Fabrication and Analysis of PM-biased Spin-valve Sensors

摘要

@@ Since the pioneered work by Dieny et al. in 1991 , Spin valve has proved to be one of the best materials applied in a variety of magnetic devices, e.g. read heads due to higher sensitivity and better linearity compared to conventional Hall-effect sensing elements and anisotropic magnetoresistive (AMR) sensing elements . For read head applications, obtaining much higher-sensitive sensors is always one of the key objections to meet the requirement of continuouslyincreased areal storage densities. In order to achieve higher resolution reading, it is common to place the spin-valve sensing elements through insulator gaps between two magnetic shields, which can eliminate the external field influence on the read signal . However, the unshielded spin-valve sensing elements also show potential applications in many other areas, such as magnetic media readers (e.g. credit card readers), and filed sensors etc. Theoretically, the spin-valve devices are intrinsically linear if the hysteresis can be eliminated. How to decrease or eliminate the hysteresis of spin-valve sensor is vital to the practical applications in linear devices. As wellknown, the hysteresis of spin-valve sensing element evoked by the multi-domain structure at two ends of the free layer is the main source of the hysteresis of spin-valve sensor. In this work, we will describe the fabrication and analysis of an unshielded GMR spin-valve sensor, of which the hysteresis is suppressed by placing a pair of permanent magnets (PM) on both ends of the sensor, as shown in Figure 1. Then, the dimension dependence of the sensor performance was investigated by measuring the transfer curves of two types of GMR spin-valve sensors patterned with different lengths and widths. The results showed that with decreased length and width of the spin-valve sensor, the GMR ratio decreased and the saturation field increased respectively. However, their experimental transfer curves are both in good agreement with the theoretic simulated ones, showing high GMR ratio and little hysteresis.