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Stable magnetic droplet solitons in spin-transfer nanocontacts

Nature Nanotechnology volume 9, pages 992–996 (2014)Cite this article

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Abstract

Magnetic thin films with perpendicular magnetic anisotropy have localized excitations that correspond to reversed, dynamically precessing magnetic moments, which are known as magnetic droplet solitons. Fundamentally, these excitations are associated with an attractive interaction between elementary spin-excitations and have been predicted to occur in perpendicularly magnetized materials in the absence of damping1,2. Although damping suppresses these excitations, it can be compensated by spin-transfer torques when an electrical current flows in nanocontacts to ferromagnetic thin films3,4. Theory predicts the appearance of magnetic droplet solitons in nanocontacts at a threshold current5 and, recently, experimental signatures of droplet nucleation have been reported6. However, to date, these solitons have been observed to be nearly reversible excitations, with only partially reversed magnetization6. Here, we show that magnetic droplet solitons exhibit a strong hysteretic response in field and current, proving the existence of bistable states: droplet and non-droplet states. In the droplet soliton state we find that the magnetization in the contact is almost fully reversed. These observations, in addition to their fundamental interest, are important to understanding and controlling droplet motion, nucleation and annihilation7,8,9.

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Figure 1: Device schematic and dynamical properties.
Figure 2: Nucleation of droplet solitons with current.
Figure 3: Hysteresis in the MR data.

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Acknowledgements

F.M. acknowledges support from the European Commission (grant no. MC-IOF 253214), from the Catalan Government through the programme COFUND-FP7 and from the Spanish Government (grant no. MAT2011-23698). This research was supported by the National Science Foundation-Division of Materials Research-1309202 and in part by the Army Research Office-Multidisciplinary University Research Initiative (grant no. W911NF-08-1-0317). Research was carried out in part at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the US Department of Energy, Office of Basic Energy Sciences (contract no. DE-AC02-98CH10886).

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Authors and Affiliations

  1. Department of Physics, New York University, New York, New York, 10003, USA

    Ferran Macià, Dirk Backes & Andrew D. Kent

  2. Grup de Magnetisme, Departament de Física Fonamental, Universitat de Barcelona, Spain

    Ferran Macià

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  1. Ferran Macià
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All three authors conceived the experiment, discussed the results and wrote the manuscript. F.M. and D.B. fabricated the samples and performed the measurements.

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Correspondence to Ferran Macià.

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The authors declare no competing financial interests.

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Macià, F., Backes, D. & Kent, A. Stable magnetic droplet solitons in spin-transfer nanocontacts. Nature Nanotech 9, 992–996 (2014). https://doi.org/10.1038/nnano.2014.255

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