Investigation of L1_0 FePt-based soft/hard composite bit-patterned media by micromagnetic simulation

The soft/hard composite patterned media have potential to be the next generation of magnetic recording, but the composing modes of soft and hard materials have not been investigated systematically. L10 FePt-based soft/hard composite patterned media with an anisotropic constant distribution are studied by micromagnetic simulation. Square arrays and hexagonal arrays with various pitch sizes are simulated for two composing types： the soft layer that encloses the hard dots and the soft layer that covers the whole surface. It is found that the soft material can reduce the switching fields of bits effectively for all models. Compared with the first type, the second type of models possess low switching fields, narrow switching field distributions, and high gain factors due to the introduction of inter-bit exchange coupling. Furthermore, the readout waveforms of the second type are not deteriorated by the inter-bit soft layers. Since the recording density of hexagonal arrays are higher than that of square arrays with the same center-to-center distances, the readout waveforrns of hexagonal arrays are a little worse, although other simulation results are similar for these two arrays.

图案化介质磁盘-磁头气体润滑动态特性分析

在小扰动条件下,提出应用偏导数法在复数域内求解可压缩气体润滑的动态Reynolds方程,以计算任意磁盘表面形状的磁盘-磁头气膜润滑的动态刚度和阻尼系数。以圆柱形和立方形比特图案化介质(BPM)磁盘为研究对象,研究了磁单元尺寸参数对气膜动态系数的影响,并比较了两种BPM对应的动态性能。数值结果表明,与光滑磁盘相比,图案化介质磁盘对应的气膜润滑动态刚度系数和阻尼系数大大减小,且随磁单元高度增大,动态系数逐渐减小。相比圆柱形BPM,立方形BPM对应的气膜具有较大动态刚度和阻尼系数,计算结果可为图案化介质磁盘的设计提供重要的理论依据。

比特图案化介质磁盘-磁头的气膜静态特性研究

为了研究比特图案化介质磁盘(bit pattern media,BPM)对磁头静态性能的影响,采用有限元法和牛顿-拉普森迭代法,对不同BPM结构和几何尺寸对应的磁头静态特性进行了计算。研究结果表明,与光滑磁盘相比,在立方形BPM上飞行的浮动块上靠近读写磁头中心区域的表面压力分布呈现离散化特征。随BPM磁单元高度增加,浮动块的最小气膜厚度和气膜承载力逐渐减小,而最大气膜压力等性能的变化则与磁单元分布密切相关。与圆柱形BPM的对比发现,立方形BPM在较小的浮动块翻转角下具有较大的最大气膜压力、承载力和最小气膜厚度,其对应的浮动块具有比圆柱形BPM更好的静态性能,这对BPM的结构及几何参数的设计有重要意义。

Nd_2Fe_(14)B图形化点阵的微磁学模拟

以微磁学理论为基础,详细研究了厚度不变,尺寸和间距的变化对Nd_2Fe_(14)B图形化点阵磁性能和磁反转过程的影响。结果显示,当点阵厚度(20 nm)和间距(30 nm)保持不变,随着点阵半径的增大,矫顽力和交换作用能降低,静磁能逐渐增大,磁化过程由一致反转的单畴态过渡到非一致反转的多畴态;保持点阵厚度(20 nm)和点阵半径(30 nm)不变,随着点阵间距的增大,磁耦合相互作用减弱,矫顽力逐渐增大,当间距增大到40~50 nm时,磁耦合相互作用基本消失,矫顽力基本不再发生变化。