Magnetoplasticity of diamagnetic crystals in microwave fields

Physical mechanisms responsible for the effect of microwave fields on magnetoplasticity and microhardness of diamagnetic crystals are formulated. Their key elements are resonant and nonresonant interactions between microwave fields and spin-selective nanoscale reactors. In ionic and covalent crystals, a nanoscale reactor is created when an electron is transferred in a “stopper + pinned dislocation” system and when a dislocation encounters a dangling bond, respectively. The former mechanism enhances microplasticity, while the latter leads to hardening via magnetic resonance. Physical implications of the mechanisms are compared with experimental observations.     

抗磁材料磁悬浮的理论模拟

抗磁材料磁悬浮磁结构简单,有广泛的应用前景.本文研究了抗磁性材料在2×2永磁铁阵列表面附近的磁悬浮.用MATLAB模拟了H的z方向分量Hz及其导数.Hz和-Hz.Hz在距离永磁铁表面不同高度的二维分布.因为Fz=-χVHz.Hz,所以-Hz.Hz的分布能反映出抗磁材料在磁场中的受力情况.三维模拟和实验表明,抗磁材料在稳恒磁场中能稳定悬浮.我们还得到了抗磁材料悬浮高度和抗磁材料尺寸的关系.     

Magnetoplasticity and diffusion in silicon single crystals

The effect of static magnetic fields on the dynamics of surface dislocation segments, as well as the diffusion mobility of a dopant in silicon single crystals, has been analyzed. It has been experimentally found that the preliminary treatment of p-type silicon plates (the dopant is boron with a concentration of 10¹⁶ cm⁻³) in the static magnetic field (B = 1 T, a treatment time of 30 min) leads to an increase in the mobility of surface dislocation segments. The characteristic times of observed changes (about 80 h) and the threshold dopant concentration (10₁₅ cm⁻³) below which the magneto-optical effect in silicon is not fixed have been determined. It has been found that diffusion processes in dislocation-free silicon are magnetically sensitive: the phosphorus diffusion depth in p-type silicon that is preliminarily aged in the static magnetic field increases (by approximately 20%) compared to the reference samples.     

On levitation of diamagnetic bodies in a magnetic field

Various methods for calculating the force characteristics of a suspension ensuring levitation of diamagnetic bodies of various origin and shape are considered. The method of calculation is based on the computation of the energy of interaction of a body upon its displacement from the center of suspension for an arbitrary configuration of the suspending field. The method of quasi-homogeneous approximation is considered and compared with the method for calculating the force characteristics based on the general formula for the magnetic energy. The necessary and sufficient conditions for conservative stability of the equilibrium state are formulated, and the stability domain is determined. It is shown that the stability domain depends on the size of the body. Calculations of force characteristics are performed specifically for the suspension of a diamagnetic sphere. The dependences of forces and stiffnesses on the magnetic field strength are obtained, which makes it possible to analyze the stability of confinement of the diamagnetic sphere in the field of the system of circular currents.     

抗磁和顺磁性材料在磁场中弱磁力实验测量

对抗磁性材料和顺磁性材料在强磁场中的弱磁力进行测量.利用设计的实验装置,成功测得抗磁性石墨片和顺磁性材料铝片在永磁铁阵列表面受到的弱磁力.研究证明弱磁力的大小与磁场及磁场梯度乘积成正比.     

Nuclear magnetic shielding and diamagnetic susceptibility of interacting hydrogen atoms

A quantum-mechanical study is made of the changes of the nuclear magnetic screening constant σ and the diamagnetic susceptibility X of two interacting hydrogen atoms due to van der Waals and overlap interatomic forces (effects of electron spin being neglected). At large distances the calculations show that van der Waals forces decrease the nuclear screening but increase the diamagnetic susceptibility (in magnitude). As the internuclear distance is reduced the first effect of overlap forces is to increase the screening in the repulsive (electronic triplet) state but this is followed by a further reduction. Attractive overlap forces (as in the ground state of H₂) ultimately lead to an increase in screening.     

Specific features of the magnetic aftereffect in high-purity diamagnetic beryllium

The behavior of the effective shear modulus and low-frequency internal friction in magnesium-thermal beryllium condensate before and after the treatment of samples in a weak constant magnetic field has been studied. The data obtained have been used for calculating the temperature and time dependences of the ratio between the dislocation motion velocities during and after the magnetic action. It has been shown that the exposure of samples to a magnetic field and their aging after the magnetic action radically change the character of the temperature dependences of the dislocation motion velocities. Empirical expressions describing these dependences have been obtained. It has been demonstrated that the magnetic aftereffect in diamagnetic beryllium has a complex character, which indicates the presence of several magnetic memory mechanisms.     

抗磁性物质磁悬浮可行性分析及实现

从理论和实验上说明石墨、铜等抗磁性的"非磁"物质在磁场中也受到磁场的作用力.实验中尝试了各种不同类型的永磁体序列,并利用4块一组的永磁铁序列产生梯度场,使磁铁表面上方产生可供抗磁性物质悬浮的稳定区域,成功实现了石墨的悬浮.此外,还利用顺磁性溶液及电磁铁实现了氧化铝和硅的悬浮.     

Hysteresis and memory of the magnetic resonance of conduction electrons in solids. From bistability to stochastic resonance

The magnetic resonance line of conduction electrons in solids may exhibit bistable hysteresis if several conditions are fulfilled. Its mechanism is presented and the manifestation of bistability in the ESR of conduction electrons in single crystal and polycrystalline samples is discussed. The characteristics of the dynamics of the bistability show that bistable resonance can be assimilated to one-dimensional overdamped motion of the spin system in the nuclear field space, driven by a bistable potential. It is shown for the first time that noise acting on this bistable resonance can create order, by the phenomenon of stochastic resonance.     

Low-temperature magnetization relaxation in magnetic molecular solids

The low temperature relaxation of the magnetization in molecular magnetic solids such as Fe₈ is studied using Monte Carlo simulations. A set of rate equations is then developed to understand the simulations, and the results are compared. The simulations show that the magnetization of an initially saturated sample deviates as a square-root in time at short times, as observed experimentally, and this law is derived from the rate equations analytically.     

Effect of diamagnetic impurities on the magnetic susceptibility of iron borate

The low-frequency magnetic susceptibility of a FeBO₃ single crystal doped with diamagnetic Mg ions was measured by a magnetooptical method. It is shown that the introduction of Mg ions into the composition of this easy-plane weak ferromagnet results in the appearance, at low temperatures, of a strong in-plane magnetocrystalline anisotropy and also causes a marked difference between the field dependences of the magnetic susceptibility measured in magnetic fields applied along different directions in the basal plane of the crystal. The revealed specific features of the field dependence of the magnetic susceptibility of the crystal studied are associated with the transformation of its magnetic structure during magnetization.     

Spin-polarized electron emission from magnetic and non-magnetic solids

The use of spin-polarization analysis in electron spectroscopy of magnetic and non-magnetic surfaces is demonstrated with a few examples. The existence and properties of spin-dependent transmission of electrons through the solid-vacuum interface is shown. The influence of surface reconstruction of Pt(110) on spin polarization and energy distribution curves in photoemission with circularly polarized light is studied. The polarization of secondary electrons from Fe(110) is observed to depend on the spin polarization of primary electrons at low energies. The temperature dependence of the exchange splitting in Ni is studied by means of spin-polarized electron energy loss spectroscopy and found to be at variance with the assumptions of the Stoner-Wohlfarth theory.     

Field-dependent diamagnetic transition in magnetic superconductor Sm1.85Ce0.15CuO4-y

The magnetic penetration depth of single crystal Sm(1.85)Ce(0.15)CuO(4-y) was measured down to 0.4 K in dc fields up to 7 kOe. For insulating Sm2CuO4, Sm3+ spins order at the Ne el temperature, T(N)=6 K, independent of the applied field. Superconducting Sm(1.85)Ce(0.15)CuO(4-y) (T(c) approximately 23 K) shows a sharp increase in diamagnetic screening below T(*)(H) which varied from 4.0 K (H=0) to 0.5 K (H=7 kOe) for a field along the c axis. If the field was aligned parallel to the conducting planes, T(*) remained unchanged. The unusual field dependence of T(*) indicates a spin-freezing transition that dramatically increases the superfluid density.     

Surface wave excitation in solids by magnetic dipoles

The paper studies the interaction of magnetic dipole moments with magnetoplasma (in semiconductors) and magnetostatic (in ferromagnets) surface waves. Expressions for energy losses of such dipoles by wave excitation are obtained; experimental realizability of mobile dipole moments are discussed; and estimates are presented. The said interaction is shown to be suitable to detect surface helicons in semiconductors.     

Effect of diamagnetic substitutions in BaFe12O19 on the magnetic properties

The exchange parameters of BaFe₁₂O₁₉ have been calculated from the temperature dependence of the saturation magnetization using the molecular field theory. Under the assumption that the exchange parameters do not change for diamagnetic substitutions of the Fe³⁺ ions, it is shown that the temperature coefficient of the magnetization at room temperature cannot be decreased without decreasing the magnetization. Diamagnetic substitution in the octahedralf ₂ site would solely increase the saturation magnetization.     

Stable diamagnetic self-levitation of a micro-magnet by improvement of its magnetic gradients

A disc-shaped SmCo magnet with a diameter of 0.85 mm is levitated above a graphite diamagnetic plate at a height of about 14 μm. The magnet is magnetised into a double dipole. The levitation of multipolar magnets above a diamagnetic material was suggested in 1956 by Boerdijk and patented in 1995 by Pelrine, but without any known published experimental results. In this letter, both theoretical and experimental results are presented.     

Coulomb ensemble of charged diamagnetic macroparticles in an inhomogeneous magnetic field under microgravity conditions

The formation of strongly nonideal Coulomb systems of a large number (∼104) of charged diamagnetic macroparticles in a cusp magnetic trap under microgravity conditions has been experimentally studied. The experiments have performed in the Russian segment of the International Space Station in the framework of the Coulomb Crystal experiment. Using the data of the videorecording of the positions of the particles in the magnetic trap, the magnetic susceptibility and charge of the particles have been estimated and the period of the oscillations of the cloud of the particles, as well as the damping rate of oscillations, has been determined.