Publications by Alexy Karenowska

Measurement of a magnonic crystal at millikelvin temperatures


S Kosen, RGE Morris, AF van Loo, AD Karenowska

Inductive detection of fieldlike and dampinglike ac inverse spin-orbit torques in ferromagnet/normal-metal bilayers

Physical Review B 97 (2018)

AJ Berger, ERJ Edwards, HT Nembach, AD Karenowska, M Weiler, TJ Silva

© 2018 American Physical Society. Functional spintronic devices rely on spin-charge interconversion effects, such as the reciprocal processes of electric field-driven spin torque and magnetization dynamics-driven spin and charge flow. Both dampinglike and fieldlike spin-orbit torques have been observed in the forward process of current-driven spin torque and dampinglike inverse spin-orbit torque has been well studied via spin pumping into heavy metal layers. Here, we demonstrate that established microwave transmission spectroscopy of ferromagnet/normal metal bilayers under ferromagnetic resonance can be used to inductively detect the ac charge currents driven by the inverse spin-charge conversion processes. This technique relies on vector network analyzer ferromagnetic resonance (VNA-FMR) measurements. We show that in addition to the commonly extracted spectroscopic information, VNA-FMR measurements can be used to quantify the magnitude and phase of all ac charge currents in the sample, including those due to spin pumping and spin-charge conversion. Our findings reveal that Ni80Fe20/Pt bilayers exhibit both dampinglike and fieldlike inverse spin-orbit torques. While the magnitudes of both the dampinglike and fieldlike inverse spin-orbit torque are of comparable scale to prior reported values for similar material systems, we observed a significant dependence of the dampinglike magnitude on the order of deposition. This suggests interface quality plays an important role in the overall strength of the dampinglike spin-to-charge conversion.

Strong coupling of magnons in a YIG sphere to photons in a planar superconducting resonator in the quantum limit.

Scientific reports 7 (2017) 11511-

RGE Morris, AF van Loo, S Kosen, AD Karenowska

We report measurements made at millikelvin temperatures of a superconducting coplanar waveguide resonator (CPWR) coupled to a sphere of yttrium-iron garnet. Systems hybridising collective spin excitations with microwave photons have recently attracted interest for their potential quantum information applications. In this experiment the non-uniform microwave field of the CPWR allows coupling to be achieved to many different magnon modes in the sphere. Calculations of the relative coupling strength of different mode families in the sphere to the CPWR are used to successfully identify the magnon modes and their frequencies. The measurements are extended to the quantum limit by reducing the drive power until, on average, less than one photon is present in the CPWR. Investigating the time-dependent response of the system to square pulses, oscillations in the output signal at the mode splitting frequency are observed. These results demonstrate the feasibility of future experiments combining magnonic elements with planar superconducting quantum devices.

Direct Measurement of Magnon Temperature: New Insight into Magnon-Phonon Coupling in Magnetic Insulators


M Agrawal, VI Vasyuchka, AA Serga, AD Karenowska, GA Melkov, B Hillebrands

ICMM 2012 foreword from the publication committee

IEEE Transactions on Magnetics 49 (2013) 955-

A Karenowska, A Chumak

Oscillatory energy exchange between waves coupled by a dynamic artificial crystal.

Phys Rev Lett 108 (2012) 015505-

AD Karenowska, JF Gregg, VS Tiberkevich, AN Slavin, AV Chumak, AA Serga, B Hillebrands

We describe a general mechanism of controllable energy exchange between waves propagating in a dynamic artificial crystal. We show that if a spatial periodicity is temporarily imposed on the transmission properties of a wave-carrying medium while a wave is inside, this wave is coupled to a secondary counterpropagating wave and energy oscillates between the two. The oscillation frequency is determined by the width of the spectral band gap created by the periodicity and the frequency difference between the coupled waves. The effect is demonstrated with spin waves in a dynamic magnonic crystal.

Oscillatory Energy Exchange between Waves Coupled by a Dynamic Artificial Crystal


AD Karenowska, JF Gregg, VS Tiberkevich, AN Slavin, AV Chumak, AA Serga, B Hillebrands

Mechanical oscillator

(2012) US13/144886

A Karenowska, JF Gregg

Delay-line self-oscillator

(2011) US/13144878

A Karenowska, JF Gregg

Temporal evolution of inverse spin Hall effect voltage in a magnetic insulator-nonmagnetic metal structure

Applied Physics Letters 99 (2011) 182512

A Karenowska, MB Jungfleisch, AV Chumak, VI Vasyuchka, AA Serga, B Obry, H Schultheiss, PA Beck, E Saitoh, B Hillebrands

Employing magnonic crystals to dictate the characteristics of auto-oscillatory spin-wave systems

Journal of Physics: Conference Series 303 (2011)

AD Karenowska, AV Chumak, AA Serga, JF Gregg, B Hillebrands

Spin-wave active rings - positive-feedback systems incorporating spin-wave waveguides - provide important insight into fundamental magnetics, enable experimental investigations into nonlinear wave phenomena, and potentially find application in microwave electronics. Such rings break into spontaneous, monomode oscillation at a certain threshold value of feedback gain. In general, the wavenumber of this initially excited, threshold mode is impossible to predict precisely. Here we discuss how, by exploiting resonant spin-wave reflections from a magnonic crystal, an active ring system having a threshold mode with a well-defined and precisely predictable wavenumber may be realized. Our work suggests that study and development of active ring systems incorporating magnonic crystals may deliver useful insight into spin-wave transmission in structured magnetic films as well as devices with technological applicability.

Spin information transfer and transport in hybrid spinmechatronic structures

Journal of Physics: Conference Series 303 (2011)

AD Karenowska, JF Gregg, AV Chumak, AA Serga, B Hillebrands

Spin waves have long been recognized as potential signal carriers in spintronic devices. However, practical development of spin wave based information platforms is its infancy. To date, work in this area has focused on one-dimensional topologies based on purely magnetic thin-film transmission systems, typically exploiting interference phenomena to perform logical operations. In this paper, we describe an alternative approach in which spinmechatronic structures combining spin-wave transmission systems with magnetically loaded micro- and nano-mechanical elements provide spin-information processing functionality.

Employing magnonic crystals to dictate the characteristics of auto-oscillatory spin-wave system


AD Karenowska, AV Chumak, AA Serga, JF Gregg, B Hillebrands

Spin information transfer and transport in hybrid spinmechatronic structures


AD Karenowska, JF Gregg, AV Chumak, AA Serga, B Hillebrands

Acoustic oscillator

(2011) US13/144888

A Karenowska, JF Gregg, C-C Coussios

Remote sensor device

(2011) US13/144880

A Karenowska

All-linear time reversal by a dynamic artificial crystal


AV Chumak, VS Tiberkevich, AD Karenowska, AA Serga, JF Gregg, AN Slavin, B Hillebrands

Magnonic crystal based forced dominant wavenumber selection in a spin-wave active ring


AD Karenowska, AV Chumak, AA Serga, JF Gregg, B Hillebrands

Rotor blade sensor

(2010) US12/0678036

A Karenowska, JF Gregg

Mechanical oscillator

(2010) PCT/GB2010/000061

A Karenowska, JF Gregg