The correlation between coercivity and exchange-field shift in a ferromagnetic/antiferromagnetic system has been investigated. By applying a spin-polarized current pulse with an external magnetic field, the exchangefield shift can be changed. Since the different magnitude of exchange fields were achieved on one sample, the coercivity and exchange-field shift can be studied without varying the structure or morphology of the film. Studies were also extended to measurements on spin valves with variable normal-metal thicknesses. Experimental results showed that the spin-polarized current applied in the film plane effectively changes the exchange-field shift while the coercivity remains the same. The results provide convincing evidence for the absence of a direct correlation between increased coercivity and exchange-field shift.Exchange bias ͑EB͒, which has been known for more than 50 years, refers to the exchange interactions at an interface between a ferromagnetic ͑FM͒ and an antiferromagnetic ͑AF͒ material. 1,2 The EB effect has potential application in magnetoresistive sensors, magnetic random access memory, and for surpassing the superparamagnetic limit in magnetic nanoparticles. [3][4][5] In studying EB, many groups have found that the exchange-field shift H ex is inversely proportional to the thickness ͑t FM ͒ of the FM layer, which is pinned by the AF layer, and the coercivity ͑H c ͒ of the pinned FM layer is increased with H ex ͑Refs. 6-9͒. Some researchers have come to the conclusion that both the increase in H ex and coercivity are the results of the interfacial exchange coupling between the AF and FM layers, and predicted that H c should depend on 1 / t FM or ͑1 / t FM ͒ 3/2 . 10,11 However, other researchers have reached completely opposite conclusions. The increase in H c and H ex are not directly related with each other in the sense that H c can be varied without changing H ex and vice versa. 12,13 Fundamentally, exchange coupling is an interfacial phenomenon while coercivity is known to be significantly affected by the microstructure of the films. In order to study exchange-field shift and coercivity simultaneously, avoiding variations in sample preparation, wedged samples or films with the same crystallographic structure have been used in the experiments. 10,14 However, these approaches do not ensure samples have been fabricated without variation in the structure or morphology of the film.Recently, both experiments and theoretical analyses have provided evidence that a polarized current can change the strength and direction of the exchange-field shift in a spin valve ͑SV͒ based on a spin-transfer ͑ST͒ effect. [15][16][17][18][19] The current-perpendicular-to-plane ͑CPP͒ geometry and the current-in-plane ͑CIP͒ geometry were involved. Furthermore, spatially nonuniform modes of reversal by ST has also been observed in an AF oxide layer coupled to a nanomagnet. 20 In general, ST between the FM layers in a SV or magnetic tunneling junction structure is expected in CPP geometry. This also applies to AF spin...

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