Holger Schmidt - Academia.edu (original) (raw)
Papers by Holger Schmidt
2003 Third IEEE Conference on Nanotechnology, 2003. IEEE-NANO 2003.
The magneto-optical Kerr effect (MOKE) is commonly used in time-resolved measurements of magnetiz... more The magneto-optical Kerr effect (MOKE) is commonly used in time-resolved measurements of magnetization. A technique is presented to amplify this rotation and improve the signal-to-noise ratio in measurements of the very small polarization changes that are needed to measure magnetization reversal in single domain nanomagnets. The largest cavityinduced enhancement to date, a factor of 16.25, was observed. Enhancement of up to three orders of magnitude is possible with optimized structures.
Physical Review B, 2018
We report a novel all-optical technique to drive and probe the spin dynamics of single nanomagnet... more We report a novel all-optical technique to drive and probe the spin dynamics of single nanomagnets. Optically generated surface acoustic waves (SAWs) drive the magnetization precession in nanomagnets via magneto-elastic (MEL) coupling. We investigate the field-swept dynamics of isolated Ni nanomagnets at various SAW frequencies, and show that this method can be used to accurately determine the intrinsic Gilbert damping of nanostructured magnetic materials. This technique opens a new avenue for studying the spin dynamics of nanoscale devices using non-thermal ("cold") excitation, enabling direct observation of the MEL driven dynamics.
Physical Review B, 2019
We report preferential excitation and detection of the precessional spin dynamics of individual n... more We report preferential excitation and detection of the precessional spin dynamics of individual nanomagnets via magneto-elastic (MEL) resonance excitation. Surface acoustic waves (SAWs) are generated by the ultrafast optical excitation of a non-magnetic grating (Al bars) with lithographically defined acoustic eigenmodes. We show that the precessional spin dynamics in two identical, elliptical nanomagnets with orthogonal orientations can be selectively excited by the SAWs via control of the applied magnetic field. Furthermore, we observe that both the amplitude and damping of the magneto-elastically induced precession depend on the relative orientation of the SAW with respect to the nanomagnets. Using magneto-mechanical simulations, we show that the acoustic excitation is most efficient when the spatial distributions of the natural and SAW-driven magnetic resonances match. These findings reveal a direct connection between the geometry and MEL excitation efficiency and have implications for the rational design of nanoscale magneto-mechanical devices.
Physical Review B, 2014
We demonstrate that elastic interactions between nanomagnets in a periodic array can determine th... more We demonstrate that elastic interactions between nanomagnets in a periodic array can determine the magnetic response according to the nanoscale array geometry. These findings are attributed to magneto-elastic coupling of the spin dynamics with simultaneously excited surface acoustic waves. Specifically, we observe three manifestations of this effect: pinning of the magnetic resonance frequency over an extended range of applied magnetic fields, generation of additional modes whose frequency can differ by more than 100% from the intrinsic element response, and an enhancement of the Fourier amplitude of the magnetic mode at crossovers with mechanical modes. Simulations of the dynamics in the presence of coupling between magnetic and mechanical degrees of freedom are in good agreement with the experiment. This suggests that magnetization dynamics can be controlled by rational structural design on the nanoscale even when the magnetostatic interactions are negligible.
The overarching goal of the project was to develop a brand new type of miniaturized rubidium (Rb)... more The overarching goal of the project was to develop a brand new type of miniaturized rubidium (Rb) cells in integrated ARROW waveguides and to demonstrate their use for quantum interference effects such as EIT, slow light, and low-level quantum-optical devices. The project was extraordinarily successful. We successfully demonstrated the first fully self-contained chip-scale atomic spectroscopy chip along with world record slow light on a photonic chip. These results have been disseminated in numerous publications and invited conference presentations (see below), most notably two seminal Nature Photonics articles and an invited review for Laser and Photonics Reviews. Our new technology is attracting growing interest from researchers and media across the globe and has large potential for future expansion and improvement. this work or contain elements related to this project (Dongliang Yin, UCSC; Philip Measor, UCSC; Evan Lunt, BYU; John Barber, BYU).
Optical engineering (Redondo Beach, Calif.), 2016
Antiresonant reflecting optical waveguide power splitters, designed for use around the 635-nm wav... more Antiresonant reflecting optical waveguide power splitters, designed for use around the 635-nm wavelength, are characterized for multiple split angles ranging from 0.5 deg to 9 deg. Theoretical expectations and simulations predict lowest transmission losses at this split junction for the lowest angles. This is confirmed by the experimental structures built in SiO2 films on silicon substrates. A fabrication nonideality affects the achievable splitting angle. Design considerations are discussed based on tradeoffs between loss and the required length for a Y-splitter.
Eighth International Symposium on Laser Metrology, 2005
We present an all-optical approach to detecting magnetization reversal events in submicron ferrom... more We present an all-optical approach to detecting magnetization reversal events in submicron ferromagnetic structures that is non-perturbative and compatible with ultrafast optical techniques. We demonstrate experimentally that structures much smaller than the wavelength of light can be probed using both near-field and far-field laser techniques combined with a cavity Kerr enhancement technique and two different polarimetry methods. Controlled magnetization reversal events are detected in nickel magnets approaching the 100nm scale. This leads to a promising way to measure subpicosecond dynamics of nanomagnets for fast device applications.
Nanoengineering: Fabrication, Properties, Optics, and Devices, 2004
We present the first near-field scanning optical magneto-optic Kerr effect (MOKE) of sub-micron m... more We present the first near-field scanning optical magneto-optic Kerr effect (MOKE) of sub-micron magnetic structures, where a Kerr rotation of 0.11º from a 0.25µm nickel magnet was observed. This is enabled by a cavity based technique to enhance the Kerr rotation of light reflected from a magnetized surface. Spatially resolved magneto-optic measurements are performed involving both conventional microscopy and near-field scanning optical microscopy (NSOM). Cavity enhancement is achieved with either a single dielectric coating or a dielectric-metal bilayer coating applied to the ferromagnetic structure of interest. We present a scattering matrix approach to calculating the enhancement resulting from a multilayer dielectric coating and show good agreement with experiment. This demonstrates a non-invasive optical technique for magnetometry with ultrahigh spatial resolution.
Physical Review B, 2012
We report the dependence of the intrinsic spin wave spectra on the three-dimensional shape in sin... more We report the dependence of the intrinsic spin wave spectra on the three-dimensional shape in single FePtnanomagnetic elements. In contrast to the well-known center and edge modes in flat, circular nanodisks, curved nanomagnets with identical nominal thickness and footprint exhibit a rich multi-mode spectrum with qualitatively different dependence on applied field, such as a low-frequency "pinned" mode. Dynamic micromagnetic modeling shows that the experimentally observed modes originate from different sections of the nanomagnet with vastly different demagnetization field. Thus, controlled shaping of a nanomagnet in all three dimensions creates the possibility of magnetization dynamics by design.
Microfluidics and Nanofluidics, 2007
We review fabrication methods and common structures for optofluidic waveguides, defined as struct... more We review fabrication methods and common structures for optofluidic waveguides, defined as structures capable of optical confinement and transmission through fluid filled cores. Cited structures include those based on total internal reflection, metallic coatings, and interference based confinement. Configurations include optical fibers and waveguides fabricated on flat substrates (integrated waveguides). Some examples of optofluidic waveguides that are included in this review are Photonic Crystal Fibers (PCFs) and two-dimensional photonic crystal arrays, Bragg fibers and waveguides, and Anti Resonant Reflecting Optical Waveguides (ARROWs). An emphasis is placed on integrated ARROWs fabricated using a thin-film deposition process, which illustrates how optofluidic waveguides can be combined with other microfluidic elements in the creation of lab-on-a-chip devices.
Microfluidics and Nanofluidics, 2007
We review recent developments and current status of liquid-core optical waveguides in optofluidic... more We review recent developments and current status of liquid-core optical waveguides in optofluidics with emphasis on suitability for creating fully planar optofluidic labs-on-a-chip. In this first of two contributions, we give an overview of the different waveguide types that are being considered for effectively combining micro and nanofluidics with integrated optics. The large number of approaches is separated into conventional index-guided waveguides and more recent implementations using wave interference. The underlying principle for waveguiding and the current status are described for each type. We then focus on reviewing recent work on microfabricated liquid-core antiresonant reflecting optical (ARROW) waveguides, including the development of intersecting 2D waveguide networks and optical fluorescence and Raman detection with planar beam geometry. Single molecule detection capability and addition of electrical control for electrokinetic manipulation and analysis of single bioparticles are demonstrated. The demonstrated performance of liquid-core ARROWs is representative of the potential of integrated waveguides for on-chip detection with ultrahigh sensitivity, and points the way towards the next generation of high-performance, low-cost and portable biomedical instruments.
Journal of Magnetism and Magnetic Materials, 2011
Journal of Applied Physics, 2013
We present a comprehensive investigation of the size-dependent switching characteristics and spin... more We present a comprehensive investigation of the size-dependent switching characteristics and spin wave modes of FePt nanoelements. Curved nanomagnets ("caps") are compared to flat disks of identical diameter and volume over a size range of 100 to 300nm. Quasi-static magnetization reversal analysis using first-order reversal curves (FORC) shows that spherical caps have lower vortex nucleation and annihilation fields than the flat disks. As the element diameter decreases, the reversal mechanism in the caps crosses over sooner to coherent rotation than in the disks. The magnetization dynamics are studied using optically induced small angle precession and reveal a strong size dependence that differs for the two shapes. Flat disks exhibit well-known center and edge modes at all sizes, but as the diameter of the caps increases from 100 to 300 nm, additional oscillation modes appear in agreement with dynamic micromagnetic simulations. In addition, we show that the three-dimensional curvature of the cap causes a much greater sensitivity to the applied field angle which provides an additional way for controlling the ultrafast response of nanomagnetic elements.
Applied Physics Letters, 2005
We report loss improvement and fluorescence detection in integrated antiresonant reflecting optic... more We report loss improvement and fluorescence detection in integrated antiresonant reflecting optical waveguides with liquid cores. The minimum waveguide loss is reduced to 0.33/ cm by compensating for thickness variations in the fabrication process. We demonstrate fluorescence detection from as few as 490 molecules in a 57 pl core using these optimized waveguides. We measure angular fluorescence collection factors as high as 15% per facet in good agreement with theory. This demonstrates the potential of integrated hollow-core waveguides as optical sensors for single-molecule spectroscopy.
Applied Physics Letters, 2007
Applied Physics Letters, 2007
Applied Physics Letters, 2004
Optics Letters, 2014
Table of Contents List of Figures .
Journal of Magnetism and Magnetic Materials, 2011
We present the measurements of the picosecond magnetization dynamics of Co/Pd multilayer films. T... more We present the measurements of the picosecond magnetization dynamics of Co/Pd multilayer films. The dynamic magnetization properties of sputtered multilayer films were analyzed as a function of Co layer thicknesses and applied bias field. Both the eigenfrequencies of the magnetization precession in the multilayers and the associated Gilbert damping exhibit extreme sensitivity to the magnetic layer thickness on an atomic monolayer scale. The eigenfrequency increases more than threefold when the Co thickness decreases from 7.5 to 2.8Å, mainly due to the changes in effective saturation magnetization and perpendicular anisotropy constant. A concomitant 2.6-fold increase in the damping of the oscillations is observed and attributed to stronger interface dissipation in thinner Co layers. In addition, we introduce a quasi-1D micromagnetic model in which the multilayer stack is described as a onedimensional chain of macrospins that represent each Co layer. This model yields excellent agreement with the observed resonance frequencies without any free parameters, while being much simpler and faster than full 3D micromagnetic modeling.
2003 Third IEEE Conference on Nanotechnology, 2003. IEEE-NANO 2003.
The magneto-optical Kerr effect (MOKE) is commonly used in time-resolved measurements of magnetiz... more The magneto-optical Kerr effect (MOKE) is commonly used in time-resolved measurements of magnetization. A technique is presented to amplify this rotation and improve the signal-to-noise ratio in measurements of the very small polarization changes that are needed to measure magnetization reversal in single domain nanomagnets. The largest cavityinduced enhancement to date, a factor of 16.25, was observed. Enhancement of up to three orders of magnitude is possible with optimized structures.
Physical Review B, 2018
We report a novel all-optical technique to drive and probe the spin dynamics of single nanomagnet... more We report a novel all-optical technique to drive and probe the spin dynamics of single nanomagnets. Optically generated surface acoustic waves (SAWs) drive the magnetization precession in nanomagnets via magneto-elastic (MEL) coupling. We investigate the field-swept dynamics of isolated Ni nanomagnets at various SAW frequencies, and show that this method can be used to accurately determine the intrinsic Gilbert damping of nanostructured magnetic materials. This technique opens a new avenue for studying the spin dynamics of nanoscale devices using non-thermal ("cold") excitation, enabling direct observation of the MEL driven dynamics.
Physical Review B, 2019
We report preferential excitation and detection of the precessional spin dynamics of individual n... more We report preferential excitation and detection of the precessional spin dynamics of individual nanomagnets via magneto-elastic (MEL) resonance excitation. Surface acoustic waves (SAWs) are generated by the ultrafast optical excitation of a non-magnetic grating (Al bars) with lithographically defined acoustic eigenmodes. We show that the precessional spin dynamics in two identical, elliptical nanomagnets with orthogonal orientations can be selectively excited by the SAWs via control of the applied magnetic field. Furthermore, we observe that both the amplitude and damping of the magneto-elastically induced precession depend on the relative orientation of the SAW with respect to the nanomagnets. Using magneto-mechanical simulations, we show that the acoustic excitation is most efficient when the spatial distributions of the natural and SAW-driven magnetic resonances match. These findings reveal a direct connection between the geometry and MEL excitation efficiency and have implications for the rational design of nanoscale magneto-mechanical devices.
Physical Review B, 2014
We demonstrate that elastic interactions between nanomagnets in a periodic array can determine th... more We demonstrate that elastic interactions between nanomagnets in a periodic array can determine the magnetic response according to the nanoscale array geometry. These findings are attributed to magneto-elastic coupling of the spin dynamics with simultaneously excited surface acoustic waves. Specifically, we observe three manifestations of this effect: pinning of the magnetic resonance frequency over an extended range of applied magnetic fields, generation of additional modes whose frequency can differ by more than 100% from the intrinsic element response, and an enhancement of the Fourier amplitude of the magnetic mode at crossovers with mechanical modes. Simulations of the dynamics in the presence of coupling between magnetic and mechanical degrees of freedom are in good agreement with the experiment. This suggests that magnetization dynamics can be controlled by rational structural design on the nanoscale even when the magnetostatic interactions are negligible.
The overarching goal of the project was to develop a brand new type of miniaturized rubidium (Rb)... more The overarching goal of the project was to develop a brand new type of miniaturized rubidium (Rb) cells in integrated ARROW waveguides and to demonstrate their use for quantum interference effects such as EIT, slow light, and low-level quantum-optical devices. The project was extraordinarily successful. We successfully demonstrated the first fully self-contained chip-scale atomic spectroscopy chip along with world record slow light on a photonic chip. These results have been disseminated in numerous publications and invited conference presentations (see below), most notably two seminal Nature Photonics articles and an invited review for Laser and Photonics Reviews. Our new technology is attracting growing interest from researchers and media across the globe and has large potential for future expansion and improvement. this work or contain elements related to this project (Dongliang Yin, UCSC; Philip Measor, UCSC; Evan Lunt, BYU; John Barber, BYU).
Optical engineering (Redondo Beach, Calif.), 2016
Antiresonant reflecting optical waveguide power splitters, designed for use around the 635-nm wav... more Antiresonant reflecting optical waveguide power splitters, designed for use around the 635-nm wavelength, are characterized for multiple split angles ranging from 0.5 deg to 9 deg. Theoretical expectations and simulations predict lowest transmission losses at this split junction for the lowest angles. This is confirmed by the experimental structures built in SiO2 films on silicon substrates. A fabrication nonideality affects the achievable splitting angle. Design considerations are discussed based on tradeoffs between loss and the required length for a Y-splitter.
Eighth International Symposium on Laser Metrology, 2005
We present an all-optical approach to detecting magnetization reversal events in submicron ferrom... more We present an all-optical approach to detecting magnetization reversal events in submicron ferromagnetic structures that is non-perturbative and compatible with ultrafast optical techniques. We demonstrate experimentally that structures much smaller than the wavelength of light can be probed using both near-field and far-field laser techniques combined with a cavity Kerr enhancement technique and two different polarimetry methods. Controlled magnetization reversal events are detected in nickel magnets approaching the 100nm scale. This leads to a promising way to measure subpicosecond dynamics of nanomagnets for fast device applications.
Nanoengineering: Fabrication, Properties, Optics, and Devices, 2004
We present the first near-field scanning optical magneto-optic Kerr effect (MOKE) of sub-micron m... more We present the first near-field scanning optical magneto-optic Kerr effect (MOKE) of sub-micron magnetic structures, where a Kerr rotation of 0.11º from a 0.25µm nickel magnet was observed. This is enabled by a cavity based technique to enhance the Kerr rotation of light reflected from a magnetized surface. Spatially resolved magneto-optic measurements are performed involving both conventional microscopy and near-field scanning optical microscopy (NSOM). Cavity enhancement is achieved with either a single dielectric coating or a dielectric-metal bilayer coating applied to the ferromagnetic structure of interest. We present a scattering matrix approach to calculating the enhancement resulting from a multilayer dielectric coating and show good agreement with experiment. This demonstrates a non-invasive optical technique for magnetometry with ultrahigh spatial resolution.
Physical Review B, 2012
We report the dependence of the intrinsic spin wave spectra on the three-dimensional shape in sin... more We report the dependence of the intrinsic spin wave spectra on the three-dimensional shape in single FePtnanomagnetic elements. In contrast to the well-known center and edge modes in flat, circular nanodisks, curved nanomagnets with identical nominal thickness and footprint exhibit a rich multi-mode spectrum with qualitatively different dependence on applied field, such as a low-frequency "pinned" mode. Dynamic micromagnetic modeling shows that the experimentally observed modes originate from different sections of the nanomagnet with vastly different demagnetization field. Thus, controlled shaping of a nanomagnet in all three dimensions creates the possibility of magnetization dynamics by design.
Microfluidics and Nanofluidics, 2007
We review fabrication methods and common structures for optofluidic waveguides, defined as struct... more We review fabrication methods and common structures for optofluidic waveguides, defined as structures capable of optical confinement and transmission through fluid filled cores. Cited structures include those based on total internal reflection, metallic coatings, and interference based confinement. Configurations include optical fibers and waveguides fabricated on flat substrates (integrated waveguides). Some examples of optofluidic waveguides that are included in this review are Photonic Crystal Fibers (PCFs) and two-dimensional photonic crystal arrays, Bragg fibers and waveguides, and Anti Resonant Reflecting Optical Waveguides (ARROWs). An emphasis is placed on integrated ARROWs fabricated using a thin-film deposition process, which illustrates how optofluidic waveguides can be combined with other microfluidic elements in the creation of lab-on-a-chip devices.
Microfluidics and Nanofluidics, 2007
We review recent developments and current status of liquid-core optical waveguides in optofluidic... more We review recent developments and current status of liquid-core optical waveguides in optofluidics with emphasis on suitability for creating fully planar optofluidic labs-on-a-chip. In this first of two contributions, we give an overview of the different waveguide types that are being considered for effectively combining micro and nanofluidics with integrated optics. The large number of approaches is separated into conventional index-guided waveguides and more recent implementations using wave interference. The underlying principle for waveguiding and the current status are described for each type. We then focus on reviewing recent work on microfabricated liquid-core antiresonant reflecting optical (ARROW) waveguides, including the development of intersecting 2D waveguide networks and optical fluorescence and Raman detection with planar beam geometry. Single molecule detection capability and addition of electrical control for electrokinetic manipulation and analysis of single bioparticles are demonstrated. The demonstrated performance of liquid-core ARROWs is representative of the potential of integrated waveguides for on-chip detection with ultrahigh sensitivity, and points the way towards the next generation of high-performance, low-cost and portable biomedical instruments.
Journal of Magnetism and Magnetic Materials, 2011
Journal of Applied Physics, 2013
We present a comprehensive investigation of the size-dependent switching characteristics and spin... more We present a comprehensive investigation of the size-dependent switching characteristics and spin wave modes of FePt nanoelements. Curved nanomagnets ("caps") are compared to flat disks of identical diameter and volume over a size range of 100 to 300nm. Quasi-static magnetization reversal analysis using first-order reversal curves (FORC) shows that spherical caps have lower vortex nucleation and annihilation fields than the flat disks. As the element diameter decreases, the reversal mechanism in the caps crosses over sooner to coherent rotation than in the disks. The magnetization dynamics are studied using optically induced small angle precession and reveal a strong size dependence that differs for the two shapes. Flat disks exhibit well-known center and edge modes at all sizes, but as the diameter of the caps increases from 100 to 300 nm, additional oscillation modes appear in agreement with dynamic micromagnetic simulations. In addition, we show that the three-dimensional curvature of the cap causes a much greater sensitivity to the applied field angle which provides an additional way for controlling the ultrafast response of nanomagnetic elements.
Applied Physics Letters, 2005
We report loss improvement and fluorescence detection in integrated antiresonant reflecting optic... more We report loss improvement and fluorescence detection in integrated antiresonant reflecting optical waveguides with liquid cores. The minimum waveguide loss is reduced to 0.33/ cm by compensating for thickness variations in the fabrication process. We demonstrate fluorescence detection from as few as 490 molecules in a 57 pl core using these optimized waveguides. We measure angular fluorescence collection factors as high as 15% per facet in good agreement with theory. This demonstrates the potential of integrated hollow-core waveguides as optical sensors for single-molecule spectroscopy.
Applied Physics Letters, 2007
Applied Physics Letters, 2007
Applied Physics Letters, 2004
Optics Letters, 2014
Table of Contents List of Figures .
Journal of Magnetism and Magnetic Materials, 2011
We present the measurements of the picosecond magnetization dynamics of Co/Pd multilayer films. T... more We present the measurements of the picosecond magnetization dynamics of Co/Pd multilayer films. The dynamic magnetization properties of sputtered multilayer films were analyzed as a function of Co layer thicknesses and applied bias field. Both the eigenfrequencies of the magnetization precession in the multilayers and the associated Gilbert damping exhibit extreme sensitivity to the magnetic layer thickness on an atomic monolayer scale. The eigenfrequency increases more than threefold when the Co thickness decreases from 7.5 to 2.8Å, mainly due to the changes in effective saturation magnetization and perpendicular anisotropy constant. A concomitant 2.6-fold increase in the damping of the oscillations is observed and attributed to stronger interface dissipation in thinner Co layers. In addition, we introduce a quasi-1D micromagnetic model in which the multilayer stack is described as a onedimensional chain of macrospins that represent each Co layer. This model yields excellent agreement with the observed resonance frequencies without any free parameters, while being much simpler and faster than full 3D micromagnetic modeling.