The relation between giant magnetoresistance (GMR) and the substrate temperature was investigated in sputtered Co/Cu multilayers. The magnetoresistance (MR) ratio is increased as the substrate temperature is decreased. The increase in the MR ratio is considered to be caused by the improvement in the sharpness of interfaces as concluded from the satellite peak intensity of the x-ray diffraction. The rough interfaces reduce the antiferromagnetic coupled areas and result in the MR ratio decrease. By lowering the substrate temperature to 20 °C, the MR ratio of 80% at room temperature was obtained.

The background pressure dependence of magnetoresistance (MR) ratio of Co/Cu multilayer films and the effect of the Fe buffer layer were studied. Secondary ion mass spectrometry (SIMS) measurement of the films and in situ quadrupole mass spectrometry (QMS) analysis in conjunction with background pressure dependence of MR ratio confirmed that the oxidation of Co/Cu gives a crucial influence to the giant magnetoresistance (GMR) effect. The oxidation of Co/Cu weakens the antiferromagnetic coupling, and results in the low MR ratio. The Fe buffer layer absorbs the residual oxygen, and this leads to the increase of the MR ratio. The MR ratio of (Co1 nm/Cu1 nm)100/Fe2.5 nm film deposited under low background pressure and high deposition rate so as to suppress oxidation reached over 80% at RT and 160% at 2 K.

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