Magnetic Field Of The Exchange Bias Field In Ferromagnetic / Antiferromagnetic Bilayers With Cooling

In recent years the magnetic thin film which was made as the high-density magnetic recording media, has attracted much attention. Especially the 2007 Nobel Prize in Physics was awarded the scientists who found the "giant magnetoresistance effect", and then the magnetic multilayer spin valve structure as to produce the effect of giant magnetoresistance became the people's research focus.Exchange bias which was found 50 years ago, is one of the essential physical mechanisms in the basic structures of hard disk driver head and magnetic random access memory at present and its mechanism has attracted much attention. It was found in experiment that the positive exchange bias will occur at large cooling field, and this interesting phenomenon provides an important clue to understand the mechanism of the exchange bias. On the other hand, the experimental results show that an antiferromagnetic interface coupling is necessary to induce positive exchange bias.Based on the ferromagnetic domain wall model, we investigate the dependence of the exchange bias on the cooling field for different interface coupling and the FM thickness dependence of the exchange bias for FM/AFM bilayer system. The physical mechanism has been investigated and hope to provide theoretical guidance to the application. The main researches include the following three parts:Firstly, we studied the dependence of the magnitude of the cooling field on the exchange bias for different interface coupling, ferromagnetic coupling and antiferromagnetic coupling, in the ferromagnetic/antiferromagnetic bilayer system. The results show that the exchange bias changes slowly with increasing the cooling field. Generally, for the antiferromagnetic coupling system the positive exchange bias is always observed with increasing the cooling field, but a transition from negative to positive will occur when the cooling field deflects a large angle from the easy axis direction. However, only negative exchange bias is observed in the ferromagnetic coupling system.Secondly, we studied the dependence of the direction of the cooling field on the exchange bias for different interface coupling, such as ferromagnetic coupling and antiferromagnetic coupling, in the ferromagnetic/antiferromagnetic bilayer system. The exchange bias changes slowly when the cooling field deflects from the easy axis, but it will decrease suddenly at critical angle, which is relative to the cooling field, for a small cooling field, the critical angle is also small.Finally, for the antiferromagnetic coupling system the thickness dependence of the exchange bias exhibits a liner dependence on the inverse FM layer thickness, but the transformation from h E∝NF?1 to hE∝NF?λwill occur at a certain FM thickness, hereλ>1; this behavior is strongly dependent on the magnitude and angle of the cooling field. N F influences the exchange bias obviously at small angle while the influence of the cooling field is also obvious at large angle.