Abstract: The origin of switching field distribution (SFD) in large arrays of magnetic nanostructures, i.e. the difference of reversal field from one nanostructure to an other, has recently attracted great interest in the view of developing new generations of high density or high speed memories such as bit patterned media, MRAM or race track memory. Indeed, in these memory designs, bit-to-bit variations in the structural and/or magnetic properties may produce unintended reversal when writing a hard switcher bit or on the contrary allows neighbours to be over-written if these have a lower reversal field [1,2]. More generally, the control of the switching field as independently as possible from the thermal stability is also targeted.
We used [Co/Pd]-based multilayers deposited onto pre-patterned substrates to develop new way to understand and control switching field distribution in nanostructures . Magnetic properties of nanodots arrays up to 1Tb/in2 have been studied. Different SFD origins (dipolar coupling, pre-patterned array quality, and magnetic media growth defects) have been identified and solutions have been proposed for lowering them [3,4]. We will particularly focus on new exchange coupled composite structures (so-called ECC media) that allow tuning both reversal field and SFD [4,5]. The gain in switching field distribution offered by ECC media originates from introducing incoherency into the magnetization reversal process, which will be discussed on the basis of micromagnetic simulation multi-spin generalization of the macro-spin potential surface model developed by Bertram and Lengsfield .
 M.E. Schabes, J. Magn. Mag. Mat. 320, 2880 (2008)
 O. Ozatay, T. Hauet et al., Chapter “Spin-based data storage”, p236, chapter 7, “Handbook of nanoscale optics and electronics” Elsevier B.V. (2009).
 O. Hellwig, T. Hauet et al., Appl. Phys. Lett. 95, 232505 (2009)
 T. Hauet et al., Appl. Phys. Lett. 95, 262504 (2009)
 T. Hauet et al., Appl. Phys. Lett. 95, 222507 (2009)
 H.N. Bertram and B. Lengsfield, IEEE Trans. Magn. 43, 2145 (2007)