Giant Magnetoresistance and Soft Magnetic Properties of NiFeCo/Cu Multilayers
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GIANT MAGNETORESISTANCE AND SOFT MAGNETIC PROPERTIES OF NiFeCo/Cu MULTILAYERS S. TSUNASHIMA, M. JIMBO*, T. KANDA, S. GOTO, AND S. UCHIYAMA Nagoya University, Nagoya, 464-01 Japan. *Daido Institute of Technology, Nagoya, 457 Japan. ABSTRACT Giant magnetoresistance(GMR) and soft magnetic properties together with their structural characteristics were investigated for Ni 6 6Fe 1 6 Co 1 8/Cu multilayers. The multilayers were prepared by the conventional rf sputtering method on glass or Si substrates using various buffer layers including Fe, NiFeCo, NiFe and CoZr. Although most of the multilayers exhibited (111) preferred orientation, Fe buffered multilayers showed a considerable (200) Xray diffraction peak at Cu thicknesses around 1 nm and 2.2 nm which corresponded to the peak positions of GMR. By using fcc or amorphous underlayers the (200) diffraction intensity decreased while antiferromagnetic coupling strength was much reduced. Cross-sectional transmission electron micrograph revealed that the (100) oriented multilayer was grown on the (100) oriented Fe underlayer. By controlling the crystal orientation and the layer structure, significantly large magnetoresistance ratio of more than 10 % can be achieved in a field as low as 30 Oe. INTRODUCTION Since the giant magenetoresistance(GMR) effect has been found in Fe/Cr and Co/Cu multilayers(MLs), many efforts have been made to achieve small saturation fields while maintaining large MR[1-6]. Magnetic multilayers with the GMR that consist of soft magnetic layers are of technological interest for the application of magnetoresistance heads. Shinjo and Yamamoto 111obtained an MR ratio of 6% with a field change of 50-100Oe by using NiFe/Cu/Co/Cu MLs; NiFe layers are soft magnetic, while Co layers are hard. When the field strength is in between the coercive fields of the Co and NiFe layers and the exchange coupling is low enough, antiferromagnetic ordering occurs during the magnetization process. Sakakima and Satomi[2] examined similar structure of NiFeCo/Cu/Co/Cu MLs, and obtained an MR ratio of 15% in a field as low as 100 Oe. Another approach is the so-called spin-valve structure[3], where two soft magnetic layers, one of which is constrained by exchange anisotropy, are separated by a noble metal layer. The magnetic layers are not coupled antiparallel, giving large changes of resistance at low fields. Multilayers with a simple structure of NiFe/Cu were examined by Parkin[4] and by Nakatani et al[51. They both found oscillation in saturation magnetoresistance as a function of Cu spacer layer thickness. The MR ratio at the first peak of the oscillation was 16 to 19 % at room temperature with saturation fields of 600 to 2 kOe. These fields seem still too high for the MR heads. Since the saturation fields become exponentially smaller with increasing spacer layer thickness, it is worthwhile to try the second peak as is in the case of the spin-valve. In case of NiFe/Cu Mls, however, the GMR becomes smaller than 10% and sometimes does not appear[4]. This may be due to the very weak
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