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.     

Diamagnetic domains and magnetostriction in beryllium

Magnetostriction was for the first time studied under the conditions of formation of diamagnetic domains (Condon domains). Transverse magnetostriction oscillations on a beryllium single crystalline plate oriented normally to magnetic field were measured in magnetic fields up to 7 T at temperatures down to 1.5 K. The relative amplitude of oscillations increased almost as the square of magnetic field and reached 10^?5. The signal had a sawtoothed shape corresponding to alternation of homogeneous and inhomogeneous (domain) states in the region of the existence of magnetic domains. The arising of domains was accompanied by singularities in the observed signals which is explained by an anomalous increase in the compressibility coefficient of the domain state: coefficient oscillations were more than 100 times larger than the value predicted by the standard theory. The observed relation between magnetization current and deformation led us to conclude that the compressibility of the metal was fully determined by conduction electrons. Magnetostriction then exactly compensated Fermi level oscillations. The position of the Fermi level therefore remained constant under magnetic field variations. In addition, the domain wall thickness had to increase as the plate grew thicker.     

Anomalous compressibility and magnetostriction of beryllium under the conditions of diamagnetic domain formation

Magnetostriction oscillations are measured for a single-crystal beryllium sample shaped like a plate perpendicular to the direction of the magnetic field. In the range of 2–5 T at a temperature of 1.5 K, i.e., in the region of diamagnetic domain formation (Condon domains), the striction signal has the saw-tooth shape corresponding to the alternation of homogeneous and nonhomogeneous (domain) states. The formation of the domain structure is accompanied by an anomalous increase in compressibility; the oscillations in this coefficient are more than one hundred times greater than the value given by the standard theory. An analysis of the results indicates that the domain wall width should increase with increasing plate thickness.     

Direct evidence for dia‐ and paramagnetic domains in beryllium

The first spectroscopic evidence for dia‐ and paramagnetic domains (Condon domains) in beryllium metal is presented. The domains, detected by the splitting of the μSR line, arise and disappear periodically in each de Haas–van Alphen cycle as the field \bf H, normal to the single crystal Be plate and parallel to its [0001] axis, is tuned near \bf H_0\approx 2.7\ T. The intensity of the lines in the doublet reflect the ratio of dia‐ to paramagnetic regions. For the difference in induction within the domains we obtain \Delta B\approx 30\mbox--40\ G in the investigated field range at T=0.8 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Capabilities of a muon method for studying the diamagnetic domains accompanying the de Haas-van Alphen effect

This paper analyzes the capabilities of a muon (μSR) method for studying the de Haas-van Alphen effect and the diamagnetic domain structure accompanying it. It is shown that, unlike the NMR method, the μSR method makes it possible to observe the formation of a diamagnetic domain structure in all metals. It is not currently known what type of domain structure accompanies the de Haas-van Alphen effect: one-dimensional (laminar) or two-dimensional. It is shown that the line shape of the Fourier spectrum of the signal makes it possible to determine both the character of the domain structure (two-dimensional or laminar) and the magnetic field distribution in the domains. Zh. éksp. Teor. Fiz. 111, 250–261 (January 1997)     

Observation of “decoupled” diamagnetic muon states in Alkali halides by muon spin resonance

The states of positive muons in KCl, NaCl and KI were studied with the muon spin resonance method under a 3 kG decoupling longitudinal field, revealing a considerably larger fraction of diamagnetic muon state than observed by the conventional spin rotation method. The origin of this fraction, which increases with temperature, is attributed to a muonium to muon transition in solids.     

Observation of domains in the helical phase of MnP

Chirality domains differentiated by the sense of rotation of the spiral are observed by polarized neutron diffraction topography in single crystals of MnP. They mainly occur as stripes perpendicular to the helix axis about 150 μm in width and several mm in length.The domain patterns and senses of spiral are repeatable on thermal cycling though polishing or application of a uniaxial stress modifies the domain structure and relative volumes. Grossly unbalanced domain populations have been observed.     

Observation of ferro- and antiferromagnetic domains in the Europium-Chalcogenides

Single crystals of the Eu-Chalcogenides show a scattering of light and a depolarization of polarized light at temperatures below the Curie- or Néel point, respectively, due to the existence of magnetic domains. These domains could be observed with a polarizing microscope. In antiferromagnetic EuSe (between 3.5° and 4.6°K), domains exist with optically active axes along the 6 [100] directions. The domain size in ferromagnetic EuS was at the limit of the resolution of the microscope. However, by applying a magnetic field larger domains were obtained. The direction of the magnetization within the domains is stabilized by internal stress. Due to the strong dichroism of the Eu-Chalcogenides, domains could be observed with only one polarizing unit.Busch, Junod andWachter [1, 2] have found a large red-shift of the absorption edge with the magnetization. By means of this effect domains with different magnetizations could be observed without any polarizer due to their different absorption.     

Observation of the penetration of subbarrier ultracold neutrons through beryllium foils and coatings

The subbarrier passage of ultracold neutrons through beryllium foils and coatings with a probability much higher than that of tunneling is observed. This effect may be responsible for the so-called anomalous loss of ultracold neutrons. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 5, 317–322 (10 September 1997)     

Observation of magnetic ripple and nanowidth domains in a layered ferromagnet

We investigated ferromagnetic domain structures on nanometer to micrometer scale for single crystals of a layered ferromagnet, La(2-2x)Sr(1+2x)Mn2O7 (0.32 < or = x < or = 0.40), as functions of x and temperature by means of Lorentz electron microscopy. We have succeeded in observing the evolution of magnetic ripple structure, dynamically, related to a spin reorientation transition where the magnetization direction switches between parallel and perpendicular to the layers. Our high-resolution magnetic domain imaging revealed that the ripple state is characterized by the evolution of magnetic nanowidth domains.     

Observation of magnetic domains in undoped ZnO grains at room temperature

The present study reports the room temperature ferromagnetism in undoped ZnO thin films grown by PVD method. The 500 nm film with small (90 nm) ZnO grains possess isolated magnetic domains with coercivity of 520 Oe. However, long range magnetic ordering with smaller coercivity of 230 Oe is observed for 1000 nm film. The long range ordering is caused by the reduction in domain wall pinning effect due to the presence of bigger (270 nm) ZnO grains. PL measurements show that these grains are semiconducting in nature. Results presented here suggest that oxygen vacancies at the surface may be responsible for the observed ferromagnetism.     

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.     

The beryllium atom and beryllium positive ion in strong magnetic fields

The ground and a few excited states of the beryllium atom in external uniform magnetic fields are calculated by means of our 2D mesh Hartree-Fock method for field strengths ranging from zero up to 2.35×10⁹ T. With changing field strength the ground state of the Be atom undergoes three transitions involving four different electronic configurations which belong to three groups with different spin projections S _z = 0, - 1, - 2. For weak fields the ground state configuration arises from the 1s ²2s ², S _z = 0 configuration. With increasing field strength the ground state evolves into the two S _z = - 1 configurations 1s ²2s2p _-1 and 1s ²2p _-13d _-2, followed by the fully spin polarised S _z = - 2 configuration 1s2p _-13d _-24f _-3. The latter configuration forms the ground state of the beryllium atom in the high field regime γ > 4.567. The analogous calculations for the Be ⁺ ion provide the sequence of the three following ground state configurations: 1s^22s and 1s ²2p _-1 (S _z = - 1/2) and 1s2p _-13d _-2 (S _z = - 3/2). Received 2 October 2000 and Received in final form 8 January 2001     

Observation and theory of strong stripe domains in amorphous sputtered FeB films

Domain structures in thin sputtered amorphous FeB films are studied by means of the longitudinal Kerr effect. In addition to the irregular domain structure characteristic of soft magnetic materials, we observe in certain regions a fine equilibrium domain structure with periodicity of a few micrometers. The Kerr contrast indicates that the magnetization at the surface of the film lies partially along the stripe direction. These characteristics and the behavior in applied fields suggests that the domains are similar to type II “strong stripe domains” observed earlier in permalloy films. Extending an earlier theory by Hara, we use a stray-field-free model with tilted orthorhombic anisotropy to show that there are at least two qualitatively different strong stripe structures: type IIa with surface magnetization perpendicular to the stripes and type IIb with surface magnetization at least partially parallel to the stripes. Type IIb is favored when K_p/K₀<cos 2θ ₀ where K₀ is the anisotropy component with axis tilted by θ₀ out of the film plane, and K_p is an in-plane anisotropy perpendicular to K₀. Strong stripes in amorphous FeB appear to be type IIb while those in permalloy are usually type IIa.     

Magnetically controlled convection in a diamagnetic fluid

We present visualization and measurement of the convection of water under a high magnetic field applied vertically to the fluid. The convection was either suppressed or enhanced depending on the direction of the magnetic force. The magnetic field effect was evaluated quantitatively by measuring the onset of convection, and discussed in terms of the Rayleigh number which includes the magnetic term. The results clearly show that the convection in a diamagnetic fluid such as water can be controlled using a common 10 T class magnet.     

Magnetoplasticity and magnetic memory in diamagnetic solids

A mechanism for the depinning of dislocations pinned by a stopper is formulated. This mechanism includes the transfer of an electron from a dislocation to the stopper and the appearance of a spin two-electron nanoreactor that has no Coulomb interaction that would hold the dislocation at the stopper in the initial state. The spin dynamics in the nanoreactor is controlled by a magnetic field; therefore, it causes magnetoplasticity and short-term magnetic memory. Another origin of magnetoplasticity is the aggregation of diffusing paramagnetic ions (stoppers) into dimers, trimers, and clusters; this aggregation is also spin-selective and magnetically sensitive. The magnetic-field dependence of the structural evolution of the stoppers provides long-term magnetic memory in diamagnetic solids. Both mechanisms of magnetoplasticity and magnetic memory can coexist and be independent of or dependent on each other.     

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.