Effect of grain size on the properties of the CoFe–NiFe/NiMn top spin valve

Abstract

The top spin valve (TSV) of NiFe 60 Å/CoFe 20Å/Cu 29 Å/CoFe 20Å/NiFe 20Å/NiMn 200 Å has been deposited on a NiFeCr seed layer on a Si/SiO2 substrate using magnetron sputtering. After deposition, the samples were subjected to ex situ magnetic annealing at 270 °C to establish the pinning field of the CoFe–NiFe pinned layer. The structure, magnetic, and magnetoresistive properties of the TSV were characterized by x-ray diffraction (XRD) and magnetic and magnetotransport measurements. It was found that the grain size of the CoFe–NiFe and NiMn layers of the TSV, as determined from XRD using Scherrer’s equation, can be controlled by changing the composition and thickness of the NiFeCr seed layer. It was also found that the grain size of the NiMn layer, and especially the CoFe–NiFe layer of the TSV, correlates with both the giant magnetoresistance (GMR) ratio (ΔR/Rmin) and pinning field of the CoFe–NiFe pinned layer. The GMR ratio increases from 3% to 12% and the pinning field decreases from 800 to 50 Oe as the CoFe–NiFe grain size increases from 90 to 210 Å.