Thermal variation of current perpendicular-to-plane giant magnetoresistance in laminated and nonlaminated spin valves

The current perpendicular-to-plane (CPP) giant magnetoresistance (GMR) was investigated as a function of temperature in 500 nm diameter spin-valve pillars of the form PtMn 7 nm/AP2/Ru 0.8 nm/AP1/Cu 3.2 nm/F. AP2/RU/AP1 represents a synthetic ferrimagnetic pinned layer and F is either a simple Co ₅₀Fe ₅₀ 5 nm free layer or a laminated (Co ₅₀Fe ₅₀ 1 nm/Cu 0.3 nm)4/Co ₅₀Fe ₅₀ 1 nm free layer. The purpose of the lamination is to increase the CPP resistance by taking advantage of the large CoFe/Cu interfacial resistance. As expected, we observed that the CPP resistance and absolute magnetoresistance (AΔR) are increased in the laminated structure. However, the CPP magnetoresistance ratio (AΔR) does not increase as much as expected if considering the increase in the relative resistance weight of the active part of the spin valve due to lamination. To understand this observation, the semiclassical theory of CPP GMR including bulk and interfacial spin relaxation effects was used to quantitatively interpret the data between 2 and 300 K. The quantitative analysis indicates that a quite significant spin-memory loss takes place at CoFe/Cu interfaces which reduces the expected GMR of the laminated multilayer. The spin-memory loss at Co ₅₀Fe ₅₀/Cu interfaces is found to be 52% at 4 K and 56% at 300 K, to be compared with 25% at 300 K for Cu/Co interfaces [Eid et al., J. Appl. Phys. 93, 3445 (2003) and Bozec et al., J. Appl. Phys. 87, 4334 (2000)].