Fabrication of exchange-biased spin valves with CoFeB amorphous layers

Amorphous Co72Fe8B20 is a soft ferromagnetic material with a high electrica l resistivity and is, therefore, unique for use as the active layer in gian t magnetoresistance (GMR) spin-valve structures. CoFeB/Cu/CoFeB/FeMn spin-v alve structures were prepared by magnetron sputtering with varying FeMn thi ckness, deposition sequence, CoFeB deposition rate, Cu deposition rate, app lied magnetic field, and annealing treatment, and their magnetic and magnet otransport properties were investigated by superconducting quantum interfer ence 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 thic knesses 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 Angs trom)/Cu(30 Angstrom)/CoFeB(20 Angstrom)/FeMn(100 Angstrom) structure. Howe ver, we expect that the size of the GMR effect can be tailored independentl y by suitable engineering of the CoFeB/Cu interface. (C) 1999 American Inst itute of Physics. [S0021-8979(99)64108-1].