1. © 2009 IBM Corporation MMM 2013 | 2013-11-05 | IBM/TUe © 2013 IBM Corporation Domain wall pinning dependent on nanomagnet state Reinier van Mourik 1,2, Charles Rettner 1, Bert Koopmans 2, Stuart Parkin 1 1. IBM Almaden Research Center, San Jose, CA 2. Eindhoven University of Technology, Eindhoven, the Netherlands BB-03

2. IBM Research MMM 2013 | 2013-11-05 | IBM/TUe © 2013 IBM Corporation Introduction Magnetic Domain Walls for memory and logic Dynamics of magnetic domain walls important for applications Precise control of DW position required, for example by pinning Parkin, S. S. P., M. Hayashi, et al. (2008). "Magnetic domain- wall racetrack memory." Science 320(5873): 190-194. MemoryLogic Allwood, D. A., G. Xiong, et al. (2005). "Magnetic Domain-Wall Logic." Science 309(5741): 1688-1692.

3. IBM Research MMM 2013 | 2013-11-05 | IBM/TUe © 2013 IBM Corporation Introduction Outline Experimental setup –Domain wall pinned at and depinned from nanomagnet site Results –Significant difference in depinning field for two nanomagnet states Discussion –Domain wall fine structure responsible for difference Applications –Tunable pinning site or nanomagnet readout Conclusions DW

4. IBM Research MMM 2013 | 2013-11-05 | IBM/TUe © 2013 IBM Corporation Methods Experimental setup AMR and Hall bar register depinning of DW nanomagnet Py 60x90x10nm AMR read hall bar read 1. inject DW 2. propagate DW by H field 3. read resistance change in AMR and Hall bar PMA [CoNi] n nanowire, 60-140nm wide DW Domain wall injection line Hall bar pulser H AMR Hall bar 0 H dep

5. IBM Research MMM 2013 | 2013-11-05 | IBM/TUe © 2013 IBM Corporation Methods Experimental setup Depinning field is measured for both nanomagnet states nanomagnet Py 60x90x10nm AMR read hall bar read 1. inject DW 2. propagate DW by H field 3. read resistance change in AMR and Hall bar PMA [CoNi] n nanowire, 60-140nm wide DW Domain wall injection line Hall bar pulser H AMR Hall bar 0 H dep

6. IBM Research MMM 2013 | 2013-11-05 | IBM/TUe © 2013 IBM Corporation Results Depinning field difference Magnetic field required to propagate DW past nanomagnet differs by 10 mT for both states. 10 mT! Depinning field difference increases with wire width. typical resultwire width dependence

7. IBM Research MMM 2013 | 2013-11-05 | IBM/TUe © 2013 IBM Corporation Discussion Micromagnetic energy calculation -200-1000100200 -1.5 -0.5 0 0.5 1 DW position [nm] energy [aJ] top viewside view

8. IBM Research MMM 2013 | 2013-11-05 | IBM/TUe © 2013 IBM Corporation Application Application potential H probe Nanomagnet acts as a DW gate if the DW is propagated at a probe field Application as: –tunable DW pinning site –nanomagnet readout AMR high AMR low

9. IBM Research MMM 2013 | 2013-11-05 | IBM/TUe © 2013 IBM Corporation AMR Application Domain wall pinning for use in NML readout In Nanomagnetic Logic, information is propagated along arrays of nanomagnets through magnetostatic coupling. Output magnet can be read out by DW pinning technique Each nanomagnet can have its own nanowire. AMR injection line DW Imre, A., G. Csaba, et al. (2006). "Majority logic gate for magnetic quantum-dot cellular automata." Science 311(5758): 205-208.

10. IBM Research MMM 2013 | 2013-11-05 | IBM/TUe © 2013 IBM Corporation Conclusion In-plane nanomagnet above PMA nanowire is single- magnet domain wall pinning site where the pinning strength depends on the nanomagnet state. The depinning field can differ by 10 mT and depends on wire width. The DW fine structure is responsible for the depinning field asymmetry. DW pinning can be applied in logic and memory applications. slides & contact: http://tinyurl.com/RvM-IBMhttp://tinyurl.com/RvM-IBM