44 results on '"Keatley, P. S."'
Search Results
2. All-optical control of spin in a 2D van der Waals magnet
- Author
-
Da̧browski, Maciej, Guo, Shi, Strungaru, Mara, Keatley, Paul S., Withers, Freddie, Santos, Elton J. G., and Hicken, Robert J.
- Published
- 2022
- Full Text
- View/download PDF
3. Graphene overcoats for ultra-high storage density magnetic media
- Author
-
Dwivedi, N., Ott, A. K., Sasikumar, K., Dou, C., Yeo, R. J., Narayanan, B., Sassi, U., Fazio, D. De, Soavi, G., Dutta, T., Balci, O., Shinde, S., Zhang, J., Katiyar, A. K., Keatley, P. S., Srivastava, A. K., Sankaranarayanan, S. K. R. S., Ferrari, A. C., and Bhatia, C. S.
- Published
- 2021
- Full Text
- View/download PDF
4. Thermal nanoconversion of ferromagnetic nanoislands.
- Author
-
Barker, O. J., Mohammadi-Motlagh, A., Wright, A. J., Batty, R., Finch, H., Vezzoli, A., Keatley, P. S., and O'Brien, L.
- Subjects
KERR magneto-optical effect ,SPHEROMAKS ,MAGNETIC properties ,THIN films ,MAGNETOOPTICS ,KERR electro-optical effect ,MAGNETIZATION - Abstract
In this work, we investigate the use of post-fabrication thermal nanoconversion (TNC), using a heated scanning probe tip, to modify the magnetic properties of Ni
80 Fe20 elliptical nanoislands with varying aspect ratio. Despite Ni80 Fe20 being unoptimized for TNC, by comparing quasistatic and dynamic magneto-optical Kerr effect microscopy measurements, we demonstrate that TNC at a contact temperature of 250 °C increases the saturation magnetization of the treated nanoislands, reaching a value close to 800 kA/m. Micromagnetic simulations of the nanoislands indicate that the TNC technique can be used to alter the remanent state, from a single domain to a vortex. These results demonstrate the opportunities afforded by TNC to modify the properties of selected areas in a thin film or a patterned sample, particularly when designing magnonic crystals and other nanomagnetic devices. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
5. Interplay between spin proximity effect and charge-dependent exciton dynamics in MoSe2/CrBr3 van der Waals heterostructures
- Author
-
Lyons, T. P., Gillard, D., Molina-Sánchez, A., Misra, A., Withers, F., Keatley, P. S., Kozikov, A., Taniguchi, T., Watanabe, K., Novoselov, K. S., Fernández-Rossier, J., and Tartakovskii, A. I.
- Published
- 2020
- Full Text
- View/download PDF
6. Temperature dependence of magnetic anisotropy and domain wall tuning in BaTiO3(111)/CoFeB multiferroics.
- Author
-
Hunt, R. G., Franke, K. J. A., Keatley, P. S., Shepley, P. M., Rogers, M., and Moore, T. A.
- Subjects
MAGNETIC domain walls ,FERROELECTRIC materials ,MULTIFERROIC materials ,MAGNETIC anisotropy ,MAGNETIC control ,HYSTERESIS loop - Abstract
Artificial multiferroics consist of two types of ferroic materials, typically a ferroelectric and a ferromagnet, often coupled interfacially by magnetostriction induced by the lattice elongations in the ferroelectric. In BaTiO
3 , the magnitude of strain induced by these elongations is heavily temperature dependent, varying greatly between each of the polar crystal phases and exerting a huge influence over the properties of a coupled magnetic film. Here, we demonstrate that temperature and, thus, strain are effective means of controlling the magnetic anisotropy in BaTiO3 (111)/CoFeB heterostructures. We investigate the three polar phases of BaTiO3 : tetragonal (T) at room temperature, orthorhombic (O) below 280 K, and rhombohedral (R) below 190 K across a total range of 77–420 K. We find two distinct responses: a step-like change in the anisotropy across the low-temperature phase transitions and a sharp high-temperature reduction around the ferroelectric Curie temperature, measured from hard axis hysteresis loops. Using our measurements of this anisotropy strength, we are then able to show by micromagnetic simulation the behavior of all possible magnetic domain wall states and determine their scaling as a function of temperature. The most significant changes occur in the head-to-head domain wall states, with a maximum change of 210 nm predicted across the entire range, effectively doubling the size of the domain wall as compared to room temperature. Notably, similar changes are seen for both high and low temperatures, which suggests different routes for potential control of magnetic anisotropy and elastically pinned magnetic domain walls. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
7. Cognitive Performance, Depression, and Anxiety 1 Year After Traumatic Brain Injury.
- Author
-
Keatley, Eva S., Bombardier, Charles H., Watson, Eric, Kumar, Raj G., Novack, Thomas, Monden, Kimberley R., and Dams-O'Connor, Kristen
- Abstract
Objectives: To evaluate associations between depression, anxiety, and cognitive impairment among individuals with complicated mild to severe traumatic brain injury (TBI) 1 year after injury. Setting: Multiple inpatient rehabilitation units across the United States. Participants: A total of 498 adults 16 years and older who completed inpatient rehabilitation for complicated mild to severe TBI. Design: Secondary analysis of a prospective, multicenter, cross-sectional observational cohort study. Main Measures: Assessments of depression (Traumatic Brain Injury Quality of Life [TBI-QOL] Depression) and anxiety (TBI-QOL Anxiety) as well as a telephone-based brief screening measure of cognitive functioning (Brief Test of Adult Cognition by Telephone [BTACT]). Results: We found an inverse relationship between self-reported depression symptoms and the BTACT Composite score (β = −0.18, P <.01) and anxiety symptoms and the BTACT Composite score (β = −0.20, P <.01). There was no evidence this relationship varied by injury severity. Exploratory analyses showed depression and anxiety were negatively correlated with both BTACT Executive Function factor score and BTACT Memory factor score. Conclusions: Both depression and anxiety have a small but significant negative association with cognitive performance in the context of complicated mild to severe TBI. These findings highlight the importance of considering depression and anxiety when interpreting TBI-related neuropsychological impairments, even among more severe TBI. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
8. Primary Care Screening Methods and Outcomes for Asylum Seekers in New York City
- Author
-
Bertelsen, Nathan S., Selden, Elizabeth, Krass, Polina, Keatley, Eva S., and Keller, Allen
- Published
- 2016
- Full Text
- View/download PDF
9. Ultrafast magnetization dynamics of spintronic nanostructures
- Author
-
Keatley, P. S., Kruglyak, V. V., Gangmei, P., and Hicken, R. J.
- Published
- 2011
10. Transition Metal Synthetic Ferrimagnets: Tunable Media for All-Optical Switching Driven by Nanoscale Spin Current.
- Author
-
Dąbrowski, Maciej, Scott, Jade N., Hendren, William R., Forbes, Colin M., Frisk, Andreas, Burn, David M., Newman, David G., Sait, Connor R. J., Keatley, Paul S., N'Diaye, Alpha T., Hesjedal, Thorsten, van der Laan, Gerrit, Bowman, Robert M., and Hicken, Robert J.
- Published
- 2021
- Full Text
- View/download PDF
11. Resonant enhancement of damping within the free layer of a microscale magnetic tunnel valve.
- Author
-
Keatley, P. S., Kruglyak, V. V., Neudert, A., Hicken, R. J., Poimanov, V. D., Childres, J. R., and Katine, J. A.
- Subjects
- *
MAGNETISM , *MAGNETIZATION , *MAGNETIC moments , *MAGNETIC anisotropy , *MAGNETIC properties - Abstract
Picosecond magnetization dynamics in the free and pinned layers of a microscale magnetic tunnel valve have been studied using time-resolved scanning Kerr microscopy. A comparison of the observed dynamics with those of individual free and pinned layers allowed the effect of interlayer coupling to be identified. A weak interlayer coupling in the tunnel valve continuous film reference sample was detected in bulk magnetometry measurements, while focused Kerr magnetometry showed that the coupling was well maintained in the patterned structure. In the tunnel valve, the free layer precession was observed to have reduced amplitude and an enhanced relaxation. During magnetization reversal in the pinned layer, its frequency approached that of the low frequency mode associated with the free layer. At the pinned layer switching field, the linewidth of the free layer became similar to that of the pinned layer. The similarity in their frequencies promotes the formation of precessional modes that exhibit strong collective properties such as frequency shifting and enhanced linewidth, while inhomogeneous magnetization of the pinned layer during reversal may also play a role in these observations. The collective character of precessional dynamics associated with mixing of the free and pinned layer magnetization dynamics must be accounted for even in tunnel valves with a small interlayer coupling. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
12. Ferromagnetic resonance of patterned chromium dioxide thin films grown by selective area chemical vapour deposition.
- Author
-
Durrant, C. J., Jokubaitis, M., Yu, W., Mohamad, H., Shelford, L. R., and Keatley, P. S.
- Subjects
CHEMICAL vapor deposition ,FERROMAGNETIC resonance ,FERROMAGNETISM ,FILM condensation ,ELLIPSOMETRY ,THIN films ,MAGNETRON sputtering - Abstract
A selective area chemical vapour deposition technique has been used to fabricate continuous and patterned epitaxial CrO
2 thin films on (100)-oriented TiO2 substrates. Precessional magnetization dynamics were stimulated both electrically and optically, and probed by means of time-resolved Kerr microscopy and vector network analyser ferromagnetic resonance techniques. The dependence of the precession frequency and the effective damping parameter upon the static applied magnetic field were investigated. All films exhibited a large in-plane uniaxial anisotropy. The effective damping parameter was found to exhibit strong field dependence in the vicinity of the hard axis saturation field. However, continuous and patterned films were found to possess generally similar dynamic properties, confirming the suitability of the deposition technique for fabrication of future spintronic devices. [ABSTRACT FROM AUTHOR]- Published
- 2015
- Full Text
- View/download PDF
13. Optically detected spin–orbit torque ferromagnetic resonance in an in-plane magnetized ellipse.
- Author
-
Keatley, P. S., Chatzimpaloglou, K., Manago, T., Androvitsaneas, P., Loughran, T. H. J., Hicken, R. J., Mihajlović, G., Wan, L., Choi, Y., and Katine, J. A.
- Subjects
- *
MAGNETIC fields , *FERROMAGNETIC resonance , *TORQUE - Abstract
Time-resolved scanning Kerr microscopy has been used to perform optically detected, phase-resolved spin–orbit torque ferromagnetic resonance (SOT-FMR) measurements on a microscale CoFeB ellipse at the center of a Pt Hall cross subject to RF and DC current. Time-resolved polar Kerr images revealed localized dynamics with large amplitude at the center and weaker amplitude at the edges. Therefore, field swept SOT-FMR spectra were acquired from the so-called center mode to probe the SOTs active at the center of the ellipse, thus minimizing non-uniform edge contributions. When the magnetic field was applied at 30° from the hard axis of the ellipse and a DC current was applied, a marked asymmetry was observed in the amplitude and linewidth of the FMR peaks as the applied field was reversed. Both absorptive and dispersive parts of the spectra were in good agreement with a macrospin calculation. The damping parameter (α) and the Slonczewski torque parameter were determined to be 0.025 and (6.75 ± 0.75) × 10−7 Oe A−1 cm2, respectively. The hard axis SOT-FMR linewidth was found to be almost independent of the DC current value, suggesting that the SOT has a minimal influence in the hard axis configuration and that thermal effects were insignificant. This study paves the way for spatially resolved measurements of SOT probed using localized modes of microscale devices that go beyond the spatially averaged capability of electrical measurement techniques. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
14. Electrical Detection of DC Spin Current Propagation Through an Epitaxial Antiferromagnetic NiO Layer.
- Author
-
Newman, D. G., Dabrowski, M., Keatley, P. S., Li, Q., Yang, M., Marmion, S. R., Hickey, B. J., Qiu, Z.-Q., and Hicken, R. J.
- Subjects
SPIN Hall effect ,MAGNETIC field measurements ,ENHANCED magnetoresistance ,ANTIFERROMAGNETIC materials ,MAGNETORESISTANCE ,ELECTRIC potential measurement - Abstract
A method for detecting dc spin current propagation through an epitaxial antiferromagnetic (AFM) NiO layer is presented. Spin current is generated by spin pumping from an adjoining ferromagnetic (FM) layer and detected in a non-magnetic metallic layer by the inverse spin Hall effect. Comparison is made with a YIG/Pt bilayer, where only the Pt layer is electrically conducting, but for which spin Hall magnetoresistance makes an additional contribution to the measured signal. The signal obtained from the multilayered stack containing the AFM NiO layer is found to contain additional contributions due to anisotropic magnetoresistance. By exciting the sample with out-of-plane rf magnetic field and making measurements with a static field applied at different orientations within the plane of the sample, a signal associated with the dc spin current may be identified. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
15. A Ferrite-Filled Cavity Resonator for Electronic Article Surveillance on Metallic Packaging.
- Author
-
Keatley, P. S., Glover, E. R., Tremain, B., Hooper, I. R., Hibbins, A. P., and Hicken, R. J.
- Subjects
- *
CAVITY resonators , *ELECTRONIC surveillance , *ALUMINUM foil , *FINITE element method , *ALUMINUM forming , *MAGNETIC flux - Abstract
Conventional electronic article surveillance (EAS) tags are ineffective on metallic packaging. The component of the RF magnetic field perpendicular to the surface of the packaging induces eddy currents that suppress the magnetic flux, linking the inductive element of the tag. In this article, an inductive quarter-wavelength planar cavity, formed by wrapping aluminum foil around a ferrite core, was extended by wrapping additional capacitive layers of foil/dielectric around the ferrite-filled central region. This so-called wrapped tag exhibits the frequency, $Q$ -factor, and read distance characteristics of existing EAS tags, but is instead driven by the RF magnetic fields parallel to the surface of the metallic packaging. In this article, we compare the observed frequency response of the wrapped tag with a simple LC resonator model that considers the tag’s geometrical features, and use the model to describe how the design and construction of the tag can be optimized. Finite-element method (FEM) modeling is used to reveal how the current flows in the wrapped foil of the tag. Prototype tags show good reproducibility, demonstrating the potential of the design as a solution to the problem of tagging metallic packaging in the EAS industry. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
16. Time resolved studies of edge modes in magnetic nanoelements (invited).
- Author
-
Kruglyak, V. V., Keatley, P. S., Hicken, R. J., Childress, J. R., and Katine, J. A.
- Subjects
- *
MAGNETIC materials , *NANOSTRUCTURED materials , *MAGNETISM , *SIMULATION methods & models , *MAGNETOMETERS , *MAGNETIZATION - Abstract
Micromagnetic simulations have been performed to investigate the frequencies and relative amplitudes of resonant magnetic modes within nanomagnetic elements of varying size that have been previously studied by time resolved Kerr magnetometry. The magnetic response of a nanoscale element generally consists of the edge and center localized modes. For 2.5 nm thick elements, a crossover from center to edge mode excitation occurs as the element size is reduced to less than 220 nm. Additional modes appear in the spin wave spectrum as the thickness of the element is increased. The frequency of the edge mode is particularly sensitive to the strength of the exchange interaction, dipolar interactions with nearest neighbor elements, and rounding of the corners of the element. Simulations with in-plane pulsed fields show that the edge mode becomes dominant in elements of somewhat larger size, emphasizing the importance of the edge mode in technological applications. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
17. Time resolved imaging of the non-linear bullet mode within an injection-locked nano-contact spin Hall nano-oscillator.
- Author
-
Spicer, T. M., Keatley, P. S., Dvornik, M., Loughran, T. H. J., Awad, A. A., Dürrenfeld, P., Houshang, A., Ranjbar, M., Åkerman, J., Kruglyak, V. V., and Hicken, R. J.
- Subjects
- *
SPIN Hall effect , *MAGNETIZATION , *KERR electro-optical effect , *FERROMAGNETIC resonance , *MICROSCOPY - Abstract
Time-resolved scanning Kerr microscopy (TRSKM) has been used to image precessional magnetization dynamics excited by a DC current within a nano-contact (NC) spin Hall nano-oscillator (SHNO). Injection of a radio frequency (RF) current was used to phase lock the SHNO to TRSKM. The out of plane magnetization was detected by means of the polar magneto optical Kerr effect (MOKE). However, longitudinal MOKE images were dominated by an artifact arising from the edges of the Au NCs. Time resolved imaging revealed the simultaneous excitation of a non-linear "bullet" mode at the centre of the device, once the DC current exceeded a threshold value, and ferromagnetic resonance (FMR) induced by the RF current. However, the FMR response observed for sub-critical DC current values exhibits an amplitude minimum at the centre, which is attributed to spreading of the RF spin current due to the reactance of the device structure. This FMR response can be subtracted to yield images of the bullet mode. As the DC current is increased above threshold, the bullet mode appears to increase in size, suggesting increased translational motion. The reduced spatial overlap of the bullet and FMR modes, and this putative translational motion, may impede the injection locking and contribute to the reduced locking range observed within NC-SHNO devices. This illustrates a more general need to control the geometry of an injection-locked oscillator so that the autonomous dynamics of the oscillator exhibit strong spatial overlap with those resulting from the injected signal. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
18. Time-resolved Kerr microscopy of coupled transverse domain walls in a pair of curved nanowires.
- Author
-
Keatley, P. S., Yu, W., O'Brien, L., Read, D. E., Cowburn, R. P., and Hicken, R. J.
- Subjects
- *
NANOSTRUCTURED materials , *NANOWIRES , *DOMAIN walls (Ferromagnetism) , *FERROMAGNETISM , *ELECTRIC wire - Abstract
Time-resolved scanning Kerr microscopy has been used to directly observe magnetostatically coupled transverse domain walls (TDWs) in a pair of closely spaced, curved nanowires (NWs). Kerr images of the precessional response of the magnetic domain to either side of the TDW revealed the TDW as a minimum in the Kerr signal in the region of closest NW separation. When the TDWs were ejected from the NW pair, the minimum in the Kerr signal was no longer observed. By imaging this transition, the static de-coupling field was estimated to be in the range from 38 to 48Oe in good agreement with a simple micromagnetic model. This work provides a novel technique by which DC and microwave assisted decoupling fields of TDWs may be explored in NW pairs of different width, separation, and curvature. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
19. Time resolved imaging of magnetization dynamics in hard disk writer yokes excited by bipolar current pulses.
- Author
-
Yu, W., Keatley, P. S., Hicken, R. J., Gubbins, M. A., Czoschke, P. J., and Lopusnik, R.
- Subjects
- *
MAGNETIZATION , *FERROMAGNETISM , *KERR electro-optical effect , *MAGNETIC flux , *YOKES - Abstract
A partially built hard disk writer structure with a NiFe/CoFe/Ru/NiFe/CoFe synthetic antiferromagnetic (SAF) yoke was studied by time and vector resolved scanning Kerr microscopy. All three time dependent components of the magnetization were recorded simultaneously as a bipolar current pulse with 1MHz repetition rate was delivered to the coil. The component of magnetization parallel to the symmetry axis of the yoke was compared at the pole and above a coil winding in the centre of the yoke. The two responses are in phase as the pulse rises, but the pole piece lags the yoke as the pulse falls. The Kerr signal is smaller within the yoke than within the confluence region during pulse cycling. This suggests funneling of flux into the confluence region. Dynamic images acquired at different time delays showed that the relaxation is faster in the centre of the yoke than in the confluence region, perhaps due to the different magnetic anisotropy in these regions. Although the SAF yoke is designed to support a single domain to aid flux conduction, no obvious flux beaming was observed, suggesting the presence of a more complicated domain structure. The SAF yoke writer hence provides relatively poor flux conduction but good control of rise time compared to single layer and multi-layered yokes studied previously. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
20. Time- and vector-resolved magneto-optical Kerr effect measurements of large angle precessional reorientation in a 2×2 μm2 ferromagnet.
- Author
-
Keatley, P. S., Kruglyak, V. V., Neudert, A., Delchini, M., Hicken, R. J., Childress, J. R., and Katine, J. A.
- Subjects
- *
MAGNETOOPTICS , *KERR electro-optical effect , *FERROMAGNETIC materials , *HYSTERESIS loop , *MAGNETIC fields , *DAMPING (Mechanics) , *MAGNETIZATION , *SIMULATION methods & models - Abstract
The precessional dynamics of a 2×2 μm2 CoFe/NiFe (4.6 nm) element stimulated by an in-plane pulsed magnetic field have been investigated using time- and vector-resolved Kerr microscopy measurements and micromagnetic simulations. The time-resolved signals were normalized to in-plane hysteresis loops obtained from the patterned material, and suggest that the magnetization reorients through an angle of 100°±10°. The simulations reveal that only the magnetization of the center region undergoes large angle reorientation, while the canted magnetization at the edges of the element remains pinned. An enhanced Gilbert damping parameter of 0.1 was required to reproduce the experimentally observed Kerr signals. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
21. Design and fabrication of plasmonic cavities for magneto-optical sensing.
- Author
-
Loughran, T. H. J., Roth, J., Keatley, P. S., Hendry, E., Barnes, W. L., Hicken, R. J., Einsle, J. F., Amy, A., Hendren, W., Bowman, R. M., and Dawson, P.
- Subjects
MAGNETO-optical sensors ,MICROFABRICATION ,PLASMONS (Physics) - Abstract
The design and fabrication of a novel plasmonic cavity, intended to allow far-field recovery of signals arising from near field magneto-optical interactions, is presented. Finite element modeling is used to describe the interaction between a gold film, containing cross-shaped cavities, with a nearby magnetic under-layer. The modeling revealed strong electric field confinement near the center of the cross structure for certain optical wavelengths, which may be tuned by varying the length of the cross through a range that is compatible with available fabrication techniques. Furthermore, the magneto optical Kerr effect (MOKE) response of the composite structure can be enhanced with respect to that of the bare magnetic film. To confirm these findings, cavities were milled within gold films deposited upon a soluble film, allowing relocation to a ferromagnetic film using a float transfer technique. Cross cavity arrays were fabricated and characterized by optical transmission spectroscopy prior to floating, revealing resonances at optical wavelengths in good agreement with the finite element modeling. Following transfer to the magnetic film, circular test apertures within the gold film yielded clear magneto-optical signals even for diameters within the sub-wavelength regime. However, no magneto-optical signal was observed for the cross cavity arrays, since the FIB milling process was found to produce nanotube structures within the soluble under-layer that adhered to the gold. Further optimization of the fabrication process should allow recovery of magneto-optical signal from cross cavity structures. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
22. Configurational anisotropy in hexagonal arrays of submicron Co elements.
- Author
-
Weekes, S. M., Ogrin, F. Y., and Keatley, P. S.
- Subjects
ANISOTROPY ,COBALT ,MAGNETIZATION ,POLYCRYSTALS ,MAGNETIC dipoles - Abstract
The angular dependence of the in-plane magnetization reversal in hexagonally ordered Co arrays has been investigated. A sixfold anisotropy has been observed which mirrors the structural symmetry of the array. The arrays consist of polycrystalline, circular elements with constant center-to-center separation and diameters of 360 nm and below. It has been observed that the anisotropy is strongly dependent on element diameter and disappears for densely packed elements. This anisotropic coupling cannot be explained by a simple model of interacting point dipoles situated at regular lattice sites, as this predicts an isotropic interaction field for a hexagonal array. Instead, it is believed that the anisotropy arises from interactions between unsaturated regions of the elements, particularly at adjacent edges. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
23. Use of microscale coplanar striplines with indium tin oxide windows in optical ferromagnetic resonance measurements.
- Author
-
Keatley, P. S., Kruglyak, V. V., Barman, A., Ladak, S., Hickena, R. J., Scott, J., and Rahman, M.
- Abstract
It is shown that a coplanar stripline structure containing indium tin oxide windows can be used to perform optical ferromagnetic resonance measurements on a sample grown on an opaque substrate, using a pulsed magnetic field of any desired orientation. The technique is demonstrated by applying it to a thin film of permalloy grown on a Si substrate. The measured precession frequency was found to be in good agreement with macrospin simulations. The phase of the oscillatory Kerr response was observed to vary as the probe spot was scanned across the coplanar stripline structure, confirming that the orientation of the pulsed field varied from parallel to perpendicular relative to the plane of the sample. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
24. Imaging the equilibrium state and magnetization dynamics of partially built hard disk write heads.
- Author
-
Valkass, R. A. J., Yu, W., Shelford, L. R., Keatley, P. S., Loughran, T. H. J., Hicken, R. J., Cavill, S. A., van der Laan, G., Dhesi, S. S., Bashir, M. A., Gubbins, M. A., Czoschke, P. J., and Lopusnik, R.
- Subjects
STATIC equilibrium (Physics) ,HARD disks ,MAGNETIZATION ,MAGNETIC circular dichroism ,MAGNETIC flux ,PHOTOEMISSION - Abstract
Four different designs of partially built hard disk write heads with a yoke comprising four repeats of NiFe (1 nm)/CoFe (50 nm) were studied by both x-ray photoemission electron microscopy (XPEEM) and time-resolved scanning Kerr microscopy (TRSKM). These techniques were used to investigate the static equilibrium domain configuration and the magnetodynamic response across the entire structure, respectively. Simulations and previous TRSKM studies have made proposals for the equilibrium domain configuration of similar structures, but no direct observation of the equilibrium state of the writers has yet been made. In this study, static XPEEM images of the equilibrium state of writer structures were acquired using x-ray magnetic circular dichroism as the contrast mechanism. These images suggest that the crystalline anisotropy dominates the equilibrium state domain configuration, but competition with shape anisotropy ultimately determines the stability of the equilibrium state. Dynamic TRSKM images were acquired from nominally identical devices. These images suggest that a longer confluence region may hinder flux conduction from the yoke into the pole tip: the shorter confluence region exhibits clear flux beaming along the symmetry axis, whereas the longer confluence region causes flux to conduct along one edge of the writer. The observed variations in dynamic response agree well with the differences in the equilibrium magnetization configuration visible in the XPEEM images, confirming that minor variations in the geometric design of the writer structure can have significant effects on the process of flux beaming. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
25. Observation of vortex dynamics in arrays of nanomagnets.
- Author
-
Yu, W., Keatley, P. S., Gangmei, P., Marcham, M. K., Loughran, T. H. J., Hicken, R. J., Cavill, S. A., van der Laan, G., Childress, J. R., and Katine, J. A.
- Subjects
- *
QUASIUNIFORM spaces , *MICROSCOPY , *DEMAGNETIZATION , *FLUX flow , *CHIRALITY - Abstract
Vortex dynamics within arrays of square ferromagnetic nanoelements have been studied by time-resolved scanning Kerr microscopy (TRSKM), while x-ray photoemission electron microscopy has been used to investigate the equilibrium magnetic state of the arrays. An alternating field demagnetization process was found to initialize a distribution of equilibrium states within the individual elements of the array, including quasiuniform states and vortex states of different chirality and core polarization. Repeated initialization revealed some evidence of stochastic behavior during the formation of the equilibrium state. TRSKM with a spatial resolution of ~300 nm was used to detect vortex gyration within arrays of square nanoelements of 250-nm lateral size. Two arrays were studied consisting of a 9 × 9 and 5 × 5 arrangement of nanoelements with 50- and 500-nm element edge-to-edge separation to encourage strong and negligible dipolar interactions, respectively. In the 5 × 5 element array, TRSKM images, acquired at a fixed phase of the driving microwave magnetic field, revealed differences in the gyrotropic phase within individual elements. While some phase variation is attributed to the dispersion in the size and shape of elements, the vortex chirality and core polarization are also shown to influence the phase. In the 9 × 9 array, strong magneto-optical response due to vortex gyration was observed across regions with length equal to either one or two elements. Micromagnetic simulations performed for 2 × 2 arrays of elements suggest that particular combinations of vortex chirality and polarization in neighboring elements are required to generate the observed magneto-optical contrast. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
26. Optical characterization of nonlocal spin transfer torque acting on a single nanomagnet.
- Author
-
Keatley, P. S., Aziz, A., Ali, M., Hickey, B. J., Blamire, M. G., and Hicken, R. J.
- Subjects
- *
NANOMAGNETICS , *SPIN transfer torque , *SPINTRONICS , *SPIN-polarized currents , *NANOTECHNOLOGY - Abstract
Time-resolved scanning Kerr microscopy (TRSKM) has been used to examine the effect of nonlocal spin transfer torque (NL-STT) within a two-terminal current perpendicular-to-plane nonlocal spin valve. A combination of Oersted field and NL-STT was used to excite and control the magnetization dynamics. By comparison with a macrospin model, the strength of the NL-STT was quantified and found to be comparable to that achieved by direct injection of spin-polarized current. The sensitivity of the magneto-optical probe to small out-of-plane deflections of the magnetization also allows the NL-STT to be quantified in quasi-dc measurements, greatly simplifying the investigation of STT phenomena. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
27. Ferrite-filled cavities for compact planar resonators.
- Author
-
Keatley, P. S., Durrant, C. J., Berry, S. J., Sirotkin, E., Hibbins, A. P., and Hicken, R. J.
- Subjects
- *
WAVELENGTH measurement , *HIGH frequency amplifiers , *RADIO frequency , *RADIO frequency identification systems , *MAGNETIC fields - Abstract
Sub-wavelength metallic planar cavities, closed at one end, have been constructed by wrapping aluminium foil around teflon or ferrite slabs. Finite cavity width perturbs the fundamental cavity mode frequency of ferrite-filled cavities due to different permeability inside and outside of the cavity, in contrast to teflon-filled cavities, while the cavity length required to achieve a specific resonance frequency is significantly reduced for a ferrite-filled cavity. Ferrite-filled cavities may be excited by an in-plane alternating magnetic field and may be advantageous for high-frequency (HF) and ultra HF tagging and radio frequency identification of metallic objects within security, manufacturing, and shipping environments. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
28. Isolating the Dynamic Dipolar Interaction between a Pair of Nanoscale Ferromagnetic Disks.
- Author
-
Keatley, P. S., Gangmei, P., Dvomik, M., Hicken, R. J., Grollier, J., and Ulysse, C.
- Subjects
- *
COORDINATE covalent bond , *FERROMAGNETIC materials , *SPIN waves , *METAMATERIALS , *MAGNETIC properties - Abstract
Dynamic dipolar interactions between spin wave eigenmodes of closely spaced nanomagnets determine the collective behavior of magnonic and spintronic metamaterials and devices. However, dynamic dipolar interactions are difficult to quantify since their effects must be disentangled from those of static dipolar interactions and variations in the shape, size, and magnetic properties of the nanomagnets. It is shown that when two imperfect nanoscale magnetic disks with similar but nonidentical modes are brought into close proximity, the effect of the dynamic dipolar interaction can be detected by considering the difference of the phase of precession within the two disks. Measurements show that the interaction is stronger than expected from micromagnetic simulations, highlighting both the need for characterization and control of magnetic properties at the deep nanoscale, and also the potential for improved control of collective magnetic phenomena. Our approach is equally applicable to other physical systems in which dynamic interactions are obscured by inhomogeneous broadening and static interactions. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
29. Influence of a Dy overlayer on the precessional dynamics of a ferromagnetic thin film.
- Author
-
Marcham, M. K., Yu, W., Keatley, P. S., Shelford, L. R., Shafer, P., Cavill, S. A., Qing, H., Neudert, A., Childress, J. R., Katine, J. A., Arenholz, E., Telling, N. D., van der Laan, G., and Hicken, R. J.
- Subjects
THIN films ,FERROMAGNETIC materials ,KERR electro-optical effect ,MAGNETIC damping (Mechanics) ,FERROMAGNETIC resonance ,NUCLEAR spin ,NUCLEAR moments - Abstract
Precessional dynamics of a Co50Fe50(0.7)/Ni90Fe10(5)/Dy(1)/Ru(3) (thicknesses in nm) thin film have been explored by low temperature time-resolved magneto-optical Kerr effect and phase-resolved x-ray ferromagnetic resonance measurements. As the temperature was decreased from 300 to 140 K, the magnetic damping was found to increase rapidly while the resonance field was strongly reduced. Static x-ray magnetic circular dichroism measurements revealed increasing ferromagnetic order of the Dy moment antiparallel to that of Co50Fe50/Ni90Fe10. Increased coupling of the Dy orbital moment to the precessing spin magnetization leads to significantly increased damping and gyromagnetic ratio of the film while leaving its magnetic anisotropy effectively unchanged. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
30. Interplay between spin proximity effect and charge-dependent exciton dynamics in MoSe2/CrBr3 van der Waals heterostructures.
- Author
-
Lyons, T. P., Gillard, D., Molina-Sánchez, A., Misra, A., Withers, F., Keatley, P. S., Kozikov, A., Taniguchi, T., Watanabe, K., Novoselov, K. S., Fernández-Rossier, J., and Tartakovskii, A. I.
- Subjects
KERR magneto-optical effect ,EXCITON theory ,MAGNETIC tunnelling ,ELECTRON gas ,OPTICAL resolution ,CHARGE transfer ,HETEROSTRUCTURES ,VAN der Waals forces - Abstract
Semiconducting ferromagnet-nonmagnet interfaces in van der Waals heterostructures present a unique opportunity to investigate magnetic proximity interactions dependent upon a multitude of phenomena including valley and layer pseudospins, moiré periodicity, or exceptionally strong Coulomb binding. Here, we report a charge-state dependency of the magnetic proximity effects between MoSe
2 and CrBr3 in photoluminescence, whereby the valley polarization of the MoSe2 trion state conforms closely to the local CrBr3 magnetization, while the neutral exciton state remains insensitive to the ferromagnet. We attribute this to spin-dependent interlayer charge transfer occurring on timescales between the exciton and trion radiative lifetimes. Going further, we uncover by both the magneto-optical Kerr effect and photoluminescence a domain-like spatial topography of contrasting valley polarization, which we infer to be labyrinthine or otherwise highly intricate, with features smaller than 400 nm corresponding to our optical resolution. Our findings offer a unique insight into the interplay between short-lived valley excitons and spin-dependent interlayer tunneling, while also highlighting MoSe2 as a promising candidate to optically interface with exotic spin textures in van der Waals structures. One advantage of van der Waals materials is the ability to combine different materials in layers to form new heterostructures. Here, the authors investigate heterostructures of CrBr3 and MoSe2 , and find that the ferromagnetism of CrBr3 enhances the valley dependent optical response of the MoSe2 . [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
31. Time- and vector-resolved Kerr microscopy of hard disk writers.
- Author
-
Gangmei, P., Keatley, P. S., Yu, W., Hicken, R. J., Gubbins, M. A., Czoschke, P. J., and Lopusnik, R.
- Subjects
- *
TIME-resolved spectroscopy , *MAGNETIZATION , *HARD disks , *COMPUTER engineering , *PHOTODIODES , *DETECTORS - Abstract
Time-resolved scanning Kerr microscopy has been used to make wafer level measurements of magnetization dynamics within the yoke and pole piece of partially built hard disk writer structures. Three Cartesian components of the vector magnetization were recorded simultaneously using a quadrant photodiode polarization bridge detector. The rise time, relaxation time, and amplitude of each component has been related to the magnetic ground state, the initial torque, and flux propagation through the yoke and pole piece. Dynamic images reveal 'flux-beaming' in which the magnetization component parallel to the symmetry axis of the yoke is largest along that axis. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
32. Excitation of propagating spin waves with global uniform microwave fields.
- Author
-
Au, Y., Davison, T., Ahmad, E., Keatley, P. S., Hicken, R. J., and Kruglyak, V. V.
- Subjects
SPIN waves ,MICROWAVES ,WAVEGUIDES ,MAGNETIC films ,MICROMETERS ,ANTENNAS (Electronics) ,INFORMATION processing - Abstract
We demonstrate a magnonic architecture that converts global free-space uniform microwaves into spin waves propagating in a stripe magnonic waveguide. The architecture is based upon dispersion mismatch between the narrow magnonic waveguide and a wide 'antenna' patch, both patterned from the same magnetic film. The spin waves injected into the waveguide travel to distances as large as several tens of micrometers. The antennas can be placed at multiple positions on a magnonic chip and used to excite mutually coherent multiple spin waves for magnonic logic operations. This demonstration paves way for 'magnonics' to become a pervasive technology for information processing. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
33. Large amplitude magnetization dynamics and the suppression of edge modes in a single nanomagnet.
- Author
-
Keatley, P. S., Gangmei, P., Dvornik, M., Hicken, R. J., Childress, J. R., and Katine, J. A.
- Subjects
- *
MAGNETIZATION , *NANOSTRUCTURED materials , *KERR electro-optical effect , *SIMULATION methods & models , *TORQUE , *OSCILLATIONS , *MICROSCOPY , *ELECTRONIC excitation - Abstract
Large amplitude magnetization dynamics of a single square nanomagnet have been studied by time-resolved Kerr microscopy. Experimental spectra revealed that only a single mode was excited for all bias field values. Micromagnetic simulations demonstrate that at larger pulsed field amplitudes the center mode dominates the dynamic response while the edge mode is almost completely suppressed. Controlled suppression of edge modes in a single nanomagnet has potential applications in the operation of nanoscale spin transfer torque oscillators and bistable switching devices for which the amplitude of the magnetization trajectory is often large and a more uniform dynamic response is desirable. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
34. Temperature dependence of the interface moments in Co2MnSi thin films.
- Author
-
Telling, N. D., Keatley, P. S., Shelford, L. R., Arenholz, E., van der Laan, G., Hicken, R. J., Sakuraba, Y., Tsunegi, S., Oogane, M., Ando, Y., Takanashi, K., and Miyazaki, T.
- Subjects
- *
THIN films , *TEMPERATURE effect , *INTERFACES (Physical sciences) , *COBALT , *MANGANESE compounds - Abstract
X-ray magnetic circular dichroism (XMCD) is utilized to explore the temperature dependence of the interface moments in Co2MnSi (CMS) thin films capped with aluminum. By increasing the thickness of the capping layer, we demonstrate enhanced interface sensitivity of the measurements. L21-ordered CMS films show no significant temperature dependence of either the Co or Mn interface moments. However, disordered CMS films show a decreased moment at low temperature possibly caused by increased Mn–Mn antiferromagnetic coupling. It is suggested that for ordered L21 CMS films the temperature dependence of the tunneling magnetoresistance is not related to changes in the interface moments. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
35. Phase-resolved x-ray ferromagnetic resonance measurements in fluorescence yield.
- Author
-
Marcham, M. K., Keatley, P. S., Neudert, A., Hicken, R. J., Cavill, S. A., Shelford, L. R., van der Laan, G., Telling, N. D., Childress, J. R., Katine, J. A., Shafer, P., and Arenholz, E.
- Subjects
- *
X-rays , *FERROMAGNETISM , *MAGNETIC resonance , *FERROMAGNETIC resonance , *MAGNETIC susceptibility - Abstract
Phase-resolved x-ray ferromagnetic resonance (XFMR) has been measured in fluorescence yield, extending the application of XFMR to opaque samples on opaque substrates. Magnetization dynamics were excited in a Co50Fe50(0.7)/Ni90Fe10(5) bilayer by means of a continuous wave microwave excitation, while x-ray magnetic circular dichroism (XMCD) spectra were measured stroboscopically at different points in the precession cycle. By tuning the x-ray energy to the L3 edges of Ni and Fe, the dependence of the real and imaginary components of the element specific magnetic susceptibility on the strength of an externally applied static bias field was determined. First results from measurements on a Co50Fe50(0.7)/Ni90Fe10(5)/Dy(1) sample confirm that enhanced damping results from the addition of the Dy cap. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
36. Magneto-optical observation of mutual phase-locking in a pair of spin-torque vortex oscillators.
- Author
-
Keatley, P. S., Sani, S., Hrkac, G., Mohseni, S., Durrenfeld, P., Akerman, J., and Hicken, R.
- Published
- 2015
- Full Text
- View/download PDF
37. Time-resolved imaging of magnetic vortex dynamics using holography with extended reference autocorrelation by linear differential operator.
- Author
-
Bukin, N., McKeever, C., Burgos-Parra, E., Keatley, P. S., Hicken, R. J., Ogrin, F. Y., Beutier, G., Dupraz, M., Popescu, H., Jaouen, N., Yakhou-Harris, F., Cavill, S. A., and van der Laan, G.
- Published
- 2016
- Full Text
- View/download PDF
38. Superharmonic injection locking of nanocontact spin-torque vortex oscillators.
- Author
-
Keatley, P. S., Sani, S. R., Hrkac, G., Mohseni, S. M., Dürrenfeld, P., Åkerman, J., and Hicken, R. J.
- Subjects
- *
TORQUE , *NANOCONTACTS , *TIME-resolved spectroscopy , *MAGNETOELECTRONICS , *MICROWAVE oscillators - Abstract
Superharmonic injection locking of single nanocontact (NC) spin-torque vortex oscillators (STVOs) subject to a small microwave current has been explored. Frequency locking was observed up to the fourth harmonic of the STVO fundamental frequency f0 in microwave magnetoelectronic measurements. The large frequency tunability of the STVO with respect to f0 allowed the device to be locked to multiple subharmonics of the microwave frequency fRF, or to the same subharmonic over a wide range of fRF by tuning the dc current. In general, analysis of the locking range, linewidth, and amplitude showed that the locking efficiency decreased as the harmonic number increased, as expected for harmonic synchronization of a nonlinear oscillator. Time-resolved scanning Kerr microscopy (TRSKM) revealed significant differences in the spatial character of the magnetization dynamics of states locked to the fundamental and harmonic frequencies, suggesting significant differences in the vortex core trajectories within the same device. Superharmonic injection locking of a NC-STVO may open up possibilities for devices such as nanoscale frequency dividers, while differences in the core trajectory may allow mutual synchronization to be achieved in multioscillator networks by tuning the spatial character of the dynamics within shared magnetic layers. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
39. Direct observation of magnetization dynamics generated by nanocontact spin-torque vortex oscillators.
- Author
-
Keatley, P. S., Sani, S. R., Hrkac, G., Mohseni, S. M., Dürrenfeld, P., Loughran, T. H. J., Åkerman, J., and Hicken, R. J.
- Subjects
- *
MAGNETIZATION , *NANOCONTACTS , *NUCLEAR spin , *PARAMETRONS , *TIME-resolved measurements , *MICROWAVE power transmission - Abstract
Time-resolved scanning Kerr microscopy has been used to directly image the magnetization dynamics of nanocontact (NC) spin-torque vortex oscillators (STVOs) when phase locked to an injected microwave (rf) current. The Kerr images reveal free-layer magnetization dynamics that extend outside the NC footprint, where they cannot be detected electrically, but which are crucial to phase-lock STVOs that share common magnetic layers. For a single NC, dynamics were observed not only when the STVO frequency was fully locked to that of the rf current, but also for a partially locked state characterized by periodic changes in the core trajectory at the rf frequency. For a pair of NCs, we explore the correlation between the spatial character of injection-locked dynamics and the free-running spectra. Insight gained from these images may improve understanding of the conditions required for mutual phase locking of multiple STVOs, and hence enhanced microwave power emission. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
40. Time resolved scanning Kerr microscopy of hard disk writer structures with a multilayered yoke.
- Author
-
Yu, W., Gangmei, P., Keatley, P. S., Hicken, R. J., Gubbins, M. A., Czoschke, P. J., and Lopusnik, R.
- Subjects
DATA disk drives ,FERROMAGNETISM ,PULSE circuits ,MAGNETIZATION ,MAGNETIC fields - Abstract
Partially built hard disk writer structures with a multilayered yoke formed from 4 repeats of a NiFe(∼1 nm)/CoFe(50 nm) bilayer were studied by time and vector resolved scanning Kerr microscopy. Dynamic images of the in-plane magnetization suggest an underlying closure domain equilibrium state. This state is found to be modified by application of a bias magnetic field and also during pulse cycling, leading to different magnetization rotation and relaxation behavior within the tip region. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
41. Resonance in magnetostatically coupled transverse domain walls.
- Author
-
Galkiewicz, A. T., O'Brien, L., Keatley, P. S., Cowburn, R. P., and Crowell, P. A.
- Subjects
- *
RESONANCE , *DOMAIN walls (Ferromagnetism) , *MAGNETOSTATICS , *FERROMAGNETIC materials , *COUPLING reactions (Chemistry) - Abstract
We have observed the eigenmodes of coupled transverse domain walls in a pair of ferromagnetic nanowires. Although the pair is coupled magnetostatically, its spectrum is determined by a combination of pinning by edge roughness and dipolar coupling of the two walls. Because the corresponding energy scales are comparable, the coupling can be observed only at the smallest wire separations. A model of the coupled wall dynamics reproduces the experiment quantitatively, allowing for comparisons with the estimated pinning and domain wall coupling energies. The results have significant implications for the dynamics of devices based on coupled domain walls. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
42. Phase-resolved x-ray ferromagnetic resonance measurements of spin pumping in spin valve structures.
- Author
-
Marcham, M. K., Shelford, L. R., Cavill, S. A., Keatley, P. S., W. Yu, Shafer, P., Neudert, A., Childress, J. R., Katine, J. A., Arenholz, E., Telling, N. D., Laan, G. Van der, and Hicken, R. J.
- Subjects
- *
FERROMAGNETIC resonance , *SPIN valves , *SPIN transfer torque , *PRECESSION , *MAGNETIC coupling , *COPPER - Abstract
Element-specific phase-resolved x-ray ferromagnetic resonance (FMR) was used to study spin pumping within Co50Fe50(3)/Cu(6)/Ni80Fe20(5) (thicknesses in nanometers) spin valve structures with large areas, so that edge effects typical of nanopillars used in standard magnetotransport experiments could be neglected. The phase of precession of the Co50Fe50 fixed layer was recorded as FMR was induced in the Ni80Fe20 free layer. The field dependence of the fixed layer phase contains a clear signature of spin transfer torque (STT) coupling due to spin pumping. Fitting the phase delay yields the spin-mixing conductance, the quantity that controls all spin transfer phenomena. The STT coupling is destroyed by insertion of Ta into the middle of the Cu layer. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
43. Direct Excitation of Propagating Spin Waves by Focused Ultrashort Optical Pulses.
- Author
-
Au, Y., Dvornik, M., Davison, T., Ahmad, E., Keatley, P. S., Vansteenkiste, A., Van Waeyenberge, B., and Kruglyak, V. V.
- Subjects
- *
SPIN waves , *ULTRASHORT laser pulses , *PHONONS , *NUCLEAR excitation , *COLLIMATED light , *ACOUSTIC surface waves , *MICROMAGNETICS - Abstract
An all-optical experiment long utilized to image phonons excited by ultrashort optical pulses has been applied to a magnetic sample. In addition to circular ripples due to surface acoustic waves, we observe an .Y-shaped pattern formed by propagating spin waves. The emission of spin waves from the optical pulse epicenter in the form of collimated beams is qualitatively reproduced by micromagnetic simulations. We explain the observed pattern in terms of the group velocity distribution of Damon-Eshbach magnetostatic spin waves in the reciprocal space and the wave vector spectrum of the focused ultrafast laser pulse. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
44. Direct Detection of Pure ac Spin Current by X-Ray Pump-Probe Measurements.
- Author
-
Li, J., Shelford, L. R., Shafer, P., Tan, A., Deng, J. X., Keatley, P. S., Hwang, C., Arenholz, E., van der Laan, G., Hicken, R. J., and Qiu, Z. Q.
- Subjects
- *
FERROMAGNETIC resonance , *NICKEL compounds , *CIRCULAR dichroism - Abstract
Despite recent progress in spin-current research, the detection of spin current has mostly remained indirect. By synchronizing a microwave waveform with synchrotron x-ray pulses, we use the ferromagnetic resonance of the Py (Ni81Fe19) layer in a Py/Cu/Cu75Mn25/Cu/Co multilayer to pump a pure ac spin current into the Cu75Mn25 and Co layers, and then directly probe the spin current within the Cu75Mn25 layer and the spin dynamics of the Co layer by x-ray magnetic circular dichroism. This element-resolved pump-probe measurement unambiguously identifies the ac spin current in the Cu75Mn25 layer. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.