Towards Flexible Magnetoelectronics: Buffer‐Enhanced And Mechanically Tunable GMR Of Co/Cu Multilayers On Plastic Substrates

Magnetoas well as flexible electronics have emerged as two of themost rapidly developing technologies of the 21st century. Low processing costs and mechanical stretchability render flexible electronic devices highly attractive for a variety of applications such as flexible circuit boards, solar cells, paper-like displays, and sensitive skin. The giant magnetoresistance (GMR) effect, discovered in 1988, is broadly applied in read heads in hard disk drives or in nonvolatile memory devices, and has helped to initiate the development of magnetoelectronics (also known as spintronics). Magnetoelectronics on flexible substrates allows the direct integration of GMR devices onto bendable supports, which can be shaped into almost any arbitrary geometry. However, only limited progress has been made over the last years towards flexible magnetoelectronics due to the relatively small GMR effect achievable on plastics. The establishment of highperformance flexible magnetoelectronics would open straightforward access to practical magnetic field sensors, as well as promising perspectives towards accurate fine-tuning of the GMR by substrate stretching or bending. In this study, we show that the GMR effect of Co/Cu multilayers (MLs) on a flexible plastic substrate can be enhanced up to 200% by introducing an appropriate buffer layer. GMR values of Co/Cu MLs on buffered flexible substrates are even larger than those on thermally oxidized Si substrates due to an increased antiferromagnetic coupling fraction. Furthermore, we experimentally demonstrate to tune (increase or decrease) the GMR effect, by applying external tensile stress through substrate stretching. The sample structure is schematically shown in Figure 1a. Following a 1nmCo bottom layer directly deposited on oxidized Si substrates or on flexible plastic substrates, N periods of Co/Cu bilayers were deposited. Except where stated differently, the plastic substrate in this study is made out of polyester, and the