Limits...
Direct observation and imaging of a spin-wave soliton with p-like symmetry.

Bonetti S, Kukreja R, Chen Z, Macià F, Hernàndez JM, Eklund A, Backes D, Frisch J, Katine J, Malm G, Urazhdin S, Kent AD, Stöhr J, Ohldag H, Dürr HA - Nat Commun (2015)

Bottom Line: Spin waves, the collective excitations of spins, can emerge as nonlinear solitons at the nanoscale when excited by an electrical current from a nanocontact.Micromagnetic simulations explain the measurements and reveal that the symmetry of the soliton can be controlled by magnetic fields.Our results broaden the understanding of spin-wave dynamics at the nanoscale, with implications for the design of magnetic nanodevices.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Stanford University, Stanford, California 94305, USA.

ABSTRACT
Spin waves, the collective excitations of spins, can emerge as nonlinear solitons at the nanoscale when excited by an electrical current from a nanocontact. These solitons are expected to have essentially cylindrical symmetry (that is, s-like), but no direct experimental observation exists to confirm this picture. Using a high-sensitivity time-resolved magnetic X-ray microscopy with 50 ps temporal resolution and 35 nm spatial resolution, we are able to create a real-space spin-wave movie and observe the emergence of a localized soliton with a nodal line, that is, with p-like symmetry. Micromagnetic simulations explain the measurements and reveal that the symmetry of the soliton can be controlled by magnetic fields. Our results broaden the understanding of spin-wave dynamics at the nanoscale, with implications for the design of magnetic nanodevices.

No MeSH data available.


Related in: MedlinePlus

Overview of the experiment.(a) Schematic of the measurement and of the sample. The circularly polarized X-rays generated at the elliptically polarizing undulator at beamline 13 at the Stanford Synchrotron Radiation Lightsource (SSRL) are focused to a 35-nm spot using a zone-plate, determining the spatial resolution. The sample comprises a NiFe(5 nm)/Cu(4 nm)/CoFe(8 nm) multilayer, where the Cu and CoFe layer are patterned into an ellipse of 150 × 50 nm2, whereas the NiFe layer is a larger mesa. Spin waves are excited when a magnetic field H is applied in the sample plane, and a direct current IDC flows into the nanocontact. A microwave current Imw is superimposed to the direct current to synchronize the spin-wave excitation with the X-ray detection and SSRL's master clock. The time-resolved variation of the magnetization along the X-ray propagation direction is probed by XMCD, measured with an avalanche photodiode as the variation of the signal transmitted through the sample. (b) X-ray image showing the topography of the sample. Scale bar, 200 nm. (c) Schematic representation of two types of spin wave symmetries.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4660209&req=5

f1: Overview of the experiment.(a) Schematic of the measurement and of the sample. The circularly polarized X-rays generated at the elliptically polarizing undulator at beamline 13 at the Stanford Synchrotron Radiation Lightsource (SSRL) are focused to a 35-nm spot using a zone-plate, determining the spatial resolution. The sample comprises a NiFe(5 nm)/Cu(4 nm)/CoFe(8 nm) multilayer, where the Cu and CoFe layer are patterned into an ellipse of 150 × 50 nm2, whereas the NiFe layer is a larger mesa. Spin waves are excited when a magnetic field H is applied in the sample plane, and a direct current IDC flows into the nanocontact. A microwave current Imw is superimposed to the direct current to synchronize the spin-wave excitation with the X-ray detection and SSRL's master clock. The time-resolved variation of the magnetization along the X-ray propagation direction is probed by XMCD, measured with an avalanche photodiode as the variation of the signal transmitted through the sample. (b) X-ray image showing the topography of the sample. Scale bar, 200 nm. (c) Schematic representation of two types of spin wave symmetries.

Mentions: It is now established that the local injection of strong spin-polarized electrical currents can generate nonlinear spin waves with both itinerant910111213 and localized111415161718 character. This character is determined by the relative orientation between the material internal field and the applied external field. Spin waves of both characters are also required to preserve the radial symmetry of the nanocontact used to inject the spin-polarized current. Such radial symmetry can be perturbed by the Oersted field generated by the current flowing through the nano-contact, however, with qualitatively different effects for itinerant and localized excitations. In case of itinerant spin waves, excited when a magnetic field saturates the magnetization out of the plane of the sample, the Oersted field does not break the in-plane symmetry of the spin-wave precession. Hence, it is expected that the spin waves form a circular pattern far away from the nano-contact9. This type of excitation has been reported with micro-focused Brillouin Light Scattering1213. For the case of localized excitations, created when an in-plane magnetic field is applied to the sample, the Oersted field does break the in-plane symmetry, and a spatial shift of the excitation away from the nano-contact has been predicted by numerical simulations192021. However, an experimental visualization of localized excitations has been hampered by the lack of a suitable imaging technique combining spatial and temporal resolution with magnetic sensitivity. Therefore, the spatial properties of localized solitons are currently unknown. For instance, it is unclear whether they can only possess the full radial symmetry (s-like) or if excitations with different symmetry (p-like) are also allowed22, as shown schematically in Fig. 1c.


Direct observation and imaging of a spin-wave soliton with p-like symmetry.

Bonetti S, Kukreja R, Chen Z, Macià F, Hernàndez JM, Eklund A, Backes D, Frisch J, Katine J, Malm G, Urazhdin S, Kent AD, Stöhr J, Ohldag H, Dürr HA - Nat Commun (2015)

Overview of the experiment.(a) Schematic of the measurement and of the sample. The circularly polarized X-rays generated at the elliptically polarizing undulator at beamline 13 at the Stanford Synchrotron Radiation Lightsource (SSRL) are focused to a 35-nm spot using a zone-plate, determining the spatial resolution. The sample comprises a NiFe(5 nm)/Cu(4 nm)/CoFe(8 nm) multilayer, where the Cu and CoFe layer are patterned into an ellipse of 150 × 50 nm2, whereas the NiFe layer is a larger mesa. Spin waves are excited when a magnetic field H is applied in the sample plane, and a direct current IDC flows into the nanocontact. A microwave current Imw is superimposed to the direct current to synchronize the spin-wave excitation with the X-ray detection and SSRL's master clock. The time-resolved variation of the magnetization along the X-ray propagation direction is probed by XMCD, measured with an avalanche photodiode as the variation of the signal transmitted through the sample. (b) X-ray image showing the topography of the sample. Scale bar, 200 nm. (c) Schematic representation of two types of spin wave symmetries.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4660209&req=5

f1: Overview of the experiment.(a) Schematic of the measurement and of the sample. The circularly polarized X-rays generated at the elliptically polarizing undulator at beamline 13 at the Stanford Synchrotron Radiation Lightsource (SSRL) are focused to a 35-nm spot using a zone-plate, determining the spatial resolution. The sample comprises a NiFe(5 nm)/Cu(4 nm)/CoFe(8 nm) multilayer, where the Cu and CoFe layer are patterned into an ellipse of 150 × 50 nm2, whereas the NiFe layer is a larger mesa. Spin waves are excited when a magnetic field H is applied in the sample plane, and a direct current IDC flows into the nanocontact. A microwave current Imw is superimposed to the direct current to synchronize the spin-wave excitation with the X-ray detection and SSRL's master clock. The time-resolved variation of the magnetization along the X-ray propagation direction is probed by XMCD, measured with an avalanche photodiode as the variation of the signal transmitted through the sample. (b) X-ray image showing the topography of the sample. Scale bar, 200 nm. (c) Schematic representation of two types of spin wave symmetries.
Mentions: It is now established that the local injection of strong spin-polarized electrical currents can generate nonlinear spin waves with both itinerant910111213 and localized111415161718 character. This character is determined by the relative orientation between the material internal field and the applied external field. Spin waves of both characters are also required to preserve the radial symmetry of the nanocontact used to inject the spin-polarized current. Such radial symmetry can be perturbed by the Oersted field generated by the current flowing through the nano-contact, however, with qualitatively different effects for itinerant and localized excitations. In case of itinerant spin waves, excited when a magnetic field saturates the magnetization out of the plane of the sample, the Oersted field does not break the in-plane symmetry of the spin-wave precession. Hence, it is expected that the spin waves form a circular pattern far away from the nano-contact9. This type of excitation has been reported with micro-focused Brillouin Light Scattering1213. For the case of localized excitations, created when an in-plane magnetic field is applied to the sample, the Oersted field does break the in-plane symmetry, and a spatial shift of the excitation away from the nano-contact has been predicted by numerical simulations192021. However, an experimental visualization of localized excitations has been hampered by the lack of a suitable imaging technique combining spatial and temporal resolution with magnetic sensitivity. Therefore, the spatial properties of localized solitons are currently unknown. For instance, it is unclear whether they can only possess the full radial symmetry (s-like) or if excitations with different symmetry (p-like) are also allowed22, as shown schematically in Fig. 1c.

Bottom Line: Spin waves, the collective excitations of spins, can emerge as nonlinear solitons at the nanoscale when excited by an electrical current from a nanocontact.Micromagnetic simulations explain the measurements and reveal that the symmetry of the soliton can be controlled by magnetic fields.Our results broaden the understanding of spin-wave dynamics at the nanoscale, with implications for the design of magnetic nanodevices.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Stanford University, Stanford, California 94305, USA.

ABSTRACT
Spin waves, the collective excitations of spins, can emerge as nonlinear solitons at the nanoscale when excited by an electrical current from a nanocontact. These solitons are expected to have essentially cylindrical symmetry (that is, s-like), but no direct experimental observation exists to confirm this picture. Using a high-sensitivity time-resolved magnetic X-ray microscopy with 50 ps temporal resolution and 35 nm spatial resolution, we are able to create a real-space spin-wave movie and observe the emergence of a localized soliton with a nodal line, that is, with p-like symmetry. Micromagnetic simulations explain the measurements and reveal that the symmetry of the soliton can be controlled by magnetic fields. Our results broaden the understanding of spin-wave dynamics at the nanoscale, with implications for the design of magnetic nanodevices.

No MeSH data available.


Related in: MedlinePlus