Article
Engineering, Electrical & Electronic
Sonal Shreya, Yasser Rezaeiyan, Alex Jenkins, Tim Bohnert, Hooman Farkhani, Ricardo Ferreira, Farshad Moradi
Summary: This study presents an analytical model based on Verilog-A for circuit-level simulation of a vortex spin-torque nano oscillator, which is functional for both linear and nonlinear dynamics of the magnetic vortex core. Nonlinear dynamics demonstrate the formation and annihilation of the magnetic vortex depending on its critical currents, and an analysis of the nanopillar's diameter and free layer thickness variations as well as the temperature effect on the device performance is conducted.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2022)
Article
Materials Science, Multidisciplinary
Anam Hanif, Arbab Abdur Rahim, Husnul Maab
Summary: The skyrmion-based spin torque nano-oscillators (STNOs) have attracted attention as potential microwave signal generators. However, the Magnus force effect causes skyrmions to accumulate or annihilate in the device. To counterbalance this effect, a hybrid polarizer system is proposed in a circular nanopillar-shaped spin valve, which enables steady circular motion of the skyrmion without annihilation or accumulation. The proposed system achieves a skyrmion oscillation frequency of up to 3.35 GHz, higher than that of a homogeneous polarizer-based STNO.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2023)
Article
Nanoscience & Nanotechnology
Steffen Wittrock, Philippe Talatchian, Miguel Romera, Mafalda Jotta Garcia, Marie-Claire Cyrille, Ricardo Ferreira, Romain Lebrun, Paolo Bortolotti, Ursula Ebels, Julie Grollier, Vincent Cros
Summary: Vortex based spin torque nano oscillators (STVOs) exhibit complex dynamics compared to gyrotropic motion, with dynamic modes and transitions controlled by experimental parameters. A stochastic transition from G-to-C state was observed at high current densities, with constant active magnetic volume in C-state oscillations. Noise measurements revealed insight into state transition frequency and an increase in flicker noise with constant oscillation volume. These results offer potential for optimizing noise properties in rf applications and exploring new possibilities in neuromorphic computing schemes.
Article
Chemistry, Multidisciplinary
Lina Chen, Yang Chen, Kaiyuan Zhou, Haotian Li, Yong Pu, Yongbing Xu, Youwei Du, Ronghua Liu
Summary: Spin-torque nano-oscillators show promise for various nanodevices due to their tunability, fabrication ease, and durability. Experimental parameters such as excitation current, magnetic field strength and orientation, and temperature can selectively excite specific frequency bullet modes. Fluctuations in magnetic properties allow for experimental control of spin-torque driven magnetization dynamics, promoting the application of nonlinear magnetization oscillators in magnon-based devices and neuromorphic computing.
Article
Materials Science, Multidisciplinary
Benjamin Wolba, Olena Gomonay, Volodymyr P. Kravchuk
Summary: Theoretical description of a terahertz nano-oscillator based on an anisotropic antiferromagnetic dynamical element driven by spin torque reveals chaotic behavior with particularly low threshold current near the spin-flop transition. Prior to the appearance of chaos, a regime of quasiperiodic dynamics on the surface of a two-frequency torus may occur.
Article
Materials Science, Multidisciplinary
R. Arun, R. Gopal, V. K. Chandrasekar, M. Lakshmanan
Summary: In this study, the dynamics of spin-torque nano-oscillator (STNO) with bilinear coupling in the absence of an external magnetic field were investigated. It was found that positive bilinear coupling can enhance the frequency of magnetization oscillations above 300 GHz, while negative bilinear coupling can enhance it up to around 30 GHz. Additionally, a transition from in-plane to out-of-plane precession was observed for both positive and negative bilinear couplings.
Article
Materials Science, Multidisciplinary
Yunxu Ma, Jianing Wang, Zhaozhuo Zeng, Yingyue Yuan, Jinxia Yang, Huibo Liu, Senfu Zhang, Jinwu Wei, Jianbo Wang, Chendong Jin, Qingfang Liu
Summary: As a spin transfer nano-oscillator based on magnetic skyrmion, the STNO has gained great interest as a microwave signal generator. However, the circular magnetic skyrmion-based oscillator only produces a microwave signal with a single oscillation frequency and detecting the precession of skyrmion in the entire nanodisk is also challenging. In this paper, we propose an STNO based on elliptical skyrmion, which can simultaneously generate a single frequency or multiple frequency oscillation signal. The method to restrict elliptical skyrmion moving in a specific orbit is suggested to reduce the difficulty of detection.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2022)
Article
Materials Science, Multidisciplinary
S. Stepanov, V. N. Nazarov, K. A. Zvezdin, E. G. Ekomasov
Summary: The coupled dynamics of two-vortex spin torque nanooscillators were investigated using micromagnetic simulation. The dynamic transformation of the vortex structure leading to the formation of C-states in this system was studied. The dynamic formation of edge vortices, which have only been observed in the presence of the Dzyaloshinskii field or an inhomogeneous external field, was demonstrated.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2022)
Article
Materials Science, Multidisciplinary
Youhua Feng, Huangkun Zhu, Xi Zhang, Gang Xiang
Summary: In this study, it was found that the oscillation frequency of Bilayer-skyrmions in a nanodisk can be significantly increased compared to Single-layer Skyrmion, reaching above 10 GHz, due to the disappearance of the skyrmion Hall effect in the antiferromagnetic-coupled system. The oscillation frequency of Bilayer-skyrmions linearly increases with the current density. Moreover, spin-torque nano-oscillators based on multiple pairs of Bilayer-skyrmions can further increase the frequency limit up to 36.5 GHz, providing potential for ultrahigh-frequency applications.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2022)
Article
Physics, Applied
R. Arun, R. Gopal, V. K. Chandrasekar, M. Lakshmanan
Summary: The dynamics of the magnetization of the free layer in a spin-torque nano oscillator influenced by a noncollinear alignment between the magnetizations of the free and pinned layers has been studied. The computed orientations of the magnetization match well with experimental results. Bilinear and biquadratic coupling strengths allow for magnetization switching or steady oscillations. Expressions for the critical currents and coupling strength have been derived. The frequency of oscillations can be tuned and increased to above 300 GHz, the highest among nanopillar-shaped STNOs.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Physics, Applied
Lina Chen, Xiang Zhan, Kaiyuan Zhou, Wenqiang Wang, Like Liang, Zhenyu Gao, Y. W. Du, R. H. Liu
Summary: We experimentally studied the efficiency of current-induced spin-orbit torque (SOT) and the spectral characteristics of current-driven coherent magnetic dynamics in Pt/Ni/Py-based spin Hall nano-oscillators (SHNOs). Our results show that the Pt/Ni/Py trilayer structure has an effective damping-like torque efficiency comparable to other systems with strong spin-orbit coupling and magnetic proximity effect. The microwave-generation spectra reveal a single nonlinear self-localized bullet mode with a frequency below fFMR and a significant current-dependent frequency red shift. At high oblique angles, two oscillating peaks were observed, indicating the spatial coexistence of two same-type nonlinear self-localized bullet modes. The observed linear temperature dependence of the minimum line width confirms the independent and spatially separated nature of these two localized bullet modes.
PHYSICAL REVIEW APPLIED
(2022)
Article
Materials Science, Multidisciplinary
Sourabh Manna, Rohit Medwal, Rajdeep Singh Rawat
Summary: In this paper, we investigate the neuronlike spiking dynamics in an elliptic ferromagnet/heavy metal bilayer-based spin Hall nano-oscillator. Regular periodic spiking and leaky integrate-and-fire behavior are demonstrated in a single spin Hall nano-oscillator by manipulating the pulse features of input current. The effect of shape anisotropy on the bias field free auto-oscillation characteristics is also discussed.
Article
Physics, Applied
Shuting Cui, Mingmin Zhu, Yang Qiu, Rongdi Guo, Guohua Wu, Guoliang Yu, Haomiao Zhou
Summary: In this study, the influence of strain on the oscillation frequency characteristics of a skyrmion-based spin-torque nano-oscillator (STNO) is investigated theoretically. The simulation results show that the strain can effectively modulate the operation frequency of the STNO. Additionally, a simplified analytical expression of the skyrmion gyration dynamics is introduced to explain the simulation results. These findings are significant for the development of wide-range frequency-tunable microwave emitters and frequency-shift keying for wireless communication.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2022)
Article
Materials Science, Multidisciplinary
Debsuvra Mukhopadhyay, Jayakrishnan M. P. Nair, G. S. Agarwal
Summary: In this paper, a scheme to substantially amplify the transfer efficiency of spin-wave excitations between separate magnetic samples through cavity-mediated magnon-magnon coupling is presented. The physical origin of the enhancement is explained, which is attributed to the recurrent multiphoton absorption by the cavity and the emergence of parametrically induced strong coherences. The enhancement can be considerably high within the stable dynamical region, leading to a significantly amplified spin-current response from one of the magnetic samples.
Article
Materials Science, Multidisciplinary
Lie Xu, Yongming Luo, Birui Wu, Menghao Jin, Hai Li, Tiejun Zhou
Summary: Vertically coupled magnetic vortices have potential applications in data storage and processing, as well as demand for neuromorphic computing. Micromagnetic simulations reveal that coupled vortices with parallel polarity have higher critical current and lower eigen-frequency, while the inter-disk spacer thickness affects the gyration amplitude of vortices.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2021)
Correction
Physics, Applied
Mio Ishibashi, Kay Yakushiji, Masashi Kawaguchi, Arata Tsukamoto, Satoru Nakatsuji, Masamitsu Hayashi
APPLIED PHYSICS LETTERS
(2022)
Article
Physics, Applied
Mio Ishibashi, Kay Yakushiji, Masashi Kawaguchi, Arata Tsukamoto, Satoru Nakatsuji, Masamitsu Hayashi
Summary: The magnetic properties of rare earth-transition metal ferrimagnetic thin films are studied. It is found that the compensation of magnetic moments of rare earth and transition metal sublattices increases with decreasing film thickness. For thin TbFeCo films, Tb atoms do not contribute to the magnetization. The perpendicular magnetic anisotropy increases with a thin Co layer but drops to zero with a thin Tb layer. The Tb concentration at which magnetic compensation occurs decreases when the underlayer is changed from Pt to Ta.
APPLIED PHYSICS LETTERS
(2022)
Article
Multidisciplinary Sciences
Miguel Romera, Philippe Talatchian, Sumito Tsunegi, Kay Yakushiji, Akio Fukushima, Hitoshi Kubota, Shinji Yuasa, Vincent Cros, Paolo Bortolotti, Maxence Ernoult, Damien Querlioz, Julie Grollier
Summary: The study demonstrates the potential of spin-torque nano-oscillators in neuromorphic computing by showing their ability to mutually synchronize and recognize temporal patterns, similar to neurons. This research is important for the construction of neural networks that perform brain-inspired computations by utilizing the non-linear dynamic properties of their components.
NATURE COMMUNICATIONS
(2022)
Article
Materials Science, Multidisciplinary
Takayuki Nozaki, Tomohiro Nozaki, Tatsuya Yamamoto, Makoto Konoto, Atsushi Sugihara, Kay Yakushiji, Hitoshi Kubota, Akio Fukushima, Shinji Yuasa
Summary: Perpendicular magnetic anisotropy (PMA) is becoming increasingly important in spintronics research, especially for high-density magnetoresistive random access memories (MRAMs). This study proposes inserting an ultrathin LiF layer at the Fe/MgO interface and achieves a large intrinsic interface PMA energy. It is also found that a coherent spin-dependent tunneling process is maintained in the ultrathin LiF layer, leading to a large tunnel magnetoresistance (TMR) effect. Atomic-scale interface engineering using fluoride can further improve the PMA and TMR properties of spintronic devices.
NPG ASIA MATERIALS
(2022)
Article
Physics, Applied
Tomohiro Ichinose, Tatsuya Yamamoto, Jun Uzuhashi, Takayuki Nozaki, Tadakatsu Ohkubo, Kay Yakushiji, Shingo Tamaru, Kazuhiro Hono, Shinji Yuasa
Summary: Thermally robust perpendicular magnetic anisotropy and voltage-controlled magnetic anisotropy effects were achieved in magnetic tunnel junctions with ultrathin CoFeB films by utilizing Ta/Mo layered adhesion structures.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Physics, Applied
Tatsuya Yamamoto, Tomohiro Ichinose, Jun Uzuhashi, Takayuki Nozaki, Tadakatsu Ohkubo, Kay Yakushiji, Shingo Tamaru, Hitoshi Kubota, Akio Fukushima, Kazuhiro Hono, Shinji Yuasa
Summary: In this study, we investigate the perpendicular magnetic anisotropy (PMA) in MgO/CoFeB (CFB)/MgO junctions by introducing an angstrom-thick Mo spacer layer. It is found that perpendicularly magnetized CFB/Mo/CFB films can be obtained for a wide range of CFB thicknesses, achieving a large PMA energy density. The voltage-controlled magnetic anisotropy effect shows a sign inversion between the 'top free' and 'bottom free' magnetic tunnel junctions, indicating the importance of the flatness of the CFB/MgO interface for improving the efficiency of the effect.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2022)
Article
Nanoscience & Nanotechnology
Takayuki Nozaki, Tomohiro Nozaki, Hiroshige Onoda, Hiroyasu Nakayama, Tomohiro Ichinose, Tatsuya Yamamoto, Makoto Konoto, Shinji Yuasa
Summary: This study investigates the effects of inserting a post-oxidized MgAl layer on the perpendicular magnetic anisotropy (PMA), tunnel magnetoresistance (TMR), and voltage-controlled magnetic anisotropy (VCMA) in epitaxial magnetic tunnel junctions (MTJs). The results show that the thickness of the MgAl layer plays a significant role in determining PMA and TMR values. A proper thickness of the MgAl layer can greatly enhance these properties. Furthermore, the VCMA coefficient increases as the MgAl layer thickness decreases, suggesting that a weakly oxidized interface provides a stronger VCMA effect.
Article
Physics, Applied
Takayuki Nozaki, Tomohiro Nozaki, Tatsuya Yamamoto, Makoto Konoto, Atsushi Sugihara, Kay Yakushiji, Shinji Yuasa
Summary: Improving the perpendicular magnetic anisotropy (PMA) and voltage-controlled magnetic anisotropy (VCMA) properties are crucial for the development of voltage-controlled magnetoresistive random access memories (VC-MRAM). By inserting an ultrathin LiF layer at the Fe/MgO interface, a significant increase in PMA has been observed, along with a large VCMA coefficient, while maintaining high TMR ratio and high interfacial PMA.
APPLIED PHYSICS LETTERS
(2022)
Article
Materials Science, Multidisciplinary
Tatsuya Yamamoto, Rie Matsumoto, Takayuki Nozaki, Hiroshi Imamura, Shinji Yuasa
Summary: This article reviews the current research status of magnetization switching utilizing the voltage-controlled magnetic anisotropy (VCMA) effect. It focuses on subnanosecond voltage pulses driven magnetization switching as a promising alternative to the existing spin-transfer-torque technology used in magnetic random-access memories. However, practical issues such as write-error rate, narrow operating window, and the need for an external bias magnetic field are faced by VCMA-driven magnetization switching. Recent developments in the field of VCMA studies are introduced to address these issues from both experimental and theoretical perspectives. Possible material designs for enhancing both the energy efficiency and reliability of VCMA-driven magnetization switching are also discussed.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2022)
Article
Materials Science, Multidisciplinary
Hiroshige Onoda, Tomohiro Nozaki, Shingo Tamaru, Takayuki Nozaki, Shinji Yuasa
Summary: This study systematically investigated the relationship between the voltage-controlled magnetic anisotropy (VCMA) coefficient and the dielectric constant. By controlling the material structure, we successfully manipulated the VCMA coefficient and dielectric constant. The results showed that increasing the dielectric constant can enhance the VCMA effect.
PHYSICAL REVIEW MATERIALS
(2022)
Article
Nanoscience & Nanotechnology
Takayuki Nozaki, Tomohiro Ichinose, Jun Uzuhashi, Tatsuya Yamamoto, Makoto Konoto, Kay Yakushiji, Tadakatsu Ohkubo, Shinji Yuasa
Summary: This study investigates the influence of the buffer material and cryogenic temperature deposition process on the voltage-controlled magnetic anisotropy (VCMA) effect in CoFeB layers in MgO-based magnetic tunnel junctions. The use of TaB buffers allows for a flat and less-contaminated CoFeB/MgO interface while cryogenic temperature deposition enhances the efficiency of the VCMA effect and its annealing tolerance. Introduction of interface engineering methods leads to a large VCMA coefficient.
