ANNIHILATION OF VERTICAL-BLOCH-LINE CHAINS IN THE WALLS OF THE SECOND KIND OF DUMBBELL DOMAINS SUBJECTED TO JOINT STATIC BIAS FIELD AND IN-PLANE FIELD

Experiments were statistically carried out on the behavior of vertical-Bloch-line(VBL) chains in the walls of the second kind of dumbbell domains (IIDs) is garnet bubble films subjected to joint action of static bias field H_b and in-plane field H_ip. The curves of the four critical in-plane fields, (H_ip)_IID-ID (H_ip)_IID-OHB (H_ip)_IID-SB and H'_ip vs H_b were measured and explained. In particular, in terms of two series of IID photos, a new experimental manifestation of the unknown "number effect" of VBL chains was found.     

直流偏场和面内场联合作用下第二类哑铃畴的自发收缩

实验研究了第二类哑铃畴在直流偏场和面内场联合作用下的自发收缩现象，发现第二类哑铃畴的自发收缩不仅与面内场的大小有关，而且还与第二类哑铃畴在面内场中所处方向有关.采用照相法形象地揭示出：当第二类哑铃畴与面内场垂直时最容易发生自发收缩；当第二类哑铃畴与面内场平行时最难发生自发收缩.实验还证明了第二类哑铃畴在自发收缩过程中存在垂直布洛赫线的丢失现象.     

INFLUENCE OF IN-PLANE FIELD ON THE STABILITY OF VERTICAL BLOCH LINE CHAINS IN HARD DOMAINS OF GARNET BUBBLE FILMS

The stability of vertical Bloch line (VBL) chains was statistically studied for all three types of bard domains in garnet bubble films subjected to an in-plane field H_ip. With a set of integrate data taken from seven bubble samples and with two typical figures of a sample, four main features of the behavior of VBL chains subjected to H_ip were summarized.     

温度对垂直布洛赫线链解体临界面内磁场区间的影响

实验研究了温度对液相外延石榴石磁泡薄膜中条状普通硬磁畴壁内的垂直布洛赫线（ＶＢＬ）链解体临界面内磁场区间的影响。发现存在一对特征温度T⁽¹⁾₀ 和 T⁽²⁾₀（前者比后者略低但均高于室温），在从室温到T⁽²⁾₀的每个温度Ｔ下，使ＶＢＬ逐渐消失的面内磁场Ｈ_ip都分布于一个与Ｔ有关的区间[H_ip⁽¹⁾(T), H_ip⁽²⁾(T)]内，称为临界面内磁场区间：H_ip^{＜H_ip(1)(T)时，ＶＢＬ链保持不变;H_ip(1)(T)< H_ip < H_ip(2)(T)时，随着Ｈ_ip的增加，越来越多的ＶＢＬ消失;H_ip > H_ip(2)(T)时，所有ＶＢＬ都消失。H_ip(1)(T),H_ip(2)(T)及H_ip(2)(T)-H_ip(1)(T)均随Ｔ的升高而下降，前二者分别于T(1)₀ 和 T(2)₀降为零。比值H_ip(2)(T)/H_ip(1)(T)随Ｔ的升高而升高，在低温段（包括室温）升高缓慢且约为21/2,在T(1)₀附近急剧升高且至T(1)₀时趋于∞。对以上结果做了理论分析。 关键词：}     

面内场对三类硬磁畴的影响

采用直流偏场整形的方法,研究了面内场对石榴石磁泡薄膜中三类硬磁畴的影响.得到面内场作用下三类硬磁畴畴壁中垂直布洛赫线(VBL)是逐步解体的,而且三类硬磁畴具有相同的临界面内场范围［H¹_ip,H²_ip］,其中H¹_ip是硬磁畴中VBL开始丢失时的临界面内场,H²_ip是VBL完全丢失 关键词： 硬磁畴 整形 垂直布洛赫线     

RADIAL CONTRACTION OF THE FIRST KIND OF DUMBBELL DOMAINS SUBJECTED TO A STATIC BIAS FIELD

On the basis of the "exercise" experiment and the phenomenon of "self-shrink", the behavior of "less-stable" IDs (first kind of dumbbell domains) in radial contraction under an "exercise" bias field, (H_b)_e, was statistically investigated in detail. It was found that the histograms of their stripe-to-bubble transition field, H_sb after exercise, become narrower and shift towards the side of lower H_sb with the increase of (H_b)_e. It illustrates how the less-stable IDs lose part of their vertical Bloch lines under different (H_b)_e. In addition, it was also found that the curve of the upper boundary of these histograms, (H_sb)_max vs. (H_b)_e, consists of two segments of straight lines. This discontinuity was proved to be due to self shrink, and the crosspoint of these two lines is just the lower limit of the self-shrink region. Furthermore, a series of photographs were taken to show the effect of radial contraction on less-stable IDs intuitively.     

面内场和静态偏磁场作用下条畴和泡畴的稳定性

实验研究面内场H_in和静态偏磁场H_b作用下,(111)面磁泡膜内条畴的消失过程。保持H_b恒定,增加H_in,测量条畴消失场H_s^*和泡畴消失场H_k^*与面内场方向β的变化关系。计及立方磁晶各向异性的影响,建立H_in和H_b共同存在时的条畴稳定性理论。定性解释了实验的主要特点。导出黑、白条畴同时消失时的角度 β_n=1/3(2nπ±arc cos│3/(2^1/2)(M_sH_b)/K₁│)(n=0,±1,±2,…)与实验基本符合。 关键词：     

Field dependence of the superconducting properties induced by proximity effects: Breakdown fields

It has been shown that the proximity-effect induced superconductivity in the normal partN of a superconductor-normal metal binary layer (such asIn Bi/Zn) can screen a magnetic field up to a critical fieldH _b. AtH _b, a sharp penetration of flux intoN occurs. However, the breakdown fieldH _b can only be observed for certain values of the thickness ofN and of temperature. We study here the domain of existence ofH _b as a function of these two parameters. We also show that studies onH _b yield some information on the properties of the pair potential inN. Thus measurements onH _b performed at the critical temperature ofN confirm the theoretical predictions concerning the remarkable behavior of the order parameter inN at this temperature.     

Magnetic structure of low-dimensional LiCu2O2 multiferroic according to 63,65Cu and 7Li NMR studies

The complex NMR study of the magnetic structure of LiCu₂O₂ multiferroic has been performed. It has been shown that the spin spirals in LiCu₂O₂ are beyond the ab, bc, and ac crystallographic planes. The external magnetic field applied along the c axis of the crystal does not change the spatial orientation of spirals in Cu²⁺ chains. A magnetic field of H ₀ = 94 kOe applied along the a and b axes rotates the planes of spin spirals in chains, tending to orient the normal n of spirals along the external magnetic field. The rotation angle of the planes of the magnetic moments are maximal at H ₀ ?? b.     

A lower bound for the volume-averaged mean-square magnetostatic stray field

Based on a micromagnetics model, we develop a method through which quantitative information on the volume-averaged mean-square magnetostatic stray field 〈|H ^b _d|²〉 _v due to non-zero divergences of the magnetization M within the bulk of a ferromagnetic body can be obtained by analysis of magnetic-field-dependent small-angle neutron scattering data. In the limit of high applied magnetic field H _a, when the direction of M deviates only sligthly from H _a, we have estimated a lower bound for 〈|H ^b _d|²〉 _v as a function of the external field, and we have applied the method to bulk samples of nanocrystalline electrodeposited Ni and Co and coarse-grained polycrystalline cold-worked Ni. The root-mean-square magnetostatic stray field, which is inherent to a particular magnetic microstructure, shows a pronounced field dependence, with values ranging from about 5 to 50mT. Even at applied fields as large as 1.7T, the quantity μ〈|H ^b _d|²〉^1/2 _v of nanocrystalline Co is still 24mT, which suggests that contributions to the total magnetostatic field originating from the bulk are significant in nanocrystalline ferromagnets; therefore, 〈|H ^b _d|²〉 _v cannot be ignored in the interpretation of e.g. measurements of magnetization or spin-wave resonance. A comparison of 〈|H ^b _d|²〉 _v with the volume-averaged mean-square anisotropy field reveals that both quantities are of comparable magnitude. Received 25 April 2002 Published online 31 October 2002 RID="a" ID="a"e-mail: anmi@nano.uni.saarland.de     

Scaling form of zero-field-cooled and field-cooled susceptibility in superparamagnet

The scaling form of the normalized ZFC and FC susceptibility of superparamagnets (SPMs) is presented as a function of the normalized temperature y(=k_BT/K_u〈V〉), normalized magnetic field h (=H/H_K), and the width σ of the log-normal distribution of the volumes of nanoparticles, based on the superparamagnetic blocking model with no interaction between the nanoparticles. Here 〈V〉 is the average volume, K_u is the anisotropy energy, and H_K is the anisotropy field. Main features of the experimental results reported in many SPMs can be well explained in terms of the present model. The normalized FC susceptibility monotonically increases as the normalized temperature y decreases. The normalized ZFC susceptibility exhibits a peak at the normalized blocking temperature y_b(=k_BT_b/K_u〈V〉), forming the y_b vs h diagram. For large , y_b starts to increase with increasing h, showing a peak at h=h_b, and decreases with further increasing h. The maximum of y_b at h=h_b is due to the nonlinearity of the Langevin function. For small σ, y_b monotonically decreases with increasing h. The derivative of the normalized FC magnetization with respect to h shows a peak at h=0 for small y. This is closely related to the pinched form of M_FC vs H curve around H=0 observed in SPMs.     

立方磁晶各向异性对面内磁场中条畴和磁泡稳定性的影响

在八个(111)面磁泡膜上,观察了施加面内(in-plane)磁场后在不同晶轴方向上条状畴的消失过程,测量了条畴消失场H_s^*和磁畴消失场H_k^*与面内磁场的方向的关系。本文计及立方磁晶各向异性,完善了面内磁场中条畴的稳定性理论。用该理论定性地解释了实验结果的主要特点。导出了H_s^*与立方各向异性及面内场方向的两种近似的理论关系,它们分别适用于面内场方向靠近和不十分靠近〈110〉晶轴的情形。它们和实验结果是大致符合的。在〈110〉晶轴上,理论关系具有下列简单的形式:H_k^*<110>=H_s^*<110>=H_k{1+(k₁/2K_u)-[al/h(4πM_s/H_k)²]^2/3},此式与实验结果符合得相当好。 关键词：     

Probing the sign-changeable interaction between dark energy and dark matter with current observations

We consider the models of vacuum energy interacting with cold dark matter in this study, in which the coupling can change sigh during the cosmological evolution. We parameterize the running coupling b by the form b(a) = b_0 a + b_e(1-a), where at the earlytime the coupling is given by a constant b_e and today the coupling is described by another constant b_0. We explore six specific models with(i) Q = b(a)H_0ρ_0,(ii) Q = b(a)H_0ρ_(de),(iii) Q = b(a)H_0ρ_c,(iv) Q = b(a)Hρ_0,(v) Q = b(a)Hρ_(de), and(vi) Q = b(a)Hρ_c.The current observational data sets we use to constrain the models include the JLA compilation of type Ia supernova data, the Planck 2015 distance priors data of cosmic microwave background observation, the baryon acoustic oscillations measurements,and the Hubble constant direct measurement. We find that, for all the models, we have b_0 0 and b_e 0 at around the 1σ level,and b_0 and b_e are in extremely strong anti-correlation. Our results show that the coupling changes sign during the evolution at about the 1σ level, i.e., the energy transfer is from dark matter to dark energy when dark matter dominates the universe and the energy transfer is from dark energy to dark matter when dark energy dominates the universe.     

NMR Studies of Agricultural Compounds. Applications of Achiral and Chiral Lanthanide Shift Reagents to the Herbicide,Fenoxaprop-Ethyl

The 200 MHz H NMR spectra of the herbicide, fenoxaprop-ethyl, 1, have been studied in CDCl₃ solution at ambient temperatures as the racemic ester free base with the added chiral lanthanide shift reagent (LSR), tris [3 - (heptafluoropropylhydroxymethylene) - (+) - camphorato]europium(III), Eu(HFC)₃, 2, with some additional runs using the achiral LSR, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium(III), Eu(FOD)₃, 3, for supplemental spectral simplification. With 2, definite enantiomeric shift differences (ΔΔδ) were observed only for the CH₃CH₂O resonance. Although increased spectral complexity for the CH₂O signal was seen with added 2, this could have resulted from anisochrony of the diastereotopic protons, H_a and H_b, of this methylene group rather than true ΔΔδ, since the achiral 3 led to near-baseline separation between the CH_aH_bO signals. Lanthanide-induced shift (LIS) magnitudes were interpreted as consistent with predominant LSR binding at the ester carbonyl.     

Specificity of magnetoelectric effects in a new GdMnO<Subscript>3</Subscript> magnetic ferroelectric

A complex study of the magnetic, electric, magnetoelectric, and magnetoelastic properties of GdMnO₃ single crystals has been performed in the low-temperature region in strong pulsed magnetic fields up to 200 kOe. An anomaly of the dielectric constant along the a axis of a crystal has been found at 20 K, where a transition from an incommensurate modulated phase to a canted antiferromagnetic phase, as well as electric polarization along the a and b axes of the crystal induced by the magnetic field H‖ b (H_cr ～ 40 kOe), is observed. Upon cooling the crystal in an electric field, the magnetic-field-induced electric polarization changes its sign depending on the sign of the electric field. The occurrence of the electric polarization is accompanied by anisotropic magnetostriction, which points to a correlation between the magnetoelectric and magnetoelastic properties. Based on these results, it has been stated that GdMnO₃ belongs to a new family of magnetoelectric materials with the perovskite structure.     

Planar ferromagnets: Low-velocity kink dynamics near to the easy plane and static solitary spin structures bifurcating from the azimuthal kink

Ferromagnetic spin chains with planar single ion anisotropy, exchange anisotropy and with an external fieldb applied in the easy plane are considered in classical continuum approximation. It is pointed out that in the static case the sine-Gordon approximation is only accidentally exact: it breaks down in the neighborhood of the easy plane already for infinitesimal kink velocities, unlessb0. It is also shown that at certain valuesb _n ,n=0, 1, 2, 3, ... of the applied field there bifurcate from the static in-plane kink (azimuthal kink) other static out-of-plane kink solutions. The azimuthal kink is linearly stable below the critical strengthb ₀ of the applied field. For increasingb, there occurs at each of the bifurcation fieldsb ₁<b ₂<b ₃... an instability with respect to an additional mode. In the undamped system the instabilities atb _2k ,k=0, 1, 2, ... are associated with the recently discovered soft-velocity change mechanism of the critical slowing-down, whereas atb _2k+1 , soft localized dynamic modes occur. If phenomenological spin damping is included, soft relaxation modes occur in the neighborhood of all the bifurcation fields.Work supported by the Swiss National Science Foundation     

Pinning of vortices and penetration of the magnetic field into a periodically modulated long Josephson contact

The upper field of the Meissner regime, H _up, and overheat field H′_c1, above which vortices start penetrating into a Josephson contact, are calculated throughout the range of pinning parameter I. The stability of likely configurations is investigated. It is shown that H _up = H′_c1 at any I. The existence of a single vortex centered at the extreme cell in the contact is demonstrated to be a possibility. At I > 3.69, such a vortex may exist even in a zero magnetic field. At 1.48 < I < 3.69, this vortex can exist in an external field in the range from some H _v to H _up. At I < 1.48, the vortex cannot exist under any conditions. From the equality of H _up and H′_c1 at any I, the conclusion is drawn that penetration of vortices into any Josephson medium is conditioned by the need to satisfy flux quantization conditions. Here, not the forces of vortex pinning at defects in the medium but quantization requirements are of major importance, which are satisfied in specific quantum ways rather than by meeting equilibrium conditions for vortices, forces, etc.     

Interrelation of anisotropy of magnetic properties and magnetodielectric effect in a Cu<Subscript>3</Subscript>B<Subscript>2</Subscript>O<Subscript>6</Subscript> single crystal

The effect of an external magnetic field on permittivity has been studied in a Cu₃B₂O₆ single crystal with a layered structure in the direction perpendicular to layers (bc-planes). It has been found that the appreciable magnetodielectric effect in the temperature range below the Néel temperature (≈10 K) takes place only at one magnetic field orientation H and one crystallographic direction, i.e., H || b. Such “selectivity” of the magnetodielectric effect correlates with the anisotropic behavior of magnetic properties of the crystal.     

关于晶体管最高振荡频率有关因素的测量分析

本文讨论了晶体管最高振荡频率有关因素的一种测量分析方法。利用在基极和集电极迴路中串入外加串联电阻后测量最高振荡频率的变动,可以同时获得晶体管共发射极短路电流放大零增益频率f_T、基极电阻γ_b、集电极电容C_c以及本征的特性频率f_Td。讨论了当基极层厚度调制作用所致的集电极电导起作用时的分析方法。最后分析了漂移晶体管最高振荡频率与晶体管外部参数的关系,结果说明,上述方法在考虑了适应于漂移晶体管的修正步骤后,除同样能得到f_Td、γ_b、C_c等有关参数外,还可以分析得出漂移晶体管基极层中的漂移电场强度。