Fabrication of exchange-biased spin valves with CoFeB amorphous layers

Amorphous Co72Fe8B20 is a soft ferromagnetic material with a high electrical resistivity and is, therefore, unique for use as the active layer in giant magnetoresistance (GMR) spin-valve structures. CoFeB/Cu/CoFeB/FeMn spin-valve structures were prepared by magnetron sputtering with varying FeMn thickness, deposition sequence, CoFeB deposition rate, Cu deposition rate, applied magnetic field, and annealing treatment, and their magnetic and magnetotransport properties were investigated by superconducting quantum interference device magnetometry and four-terminal magnetoresistance measurements. FeMn, above a critical thickness of 100 Angstrom, is found to be a suitable biasing layer only if deposited on top of CoFeB. Optimum CoFeB and Cu thicknesses and deposition rates were also determined. A modest GMR ratio of 1.2% in a field range 10 Oe<H<15 Oe is achieved at T=10 K in a CoFeB (40 Angstrom)/Cu(30 Angstrom)/CoFeB(20 Angstrom)/FeMn(100 Angstrom) structure. However, we expect that the size of the GMR effect can be tailored independently by suitable engineering of the CoFeB/Cu interface. (C) 1999 American Institute of Physics. [S0021-8979(99)64108-1].