Electron trajectories and gain in free-electron lasers with three-dimensional helical wiggler and ion-channel guiding Phys. Plasmas 12, 093108 (2005); 10.1063/1.2013307 Electron trajectories and gain in a free-electron laser with realizable helical wiggler and ion-channel guiding Phys. Plasmas 12, 093103 (2005); 10.1063/1.2006690 Self-fields in a free-electron laser with helical wiggler and ion-channel guiding Phys. Plasmas 10, 905 (2003);A theory is developed for a free-electron laser with electromagnetic wiggler and ion-channel guiding. The electron trajectories due to a large amplitude backward propagating electromagnetic wiggler and an ion-channel electrostatic field are obtained and the stability of orbits is discussed. Then the gain equation describing the interaction between an electron and the radiation field is derived in the low-gain-per-pass limit. The results of a numerical study of electron orbits and gain are presented and discussed. It is shown that the maximum gain obtained in an electromagnetic wiggler is about twice the maximum gain obtained in a magnetostatic wiggler.
FePt -TiO 2 exchange coupled composite media with well-isolated columnar microstructure for high density magnetic recording Effect of orientation on the thermal stability in advanced metal particulate tapes Ultra high-density magnetic data storage requires magnetic grains of <5 nm diameters. Thermal stability of such small magnetic grain demands materials with very large magneto-crystalline anisotropy, which makes data write process almost impossible, even when Heat Assisted Magnetic Recording (HAMR) technology is deployed. Here, we propose an alternative method of strengthening the thermal stability of the magnetic grains via elasto-mechanical coupling between the magnetic data storage layer and a piezo-ferroelectric substrate. Using Stoner-Wohlfarth single domain model, we show that the correct tuning of this coupling can increase the effective magnetocrystalline anisotropy of the magnetic grains making them stable beyond the super-paramagnetic limit. However, the effective magnetic anisotropy can also be lowered or even switched off during the write process by simply altering the applied voltage to the substrate. Based on these effects, we propose two magnetic data storage protocols, one of which could potentially replace HAMR technology, with both schemes promising unprecedented increases in the data storage areal density beyond the super-paramagnetic size limit. V C 2014 AIP Publishing LLC.
Spin-inversion properties of an electron in nanoscale graphene sheets with a Rashba spin-orbit barrier is studied using transfer matrix method. It is found that for proper values of Rashba spin-orbit strength, perfect spin-inversion can occur in a wide range of electron incident angle near the normal incident. In this case, the graphene sheet with Rashba spin-orbit barrier can be considered as an electron spin-inverter. The efficiency of spin-inverter can increase up to a very high value by increasing the length of Rashba spin-orbit barrier. The effect of intrinsic spin-orbit interaction on electron spin inversion is then studied. It is shown that the efficiency of spin-inverter decreases slightly in the presence of intrinsic spin-orbit interaction. The present study can be used to design graphene-based spintronic devices.
We report studies of quasi-remanent polarization states in Pb0.99Nb0.02 [(Zr0.57Sn0.43)0.94Ti0.06]0.98O3 (PNZST) antiferroelectric ceramics and investigation of their relaxation effects using unique in-situ electrically activated time-resolved Synchrotron X-ray powder diffraction (SXPD) and 119 Sn Mössbauer Spectroscopy (MS). The SXPD patterns are consistent with a phase transition from quasi-tetragonal perovskite in 0V relaxed antiferroelectric state to rhombohedral distortion in ferroelectric state under saturating applied voltages of ±2kV. The observed quasi-remanent polarization relaxation processes are due to the fact that tetragonal to rhombohedral distortion does not occur at the applied voltage required to access the quasi-remanent polarization states, and the tetragonal symmetry restored after the removal of the applied electric field is preserved. Since these quasi-remanent polarization states were seen as possibly suitable for memory applications, the implications of this study are that anti-ferroelectrics are more feasible for multi-state dynamic random access memories (DRAM), while their application to non-volatile memories requires development of more sophisticated "read-out" protocols, possibly involving dc electrical biasing.
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