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Magnetic droplet nucleation boundary in orthogonal spin-torque nano-oscillators.

Chung S, Eklund A, Iacocca E, Mohseni SM, Sani SR, Bookman L, Hoefer MA, Dumas RK, Åkerman J - Nat Commun (2016)

Bottom Line: Static and dynamic magnetic solitons play a critical role in applied nanomagnetism.Magnetic droplets, a type of non-topological dissipative soliton, can be nucleated and sustained in nanocontact spin-torque oscillators with perpendicular magnetic anisotropy free layers.Furthermore, our analytical model both highlights the relation between the fixed layer material and the droplet nucleation current magnitude, and provides an accurate method to experimentally determine the spin transfer torque asymmetry of each device.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden.

ABSTRACT
Static and dynamic magnetic solitons play a critical role in applied nanomagnetism. Magnetic droplets, a type of non-topological dissipative soliton, can be nucleated and sustained in nanocontact spin-torque oscillators with perpendicular magnetic anisotropy free layers. Here, we perform a detailed experimental determination of the full droplet nucleation boundary in the current-field plane for a wide range of nanocontact sizes and demonstrate its excellent agreement with an analytical expression originating from a stability analysis. Our results reconcile recent contradicting reports of the field dependence of the droplet nucleation. Furthermore, our analytical model both highlights the relation between the fixed layer material and the droplet nucleation current magnitude, and provides an accurate method to experimentally determine the spin transfer torque asymmetry of each device.

No MeSH data available.


Related in: MedlinePlus

Magnetoresistance measurements.(a,b) Show the magnetoresistance (MR) measured by sweeping either the field or current, respectively. Each MR curve is vertically shifted for clarity. The transition resistance for droplet nucleation (collapse) is shown by a solid (empty) triangle. The solid diamonds in a indicate minor MR variations after the droplet has been nucleated and can be attributed to unstable dynamics.
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f2: Magnetoresistance measurements.(a,b) Show the magnetoresistance (MR) measured by sweeping either the field or current, respectively. Each MR curve is vertically shifted for clarity. The transition resistance for droplet nucleation (collapse) is shown by a solid (empty) triangle. The solid diamonds in a indicate minor MR variations after the droplet has been nucleated and can be attributed to unstable dynamics.

Mentions: Detailed MR measurements for an NC with a radius of 40 nm are plotted in Fig. 2 as a function of both field and current. Figure 2a shows field-dependent sweeps from 0.05 to 2.05 T using a field step of 0.01 T. In between each field-sweep, the current is varied in steps of −0.1 mA from −5.9 to −9 mA with data from each sweep vertically offset for clarity. Filled triangles indicate droplet nucleation, whereas hollow triangles indicate droplet collapse. In addition, small MR fluctuations are observed inside the region where the droplet exists (diamond markers in Fig. 2). These minor features, while not further analysed, may be attributable to small changes in the droplet dynamics generated by inhomogeneities in the magnetic films23. Although the droplet nucleation field shows a monotonic dependence on current, the droplet collapse field sometimes displays a much greater variation, for example, at −6.9 and −7.0 mA and at the lowest currents. We attribute this variation to a general high degree of drift instability, except at a few current conditions where the droplet appears more stable. The high microwave noise power observed at most field and current conditions where the droplet exists corroborates this picture and suggests that the droplet leaves the NC region relatively quickly after nucleation to give way for the immediate renucleation of another droplet, in good agreement with numerical predictions17. At field and current conditions outside of the nucleation boundary, droplet renucleation is however no longer possible, and as a consequence, most of the collapse fields in Fig. 2a can be used to trace out the high field part of the nucleation boundary.


Magnetic droplet nucleation boundary in orthogonal spin-torque nano-oscillators.

Chung S, Eklund A, Iacocca E, Mohseni SM, Sani SR, Bookman L, Hoefer MA, Dumas RK, Åkerman J - Nat Commun (2016)

Magnetoresistance measurements.(a,b) Show the magnetoresistance (MR) measured by sweeping either the field or current, respectively. Each MR curve is vertically shifted for clarity. The transition resistance for droplet nucleation (collapse) is shown by a solid (empty) triangle. The solid diamonds in a indicate minor MR variations after the droplet has been nucleated and can be attributed to unstable dynamics.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837446&req=5

f2: Magnetoresistance measurements.(a,b) Show the magnetoresistance (MR) measured by sweeping either the field or current, respectively. Each MR curve is vertically shifted for clarity. The transition resistance for droplet nucleation (collapse) is shown by a solid (empty) triangle. The solid diamonds in a indicate minor MR variations after the droplet has been nucleated and can be attributed to unstable dynamics.
Mentions: Detailed MR measurements for an NC with a radius of 40 nm are plotted in Fig. 2 as a function of both field and current. Figure 2a shows field-dependent sweeps from 0.05 to 2.05 T using a field step of 0.01 T. In between each field-sweep, the current is varied in steps of −0.1 mA from −5.9 to −9 mA with data from each sweep vertically offset for clarity. Filled triangles indicate droplet nucleation, whereas hollow triangles indicate droplet collapse. In addition, small MR fluctuations are observed inside the region where the droplet exists (diamond markers in Fig. 2). These minor features, while not further analysed, may be attributable to small changes in the droplet dynamics generated by inhomogeneities in the magnetic films23. Although the droplet nucleation field shows a monotonic dependence on current, the droplet collapse field sometimes displays a much greater variation, for example, at −6.9 and −7.0 mA and at the lowest currents. We attribute this variation to a general high degree of drift instability, except at a few current conditions where the droplet appears more stable. The high microwave noise power observed at most field and current conditions where the droplet exists corroborates this picture and suggests that the droplet leaves the NC region relatively quickly after nucleation to give way for the immediate renucleation of another droplet, in good agreement with numerical predictions17. At field and current conditions outside of the nucleation boundary, droplet renucleation is however no longer possible, and as a consequence, most of the collapse fields in Fig. 2a can be used to trace out the high field part of the nucleation boundary.

Bottom Line: Static and dynamic magnetic solitons play a critical role in applied nanomagnetism.Magnetic droplets, a type of non-topological dissipative soliton, can be nucleated and sustained in nanocontact spin-torque oscillators with perpendicular magnetic anisotropy free layers.Furthermore, our analytical model both highlights the relation between the fixed layer material and the droplet nucleation current magnitude, and provides an accurate method to experimentally determine the spin transfer torque asymmetry of each device.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden.

ABSTRACT
Static and dynamic magnetic solitons play a critical role in applied nanomagnetism. Magnetic droplets, a type of non-topological dissipative soliton, can be nucleated and sustained in nanocontact spin-torque oscillators with perpendicular magnetic anisotropy free layers. Here, we perform a detailed experimental determination of the full droplet nucleation boundary in the current-field plane for a wide range of nanocontact sizes and demonstrate its excellent agreement with an analytical expression originating from a stability analysis. Our results reconcile recent contradicting reports of the field dependence of the droplet nucleation. Furthermore, our analytical model both highlights the relation between the fixed layer material and the droplet nucleation current magnitude, and provides an accurate method to experimentally determine the spin transfer torque asymmetry of each device.

No MeSH data available.


Related in: MedlinePlus