L. I. Naumova

High-sensitive hysteresisless spin valve with a composite free layer

Method of dc magnetron deposition has been used to prepare metallic nanostructures of the (Si, Al2O3, glass)/Ta/[NiFe/CoFe]/Cu/CoFe/(FeMn, MnIr)/Ta spin-valve type with a composite “free layer” Ni80Fe20/Co90Fe10. A three-stage method of decreasing hysteresis of the free layer has been suggested. The dependence of the magnitude of the giant magnetoresistance and hysteresis has been investigated depending on the angle between the direction of the easy magnetization axis of the free layer and the direction of the applied magnetic field in the plane of layers. It is shown that in the spin valves studied the hysteresis can be reduced to a few tenths of an oersted at the magnitude of the magnetoresistance more than 8%. In the case of a spin valve with an antiferromagnet Fe50Mn50 the magnetoresistive sensitivity in the range of the hysteresisless variation of the magnetoresistance was equal to 1%/Oe, whereas the maximum sensitivity in the presence of a hysteresis exceeded 6%/Oe. A greater sensitivity (2.5%/Oe) at the magnitude of the free-layer hysteresis of 0.6 Oe was obtained for spin valves on the basis of the antiferromagnetic Mn75Ir25 alloy. For them, the maximum magnetoresistance was equal to 11.6%.

Giant changes in magnetic and magnetoresistive properties of CoFe/Cu multilayers at subnanosized variations in the thickness of the chromium buffer layer

The article discusses the magnetic and magnetoresistive properties of the [Co90Fe10/Cu]n multilayers prepared by magnetron sputtering as a function of the type of the substrate and the material and thickness of a buffer layer (Co90Fe10, Cu, Cr, Fe). The multilayers with a chromium buffer layer exhibit a sharp transition from low-coercive to high-coercive state at low variations in the thickness of the chromium layer (from 15 to 20 Å). It has been demonstrated that the revealed sudden change in the hysteresis properties of the multilayers with a Cr buffer layer is accompanied by structural changes in the Cu and Co90Fe10 layers, characterized by the disappearance of the 〈111〉 texture at tCr > 20 Å. It has been found that the most efficient buffer layer, which at room temperature ensures a threefold increase in the magnetoresistance at a minimum increase in hysteresis, is the Co90Fe10 (15 Å) layer. It has been established that the substrate type ((100)Si,

Degree of perfection of the 〈111〉 texture and the hysteresis of magnetoresistance in MnIr-based top spin valves

(10\bar 12)

Sharp Angular Dependence of Free Layer Coercivity in Spin Valves with Ferromagnetic Interlayer Coupling

Al2O3, glass) does not exert a significant effect on the magnetoresistive properties of the multilayers studied.

Magnetoresistive sensitivity and uniaxial anisotropy of spin-valve microstrips with a synthetic antiferromagnet

The hysteresis of magnetoresistance has been studied as a function of the angle between the magnetic field applied in the plane of layers and the easy axis for spin valves with the composition [Ta, (Ni80Fe20)60Cr40] /Ni80Fe20/Co90Fe10/Cu/Co90Fe10/Mn75Ir25/Ta. In spin valves with a strong interlayer coupling at a small deviation of the magnetic-field direction from the easy axis there was revealed a sharp (to a few tenths of an oersted) narrowing of the hysteresis loop of the magnetization reversal of the free layer. Based on an analysis of the angular dependences of the hysteresis, critical angles at which a change occurs in the mode of the magnetization reversal have been determined. In terms of the Stoner-Wohlfarth model of the coherent rotation of the magnetization, the angles at which a transition to an anhysteretic magnetization reversal is observed have been estimated theoretically for the spin valves with a strong interlayer coupling.

Effect of annealing on magnetoresistance and microstructure of multilayered CoFe/Cu systems with different buffer layer

Dc magnetron sputtering was used to prepare spin valves based on an Mn75Ir25 antiferromagnet with a composite free layer Ni80Fe20/Co90Fe10 and different thicknesses of the magnetic and nonmagnetic layers. Investigations of the microstructure and texture have been performed using X-ray diffraction and transmission electron microscopy. Field dependences of the magnetoresistance were measured for samples with a different degree of perfection of the axial texture 〈111〉: from sharp (with an orientation spread angle of 3.3°) to strongly smeared (with an orientation spread angle of 19.3°). It has been found that the width of the low-field loop of the magnetoresistance hysteresis increases monotonically with a decrease in the texture strength from sample to sample. The results are interpreted with allowance for the dependence of the hysteresis-loop width on the mutual orientation of the external magnetic field and easy axes of individual crystallites of the textured film.

Giant Magnetoresistance of Metallic Exchange-Coupled Multilayers and Spin Valves

Magnetron sputtering was used to prepare spin valves with the Ta/Ni80Fe20/Co90Fe10/Cu/Co90Fe10/Ru/Co90Fe10/Fe50Mn50/Ta composition. Changes in the functional characteristics of the spin valves were studied in a temperature range of–180 to +160°C. The maximum temperature at which the functional characteristics of spin valve remain unchanged was shown to depend on the relationship of thicknesses of Co90Fe10 layers separated by the Ru interlayer.

Crystal structure and magnetic properties of Fe/Cr/Gd superlattices

The dependence of free layer coercivity on the angle between easy axis and applied magnetic field was studied on [Ta, (Ni80Fe20)60Cr40]/ Ni80Fe20/Co90Fe10/Cu/Co90Fe10/Mn75Ir25/Ta spin valves with various interlayer coupling. Sharp decrease on the angle was observed for ferromagnetically coupled spin valves. The coercivity was reduced down to tenth of Oersted without any decrease of GMR-effect by forming nearly parallel anisotropy configuration. The angles at which the transition from hysteretic to anhysteretic magnetic reversal takes place are detected by analyses of the angle dependence of coercivity. Interpretation of experimental data is based on Stoner-Wohlfarth coherent rotation approach.