  We develop a high-throughput method for measuring the composition dependence
of magnetoresistance (MR) and spin-transfer-torque (STT) effects in
current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices and
report its application to the CoFe system. The method is based on the use of
composition-gradient films deposited by combinatorial sputtering. This
structure allows the fabrication of devices with different compositions on a
single substrate, drastically enhancing the throughput in investigating
composition dependence. We fabricated CPP-GMR devices on a single GMR film
consisting of a Co$_{x}$Fe$_{1-x}$ (0 $\le$ $\textit{x}$ $\le$ 1)
composition-gradient layer, a Cu spacer layer, and a NiFe layer. The MR ratio
obtained from resistance-field measurements exhibited the maximum in the broad
Co concentration range of 0.3 $\le$ $\textit{x}$ $\le$ 0.65. In addition, the
STT efficiency was estimated from the current to induce magnetization reversal
of the NiFe layer by spin injection from the Co$_{x}$Fe$_{1-x}$ layer. The STT
efficiency was also the highest around the same Co concentration range as for
the MR ratio, and this correlation was theoretically explained by the change in
the spin polarization of the Co$_{x}$Fe$_{1-x}$ layer. The results revealed the
Co$_{x}$Fe$_{1-x}$ composition range suitable for spintronic applications,
demonstrating the advantages of the developed method.
