Vitaliy Lomakin

This work reports on achieving synchronization in a large 2D array of spin-transfer torque nano-oscillators (STNOs) by means of propagating spin waves. The synchronization is made possible by means of a honeycomb structure in the magnetic film with interchanging regions with higher and lower magnetic damping. Such a structure creates a network of nearest-neighbor interactions between the STNOs with an equal properly tuned phase shift. Micromagnetic simulations demonstrate the efficiency of synchronization, including phase and frequency locking across the entire large STNO array. Synchronization is obtained at zero and room temperatures as well as for structures with distributions of the material parameters. Synchronization can be tuned by enabling or disabling next-nearest-neighbor interactions, and such tunability allows selectively synchronizing or desynchronizing subarrays of the entire large array. The presented ideas may find applications as microwave sources and for neuromorphic computing and signal processing.

The coherent x-ray diffraction imaging (CXDI) technique offers unique insights into the nanoscale world, enabling the reconstruction of 3D structures with a nanoscale resolution achieved through computational phase reconstruction from measured scattered intensity maps. However, the computational demands of 3D coherent x-ray diffraction imaging limit its real-time application in experimental settings. This Letter presents a carousel phase retrieval algorithm (CPRA) that enables the real-time, high-resolution reconstruction of computationally complex 3D objects. CPRA is based on representing the 3D reconstruction problem as a set of 2D reconstructions of projected images corresponding to different experimentally collected angles via the Fourier slice theorem. The consistency between the 2D reconstructed images is based on an iterative procedure in which each 2D reconstruction accounts for the adjacent 2D reconstructed images in a periodic (carousel) manner. Demonstrations on complex systems, including a lithium-rich layered oxide particle and a biological cell of Staphylococcus aureus, demonstrate that CPRA significantly enhances the reconstruction quality and enables the reconstruction process to be completed in real time during the experiment.

Synchronization of coupled oscillators is a fundamental phenomenon that has been observed in many natural and engineered systems, ranging from biological cells to electronic circuits. In recent years, spin torque nano-oscillators (STNOs) have emerged as a promising platform for a variety of applications in nanoscale systems such as neuromorphic computing, due to their compact size, low power consumption, and tunable properties. However, achieving synchronization in a large array of STNOs remains a challenge, for the complexity of the interactions between the oscillators. To address this challenge, we report on the achievement of synchronization across a 2D array of STNOs. We designed a honeycomb model that created a network of interactions among the oscillators that only involved nearest neighbors. Using micromagnetic simulations, we demonstrated the effectiveness of our design and observed that global synchronization across the whole array. Such global synchronization can also be tuned by enable/disenable next-nearest neighbor interactions. We also found that our design enables synchronization at room temperature, which is crucial for practical applications. Our work contributes to the growing body of research on the synchronization of coupled oscillators in spintronics and could pave the way for the development of new types of spintronic devices and potential applications.

Coherent X-ray Diffraction Imaging (CXDI) technique offers unique insights into the nanoscale world, enabling the reconstruction of 3D structures with a nanoscale resolution achieved through computational phase reconstruction from measured scattered intensity maps. Computational demands of 3D CXDI, however, limit its real-time application in experimental settings. This work presents a carousel phase retrieval algorithm (CPRA) that enables the real-time, high-resolution reconstruction of computationally complex 3D objects. CPRA is based on representing the 3D reconstruction problem as a set of 2D reconstructions of projected images corresponding to different experimentally collected angles via the Fourier slice theorem. Consistency between the 2D reconstructed images is based on an iterative procedure, in which each 2D reconstruction accounts for the adjacent 2D reconstructed images in a periodic (carousel) manner. Demonstrations on complex systems, including a lithium-rich layered oxide particle and a Staphylococcus aureus biological cell, demonstrate that CPRA significantly enhances the reconstruction quality and enables the reconstruction process to be completed in real time during experiment.

Chiral magnets are known to possess interesting electromagnetic properties that result from the coupling of electrons with nontrivial magnetic phases, such as particle-like magnetic spin textures termed skyrmions. So far, it is unclear how the local and global chirality of magnetic spin textures contributes to the electromagnetic transport responses that have so far been observed. In this work, we focus on unraveling the contributions in the field-dependent longitudinal resistivity response that arises from magnetic spin textures in a centrosymmetric Fe/Gd multilayer that exhibits an array of magnetic phases ranging from stripe, mixed stripe-skyrmion, skyrmion lattice, and disordered skyrmion. Using a combination of transport measurements and micromagnetic simulations, we demonstrate a domain wall chirality reconfiguration occurs as the domain morphology transitions from disordered stripe to skyrmion lattice phase under applied fields that is responsible for the interesting transport responses noted in the field-dependent longitudinal resistivity.

We present an antiferromagnetically exchange-coupled composite (soft and hard layers) spin torque oscillator (AF-ECC STO) and demonstrate its operation via both analytical and micromagnetic modeling. The operation exploits the exchange field due to the antiferromagnetic coupling between soft and hard sublayers of the free layer as well as on the easy-plane anisotropy of the soft sublayer. Optimized AF-ECC STO structures can generate large-amplitude magnetization oscillations, which can be tuned over a broad frequency range with precessions mostly generated by the soft layer. We demonstrate that the AF-ECC STO structure offers flexibility in current control of the oscillation frequency and magnetization angle for realistic material parameters.