Showing 1–15 of 15 results for author: Checinski, J

Confirmation of four hot Jupiters detected by TESS using follow-up spectroscopy from MaHPS at Wendelstein together with NEID and TRES

Authors: Juliana Ehrhardt, Luis Thomas, Hanna Kellermann, Christine Freitag, Frank Grupp, Samuel W. Yee, Joshua N. Winn, Joel D. Hartman, Karen A. Collins, Cristilyn N. Watkins, Keivan G. Stassun, Paul Benni, Allyson Bieryla, Kylee Carden, Jacek Checinski, Dmitry V. Cheryasov, Brendan Diamond, Nicholas Dowling, Courtney D. Dressing, Emma Esparza-Borges, Phil Evans, Raquel Forés-Toribio, Akihiko Fukui, Steven Giacalone, Eric Girardin , et al. (35 additional authors not shown)

Abstract: We report the confirmation and characterization of four hot Jupiter-type exoplanets initially detected by TESS: TOI-1295 b, TOI-2580 b, TOI-6016 b, and TOI-6130 b. Using observations with the high-resolution echelle spectrograph MaHPS on the 2.1m telescope at Wendelstein Observatory, together with NEID at Kitt Peak National Observatory and TRES at the Fred Lawrence Whipple Observatory, we confirme… ▽ More We report the confirmation and characterization of four hot Jupiter-type exoplanets initially detected by TESS: TOI-1295 b, TOI-2580 b, TOI-6016 b, and TOI-6130 b. Using observations with the high-resolution echelle spectrograph MaHPS on the 2.1m telescope at Wendelstein Observatory, together with NEID at Kitt Peak National Observatory and TRES at the Fred Lawrence Whipple Observatory, we confirmed the planetary nature of these four planet candidates. We also performed precise mass measurements. All four planets are found to be hot Jupiters with orbital periods between 2.4 and 4.0 days. The sizes of these planets range from 1.29 to 1.64 Jupiter radii, while their masses range from 0.6 to 1.5 Jupiter masses. Additionally, we investigated whether there are signs of other planets in the systems but have found none. Lastly, we compared the radii of our four objects to the results of an empirical study of radius inflation and see that all four demonstrate a good fit with the current models. These four planets belong to the first array of planets confirmed with MaHPS data, supporting the ability of the spectrograph to detect planets around fainter stars as faint as V=12. △ Less

Submitted 8 January, 2025; originally announced January 2025.

Journal ref: Astronomy & Astrophysics, Volume 692, id.A220, 20 pp., December 2024

Caught in the Act: Observations of the Double-mode RR Lyrae V338 Boo During the Disappearance of a Pulsation Mode

Authors: Kenneth Carrell, Ronald Wilhelm, Andrew Tom, Horace Smith, Adam Popowicz, Gary Hug, Stephen M. Brincat, Fabio Salvaggio, Keith Nakonechny, Darrell Lee, Teofilo Arranz Heras, Tony Vale, Davide Mortari, Andre Steenkamp, Ralph Rogge, Jacek Checinski

Abstract: New results on the behavior of the double-mode RR Lyrae V338 Boo are presented. The Transiting Exoplanet Survey Satellite (TESS) observed this star again in 2022, and an observing campaign of the American Association of Variable Star Observers (AAVSO) was completed after the TESS observations as a follow-up. We find that the first overtone pulsation mode in this star completely disappears during t… ▽ More New results on the behavior of the double-mode RR Lyrae V338 Boo are presented. The Transiting Exoplanet Survey Satellite (TESS) observed this star again in 2022, and an observing campaign of the American Association of Variable Star Observers (AAVSO) was completed after the TESS observations as a follow-up. We find that the first overtone pulsation mode in this star completely disappears during the TESS observing window. This mode reappears at the end of the TESS observations, and the AAVSO observing campaign shows that in the months that followed, the first overtone mode was not only present, but was the dominant mode of pulsation. This star, and potentially others like it, could hold the key to finally solving the mystery of the Blazhko effect in RR Lyrae. △ Less

Submitted 14 November, 2024; originally announced November 2024.

Comments: 11 pages, 7 figures; published in ApJ

Journal ref: ApJ, 973, 157 (2024)

Study of Spin-Orbit Interactions and Interlayer Ferromagnetic Coupling in Co/Pt/Co Trilayers in Wide Range of Heavy Metal Thickness

Authors: Piotr Ogrodnik, Krzysztof Grochot, Łukasz Karwacki, Jarosław Kanak, Michał Prokop, Jakub Chęciński, Witold Skowroński, Sławomir Ziętek, Tomasz Stobiecki

Abstract: The spin-orbit torque, a torque induced by a charge current flowing through the heavy-metal conducting layer with strong spin-orbit interactions, provides an efficient way to control the magnetization direction in heavy-metal/ferromagnet nanostructures, required for applications in the emergent magnetic technologies like random access memories, high-frequency nano oscillators, or bio-inspired neur… ▽ More The spin-orbit torque, a torque induced by a charge current flowing through the heavy-metal conducting layer with strong spin-orbit interactions, provides an efficient way to control the magnetization direction in heavy-metal/ferromagnet nanostructures, required for applications in the emergent magnetic technologies like random access memories, high-frequency nano oscillators, or bio-inspired neuromorphic computations. We study the interface properties, magnetization dynamics, magnetostatic features and spin-orbit interactions within the multilayer system Ti(2)/Co(1)/Pt(0-4)/Co(1)/MgO(2)/Ti(2) (thicknesses in nanometers) patterned by optical lithography on micrometer-sized bars. In the investigated devices, Pt is used as a source of the spin current and as a non-magnetic spacer with variable thickness, which enables the magnitude of the interlayer ferromagnetic exchange coupling to be effectively tuned. We also find the Pt thickness-dependent changes in magnetic anisotropies, magnetoresistance, effective Hall angle and, eventually, spin-orbit torque fields at interfaces. The experimental findings are supported by the relevant interface structure-related simulations, micromagnetic, macrospin, as well as the spin drift-diffusion models. Finally, the contribution of the spin-orbital Edelstein-Rashba interfacial fields is also briefly discussed in the analysis. △ Less

Submitted 18 June, 2021; originally announced June 2021.

Comments: 39 pages, 14 figures

Multi-state MRAM cells for hardware neuromorphic computing

Authors: Piotr Rzeszut, Jakub Chęciński, Ireneusz Brzozowski, Sławomir Ziętek, Witold Skowroński, Tomasz Stobiecki

Abstract: Magnetic tunnel junctions (MTJ) have been successfully applied in various sensing application and digital information storage technologies. Currently, a number of new potential applications of MTJs are being actively studied, including high-frequency electronics, energy harvesting or random number generators. Recently, MTJs have been also proposed in designs of a new platforms for unconventional o… ▽ More Magnetic tunnel junctions (MTJ) have been successfully applied in various sensing application and digital information storage technologies. Currently, a number of new potential applications of MTJs are being actively studied, including high-frequency electronics, energy harvesting or random number generators. Recently, MTJs have been also proposed in designs of a new platforms for unconventional or bio-inspired computing. In the present work, it is shown that serially connected MTJs forming a multi-state memory cell can be used in a hardware implementation of a neural computing device. A behavioral model of the multi-cell is proposed based on the experimentally determined MTJ parameters. The main purpose of the mutli-cell is the formation of the quantized weights of the network, which can be programmed using the proposed electronic circuit. Mutli-cells are connected to CMOS-based summing amplifier and sigmoid function generator, forming an artificial neuron. The operation of the designed network is tested using a recognition of the hand-written digits in 20x20 pixel matrix and shows detection ratio comparable to the software algorithm, using the weight stored in a multi-cell consisting of four MTJs or more. △ Less

Submitted 5 February, 2021; originally announced February 2021.

A Spin Hall Ising Machine

Authors: Afshin Houshang, Mohammad Zahedinejad, Shreyas Muralidhar, Jakub Checinski, Ahmad A. Awad, Johan Åkerman

Abstract: Ising Machines (IMs) are physical systems designed to find solutions to combinatorial optimization (CO) problems mapped onto the IM via the coupling strengths of its binary spins. Using the intrinsic dynamics and different annealing schemes, the IM relaxes over time to its lowest energy state, which is the solution to the CO problem. IMs have been implemented in quantum, optical, and electronic ha… ▽ More Ising Machines (IMs) are physical systems designed to find solutions to combinatorial optimization (CO) problems mapped onto the IM via the coupling strengths of its binary spins. Using the intrinsic dynamics and different annealing schemes, the IM relaxes over time to its lowest energy state, which is the solution to the CO problem. IMs have been implemented in quantum, optical, and electronic hardware. One promising approach uses interacting nonlinear oscillators whose phases have been binarized through injection locking at twice their natural frequency. Here we demonstrate such Oscillator IMs using nano-constriction spin Hall nano-oscillator (SHNO) arrays. We show how the SHNO arrays can be readily phase binarized and how the resulting microwave power corresponds to well-defined global phase states. To distinguish between degenerate states we use phase-resolved Brillouin Light Scattering (BLS) microscopy to directly observe the individual phase of each nano-constriction. △ Less

Submitted 3 June, 2020; originally announced June 2020.

Synchronization properties and reservoir computing capability of hexagonal spintronic oscillator arrays

Authors: Jakub Chęciński

Abstract: The influence of array geometry on synchronization properties of a 2-D oscillator array is investigated based on a comparison between a rectangular and a hexagonal grid. The Kuramoto model is solved for a nearest-neighbor case with periodic boundary conditions and for a small-scale, realistic coupling case with 1/r^3 decay characteristic of spintronic oscillators. In both cases, it is found that t… ▽ More The influence of array geometry on synchronization properties of a 2-D oscillator array is investigated based on a comparison between a rectangular and a hexagonal grid. The Kuramoto model is solved for a nearest-neighbor case with periodic boundary conditions and for a small-scale, realistic coupling case with 1/r^3 decay characteristic of spintronic oscillators. In both cases, it is found that the hexagonal grid choice leads to lower synchronization threshold and higher emission power than its rectangular counterpart, which results from increased connectivity, as well as, in the realistic-coupling case, from decreased contributions of the array edges. Additionally, a more general spin-torque oscillator model including both amplitude and phase as degrees of freedom is employed for reservoir computing simulations, showing that by using hexagonal grid one can increase the short-term memory capacity but not the parity-check capacity of the system. △ Less

Submitted 14 February, 2020; originally announced February 2020.

Microwave magnetic field modulation of spin torque oscillator based on perpendicular magnetic tunnel junctions

Authors: Witold Skowroński, Jakub Chęciński, Sławomir Ziętek, Kay Yakushiji, Shinji Yuasa

Abstract: Modulation of a spin-torque oscillator (STO) signal based on a magnetic tunnel junction (MTJ) with perpendicularly magnetized free layer is investigated. Magnetic field inductive loop was created during MTJ fabrication process, which enables microwave field application during STO operation. The frequency modulation by the microwave magnetic field of up to 3 GHz is explored, showing a potential for… ▽ More Modulation of a spin-torque oscillator (STO) signal based on a magnetic tunnel junction (MTJ) with perpendicularly magnetized free layer is investigated. Magnetic field inductive loop was created during MTJ fabrication process, which enables microwave field application during STO operation. The frequency modulation by the microwave magnetic field of up to 3 GHz is explored, showing a potential for application in high-data-rate communication technologies. Moreover, an inductive loop is used for self-synchronization of the STO signal, which after field-locking exhibits significant improvement of the linewidth and oscillation power. △ Less

Submitted 20 September, 2019; originally announced September 2019.

Comments: 4 pages, 5 figures

High frequency voltage-induced ferromagnetic resonance in magnetic tunnel junctions

Authors: Witold Skowronski, Stanislaw Lazarski, Jakub Mojsiejuk, Jakub Checinski, Marek Frankowski, Takayuki Nozaki, Kay Yakushiji, Shinji Yuasa

Abstract: Voltage-induced ferromagnetic resonance (V-FMR) in magnetic tunnel junctions (MTJs) with a W buffer is investigated. Perpendicular magnetic anisotropy (PMA) energy is controlled by both thickness of a CoFeB free layer deposited directly on the W buffer and a post-annealing process at different temperatures. The PMA energy as well as the magnetization damping are determined by analysing field-depen… ▽ More Voltage-induced ferromagnetic resonance (V-FMR) in magnetic tunnel junctions (MTJs) with a W buffer is investigated. Perpendicular magnetic anisotropy (PMA) energy is controlled by both thickness of a CoFeB free layer deposited directly on the W buffer and a post-annealing process at different temperatures. The PMA energy as well as the magnetization damping are determined by analysing field-dependent FMR signals in different field geometries. An optimized MTJ structure enabled excitation of V-FMR at frequencies exceeding 30 GHz. The macrospin modelling is used to analyse the field- and angular-dependence of the V-FMR signal and to support experimental magnetization damping extraction. △ Less

Submitted 4 June, 2019; originally announced June 2019.

Comments: Manuscript containing 4 pages and 4 figures

Antiferromagnetic nano-oscillator in external magnetic fields

Authors: Jakub Chęciński, Marek Frankowski, Tomasz Stobiecki

Abstract: We describe the dynamics of an antiferromagnetic nano-oscillator in an external magnetic field of any given time distribution. The oscillator is powered by a spin current originating from spin-orbit effects in a neighboring heavy metal layer, and is capable of emitting a THz signal in the presence of an additional easy-plane anisotropy. We derive an analytical formula describing the interaction be… ▽ More We describe the dynamics of an antiferromagnetic nano-oscillator in an external magnetic field of any given time distribution. The oscillator is powered by a spin current originating from spin-orbit effects in a neighboring heavy metal layer, and is capable of emitting a THz signal in the presence of an additional easy-plane anisotropy. We derive an analytical formula describing the interaction between such a system and an external field, which can affect the output signal character. Interactions with magnetic pulses of different shapes, with a sinusoidal magnetic field and with a sequence of rapidly changing magnetic fields are discussed. We also perform numerical simulations based on the Landau-Lifshitz-Gilbert equation with spin-transfer torque effects to verify the obtained results and find a very good quantitative agreement between analytical and numerical predictions. △ Less

Submitted 23 November, 2017; v1 submitted 18 August, 2017; originally announced August 2017.

Journal ref: Phys. Rev. B 96, 174438 (2017)

Field- and temperature-modulated spin-diode effect in a GMR nanowire with dipolar coupling

Authors: Piotr Ogrodnik, Tomasz Stobiecki, Józef Barnaś, Marek Frankowski, Jakub Chęciński, Francesco Antonio Vetrò, Jean-Philippe Ansermet

Abstract: An analytical model of the spin-diode effect induced by resonant spin-transfer torque in a ferromagnetic bilayer with strong dipolar coupling provides the resonance frequencies and the lineshapes of the magnetic field spectra obtained under field or laser-light modulation. The effect of laser irradiation is accounted for by introducing the temperature dependence of the saturation magnetization and… ▽ More An analytical model of the spin-diode effect induced by resonant spin-transfer torque in a ferromagnetic bilayer with strong dipolar coupling provides the resonance frequencies and the lineshapes of the magnetic field spectra obtained under field or laser-light modulation. The effect of laser irradiation is accounted for by introducing the temperature dependence of the saturation magnetization and anisotropy, as well as thermal spin-transfer torques. The predictions of the model are compared with experimental data obtained with single Co/Cu/Co spin valves, embedded in nanowires and produced by electrodeposition. Temperature modulation provides excellent signal-to-noise ratio. High temperature-modulation frequency is possible because these nanostructures have a very small heat capacity and are only weakly heat-sunk. The two forms of modulation give rise to qualitative differences in the spectra that are accounted for by the model. △ Less

Submitted 4 June, 2017; originally announced June 2017.

Journal ref: J. Phys. D: Appl. Phys. 52 065002 (2019)

Simultaneous readout of two adjacent bit tracks with a spin-torque oscillator

Authors: Jakub Chęciński, Marek Frankowski, Tomasz Stobiecki

Abstract: We propose a novel setup for a spin-torque oscillator reader in magnetic hard disk drive technology. Two adjacent bit tracks are to be read simultaneously, leading to high data transfer rate and increased resilience to noise as the lateral size of the oscillator device is allowed to remain larger than the bit width. We perform micromagnetic simulations of an example system and find that the magnet… ▽ More We propose a novel setup for a spin-torque oscillator reader in magnetic hard disk drive technology. Two adjacent bit tracks are to be read simultaneously, leading to high data transfer rate and increased resilience to noise as the lateral size of the oscillator device is allowed to remain larger than the bit width. We perform micromagnetic simulations of an example system and find that the magnetization response has a clear unimodal character, which enables for detection of two bit values at the same time. We analyze the frequency of the device under the influence of two different external fields and conduct a simulation of a successful dynamic readout. We estimate the signal linewidth and signal-to-noise ratios of the setup and show that it may be potentially beneficial for magnetic readout applications. △ Less

Submitted 8 May, 2017; originally announced May 2017.

Understanding stability diagram of perpendicular magnetic tunnel junctions

Authors: Witold Skowroński, Maiej Czapkiewicz, Sławomir Ziętek, Jakub Chęciński, Marek Frankowski, Piotr Rzeszut, Jerzy Wrona

Abstract: Perpendicular magnetic tunnel junctions (MTJ) with a bottom pinned reference layer and a composite free layer (FL) are investigated. Different thicknesses of the FL were tested to obtain an optimal balance between tunneling magnetoresistance (TMR) ratio and perpendicular magnetic anisotropy. After annealing at 400 $^\circ$C, the TMR ratio for 1.5 nm thick CoFeB sublayer reached 180 % at room tempe… ▽ More Perpendicular magnetic tunnel junctions (MTJ) with a bottom pinned reference layer and a composite free layer (FL) are investigated. Different thicknesses of the FL were tested to obtain an optimal balance between tunneling magnetoresistance (TMR) ratio and perpendicular magnetic anisotropy. After annealing at 400 $^\circ$C, the TMR ratio for 1.5 nm thick CoFeB sublayer reached 180 % at room temperature and 280 % at 20 K with an MgO tunnel barrier thickness corresponding to the resistance area product RA = 10 Ohm$\mathrmμ$m$^2$. The voltage vs. magnetic field stability diagrams measured in pillar-shaped MTJs with 130 nm diameter indicate the competition between spin transfer torque (STT), voltage controlled magnetic anisotropy (VCMA) and temperature effects in the switching process. An extended stability phase diagram model that takes into account all three parameters and the effective damping measured independently using broadband ferromagnetic resonance technique enabled the determination of both STT and VCMA coefficients that are responsible for the FL magnetization switching. △ Less

Submitted 23 January, 2017; originally announced January 2017.

Comments: 6 pages 4 figures

Electric-field tunable spin waves in PMN-PT/NiFe heterostructure: experiment and micromagnetic simulations

Authors: Slawomir Zietek, Jakub Checinski, Marek Frankowski, Witold Skowronski, Tomasz Stobiecki

Abstract: We present a comprehensive theoretical and experimental study of voltage-controlled standing spin waves resonance (SSWR) in PMN-PT/NiFe multiferroic heterostructures patterned into microstrips. A spin-diode technique was used to observe ferromagnetic resonance (FMR) mode and SSWR in NiFe strip mechanically coupled with a piezoelectric substrate. Application of an electric field to a PMNPT creates… ▽ More We present a comprehensive theoretical and experimental study of voltage-controlled standing spin waves resonance (SSWR) in PMN-PT/NiFe multiferroic heterostructures patterned into microstrips. A spin-diode technique was used to observe ferromagnetic resonance (FMR) mode and SSWR in NiFe strip mechanically coupled with a piezoelectric substrate. Application of an electric field to a PMNPT creates a strain in permalloy and thus shifts the FMR and SSWR fields due to the magnetostriction effect. The experimental results are compared with micromagnetic simulations and a good agreement between them is found for dynamics of FMR and SSWR with and without electric field. Moreover, micromagnetic simulations enable us to discuss the amplitude and phase spatial distributions of FMR and SSWR modes, which are not directly observable by means of spin diode detection technique. △ Less

Submitted 14 October, 2016; originally announced October 2016.

Buffer influence on magnetic dead layer, critical current and thermal stability in magnetic tunnel junctions with perpendicular magnetic anisotropy

Authors: Marek Frankowski, Antoni Żywczak, Maciej Czapkiewicz, Sławomir Ziętek, Jarosław Kanak, Monika Banasik, Wiesław Powroźnik, Witold Skowroński, Jakub Chęciński, Jerzy Wrona, Hubert Głowiński, Janusz Dubowik, Jean-Philippe Ansermet, Tomasz Stobiecki

Abstract: We present a thorough research on Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of MTJs, such as critical switching current and thermal stability. We investigate devices consisting of buffer/FeCoB/MgO/FeCoB/Ta/Ru multilayers for three different buffers: Ta 5 / Ru 10 / Ta 3, Ta 5 / Ru 10 / Ta 10 and Ta 5 / Ru 20 / Ta 5 (all thicknesses in nm). In… ▽ More We present a thorough research on Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of MTJs, such as critical switching current and thermal stability. We investigate devices consisting of buffer/FeCoB/MgO/FeCoB/Ta/Ru multilayers for three different buffers: Ta 5 / Ru 10 / Ta 3, Ta 5 / Ru 10 / Ta 10 and Ta 5 / Ru 20 / Ta 5 (all thicknesses in nm). In addition, we study systems with a single FeCoB layer deposited above as well as below the MgO barrier. The crystallographic texture and the roughness of the buffers are determined by means of XRD and atomic force microscopy measurements. Furthermore, we examine the magnetic domain pattern, the magnetic dead layer thickness and the perpendicular magnetic anisotropy fields for each sample. Finally, we investigate the effect of the current induced magnetization switching for nanopillar junctions with lateral dimensions ranging from 1 μm down to 140 nm. Buffer Ta 5 / Ru 10 / Ta 3, which has the thickest dead layer, exhibits a large increase in the thermal stability factor while featuring a slightly lower critical current density value when compared to the buffer with the thinnest dead layer Ta 5 / Ru 20 / Ta 5. △ Less

Submitted 23 February, 2015; originally announced February 2015.

Rectification of radio frequency current in giant magnetoresistance spin valve

Authors: Sławomir Ziętek, Piotr Ogrodnik, Marek Frankowski, Jakub Chęciński, Piotr Wiśniowski, Witold Skowroński, Jerzy Wrona, Tomasz Stobiecki, Antoni Żywczak, Józef Barnaś

Abstract: We report on a highly efficient spin diode effect in an exchange-biased spin-valve giant magnetoresistance (GMR) strips. In such multilayer structures, symmetry of the current distribution along the vertical direction is broken and, as a result, a non-compensated Oersted field acting on the magnetic free layer appears. This field, in turn, is a driving force of magnetization precessions. Due to th… ▽ More We report on a highly efficient spin diode effect in an exchange-biased spin-valve giant magnetoresistance (GMR) strips. In such multilayer structures, symmetry of the current distribution along the vertical direction is broken and, as a result, a non-compensated Oersted field acting on the magnetic free layer appears. This field, in turn, is a driving force of magnetization precessions. Due to the GMR effect, resistance of the strip oscillates following the magnetization dynamics. This leads to rectification of the applied radio frequency current and induces a direct current voltage $V_{DC}$. We present a theoretical description of this phenomenon and calculate the spin diode signal, $V_{DC}$, as a function of frequency, external magnetic field, and angle at which the external field is applied. A satisfactory quantitative agreement between theoretical predictions and experimental data has been achieved. Finally, we show that the spin diode signal in GMR devices is significantly stronger than in the anisotropic magnetoresistance permalloy-based devices. △ Less

Submitted 24 October, 2014; originally announced October 2014.

Comments: 10 pages, 8 figures