Controlled synthesis of ferromagnetic MnSe_x particles

The MnSe_x(x = 1,2) nanoparticles were synthesized under hydrothermal condition,by reaction of the reduced selenium and Mn~(2+) ion in the presence of hydrazine and acetic acid.By precisely controlling the pH value of the solution,a series of MnSe_x particles were synthesized.The structure and morphology of as-prepared particles were examined with x-ray diffractometer(XRD),transmission electron microscopy(TEM),and scanning electron microscopy(SEM).The average sizes of as-prepared particles varied from nanoscale to microscale with pH value increase.Furthermore,the nucleation and growth mechanism associated with pH values were discussed,which can be applied to the hydrothermal synthesis of metal chalcogenide in general.Finally,the optical and magnetic properties of as-prepared particles were measured.All as-made particles exhibit a ferromagnetic behavior with low coercivity and remanence at room temperature.     

稳定核84Sr的高自旋态研究

利用75MeV的¹⁸O束流,通过⁷⁰Zn(¹⁸O,4n)反应布居了⁸⁴Sr核的高自旋态,测量了激发函数,γ–γ符合及DCO比值和γ射线强度,观察到了12条新能级,近30条新γ跃迁,建立了新的能级纲图,与D.C.M.(deformod configuration-mixing shell model)理论计算结果符合得很好,发现其负宇称带有强烈的振动性.     

晶粒尺寸对软-硬磁性晶粒间交换耦合相互作用和有效各向异性的影响

以软磁性相α—Fe和硬磁性相Nd2Fe14B为例，研究了软、硬磁性晶粒间的交换耦合作用和有效各向异性随晶粒尺寸和软、硬磁性晶粒不同尺寸比例(Ds：Dh)的变化关系。当晶粒尺寸大于其铁磁交换长度时，晶粒的各向异性分为晶粒内部无交换耦合和晶粒表面有交换耦合部分，其各向异性常数为两部分的统计平均值。计算结果表明：软、硬磁性晶粒间的有效各向异性随晶粒尺寸的减小而下降，随软、硬磁性晶粒尺寸比值(Ds：Dh)的减小而增加。为使软、硬磁性晶粒间的有效各向异性常数Keff保持较高的值，应控制硬磁性晶粒大于30nm。软磁性晶粒在10nm左右。     

纳米复合永磁材料的有效各向异性与矫顽力

研究了纳米Nd2Fe14B/α-Fe复合永磁材料中晶粒交换耦合相互作用对有效各向异性的影响和变化规律.结果表明：晶粒之间的交换耦合作用使材料的有效各向异性Keff随晶粒尺寸的减小而下降、随软磁性相成分的增加而降低. 当晶粒尺寸 减小到4nm时，Keff值减小为其各自通常各向异性常数值的1/3—1/4.有效各向异性的变化特点与矫顽力的变化规律基本相同.纳米复合永磁材料矫顽力的降低主要由于有效各向异性的减小而引起. 关键词： 纳米复合永磁材料 交换耦合相互作用 有效各向异性 矫顽力     

相分布和晶粒尺寸对Nd2Fe14B/ɑ-Fe纳米复合永磁材料矫顽力的影响

本文采用统计平均方法研究了软、硬磁性晶粒尺寸及相分布对Nd2Fe14B/α-Fe纳米复合永磁材料矫顽力的影响。计算结果表明：对于单相纳米硬磁材料，磁体矫顽力随着硬磁性晶粒尺寸的减小而降低；对于软、硬两磁性相组成的Nd2Fe14B/a-Fe纳米复合永磁材料，两相的随机分布将导致磁体矫顽力随硬磁性晶粒尺寸的减小呈现极大值。本文的计算结果还表明当硬磁性晶粒尺寸大于软磁性晶粒的最佳尺寸时(15nm)，具有多层膜结构的Nd2Fe14B/a-Fe纳米复合永磁材料将比两相随机分布时具有更大的矫顽力。     

Spin-independent transparency of pure spin current at normal/ferromagnetic metal interface

The spin transparency at the normal/ferromagnetic metal(NM/FM) interface was studied in Pt/YIG/Cu/FM multilayers. The spin current generated by the spin Hall effect(SHE) in Pt flows into Cu/FM due to magnetic insulator YIG blocking charge current and transmitting spin current via the magnon current. Therefore, the nonlocal voltage induced by an inverse spin Hall effect(ISHE) in FM can be detected. With the magnetization of FM parallel or antiparallel to the spin polarization of pure spin currents(σ(sc)), the spin-independent nonlocal voltage is induced. This indicates that the spin transparency at the Cu/FM interface is spin-independent, which demonstrates that the influence of spin-dependent electrochemical potential due to spin accumulation on the interfacial spin transparency is negligible. Furthermore, a larger spin Hall angle of Fe_(20)Ni_(80) (Py) than that of Ni is obtained from the nonlocal voltage measurements.     

Effective anisotropy and coercivity in nanocrystalline single-phase NdFeB permanent magnetic material

The effect of exchange-coupling interaction on the effective anisotropy and its varying tendency in nanocrystalline single-phase NdFeB permanent magnetic material have been investigated. The results show that the exchange-coupling interaction between grains makes the effective anisotropy of material, Keff, decrease with the reduction of grain size. The variation of Keff is basically the same as that of coercivity. The decrease in effective anisotropy is the main reason of the reduction of coercivity for nanocrystalline single-phase NdFeB permanent magnetic material. In order to get high anisotropy and coercivity in nanocrystalline single-phase NdFeB permanent material, the grain size should be larger than 35 nm.     

磁转动带研究

介绍了原子核高自旋态的磁转动带结构实验证据,理论模型及在北京串列加速器上⁸⁴Rb磁转动带的研究.     

The origin of spin current in YIG/nonmagnetic metal multilayers at ferromagnetic resonance

Spin pumping in yttrium-iron-garnet(YIG)/nonmagnetic-metal(NM) layer systems under ferromagnetic resonance(FMR) conditions is a popular method of generating spin current in the NM layer.A good understanding of the spin current source is essential in extracting spin Hall angle of the NM and in potential spintronics applications.It is widely believed that spin current is pumped from precessing YIG magnetization into NM layer.Here,by combining microwave absorption and DC-voltage measurements on thin YIG/Pt and YIG/NM_1/NM_2(NM_1 =Cu or Al,NM_2 =Pt or Ta),we unambiguously showed that spin current in NM,instead of from the precessing YIG magnetization,came from the magnetized NM surface(in contact with thin YIG),either due to the magnetic proximity effect(MPE) or from the inevitable diffused Fe ions from YIG to NM.This conclusion is reached through analyzing the FMR microwave absorption peaks with the DC-voltage peak from the inverse spin Hall effect(ISHE).The voltage signal is attributed to the magnetized NM surface,hardly observed in the conventional FMR experiments,and was greatly amplified when the electrical detection circuit was switched on.     

Synchronization of nanowire-based spin Hall nano-oscillators

The synchronization of the spin Hall nano-oscillator (SHNO) device driven by the pure spin current has been investigated with micromagnetic simulations. It was found that the power spectra of nanowire-based SHNO devices can be synchronized by varying the current flowing in the heavy metal (HM) layer. The synchronized signals have relatively high power and narrow linewidth, favoring the potential applications. We also found that the synchronized spectra are strongly dependent on both the number and length of nanowires. Moreover, a periodic modulation of power spectra can be obtained by introducing interfacial Dzyaloshinskii-Moriya interaction (iDMI). Our findings could enrich the current understanding of spin dynamics driven by the pure spin current. Further, it could help to design novel spintronic devices.