arXiv subjects

K. Fan

Publications and source records attributed to K. Fan.

5 recordsLinked to original sources

arXiv2026

Impact of gate voltage on switching field of perpendicular magnetic tunnel junctions with a synthetic antiferromagnetic free layer

We present micromagnetic simulations and experiments on voltage-assisted field switching in perpendicular magnetic tunnel junctions (MTJs) with a synthetic antiferromagnetic (SAF) free layer, where the magnetic state of one sublayer is detected via tunneling magnetoresistance (TMR). Simulations reveal that local modulation of perpendicular magnetic anisotropy (PMA) in one SAF sublayer leads to distinct switching characteristics. The switching field varies linearly with the anisotropy field, indicating voltage-controlled magnetic anisotropy (VCMA)-dominated dynamics similar to single free-layer devices. We then experimentally study the magnetic switching field of MTJ devices with SAF free layers under applied gate voltage. By varying the MgO tunnel barrier thickness to systematically modulate the resistance-area (RA) product, we enable quantitative separation of spin-transfer torque (STT), VCMA, and Joule heating contributions. Our findings indicate that VCMA dominates in devices with a high RA product, while low-RA devices exhibit nonlinear switching behavior due to enhanced contributions from STT and Joule heating. Furthermore, the effective fields derived from STT, VCMA, and Joule heating contributions under various gate voltages show minimal dependence on device critical dimensions, indicating favorable scaling behavior. This work presents a unified framework analyzing the roles of STT, VCMA, and Joule heating in SAF-based voltage-gated spin-orbit torque (SOT) MRAM, offering key insights for the optimization of performance, energy efficiency, and scalability in SOT-MRAM technologies.

cond-mat.mes-hall↗

arXiv2011

Present Performance of Electron Cooling at Cosy-Jülich

At COSY, electron cooling is used after stripping injection of H- or D- ions in order to prepare phase-space-dense ion beams before acceleration to a requested energy. The electron-cooled beam has been successfully applied for specific external experiments. The achievable beam intensity is limited by instabilities during the cooling process. Besides initial losses after injection, as long as the beam has still large emittances, the self-excitation of coherent betatron oscillations is the dominating beam loss mechanism. Perspectives for possible improvements are briefly addressed.

physics.acc-ph↗

arXiv2008

Highly-flexible wide angle of incidence terahertz metamaterial absorber

We present the design, fabrication, and characterization of a metamaterial absorber which is resonant at terahertz frequencies. We experimentally demonstrate an absorptivity of 0.97 at 1.6 terahertz. Importantly, this free-standing absorber is only 16 microns thick resulting in a highly flexible material that, further, operates over a wide range of angles of incidence for both transverse electric and transverse magnetic radiation.

cond-mat.mtrl-sci↗

arXiv2008

Terahertz metamaterials on free-standing highly-flexible polyimide substrates

We have fabricated resonant terahertz metamaterials on free standing polyimide substrates. The low-loss polyimide substrates can be as thin as 5.5 micron yielding robust large-area metamaterials which are easily wrapped into cylinders with a radius of a few millimeters. Our results provide a path forward for creating multi-layer non-planar metamaterials at terahertz frequencies.

cond-mat.mtrl-sci↗

arXiv2001

Modeling two-state cooperativity in protein folding

A protein model with the pairwise interaction energies varying as local environment changes, i.e., including some kinds of collective effect between the contacts, is proposed. Lattice Monte Carlo simulations on the thermodynamical characteristics and free energy profile show a well-defined two-state behavior and cooperativity of folding for such a model. As a comparison, related simulations for the usual Gō model, where the interaction energies are independent of the local conformations, are also made. Our results indicate that the evolution of interactions during the folding process plays an important role in the two-state cooperativity in protein folding.

cond-mat.soft↗