Negative Magnetoresistance in Dual Spin Valve Structures With a Synthetic Antiferromagnetic Free Layer

• Published in: IEEE transactions on magnetics Vol. 45; no. 6; pp. 2403 - 2406
• Main Authors: Fowley, C., Chun, B.S., Coey, J.M.D.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01.06.2009; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Antiferromagnetic materials; Asymmetry; Chromium; Copper; Cross-disciplinary physics: materials science; rheology; Dual spin valve; Educational institutions; Electrons; Exact sciences and technology; Ferromagnetism; Giant magnetoresistance; Iron; Magnetic separation; Magnetism; Magnetoresistivity; Materials science; negative GMR; Oscillations; Other topics in materials science; Physics; Scattering; Spacers; Spin valves; synthetic antiferromagnet; Valves; negative GMR; Magnetoresistance; Dual spin valve; synthetic antiferromagnet; Magnetic properties
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/TMAG.2009.2018589

Giant magnetoresistance (GMR) in spin valves is due to spin-dependent scattering occurring at ferromagnet/normal metal (F/N) interfaces and/or in the ferromagnetic layers. In a spin valve with a typical F/N/F structure where the spin scattering asymmetry factor (alpha) of both F/N interfaces is the same (more or less than 1), the GMR is expected to be positive. If alpha is greater than one at one F/N interface and less than one at the other F/N interface, however, the GMR is expected to be negative. Here, we show that the F1/Cu/SAF/Cu/F2/IrMn dual spin valve structure exhibits negative GMR, where F1 and F2 are CoFe and SAF = CoFe/Ru t/CoFe, due to both opposite electron spin scattering asymmetry factor at the CoFe/Ru/CoFe interfaces as well as the electrical separation of the overall structure into two GMR spin valves connected in parallel. A GMR of 6% is observed in the structure without the Ru spacer layer, insertion of a 0.6 nm thick Ru in the SAF results in a negative GMR ratio of -3% , which becomes positive again at the Ru thickness of 0.8 nm, the oscillation from positive to negative MR is consistent with interlayer exchange coupling period across the Ru spacer.