共查询到19条相似文献,搜索用时 46 毫秒
1.
根据实验数据,构造了接近实际纳米晶永磁Pr2Fe14B的样品,用微磁学有限元法进行了模拟计算.计算结果表明,晶界处各向异性的下降会导致矫顽力减小、剩磁值增大,而晶界处交换作用常数的减小则会使剩磁值减小、矫顽力增大.通过对实验样品的模拟研究发现,晶界处各向异性和交换作用常数的共同减小能够同时拟合出真实的矫顽力和剩磁值.模拟计算与实验在退磁曲线形状上的差距则说明模拟还存在不足.
关键词:
纳米晶永磁
磁滞回线
矫顽力
剩磁 相似文献
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可逆磁化区对退磁过程的影响研究 总被引:1,自引:0,他引:1
静态磁化曲线与磁滞回线测量实验中,材料剩磁较小时(不超过2.5 mT)所需加的反向外磁场强度不易把握,很难实现完全退磁.结合原理,本文对退磁过程和可逆磁化区的关系进行了定量研究,结果表明:退磁过程所需加的最小有效反向外磁场强度与可逆磁化区到不可逆磁化区的临界外磁场强度近似相等,且该值接近材料矫顽力的0.55倍. 相似文献
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对于垂直磁记录薄膜,进行剩余磁化强度的测量时,必须补偿退磁场.提出一种新方法,在直流退磁剩磁和等温剩磁测量中采用有效反向磁场来直接补偿退磁场.从而可以正确地得出垂直磁记录薄膜的ΔM曲线并评价晶粒间的磁相互作用.还采用了三种方法来确定其中的关键参数——退磁因子.结果表明,c轴垂直取向的钡铁氧体薄膜中,晶粒间的磁相互作用是交换偶合型的;而Co-Cr-Ta薄膜中,晶粒间磁相互作用是静磁相互作用.
关键词:
退磁场补偿
直流退磁剩磁(DCD)
等温剩磁(IRM)
ΔM曲线 相似文献
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本文就纳米复合永磁材料中软磁相被交换硬化问题,从一维模型和三维模拟计算进行了分析研究. 一维和三维各向异性样品研究表明,在相同微结构下,当硬磁相的各向异性降低时,除矫顽力降低外,在磁矩全部反转之前退磁曲线是一样的. 因此,硬磁相各向异性的降低不会导致最大磁能积(BH)max增大和剩磁增加. 对于三维各向同性样品的模拟计算表明,降低硬磁相的各向异性会使剩磁和(BH)max都明显降低. 因此,增强硬磁相的各向异性并增大硬磁相晶粒尺寸是提高
关键词:
纳米复合永磁
矫顽力
剩磁
磁能积 相似文献
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研究了半掺杂相分离锰氧化物Eu0.5Sr0.5MnO3样品的结构和电磁输运特性.在半掺杂情况下,该样品呈O′型正交结构,表明样品存在典型的Jahn-Teller畸变;在75 K附近样品的顺磁/反铁磁背景中开始出现铁磁相,在更低的温度42 K,4000 A/m磁场下M-T的场冷曲线和零场冷曲线出现明显分岔,样品的交流磁化率实部随温度的变化曲线中也在42 K观察到尖峰的出现,表现出团簇玻璃行为.在无外加磁场下该样品在
关键词:
多相竞争
半掺杂
铁磁团簇 相似文献
9.
采用局域Monte Carlo方法模拟不同易轴分布的简单立方排列单分散单畴Fe纳米颗粒系统的ZFC-FC曲线及磁滞回线.结果表明:随着偶极相互作用的增强,系统的阻塞温度TB逐渐增大,且ZFC曲线的峰变宽.说明偶极相互作用使得系统的有效能垒提高,分布宽度增加.研究FC曲线磁化强度的倒数与温度关系,发现偶极相互作用系统中存在反铁磁有序.系统的阻塞态及超顺磁态的磁滞回线表明,极低低温下,随着偶极相互作用的增强,系统的矫顽力和剩磁减小,偶极相互作用阻碍系统的磁化;系统处于超顺磁态,各向异性作用及偶极相互作用使得系统的磁化曲线偏离Langevin曲线且偶极相互作用展现出退磁相互作用效应.偶极相互作用增强,系统磁化曲线与Langevin曲线偏差量的最大值向低场移动.在偶极相互作用下,易轴与外场夹角为45°的磁性纳米颗粒系统的平均有效能垒和有效能垒分布宽度较易轴随机分布系统的大. 相似文献
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The spin-flip (SF) Eliashberg function is calculated from first principles for ferromagnetic Ni to accurately establish the contribution of Elliott-Yafet electron-phonon SF scattering to Ni's femtosecond laser-driven demagnetization. This is used to compute the SF probability and demagnetization rate for laser-created thermalized as well as nonequilibrium electron distributions. Increased SF probabilities are found for thermalized electrons, but the induced demagnetization rate is extremely small. A larger demagnetization rate is obtained for nonequilibrium electron distributions, but its contribution is too small to account for femtosecond demagnetization. 相似文献
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The local demagnetization factor for the ring-core flux gate is derived analytically, based on a tangential magnetization model. The results are in good agreement with experimental data for a wide range of ring shape parameters. Approximate expressions in the limit of a narrow, thin ring are obtained, and indicate that the local demagnetization factor scales with the ratio of the cross-sectional area to the total area of the ring. Analytical modeling of the demagnetization factors for a uniform magnetization state results in an underestimate of the local cross-section averaged demagnetization factors by 50% or more. 相似文献
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Spin transfer-related phenomena in nanomagnets have attracted extensive studies. In this paper we shall focus on analysis of individual and combined effects of the external, anisotropy, and demagnetization fields on magnetization dynamics and spin transfer noise. It is found that individual roles of the external, anisotropy, and demagnetization fields, as well as the combined roles of external plus anisotropy fields and anisotropy plus demagnetization fields, do not change the behavior of current induced magnetization switching. Such magnetization reversal procedures are of low noise. Our dynamics and power spectral density calculations show that it is the demagnetization field that plays a major role in inducing spin transfer noise: the demagnetization field itself or in combination with the anisotropy field will result in wave-like switching; moreover, the demagnetization field, together with the external field (not too small), will lead to precession and hence the system would be in noisy states. Our modeling work for an elliptical Py alloy is qualitatively consistent with Cornell's experiment and simulation [Science 307 (2005) 228]. 相似文献
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The intrinsic angular-dependent hysteresis loops in perpendicular recording media have been measured by iteratively correcting the demagnetization effect in order to maintain the internal total field at a fixed angle. Both the angle and the magnitude of the applied field are adjusted simultaneously to compensate for the demagnetization field change. Significant differences have been observed between the conventional angular-dependent hysteresis loop with a constant applied field angle and the intrinsic angular-dependent hysteresis loop with a fixed total field angle. Without demagnetization corrections, the field range in which irreversible magnetization occurs changes as a function of the field angle, whereas it remains constant if proper demagnetization field corrections are applied. 相似文献
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《Current Applied Physics》2009,9(5):985-988
Solving the Landau–Lifshitz–Gilbert–Slonczewski equation numerically, we show that switching current density for the current-induced magnetization switching decreases by introducing the perpendicular anisotropy smaller than the out-of-plane demagnetization energy in the switched layer as predicted by theories. Interestingly, the introduction of the perpendicular anisotropy does not decrease the thermal stability of magnetization, but rather slightly increases. The reduction in switching current density results from the decrease of demagnetization effect whereas the increase of thermal stability results from the decrease of attempt frequency. 相似文献
17.
If one knows the diagram of demagnetization of the magnet in plastic binder and knows the packing density, the curve of demagnetization of the used magnetic powder can be plotted. This procedure may also be inverted. Using anisotropic magnets with binders, a technical sufficient orientation must be required for calculating the curve of demagnetization. By comparing calculated and measured values, defects of the base materials, grindet powder, granulate, molding process, or magnetic orientation may be become known and removed. 相似文献
18.
Laser-induced ultrafast demagnetization in ferromagnetic metals 总被引:1,自引:0,他引:1
The laser-induced femtosecond demagnetization in ferromagnetic metals is investigated theoretically. Different from the conventional nanosecond one, this ultrafast demagnetization is a cooperative effect of the external laser field and the internal spin-orbit coupling. The spin-orbit coupling smears out the original identities of triplets and singlets while the laser field uses it as an avenue to influence demagnetization. Importantly, this demagnetization can be manipulated controllably, an essential point to future applications, such as ultrafast control of magneto-optical gating. Finally, the polarization filter effect on the ultrafast time scale is discussed based upon the present theoretical results. 相似文献
19.
Magnetostatic self and interaction energies can be computed via demagnetization factors whenever the magnetic state is close to a uniform state, e.g. in the presence of a strong applied field, or when the dimensions involved are within the single-domain limit. We derive analytical expressions for the demagnetization factors of cylindrical shells and rings with rectangular and square cross-sections. The factors are given either as a combination of elliptic integrals or as a series expansion in powers of the dimensionless ratio between inner and outer radii. Limiting cases are analysed for particular ranges of the shape parameters. We also investigate the ring with a square cross-section, and the elliptic ring, where analytical expressions are provided only for small eccentricity. Finally, we introduce the dipolar coupling integral encoding magnetostatic interactions between a magnetized cylinder and a thin coating on its lateral surface. 相似文献