Exchange Coupling And Electronic Transport Properties In Ferromagnetic-antiferromagnetic Films

As one of the key elements in spintronics, the magnetic multilayer thin films have complex exchange coupling and electronic transporting behaviors and abundant physical connotations. The interlayer coupling between two ferromagnetic layers through a non-magnetic spacer, as well as the interfacial coupling at the ferromagnetic/antiferromagnetic interface, plays very significant roles in spintronic devices. Therefore, the researches on them have long been highly concerned. In this thesis, we focus on the ferromagnetic/antiferromagnetic interfacial exchange coupling and its relevant issues. The configuration of the interfacial spins, the asymmetric magnetization reversal, the mechanisms of training effect, and their relevance in exchange-bias multilayer films, in which the FeMn alloy served as the antiferromagnetic layer, were investigated. The specific content includes:By inserting an ultrathin Pt spacer layer at the ferromagnetic/antiferromagnetic interface, or inserting an ultrathin Pt spacer layer into the antiferromagnetic layer, or diluting the interfacial zone of the FeMn layer with Pt, and optimizing the thickness as well as the position of the spacer and diluted layer, the exchange bias field was significantly enhanced (by-80%at most). Mechanism analyses indicate that the the amount and state of the uncompensated antiferromagnetic spins were manipulated by the Pt insertions, which is responsible to the enhancement of exchange bias field.In (Pt/Co)6/Pt(t)/Co,(Pt/Co)6/Pt(/)/Co/FeMn, and Co/Pt(t)/[Co/(Pt/Co)5]/FeMn multilayers, it was found that the interlayer exchange coupling between the (Pt/Co)6, period stacks and the Co single layer across the Pt(t) spacer layer have an oscillatory decaying dependence on the increment of the Pt spacer thickness t. The oscillating period and the decaying length of the interlayer coupling is far beyond that of most ferromagnetic/non-magnetic/ferromagnetic systems. Besides, in (Pt/Co)6/Pt(t)/Co/FeMn, the ferromagnetic/antiferromagnetic interfacial coupling at the Co/FeMn interface could be regulated by the ferromagnetic/non-magnetic/ferromagnetic interlayer exchange coupling in (Pt/Co)6/Pt(t)/Co, resulting in an oscillatory change of the Co/FeMn interfacial coupling with the variation of Pt spacer thickness t. Then the exchange bias in Co/FeMn bilayer, as the inducing field is applied along the hard-axis of the Co layer (perpendicular to the film plane) during the sample growing process, was studied. A number of uncompensated antiferromagnetic spins, which is much more than usual exchange bias systems, were observed. The magnetization reversal behaviors of this bilayer exhibit strong asymmetric characteristics, and vary with the thickness of the Co layer and the FeMn layer, respectively. Moreover, the key factors influencing the asymmetric magnetization reversal behaviors in the exchange bias systems were discussed, implying a connection between the two origins of the asymmetric magnetization reversal.The anisotropic magnetoresistance in NiFe/FeMn bilayers was measured, so as to discover the angular dependence of the training effect of exchange bias The training effect in NiFe/FeMn bilayers shows multiple mechanisms. A new attenuation mechanism of the exchange bias field based on domain-state-model was proposed, providing a good explanation of the specific and odd behaviors in the very first cycle of the training process.