Annealing Dependence of Exchange Bias in MnO/Ga<Subscript>1−</Subscript><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>As Heterostructures

We discuss the annealing-dependence of exchange bias in Ga_{1− x} Mn _x As epilayers that are overgrown with Mn. Although pure Mn is a known antiferromagnet, we find that the as-grown Mn overlayer does not produce any exchange coupling with Ga_{1− x} Mn _x As. Rather, our studies indicate that annealing in air is essential for creating the standard signatures of exchange bias (a clear shift in the magnetization hysteresis loop and an increased coercive field). We use X-ray photoelectron spectroscopy to characterize the compositional depth profile of both as-grown and rapid thermal annealed samples. These studies demonstrate that the cleanest exchange bias arises when the Mn overlayer is completely converted into MnO.     

Static hole in a two-dimensional antiferromagnet

The energetics of static hole in a 2D antiferromagnetic (AF) is studied. AF is described by magnon operators in the LSW approximation, while the holes by fermionic operators. The energy spectrum of the magnons in the presence of the hole is determined from the perturbed Green’s function.     

非线性反铁磁介质中双稳和多稳态研究

本文分析了远红外光（或亚毫米波）在线性介质－－非线性反铁磁介质－－线性介质系统中的透射特性，数值分析表明该系统具有双稳和多稳特性。分析了非线笥反铁磁介质厚度ｄ、介电常数ε２以及线性介质的介电常数ε２以及线性介质的介电常数ε１，ε２对系统输出功率与输入功率关系的影响，结果表明：非线性反铁磁介质层越厚，实现双稳工作所要求的门限功率越小，输出效率越低；ε２越大，门限功率越小，输出效率越高，双稳动态范围越     

ARPES Spectra from Bond-Centered Stripe Phase of Moderately Doped Cuprates

Using a combination of the bond formalism and the spin polaron approach we calculate the single particle spectral function for the system of stripes which take the form of two-leg ladder-like domain walls (DWs) between antiferromagnetic (AF) domains with the changing across each DW by π phase of the sublattice magnetization. We assume that the ordered bonds which are in the singlet state, form in the DW a pattern which resembles two layers of a brick wall. We concentrate on the doping level 1/8 and on levels slightly above this value when, as suggested by experiments, the distance between axes of nearest stripes is four lattice spacings and the linear filling of stripes is about 1/2. By comparing the calculated and measured spectra we demonstrate that among three simplest choices of bond order in the DW, singlets formed on rungs, singlets formed on nearest legs on both sides of the stripe axis and the brick wall structure, a most obvious resemblance to the ARPES spectra at the Fermi energy from the doped La₂CuO₄ in the stripe phase shows the single particle spectral weight of the stripe system formed in the underlying spin background with bond order on the nearest leg on both sides of the stripe axis. This conclusion is consistent with the result of the stability analysis reported in a separate paper.     

Intrinsic Localized Modes in an Order-parameter-preserving Antiferromagnet

Intrinsic localized modes in an order-parameter-preserving antiferromagnet are investigated withemploying the Dyson-Maleev transformation and the coherent-state ansatz. These modes which be-low the magnon frequency band correspond to a local large-angle, low-frequency precessional mo-tion of spins, quantum states of which are characterized by the indefiniteness of the number of rele-vant magnons.     

Preparation and magnetic properties of Bim + 1Fem − 3Ti3O3m + 3 thin films with magnetic order above room temperature

Thin films of Bi_m + 1Fe_m − 3Ti₃O_3m + 3 (BFTO) with m ≦ 9 have been successfully grown on (100) SrTiO₃ by chemical solution deposition. These films had the c axis normal to the film plane. The conversion electron Mössbauer spectoroscopy (CEMS) showed that the spectra of BFTO thin films exhibit an asymmetric quadrupole doublet for m = 8 at 300 K, indicative of being paramagnetic, while, for m = 9, clearly show six hyperfine lines indicating presence of magnetic order at 300 K. From the intensity ratio of asymmetric peaks, the polarization axis of BFTO films with m ≥ 8 was deduced to be likely along <101> of the perovskite-like unit. On the other hand, it was found from the spectral fitting that the BFTO thin film with m = 9 has the Néel temperature around 310 K and the spin axis making an angle of about 60° to the c-axis. These indicate that the BFTO (m = 9) thin film is a promising candidate for room-temperature multiferroics.     

Sputter-epitaxy and electric properties of multiferroic Bim + 1Fem-3Ti3O3m + 3 thin films

Growth conditions suitable for sputter-epitaxy of Bi_m + 1Fe_m-3Ti₃O_3m + 3 (BFTO) thin films with layered structure have been investigated. The amount of oxygen during deposition was found to be specifically essential for obtaining a good-quality thin film of BFTO with a large m. The (001) epitaxial thin films of BFTO with m of nearly 10 which is expected to retain magnetic order up to room temperature have been successfully grown on (001) SrTiO₃ substrates under the determined optimum condition. The film exhibited leakage current as low as order of 10⁻²-10⁻¹ A/m² limited by Schottky emission at the interfaces between the electrodes and the film. In addition, the film showed a ferroelectric polarization curve with Pr = 6 μC/cm² for applied field of 35 MV/m at room temperature though the curve was unsaturated. These indicate that the BFTO (m = 10) thin films are promising as multiferroics at room temperature.     

自旋阀结构中的力致磁阻效应

采用变分法研究了外应力场下铁磁单层膜、铁磁/反铁磁双层膜系统的磁化性质,进而研究了由铁磁单层膜和铁磁/反铁磁双层膜所构建的自旋阀结构中的磁电阻与外应力场之间的关系.结果表明,铁磁膜中的磁化性质与膜面内所加应力场的大小,方向密切相关,而反铁磁层的嵌入将明显地改变着铁磁层的磁矩向应力场方向磁化的行为.特别地,在应力场方向垂直于铁磁易轴情况下,当应力场日H_λ=2(K_1+K_(up)/3M)时,将发生磁化从易轴方向到应力方向的突变.为此,可采用自旋阀结构,通过其膜面内的应力场所调控的磁电阻效应,构建纳米尺度下的力磁传感器.     

Optically Inspired Nanomagnonics with Nonreciprocal Spin Waves in Synthetic Antiferromagnets

Integrated optically inspired wave-based processing is envisioned to outperform digital architectures in specific tasks, such as image processing and speech recognition. In this view, spin waves represent a promising route due to their nanoscale wavelength in the gigahertz frequency range and rich phenomenology. Here, a versatile, optically inspired platform using spin waves is realized, demonstrating the wavefront engineering, focusing, and robust interference of spin waves with nanoscale wavelength. In particular, magnonic nanoantennas based on tailored spin textures are used for launching spatially shaped coherent wavefronts, diffraction-limited spin-wave beams, and generating robust multi-beam interference patterns, which spatially extend for several times the spin-wave wavelength. Furthermore, it is shown that intriguing features, such as resilience to back reflection, naturally arise from the spin-wave nonreciprocity in synthetic antiferromagnets, preserving the high quality of the interference patterns from spurious counterpropagating modes. This work represents a fundamental step toward the realization of nanoscale optically inspired devices based on spin waves.