Prof. Dr. Olav Hellwig Research Group Head o.hellwig@hzdr.de Tel.: (0351) 260 - 2461

Magnetic domain formation in antiferromagnetically (AF) coupled perpendicular anisotropy multilayers

 

Magnetic domain formation and field reversal behavior in antiferromagnetically (AF) coupled perpendicular anisotropy multilayers are rich in nature as demagnetization and exchange energies compete with each other and thus give rise to phase transitions as both interaction become comparable in size [1-3]. In the AF-exchange dominated regime the magnetization is ferromagnetically ordered within the film plane with the magnetization of adjacent layers anti-parallel thus minimizing the interlayer AF exchange energy. In the dipolar dominated regime the magnetization pattern forms ferromagnetic (FM) stripe domains where adjacent layers are vertically correlated, but laterally anti-correlated thus minimizing the dipolar energy at the expense of the AF interlayer coupling. 

 


 

Figure 3: (a) Schematic illustration of the ML structure for the case X = 3 and N = 4. The Co/Pt stacks can be viewed as uniform FM units with the magnetization pointing either parallel or antiparallel to the film normal. Each FM layer stack is AF-coupled to its adjacent stacks via Ru inter-layers, while dipolar fields favor a parallel alignment of the moments in adjacent stacks. (b) AF domain structure of lateral periodicity lAF. As an example we show an experimental MFM image (10 mm)2 of a N = 17, X = 6 sample after trapping domains via AC demagnetization. (c) FM stripe domain structure of lateral periodicity lFM. As an example we show an experimental MFM image (10 mm)2 of a N = 18, X = 9 sample after AC demagnetization.

 

As a consequence one can stabilize for example the coexistence of different remanent states [3] and the formation of new types of AF domain wall topologies that may be used for future magnetic information storage or processing. In this context we will explore reversal modes via Magnetic Force Microscopy (MFM) in an external field as well as magnetotransport properties during field reversal as well as for different remanent domain topologies.

 

References:

[1] O. Hellwig, T. L. Kirk, J. B. Kortright, A. Berger, and E. E. Fullerton, Nature Materials 2 (2003) 112.

[2] O. Hellwig, A. Berger and E. E. Fullerton, Phys. Rev. Lett. 91 (2003) 197203.

[3] O. Hellwig, J. B. Kortright, A. Berger and E. E. Fullerton, J. Magn. Magn. Mater. 319 (2007) 13.

 

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