Influence of CoFe and NiFe pinned layers on sensitivity of planar Hall biosensors based on spin-valve structures

Dinh Tu Bui, Mau Danh Tran, Huu Duc Nguyen and Hai Binh Nguyen

Abstract

This paper deals with the magnetization, magnetoresistance and planar Hall effect (PHE) of NiFe(10)/Cu(1.2)/NiFe(t_p)/IrMn(15) (nm) and NiFe(10)/Cu(1.2)/CoFe(t_p)/IrMn(15) (nm) spin-valve structures with various thicknesses of pinned layer t_p = 2, 6, 9, 12 nm and a fixed free layer NiFe of t_f = 10 nm. Experimental investigations are performed for 50 × 50 μm junctions fabricated using lithography technique. The results show that the thinner the pinned layers, the higher is the PHE sensitivity obtained in both systems. In addition, in the spin-valve structures with the same pinned layer thickness, the CoFe-based system exhibits higher magnetoresistive ratio, but lower PHE sensitivity with respect to those of the FeNi-based system. The results are discussed in terms of the spin twist as well as the coherent rotation of the magnetization in the individual ferromagnetic layers. The highest PHE sensitivity S of 110 μV (kA m⁻¹)⁻¹ has been obtained in the FeNi-based spin-valve structure with t_p = 2 nm. This result is rather promising for the spintronic biochip developments