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Anisotropic Magnetoresistance (AMR): Film Thickness Dependence and Nanowire DW Behaviour

Del ATKINSON, Durham University, UK


Anisotropic magnetoresistance (AMR) has a long history both in terms of the fundamental physics and for applications in sensor technology. More recently, AMR has become highly relevant for understanding the magnetization behaviour of magnetic structures and especially domain walls in planar nanowires [1]. Such applications of AMR have been based on simplified assumptions [2] whilst more recent modeling has improved on these simplifications by using detailed micromagnetic structures and thickness dependent resistivity data [3]. This talk describes some of the fundamental behaviour of anisotropic magnetoresistance and its application to the study of nanowires magnetization behaviour.

In order to fully develop and use AMR measurements for the interpretation of the micromagnetic configurations within nanostructures a detailed knowledge of the basic AMR dependence of the material is needed. This includes the thickness dependence of the resistivity, along with variations in grain size and texture, and importantly the magnetoresistance change as a function of thickness. The absolute size of the field dependent resistance change is more significant than simply the magnetoresistance ratio as the latter is complicated by the thickness dependent of the total resistivity. The AMR mechanism will be discussed.

Time permitting, the magnetoresistance measurements of individual lithographic planar nanowires with nucleation pads and single pinning structures will be discussed. Individual magnetic switching events were measured as a function of magnetic field. The changes in magnetoresistance reveal considerable detail in the switching process. The results show significant variation in behaviour between successive DW switching events. Some consistencies emerge from the measurements but overall the behaviour reveal complexity in the switching processes involving domain wall chirality and thermally activated switching.

 

[1] M. Hayashi, L. Thomas, C. Rettner, R. Moriya, X. Jiang, and S. S. P. Parkin, Phys. Rev. Lett. 97, 207205 (2006)

[2] L. Thomas, and S. S. P. Parkin, in ‘Handbook of Magnetism and Advanced Magnetic Materials’ vol. 2. H. Kronmüller and S. S. P. Parkin (Eds) John Wiley & Sons Ltd Chichester (2007)

[3] L. K. Bogart & D. Atkinson Appl. Phys. Letts. 94, 042511 (2009)