T. A. Chernyshova

Thermal stability of spin valves based on a synthetic antiferromagnet and Fe50Mn50 alloy

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.

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

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.

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

Microobjects (strips) were formed by contact photolithography using Та/Ni80Fe20/Co90Fe10/Cu/Co90Fe10/Ru/Co90Fe10/Fe50Mn50/Ta spin-valves prepared by magnetron sputtering. A mutually perpendicular arrangement of uniaxial and unidirectional anisotropy axes in microobjects has been formed using two different thermomagnetic treatment regimes. The magnetoresistive sensitivity of spin valve and spin-valve-based microobject has been found to depend on the mutual arrangement of the easy magnetization axis and direction of magnetic field applied upon thermomagnetic treatment. The obtained data have been interpreted taking into account changes in the induced anisotropy and anisotropy due to the shape of the microobject.

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

The effects of annealing on the structure, magnetic hysteresis, and magnetoresistance of [Co90Fe10(15 Å)/Cu(23 Å)]n superlattices with Cr and Co90Fe10 buffer layers of different thicknesses have been studied. The optimum temperature and time of annealing that increase the magnetoresistance were shown to depend on the buffer layer thickness. The coefficients of effective interlayer diffusion due to the annealing have been determined.

Spin-flop states in a synthetic antiferromagnet and variations of unidirectional anisotropy in FeMn-based spin valves

Spin valves with a synthetic antiferromagnet have been prepared by magnetron sputtering. Regularities of the formation of single- and two-phase spin-flop states in the synthetic antiferromagnet have been studied using magnetoresistance measurements and imaging the magnetic structure. A thermomagnetic treatment of spin valve in a field that corresponds to the single-phase spin-flop state of synthetic antiferromagnet was shown to allow us to obtain a magnetically sensitive material characterized by hysteresis-free field dependence of the magnetoresistance.

Spin-Flop in Synthetic Antiferromagnet and Anhysteretic Magnetic Reversal in FeMn-Based Spin Valves

The deviation of the pinning direction from the easy axis was created in spin valves by thermomagnetic treatment. The angle between the uniaxial and the unidirectional magnetic anisotropy axes is shown to depend on the value of the field applied during the thermomagnetic treatment. Anhysteretic dependence of magnetoresistance on the magnetic field is obtained for the spin valves with crossed anisotropy configuration. The interval within which the magnetic field dependence of magnetoresistance is linear depends on the spacer thickness.

Spin Valves with the Controlled Shift of Low-Field Hysteresis Loop and High-Sensitive Sensing Elements on Their Basis

Metallic multilayer spin-valve nanostructures that comprise the exchange-coupled ferromagnet/ Ru/ferromagnet structure in the free layer have been synthesized by magnetron sputtering. For microobjects (meanders) formed from CoFe/Cu/CoFe/Ru/CoFe/FeMn/Ta spin valves with different thicknesses of ruthenium and copper layers, the dependences of the magnetoresistive sensitivity and low-field hysteresis loop shift on the meander strip width have been studied. Sensing elements characterized by high magnetoresistive sensitivity have been manufactured.

Control of Low-Field Hysteresis Loop Shift of Spin Valves

Spin valves that comprise synthetic antiferromagnet as a component of pinned layer and an exchange-coupled ferromagnet/Ru/ferromagnet structure in the free layer have been prepared by magnetron sputtering. Microobjects have been formed from spin valves by optical and electron-beam lithography. It has been shown that the shift of the low-field magnetoresistance hysteresis loop decreases as the thicknes of the Ru spacer in the free layer of spin valve increases. The almost hysteresis-free odd-field dependences of the magnetoresistance were obtained for micron-sized samples; in this case, the sensitivity is 0.2%/Oe.

Magnetization reversal and inverted magnetoresistance of exchange-biased spin valves with a gadolinium layer

FeMn-based spin valves with a gadolinium layer have been fabricated by magnetron sputtering. The magnetoresistive properties of the spin valves have been investigated at temperatures of 80–293 K. Temperature-induced switching between low- and high-resistance magnetic states has been revealed. Realization of the low- or high-resistance states depends on which magnetic moment dominates in the exchange-coupled Gd/CoFe, of Gd or CoFe. It has been shown that the switching temperature depends on the thickness of the gadolinium layer.

NiFeCo/Cu superlattices with high magnetoresistive sensitivity and weak hysteresis

The microstructure and the magetoresistive characteristics of [NiFeCo/Cu]8 superlattices prepared by magnetron sputtering with various thickness of the buffer NiFeCr layer and exhibiting a giant magnetoresistive effect have been studied. It has been found that these nanostructures are formed with a strong or weak hysteresis depending on the structure (bcc or fcc) formed in the NiFeCr buffer layer. The method of the substantial decrease in the hysteresis loop width of the magnetoresistance by using the composite Ta/NiFeCr buffer layer has been suggested.