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301.
各向异性材料模型的一般计算方法需要编辑偏轴坐标系中的弹性矩阵,其推导过程十分复杂.针对这一问题,提出了一种基于FEM软件中两个坐标系(基本坐标系与辅助坐标系)的新方法.FEM软件自动转换两个坐标系的关系,因此该方法没必要编辑偏轴坐标系中的弹性矩阵,可简化各向异性模型的计算过程.计算结果很好地反映了各向异性材料的方向变化对巷道围岩应力分布的影响. 相似文献
302.
B. Borca O. Fruchart E. Kritsikis F. Cheynis A. Rousseau Ph. David C. Meyer J.C. Toussaint 《Journal of magnetism and magnetic materials》2010,322(2):257-264
We report a detailed magnetic study of a new type of self-organized nanowires discussed briefly previously [B. Borca et al., Appl. Phys. Lett. 90 (2007) 142507]. The templates, prepared on sapphire wafers in a kinetically limited regime, consist of uniaxially grooved W(1 1 0) surfaces, with a lateral period here tuned to 15 nm. Fe deposition leads to the formation of (1 1 0) 7 nm-wide wires located at the bottom of the grooves. The effect of capping layers (Mo, Pd, Au, Al) and underlayers (Mo, W) on the magnetic anisotropy of the wires was studied. Significant discrepancies with figures known for thin flat films are evidenced and discussed in terms of step anisotropy and strain-dependent surface anisotropy. Demagnetizing coefficients of cylinders with a triangular isosceles cross-section have also been calculated, to estimate the contribution of dipolar anisotropy. Finally, the dependence of magnetic anisotropy with the interface element was used to tune the blocking temperature of the wires, here from 50 to 200 K. 相似文献
303.
C. Meyer B.J. Ruck G.V.M. Williams 《Journal of magnetism and magnetic materials》2010,322(14):1973-1978
We report a magnetization study of stoichiometric ErN nanocrystalline films grown on Si and protected by a GaN passivating layer. According to the temperature dependence of the resistivity the films are heavily doped semiconductors. Above 100 K the magnetization data fit well to a Curie-Weiss behavior with a moment expected within the free-ion Er3+ multiplet. Below 50 K the Curie-Weiss plot steepens to an effective moment corresponding to that in the crystal-field determined quartet ground state, and develops a clear paramagnetic Curie-Weiss temperature of about 4.5 K. Zero-field- and field-cooled magnetization curves and the AC susceptibility firmly establish a ferromagnetic ground state within that multiplet below a Curie temperature of . Due to the (1 1 1) texture of the film the comparison between the magnetization behavior, when the field is applied parallel and perpendicular to the film plane, gives new information about the magnetic structure. An arrangement of the moments according to the model derived from neutron diffraction for bulk HoN is strongly suggested. 相似文献
304.
Epitaxial Fe(1 1 0) films with thicknesses of 100-800 nm on Cu(0 0 1) and Ni(0 0 1) buffer layers grown on MgO(0 0 1) substrates have been fabricated. These films contain Fe(1 1 0) crystallites which are in the Pitsch orientation relationship. Magnetization and the fourfold in-plane magnetic anisotropy constants of these films have been determined by torque measurements. All the samples under study are characterized by a fourfold magnetic anisotropy with easy axes parallel to the [1 0 0] and [0 1 0] directions of Cu(0 0 1) and Ni(0 0 1) layers. The measured values of the constant for Fe(1 1 0)/Cu(0 0 1) are found to depend on deposition temperature; a maximum value of (2.5±0.1)×105 erg/cm3 is reached after annealing at 600 °С. The in-plane torque measurements on Fe(1 1 0)/Ni(0 0 1) bilayers obtained at 300 °С, on the other hand, exhibit a constant value of (2.7±0.1)×105 erg/cm3. Assuming an exchange interaction between the Fe(1 1 0) crystallites, which are in the Pitsch orientation relationship, the fourfold in-plane magnetic anisotropy has been calculated as 2.8×105 erg/cm3. The deviations of the experimental values from the predicted one may be explained by the formation of a polycrystalline phase within the Fe(1 1 0) layer and a partial disorientation of the epitaxial crystallites. 相似文献
305.
306.
Jihong Chen Yuwei Li Baoshan Zhang Yi Yang Mu Lu Huaixian Lu 《Journal of magnetism and magnetic materials》2010,322(20):3109-3111
[NiO/Fe65Co35]10 exchange-coupled multilayer films for high frequency applications are fabricated, and their static magnetic property and microwave permeability are studied systematically. Both exchange bias field and ferromagnetic resonance frequency of the multilayers increase with decreasing Fe65Co35 thickness, which means that the microwave properties such as permeability and FMR frequency can be controlled by changing Fe65Co35 thickness in the exchange-coupled films. Ferromagnetic resonance frequencies beyond 7 GHz of the films are measured and reported for the first time. 相似文献
307.
L. Chen 《Journal of magnetism and magnetic materials》2010,322(21):3250-3254
We present a study of magnetic anisotropy by using magneto-transport and direct magnetization measurements on tensile strained (Ga,Mn)As films. The magnetic easy axis of the films is in-plane at low temperatures, while the easy axis flips to out-of-plane when temperature is raised or hole concentration is increased. This easy axis reorientation is explained qualitatively in a simple physical picture by Zener’s p-d model. In addition, the magneto-crystalline anisotropic resistance was also investigated experimentally and theoretically based on the single magnetic domain model. The dependence of sheet resistance on the angle between the magnetic field and [1 0 0] direction was measured. It is found that the magnetization vector M in the single-domain state deviates from the external magnetic field H direction at low magnetic field, while for high magnetic field, M continuously moves following the field direction, which leads to different resistivity function behaviors. 相似文献
308.
The out-of-plane magnetic anisotropy and out-of-plane magnetization reversal process of nanoscale Ni80Fe20 antidot arrays deposited by magnetron sputtering technique on an anodic aluminum oxide (AAO) membrane are investigated. The angular dependence of out-of-plane remanent magnetization of Ni80Fe20 antidot arrays shows that the maximum remanence is in-plane and the squareness of the out-of-plane hysteresis loop follow a |cos θ| dependence. The angular dependence of out-of-plane coercivity of Ni80Fe20 antidot arrays shows that the maximum coercivity lies on the surface of a cone with its symmetric axis normal to the sample plane, which indicates a transition of magnetic reversal from curling to coherent rotation when changing the angle between the applied magnetic field and the sample plane. 相似文献
309.
Savannah C. Partridge Revathi S. Murthy Ali Ziadloo Steven W. White Kimberly H. Allison Constance D. Lehman 《Magnetic resonance imaging》2010
Purpose
The objective of this study was to evaluate diffusion anisotropy of the breast parenchyma and assess the range and repeatability of diffusion tensor imaging (DTI) parameters in normal breast tissue.Materials and Methods
The study was approved by our institutional review board and included 12 healthy females (median age, 36 years). Diffusion tensor imaging was performed at 1.5 T using a diffusion-weighted echo planar imaging sequence. Diffusion tensor imaging parameters including tensor eigenvalues (λ1, λ2, λ3), fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured for anterior, central and posterior breast regions.Results
Mean normal breast DTI measures were λ1=2.51×10−3 mm2/s, λ2=1.89×10−3 mm2/s, λ3=1.39×10−3 mm2/s, ADC=1.95±0.24×10−3 mm2/s and FA=0.29±0.05 for b=600 s/mm2. Significant regional differences were observed for both FA and ADC (P<.05), with higher ADC in the central breast and higher FA in the posterior breast. Comparison of DTI values calculated using b=0, 600 s/mm2 vs. b=0, 1000 s/mm2, showed significant differences in ADC (P<.001), but not FA. Repeatability assessment produced within-subject coefficient of variations of 4.5% for ADC and 11.4% for FA measures.Conclusion
This study demonstrates anisotropy of water diffusion in normal breast tissue and establishes a normative range of breast FA values. Attention to the influence of breast region and b value on breast DTI measurements may be important for clinical interpretation and standardization of techniques. 相似文献310.
本文在一维海森堡模型的基础上,采用界面参数化方法,研究了铁磁/反铁磁双层薄膜中自旋波低温激发问题.重点讨论了表面各向异性对薄膜中自旋波共振谱的影响.结果表明:体系中的自旋波本征模存在共振行为,表面各向异性场对体模、完全禁闭模的共振谱影响较大,对界面模没有影响. 相似文献