Spin-dependent effects in inelastic scattering

The differential cross sections for the inelastic scattering of 10 MeV, 19.6 MeV, 30.4 MeV, 40 MeV and 49.35 MeV protons to the 2⁺ state (1.409 MeV) in ⁵⁴Fe and of 19.6 MeV protons to the 2⁺ state (0.846 MeV) in ⁵⁶Fe are analyzed in conjunction with the available data on the asymmetries and spin-flip probability amplitudes. The scattering amplitudes for both one step (valence plus core polarization) and two step (intermediate resonance) processes are evaluated using an antisymmetrized distorted wave approximation. Collective model representations for both the one step (core polarization) and two step (intermediate resonance) processes are used, and included are the effects of deforming the full Thomas spin-orbit potentials. The one step processes are fixed by the analyses of the scattering of 30.4, 40 and 49.35 MeV protons, with the core polarization contributions being constrained by the B(E2) values for the γ-ray deexcitation of the 2⁺ states. The analyses of the 19.6 MeV data demonstrates the need for an extra (two step) contribution to the reaction process and are consistent with the virtual formation of an L = 3 giant resonance. The 10 MeV data most certainly demonstrate compound nucleus effects but could also have some strength due to the virtual formation of an intermediate L = 2 giant resonance. The resonance parameters are consistent with recent information concerning the mass variation of giant resonances.     

Giant injection magnetoresistance in the heterostructure gallium arsenide/granular film with cobalt nanoparticles

We have studied the electron transport and have observed new phenomenon—the positive injection magnetoresistance on heterostructures gallium arsenide/granular film SiO₂ with Co nanoparticles and gallium arsenide/granular film TiO₂ with Co island layers.     

Spin-dependent scattering in multilayered magnetic rings

Narrow mesoscopic NiFe/Cu/Co elliptical rings exhibit room-temperature giant magnetoresistance with distinct resistance levels corresponding to three different micromagnetic states. The highest and lowest resistance states of the multilayer rings correspond to the Co layer being in a bidomain state, antiparallel or parallel, respectively, to the NiFe, while the intermediate resistance corresponds to the Co layer being in a vortex state. Micromagnetic simulations suggest that the behavior of these rings is dominated by magnetostatic interactions between the domain walls in the Co and NiFe layers. Additional magnetization states in the NiFe at low applied fields can account for the minor loop behavior.     

Giant magnetoimpedance in thin amorphous and nanocrystalline microwires

We present the results on Giant magneto-impedance effect (GMI) in amorphous and nanocrystalline microwires at frequencies until 4 GHz, paying special attention to tailoring the frequency and magnetic field dependence of the GMI effect. Correlation between magnetoelastic anisotropy and magnetic field dependences of diagonal and off-diagonal impedance components are observed.     

Giant piezoresistance effects in silicon nanowires and microwires

The giant piezoresistance (PZR) previously reported in silicon nanowires is experimentally investigated in a large number of depleted silicon nano- and microstructures. The resistance is shown to vary strongly with time due to electron and hole trapping at the sample surfaces independent of the applied stress. Importantly, this time-varying resistance manifests itself as an apparent giant PZR identical to that reported elsewhere. By modulating the applied stress in time, the true PZR of the structures is found to be comparable with that of bulk silicon.     

Spin-dependent electron-proton scattering in the Delta-excitation region

We report on measurements of the cross section and provide first data on spin correlation parameters A(TT') and A(TL') in inclusive scattering of longitudinally polarized electrons from nuclear-polarized hydrogen. Polarized electrons were injected into an electron storage ring operated at a beam energy of 720 MeV. Polarized hydrogen was produced by an atomic beam source and injected into an open-ended cylindrical cell, located in the electron storage ring. The four-momentum transfer squared ranged from Q2 = 0.2 GeV(2)/c(2) at the elastic scattering peak to Q2 = 0.11 GeV(2)/c(2) at the Delta(1232) resonance. The data provide a stringent test of pion electroproduction models.     

Giant magnetoresistance in Ce-doped manganite systems

The fascinating properties like giant magnetoresistance (GMR) effect, metal-insulator transition, charge ordering phenomenon etc. have made the divalent ion doped RMnO₃ (R = rare-earth elements) an attractive system for investigation. Resistivity of these compounds shows a peak near the ferromagnetic transition temperature (T _c ). The application of magnetic field inhibits the spin-disorder scattering and the resistivity decreases drastically. Keeping electrondoped superconductor Nd_2?x Ce _x CuO₄ in mind we have doped RMnO₃ (R = La, Pr, Nd) with tetravalent Ce ion. These compounds are very susceptible to the annealing treatment and belong to the orthorhombic perovskite phase. They show a very high value of resistivity at the peak and under the magnetic field the GMR effect is observed. For La_0.7Ce_0.3MnO₃ and Pr_0.7Ce_0.3MnO₃ the magnetoresistance ratio reaches about 54% and 82.5% respectively at 7.7 T. With the increase of the temperature the magnetic state changes from ferromagnetic to paramagnetic regime. This magnetic transition is not very sharp and the resistivity peak appears at a temperature higher than T _c .     

Giant magnetoresistance in a ferromagnet-polymer system

Giant magnetoresistance in a ferromagnet-electroactive polymer-nonmagnetic metal structure is studied. The insulator-to-metal transition in the conductivity of the system is attributed to the change in the shape of the current-voltage characteristics of the sample in a magnetic field. It is concluded that the giant magnetoresistance observed in the experiment may be of injection nature, and this is why the effect is realized at the ferromagnet-electroactive polymer interface alone.     

Giant magneto impedance in electroplated NiFeMo/Cu microwires

Electroplated soft magnetic FeNiMo alloy films on Cu mircrowires show magneto impedance effects larger than 1000%. The magnetic anisotropy generated by the axial deposition of the alloy seems to be an important factor for the achievement of magnetoimpedance. The extent of this effect also increases with the layer thickness. Furthermore, the impedance is markedly improved after the annealing of the coating under an external magnetic field.     

Spin-dependent tunneling in Co/insulating granular systems: an AC approach

The spin-dependent tunneling of cobalt clusters embedded in Al₂O₃ or SiO_x has been analyzed as a function of the frequency at room temperature. Two sets of samples, with one or several layers of clusters, have been produced by alternate physical deposition of the metal and the insulator. The impedance versus frequency curves were measured with and without an external magnetic field. The results suggest that when the distance between successive cluster layers is small, some correlations between the cluster positions are present.     

Giant magnetoimpedance in glass-covered amorphous microwires at microwave frequencies

In this work, results on the giant magnetoimpedance (GMI) of a glass-covered amorphous microwires with nominal compositions Co_70.4Fe_4.6Si₁₅B₁₀ and Fe_77.5Si_7.5B₁₅ are presented. The impedance Z=R+iX has been investigated as function of frequency (up to 1.8 GHz) and magnetic field (up to ±400 Oe), using a HP4396B impedance analyzer and an appropriate coaxial microwave cavity. The effects of the thermal treatments (Joule heating, from 20 mA up to 100 mA for 10 min) for anisotropy induction and, as a consequence, for GMI effect have been investigated.     

Giant magnetoresistance:history,development and beyond

With the discovery of giant magnetoresistance(GMR),research effort has been made to exploiting the influence of spins on the mobility of electrons in ferromagnetic materials and/or artificial structures,which has lead to the idea of spintronics.A brief introduction is given to GMR effects from scientific background to experimental observations and theoretical models.In addition,the mechanisms of various magnetoresistance beyond the GMR are reviewed,for instance,tunnelling magnetoresistance,colossal magnetoresistance,and magnetoresistance in ferromagnetic semiconductors,nanowires,organic spintronics and non-magnetic systems.