Temperature dependence of magnetoresistive properties in bottom spin valve films employing very thin Cu spacers

Abstract

Temperature dependence of magnetoresistive properties in bottom spin valve films having very thin Cu spacers are reported. NiFeCr55 angstrom/NiFe10 angstrom/IrMn70 angstrom/CoFet angstrom/Ru4 angstrom/CoFe(t+3)angstrom/Cu/CoFe t angstrom/NiFe10 angstrom/Ta50 angstrom bottom spin valve films were deposited using a DC magnetron sputter deposition system. Magnetoresistance (MR) ratio reached a maximum of 13.5% and 11.9% at the Cu thickness of 10.4 angstrom, when the thickness of the CoFe layers t was 20 and 10 angstrom, respectively. Unlike the top spin valves reported earlier, the dip in the MR ratio was not observed when the interlayer coupling between the free layer and reference layer became zero. Sheet resistance change (DRs) reached a maximum of 4.22 Omega/square at the Cu spacer thickness of 10 angstrom when the CoFe thickness t was 10 angstrom. Temperature dependences of MR ratio, DRs, interlayer coupling field (H-i), and sensitivity showed mostly monotonic decrease as the temperature was increased up to 200 degrees C. It turns out that DRs for the film having 10.4 angstrom of Cu spacer thickness at 200 degrees C was larger than the DRs for the film having 20 angstrom of Cu spacer thickness at 40 degrees C. This suggests a high output voltage of the spin valve sensor made of the thin Cu spacer even at high operating temperature. These very thin Cu spacers could be utilized for very small devices where the interlayer coupling field is dominated by high demagnetizing fields. (c) 2007 Elsevier B.V. All rights reserved.