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首页> 外文学位 >Chromium-alloyed manganese bismuth thin films for blue-wavelength magnetooptical recording.
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Chromium-alloyed manganese bismuth thin films for blue-wavelength magnetooptical recording.

机译：用于蓝光磁光记录的铬合金锰铋薄膜。

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摘要

MnBi films have been considered for short-wavelength rewritable optical recording media due to the very large magneto-optical Kerr rotation and perpendicular anisotropy (Ku) of the hexagonal magnetic low temperature phase. However, coincident structural and magnetic transformations near 360°C and the presence of the MnBi-Bi eutectic at ∼270°C result in poor thermal cycling behavior, and have inhibited the application of MnBi thin films to high-density data storage. In this thesis, it is shown that partial substitution of Cr for Mn should both lower the Curie temperature (T C), and decouple the lattice and magnetic transitions, which would allow for reversible Curie point writing. It is found from magneto-optic measurements that 5% substitution of Cr for Mn reduces the apparent TC to ∼250°C, while retaining Kerr rotation angles greater than 1° at 633 nm and 0.7° at 370 nm. The magnitude of reduction was also theoretically confirmed by a bandstructure approach, which leads to a higher degree of confidence in the hypothesized effect of chromium in inducing antiferromagnetic interactions in the MnBi lattice. A high degree of perpendicular anisotropy is indicated from x-ray diffraction and magnetic measurements, while transmission electron microscopy (TEM) analyses indicate a small grain size (<50 nm) for the Cr alloyed MnBi films. In this thesis, the MnBi phase transformation problem and the magnetism in the crystal structure have been tackled in greater depth and with a greater degree of success than has been had in the past forty years. However, the increasing coercivity (HC) observed in both MnBi and (MnCr)Bi thin films, as the temperature is increased, is a potential obstacle to the application of these materials in conventional thermomagnetic Curie point writing. Furthermore, this unusual behavior calls into question the long-standing view that the transition is of the ferromagnetic-paramagnetic type. Nevertheless, it is demonstrated that Cr-alloyed MnBi films possess the favorable magneto-optical properties and uniaxial texture of MnBi while exhibiting the desirable characteristics of reduced TC, smaller lateral grain size and greater corrosion resistance.
机译：由于非常大的磁光Kerr旋转和六角形磁性低温相的垂直各向异性（Ku），已将MnBi膜用于短波长可重写光学记录介质。但是，在360°C附近同时发生结构和磁转变，以及在270°C左右存在MnBi-Bi共晶，导致热循环性能较差，并阻碍了MnBi薄膜在高密度数据存储中的应用。在本文中，表明用Cr替代Mn既可以降低居里温度（T C），又可以使晶格和磁跃迁解耦，这将允许可逆的居里点写入。从磁光测量发现，Cr取代Mn 5％可以将表观TC降低至〜250°C，同时在633 nm处保持Kerr旋转角大于1°，在370 nm处保持0.7°的Kerr旋转角。还原的幅度在理论上也通过能带结构方法得到了证实，这使人们对铬在MnBi晶格中诱导反铁磁相互作用的假设效应具有更高的置信度。 X射线衍射和磁测量表明高度垂直各向异性，而透射电子显微镜（TEM）分析表明Cr合金化MnBi膜的晶粒尺寸小（<50 nm）。与过去四十年来相比，本论文更深入地解决了MnBi相变问题和晶体结构中的磁性问题。但是，随着温度的升高，在MnBi和（MnCr）Bi薄膜中都观察到矫顽力（HC）的增加，这是这些材料在常规热磁居里点写入中应用的潜在障碍。此外，这种不寻常的行为使人们长期以来一直认为过渡是铁磁-顺磁类型的。然而，已证明铬合金化的MnBi膜具有良好的磁光性能和MnBi的单轴织构，同时表现出所需的TC降低，较小的横向晶粒尺寸和较大的耐蚀性。

著录项

  • 作者

    Bandaru, Prabhakar Rao.;

  • 作者单位

    University of California, Berkeley.;

  • 授予单位 University of California, Berkeley.;
  • 学科 Materials science.;Inorganic chemistry.;Electrical engineering.;Condensed matter physics.
  • 学位 Ph.D.
  • 年度 1998
  • 页码 162 p.
  • 总页数 162
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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