Enhancement Of Magnetoresistance Effect Research Articles

Electrical transport and magnetoresistance properties in (1 − x)La 2/3Ca 1/3MnO 3/ xSb 2O 5 composites

The composites with the nominal composition of (1 − x)La 2/3Ca 1/3MnO 3 (LCMO)/ xSb 2O 5 were fabricated, and their electrical transport and magnetoresistance (MR) behavior were investigated. Experimental results show that the metal–insulator transition temperature ( T MI) and resitivity ( ρ) of the composites are largely dependent on Sb 2O 5 addition level x. T MI shifts downwards and ρ increases with the increase of x at the range of x ≤ 3%, but T MI shifts upwards and ρ decreases with further increasing of x ≥ 3%. The high temperature ( T > T MI) semi-conducting part of the ρ data follow a small polaron hopping (SPH) conduction mechanism, and the metallic behavior of the samples ( T < T MI) fits the model in terms of electron–magnon scattering of the carriers. Furthermore, the MR effect can be largely enhanced over a wide temperature range in the composites compared with pure LCMO. At 3 T field, the MR rises from a base value ∼46%, for pure LCMO, to a maximum value of ∼86.7% for the case of x = 3%. It is argued that the enhancement of MR effect is attributed to the enhanced spin-polarized tunneling, which is manipulated by magnetic disorder especially at LCMO grain boundaries caused by Sb 2O 5 addition.

Suppression of interlayer coupling and enhancement of magnetoresistance in spin valves with oxide layer

The interlayer coupling field (Hint) between the free and pinned ferromagnetic (FM) layers in an exchange-biased spin valve deposited by magnetron sputtering is usually dominated by the Néel “orange peel” coupling. The orange peel coupling is suppressed dramatically when an oxide layer (OXL) is inserted into the free/pinned FM layers due to smoother surface roughness at the interface. Hint decreases with increasing oxygen exposure dose of the free/pinned FM layers to pure O2 gas. And it is found that Ruderman–Kittel–Kasuya–Yoshida exchange coupling dominates in OXL spin valves due to smoother surface roughness and enhanced specular electron scattering at the interface between OXL and pinned/free FM layers, which also results in enhancement of magnetoresistance effect.

Structural, magnetic and transport properties of Sc-doped La0.7Sr0.3MnO3

The Sc-doped La0.7Sr0.3MnO3 polycrystallines were prepared by thermal decomposition of complexes of metal ions with ethylenediamine-tetraacetic acid (EDTA). The dependence of structural, magnetic and transport properties on Sc doping was investigated. Moderate Sc doping level results in a sharp drop in Curie temperature, an increase in resistance and enhancement of magnetoresistance effect. At temperatures aboveTMI,R(T) can be described asR(T) = R0exp(T0/T)1/4, which indicates that conduction takes place by hopping between the localized states. The experimental data reveal that the change in magnetoresistance property is related to the structure.

Enhanced tunneling magnetoresistance ofFe−Al2O3granular films in the Coulomb blockade regime

Tunneling giant magnetoresistance (MR) effects in ${\mathrm{F}\mathrm{e}\ensuremath{-}\mathrm{A}\mathrm{l}}_{2}{\mathrm{O}}_{3}$ granular films that were prepared by cosputtering have been reported. MR of the samples have been measured over a wide range of volume fractions of Fe (x) and it takes a maximum of 4.4% at room temperature for the film with $x=0.45$ when a magnetic field of 10 kOe was applied parallel to the film plane. The small tunneling MR at room temperature can be explained by the results of spin-flip processes. However, the observed temperature dependence of MR reveals an enhanced tunneling MR effect in the Coulomb blockade regime. The MR for $x=0.45$ remarkably increases with decreasing temperature resulting in $\mathrm{MR}=20.1%$ at 5 K, which is larger than the theory value for Fe-based granular systems. This enhancement of MR effect in the Coulomb blockade regime seems to arise not only from the suppression of the spin-flip process with decreasing temperature, but also from the spin dependent cotunneling in the Coulomb blockade regime.