The magnetic behavior of antiferromagnetic spin $1/2$ chains with site-centered impurities in a magnetic field is investigated. The effect of impurities is implemented by considering different situations of both diagonal and off-diagonal disorder. The resulting magnetization curves present a wide variety of plateaus, whose position strongly depends on the kind of disorder considered. The relevance of these results to experimental situations is also discussed.

• Received 26 November 2001

DOI:https://doi.org/10.1103/PhysRevB.66.104401