  Exchange bias (EB) and the training effects (TE) in an antiferromagnetically
coupled La0.7Sr0.3MnO3 / SrRuO3 superlattices were studied in the temperature
range 1.8 - 150 K. Strong antiferromagnetic (AFM) interlayer coupling is
evidenced from AC - susceptibility measurements. Below 100 K, vertical
magnetization shifts are present due to the two remanent states corresponding
to the two ferromagnetic (FM) layers at FM and AFM coupling condition. After
field cooling (FC), significant decrease in the exchange bias field (HEB) is
observed when cycling the system through several consecutive hysteresis loops.
Quantitative analysis for the variation of HEB vs. number of field cycles (n)
indicates an excellent agreement between the theory, based on triggered
relaxation phenomena, and our experimental observations. Nevertheless, the
crucial fitting parameter K indicates smooth training effect upon repeated
field cycling, in accordance with our observation.
