymmetric states were observed in a heavily doped InGaAs/InAlAs quantum well by using variable temperature Hall measurement. The energy gap of symmetric and antisymmetric states is estimated to be 4meV from the analysis of beating node positions. In addition, the temperature dependences of the subband electron mobility and concentration were also studied from the mobility spectrum and multicarrier fitting procedure.

Magneto-transport characteristics of two-dimensional electron gas for Si delta-doped InAlAs/InGaAs single quantum well

Magneto-transport measurements have been carried out on a Si heavily delta-doped In0.52Al0.48As/In(0.53)G(0.47)As single quantum well in the temperature range between 1.5 and 60 K under magnetic field up to 10 T. We studied the Shubnikov-de Haas(SdH) effect and the Hall effect for the In0.52Al0.48As/In(0.53)G(0.47)As single quantum well occupied by two subbands, and have obtained the electron concentration, mobility, effective mass and energy levels respectively. The electron concentrations of the two subbands derived from mobility spectrum combined with multi-carrier fitting analysis are well consistent with the result from the SdH oscillation. From fast Fourier transform analysis for d(2)rho/dB(2)-1/B, it is observed that there is a frequency of f(1)-f(2) insensitive to the temperature, besides the frequencies f(1), f(2) for the two subbands and the frequency doubling 2f(1), both dependent on the temperature. This is because That the electrons occupying the two different subbands almost have the same effective mass in the quantum well and the magneto-intersubband scattering between the two subbands is strong.

Magneto-optical properties of diluted magnetic semiconductor quantum dots

The magnetoexciton polaron (MP) is investigated theoretically in a diluted magnetic semiconductor quantum dot (QD), with the Coulomb interaction and the sp-d exchange interaction included. The MP energy decreases rapidly with increasing magnetic field at low magnetic field and saturates at high magnetic field for small QDs, and the dependences of the MP energy on magnetic field are quite different for different QD radii due to the different carrier-induced magnetic fields B-MP. The competition between the sp-d exchange interaction and the band gap shrinkage results in there being a maximum exhibited by the MP energy With increasing temperature. Our numerical results are in good agreement with experiment (Maksimov A A, Bacher G, MacDonald A, Kulakovskii V D, Forchel A, Becker C R, Landwehr G and Molenkamp L W 2000 Phys. Rev. B 62 R7767).

Quantum-confined magneto-Stark effect in diluted magnetic semiconductor coupled quantum wells

The magneto-Stark effect in a diluted magnetic semiconductor (DMS) coupled quantum well (CQW) induced by an in-plane magnetic field is investigate theoretically. Unlike the usual electro-Stark effects, in a DMS CQW the Lorenz force leads to a spatially separated exciton. The in-plane magnetic field can shift the ground state of the magnetoexciton from a zero in-plane center of mass (CM)/momentum to a finite CM momentum, and render the ground state of magnetoexciton stable against radiative recombination due to momentum conservation. (C) 2002 American Institute of Physics.

Oscillatory magneto-conductance in quantum waveguides with lateral multi-barrier structures

The magneto-transport properties of a narrow quantum waveguide with lateral multibarrier modulation are investigated theoretically. It is found that the magnetoconductance as a function of Fermi energy or magnetic field exhibits square-wave-like oscillations. In the presence of magnetic field, the edge states are formed near each barrier and the boundaries. Therefore, the number of edge states increases with the number of lateral barriers, leading to the increase of the propagating modes. On the other hand, owing to the tunneling effect a pair of edge states around the barrier region with opposite moving directions may be coupled and formed a circulating localized state, leading to the quenching of the related propagating states. The resulting dispersion relation exhibits oscillation structures superimposed on the bulk Landau levels. These novel conductance characteristics may provide potential applications to the fabrication of new quantum devices.