首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 390 毫秒
1.
The surface energy density, γ, of domain walls in thin uniaxial films with perpendicular easy axis is usually found either by measurements of the domain pattern period of the stripe domain pattern or by determination of the bubble collapse field and diameter. However, when the saturation magnetization is large, the widths of stripe domains and bubbles become smaller than the minimum optical resolution, and optical observation becomes impossible. The method proposed in this paper is based on measurements of the susceptibility S = d (M/Ms)/d(Ha/4πMs) of the stripe pattern at M = 0. Optical observations are avoided. The only additional important quantities are the saturation magnetization Ms and the film thickness. The method has been successfully applied to MnBi films (Ms = 625 G). The determination of γ in this material yields γ = (15 ± 1) erg/cm2.  相似文献   

2.
A review of domain structures and magnetization processes in permalloy overlays is given, together with some new results. The simplest domain structure for a given element consists of a loop of magnetic flux, but in elements with irregular geometry the circulating flux is not constant. More complex structures arise when an element contains internal closure domains. In-plane anisotropy in permalloy affects the distribution of closure domains but with decreasing bar width the influence of anisotropy is reduced. Reversible wall motion in weak fields gives way to hysteresis effects when the applied field exceeds a certain level, Hs. In particular magnetization buckling may occur. Some details of buckling in asymmetric chevrons and half-discs are given and compared with the behaviour in an I-bar. The proximity of a bubble medium containing stripe domains is shown to reduce considerably the applied fields needed for buckling in overlay components. Following saturation, changes in the demagnetized state are usually apparent. On a simple level, the spin structure and polarity of Bloch walls is altered. More noticeably the wall pattern itself can change when closure domains are created or annihilated in pairs. The significance of these fluctuations for bubble propagation is assessed by considering the intrinsic stray field profile of a Bloch wall segment. A simple wall model is employed. It is demonstrated that a curved domain wall provides a reasonable basis for modelling the field of a magnetized bar up to saturation. Calculated values of Hs agree qualitatively with experiment. The external field of the bar is rather insensitive to the exact distribution of free-pole density. Together with the observed complexities of domain behabiour this reaffirms the validity of the continuum approach to modelling.  相似文献   

3.
霍素国  聂向富  韩宝善 《物理学报》1991,40(12):2012-2017
实验研究面内场Hin和静态偏磁场Hb作用下,(111)面磁泡膜内条畴的消失过程。保持Hb恒定,增加Hin,测量条畴消失场Hs*和泡畴消失场Hk*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Hin和Hb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 βn=1/3(2nπ±arc cos│3/(21/2)(MsHb)/K1│)(n=0,±1,±2,…)与实验基本符合。 关键词:  相似文献   

4.
邓娅  赵国平  薄鸟 《物理学报》2011,60(3):37502-037502
本文以界面交换耦合常数Ji和软磁相厚度Ls为主要参变量,研究了易轴与膜面平行情况下的Nd2Fe14B/α-Fe磁性多层膜的磁矩随外场变化的取向及磁滞回线,并得到了成核场的解析公式.分析发现,Ji对磁矩取向、钉扎场和矫顽力机理有着较大的影响.当Ls较小时,钉扎场等于成核场,随着Ji的减小 关键词: 成核场 钉扎场 矫顽力 磁滞回线  相似文献   

5.
在室温条件下用自己研制的超快电子衍射实验设备精确测量了金属铝的电子格林艾森常数(γe).当飞秒脉冲激光瞬间加热铝膜时,电子和晶格对固体热膨胀的作用在时间域上是不同步的,借助于超快电子衍射实验设备的高时间分辨能力,可以摆脱以往测量非磁性金属材料时低温的限制,在室温条件下,实验通过直接观测瞬间加热的铝膜中电子和晶格对热膨胀的不同贡献得到电子的格林艾森常数. 关键词: 格林艾森常数 超快电子衍射 晶格热运动 电子热运动  相似文献   

6.
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Hs*和磁畴消失场Hk*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Hs*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:Hk*<110>=Hs*<110>=Hk{1+(k1/2Ku)-[al/h(4πMs/Hk)2]2/3},此式与实验结果符合得相当好。 关键词:  相似文献   

7.
运用微磁学方法结合物质参数探究了垂直取向Nd2Fe14B/α-Fe磁性三层膜的磁化反转过程,计算出成核场、钉扎场以及磁滞回线随s(软磁相厚度)的变化,并与相关的实验和理论数据进行比较.由于考虑了退磁能量项,垂直取向的成核场比平行取向时低,在外磁场还没有反向时就发生了成核.随着软磁相厚度的增加,理论矫顽力从等于成核场(同时也等于钉扎场),到等于钉扎场,再到小于钉扎场,矫顽力机理由成核变为钉扎. 关键词: 成核场 钉扎场 矫顽力 磁滞回线  相似文献   

8.
Radiofrequency pulse sequences are described which have the same overall effect as a single 90° or 180° pulse but which compensate the undesirable effects of resonance offset and spatial inhomogeneity of the radiofrequency field H1. These “composite” pulses are built up from a small number of conventional pulses which rotate the nuclear magnetization vectors about different axes in the rotating frame, while in the intervals between pulses a limited amount of free precession may be allowed to occur. Insight into the way in which pulse imperfections are compensated is obtained by computer simulation of trajectories of families of nuclear spin “isochromats” representing a distribution of H1 intensity or resonance offset. Composite 90° pulses are suggested as a method of reducing systematic errors in spin-lattice relaxation times derived from progressive saturation or saturation-recovery experiments, and as the preparation pulse of a spin-locking experiment. A test of the effectiveness of the composite 180° pulse sequence has been made by using it for population inversion in a spin-lattice relaxation measurement, where T1 is derived from the null point in the recovery curve, a technique known to be very sensitive to pulse imperfections.  相似文献   

9.
Surface magnetoelastic Love waves and nonuniform distributions of the magnetization and elastic strains are investigated in a uniaxial ferromagnetic film on a massive nonmagnetic substrate in a tangential external magnetic field. A new inhomogeneous phase is predicted having spatial modulation of the order parameter, arising from magnetostrictive coupling of the magnetization with lattice strains near the interface of the magnetoelastic and elastic media. It is shown that, at some critical magnetic field H c, different from the orientational transition field in an isolated sample, a magnetoelastic Love wave propagating parallel to the magnetization vector in the film plane becomes unstable. The frequency and group velocity of the wave vanish at wave number k=k c≠0 and the wave freezes, forming a domain structure localized in the film and adjoining substrate. Fiz. Tverd. Tela (St. Petersburg) 41, 665–671 (April 1999)  相似文献   

10.
Within the Franck–Condon approximation, the single ionisation of H2 leaves H+2 in a coherent superposition of 19 nuclear vibrational states. We numerically design an optimal laser pulse train to transfer such a coherent nuclear wave packet to the ground vibrational state of H+2. Frequency analysis of the designed optimal pulse reveals that the transfer principle is mainly an anti-Stokes transition, i.e. the H+2 in 1sσg with excited nuclear vibrational states is first pumped to 2pσg state by the pulse at an appropriate time, and then dumped back to 1sσg with lower excited or ground vibrational states. The simulation results show that the population of the ground state after the transfer is more than 91%. To the best of our knowledge, this is the highest transition probability when the driving laser field is dozens of femtoseconds.  相似文献   

11.
韩宝善  聂向富  唐贵德  奚卫 《物理学报》1985,34(11):1396-1406
实验研究了一次脉冲偏场作用下外延石榴石膜硬磁泡的形成规律。通过实验和计算,证明了硬泡畴壁中同号的VBL一般地说并非一个脉冲产生一对。通过双重曝光照相法揭示出软畴段的硬化与畴段运动形式的关系,发现了最适于硬泡形成的两种运动形式,并阐明了“软硬磁泡形成的分界场”H[b]的物理意义。 关键词:  相似文献   

12.
It is shown that in the presence of superflow, υs, parallel to a strong magnetic field H (|H| ? 20 Oe), the uniform texture becomes unstable againts the formation of a one dimensional soliton lattice forυs ? υc2 (≈1 mm/s). The period of the resulting soliton lattice as well as the related NMR frequencies are determined as functions of υs.  相似文献   

13.
Positive exchange bias field (He) is observed in Tb/Cr (tCr)/FeCo trilayers at 5 K without cooling field, and negative He for Tb/FeCo bilayer. The negative He of Tb/FeCo implies the FM coupling at the interface due to Co and Fe dominate in the magnetization of the ferrimagnetic interlayer alloy of FeCo and Tb. With the inserting of Cr layer, this situation is broken, and the positive He implies the antiferromagnetic interlayer coupling. A peak of He = 6.0 mT for trilayers with tCr = 1.5 nm is corresponding to the minimum value of coercivity as a function of tCr at 5 K, which is used to study the effect of the cooling field (Hfc) on He as a function of temperature. It is found that Hfc of 100 mT triggers He from positive to negative at T ≤ 15 K. The magnetoresistance results also confirm the coexistence of multiple MR mechanisms in these trilayers.  相似文献   

14.
A MHD, symmetrical, nonpotential waves in nonuniform, cylindrical nonisothermal plasma waveguide placed in a finite external magnetic field H 0 directed along the axis of the waveguide are considered. The thermal velocity of the electrons νTe = (kTe/me)1/2 (k — Boltzman's constant, Te — temperature, me — mass of the electron) is not neglected. As a consequence we obtain one more solution in the plasma region and respectively an equation of third power on χ2 — the transverse wave number. As far as we know only equations of second power on χ2 describing non-potential waves are investigated. The dispersion equations are written solving the boundary-value problem. Our results coincide with well known ones when the electron thermal velocity tends to zero.  相似文献   

15.
邢峰  何文望 《物理学报》1990,39(6):169-174
本文中研究了从Nd14Fe78B8过渡到Nd14Fe78C8时化合物的晶体结构与内禀磁性。指出轻稀土-Fe-C化合物形成P42/mnm型四方结构的结晶学条件在于适当的热处理温度。在Nd14Fe78B8-xCx系列中,随着C含量的增加,居里温度略有减少,饱和磁化强度σs出现一个平缓的峰值变化,室温下的剩磁σr、内禀矫顽力 iHe和磁晶各向异性场Ha都明显增大。含碳样品的各向异性行为与Nd-Fe-B相似,室温下易磁化方向沿e轴,低温下易轴各向异性转变成易锥型。自旋再取向温度随C的增加逐渐降低,但1.5K下的锥角有轻微的增大,这表明在Nd和Fe次晶格的各向异性之间存在着复杂的耦合。此外,适当富Nd的Nd-Fe-C化合物有强的各向异性。 关键词:  相似文献   

16.
The electronic Grüneisen parameter, γ e , is a fundamental parameter characterizing the relationship between thermal expansion and electronic specific heat. Conventionally, γ e is measured at low temperatures for minimizing the lattice contribution to thermal expansion. In this paper, we extract γ e by separating the electron and lattice contributions in time domain using ultrashort pulse excitation. We show that γ e cannot be considered as a constant during the electron-lattice thermal nonequilibrium state. Instead, a revised expression for γ e is proposed for the non-equilibrium electron–phonon system.  相似文献   

17.
The gain saturation in the 46.9 nm line of the Ar+8 laser is analyzed using an atomic kinetics code. The dependence of the gain (G) on the electron kinetic temperature (Te) in the region (50 ‐150 eV) is calculated in the quasi steady‐state approximation for the different values of the electron density (Ne) and the plasma radius (rpl). The influence of radiat on trapping, ion random and mean velocities, Stark line broadening and refraction losses on the gain saturation is taken into consideration. For rpl = 150‐600 μm, the amplplication (G > 0 cm‐1) exists in the large temperature/density domain (Te = 60‐150 eV, Ne = 0.5‐10 × 1018 cm‐3). However, the value Gs ∼ 1.4 cm‐1 required for the gain saturation at the typical plasma length Lpl ∼ 15 cm is reached in the extremely narrow density regions at the high temperatures. The saturation is reached for rpl = 600 μm at Tse = 150 eV in the region Nse = 1.8‐2 × 1018 cm ‐3, for rpl = 300 μm at Tse = 125 eV and Nse = 2.5‐3 × 1018 cm‐3, and for rpl = 150 μm at Tse = 110 eV and Nse = 3‐4 × 1018 cm‐3. The broadest density region (Nse = 2 ‐8 × 1018 cm‐3) is predicted for the narrowest column (rpl = 150 μm) at the highest temperature (Tse = 150 eV). The operation in the broadest density region Nse, should make easier achievement of the gain saturation in the experiments.  相似文献   

18.
The time dependence of remanence coercivity and thermal stability were investigated for hard/soft-stacked media consisting of a magnetically hard granular layer underneath a very thin soft layer with a large saturation magnetization, Ms. The values of remanence coercivity at measurement times t′=103 and 10−5 s (pulse field) were measured, and defined as Hr and HrP. The remanence coercivity on the recording time scale, Hr (1 ns), and the energy barrier, ΔE/kT, were evaluated by fitting Hr and HrP to Sharrock's equation taking into account the power law variation of the energy barrier, n. The value of Hr (1 ns) for a (Co–Pt)–SiO2 (9 nm)/Co–SiO2 (2 nm) stacked medium with an interfacial coupling control layer was about 9 kOe, which was less than half of that of a (Co–Pt)–SiO2 (9 nm) conventional medium (=21.3 kOe). The value of ΔE/kT for the stacked medium was about 111 (n=0.7), and was not significantly different from the conventional medium. Moreover, no significant difference in the rate of decrease of Hr with increasing temperature was observed between media with and without interlayers. These results indicate that the use of a thin soft layer with high Ms was effective at significantly reducing Hr with no notable change in thermal stability.  相似文献   

19.
The Fourier transform infrared (FTIR) spectra and switching current response in sodium nitrite:poly(vinyl alcohol) nanocomposite films have been studied as a function of composition of NaNO2. The switching current data fitted well to infinite-grain model (IGM) in the region t<t s and to finite-grain model (FGM) in the region tt s . The microscopic parameters like the dimensionality, the domain wall velocity, and the nucleation rate have been evaluated which provide more physical insight of the switching phenomena in the composite films. The polarization current and nucleation rate are optimum in 50 wt.% composite film and have been discussed in terms of grain size and strain variations with the composition. The effect of applied field and pulse width variation on the switching behavior of 50 wt.% composition has also been studied. The exponential field dependence of the domain wall velocity and the nucleation rate indicate that nucleation mechanism is responsible for switching phenomena in the composite films. The writing pulse width affects significantly on the switching behavior of the composite films.  相似文献   

20.
Accurate measurements of magnetic aftereffect and coercivity in a magnetic bubble garnet are presented in the temperature range (-35°C, +60°C). The bubble material is an epitaxial Y2.6Sm0.4Ga1.1Fe3.9O12 composition supporting 4 μm bubbles. The duration of the drive field pulse is varied between 100 ns and 2 ms. The curves taken at different temperatures of the minimum drive field duration versus its amplitude show similar hyperbolic shape. They are shifted towards small magnetic fields when the temperature increases. The experimental data are compared with a phenomenological model based on thermal activation. A good fit is obtained by taking the values at 20°C as a reference and comparing the experimental data with the calculated values for the different temperatures.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号