Magnetoresistive Properties of Discontinuous Thin-film Systems Based on Ni80Fe20 and SiOx (x ≅ 1)

The paper presents the results of experimental studies of the structure and magnetoresistive properties of discontinuous multilayers [Ni80Fe20(d)/SiOx(5)]5/Substrate, x ≅ 1. The method of layer-by-layer electron-beam evaporation was used for the deposition of samples. The thickness of the magnetic layers (d) varied from 4 to 8 nm. To investigate the annealing temperature effect on magnetoresistive properties, samples were annealed at step-increasing temperatures within the Tann  300 – 700 K range. It was demonstrated that an anisotropic character of magnetoresistance (positive longitudinal and negative transverse magnetoresistance) is observed for all as-deposited and annealed at 400 K samples, which are typical for single-layer structurally continuous films of the Ni80Fe20 alloy. Familiar to all field dependences (R/R0)(B) with an anisotropic character is a sharp change in magnetoresistance in the field range of – 10 – + 10 mT and a tendency to saturate in more vital fields. It was found that annealing the samples at a temperature of 500 K with d = 4 – 5 nm leads to the transition to isotropic magnetoresistance. This is due to an increase in the size of permalloy granules to 10 nm and the formation of insulator channels with a width of 1 – 2 nm between them. The maximum values of isotropic magnetoresistance at room temperature are about 0.1 %. After annealing at a temperature of 600 K, the reappearance of anisotropic magnetoresistance in structures with d = 4 nm is observed. The reason for this transition is the destruction of the structural continuity of the insulator layers and, as a result, the formation of a metal cluster throughout the structure. It is shown that an increase in the annealing temperature to 700 K does not cause a change in the nature of the magnetoresistance but only leads to a rise in its value.