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首页> 外文学位 >Magnetic thermal hysteresis in dysprosium, gadolinium and gadolinium/dysprosium/gadolinium nanolayers and experimental determination of thermodynamic properties of thin film systems.
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Magnetic thermal hysteresis in dysprosium, gadolinium and gadolinium/dysprosium/gadolinium nanolayers and experimental determination of thermodynamic properties of thin film systems.

机译：nano 、,和// dy / ga纳米层中的磁热滞后效应以及薄膜系统热力学性质的实验测定。

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摘要

Magnetic thermal hysteresis (MTH) is observed when the temperature dependent magnetic properties of a material are reliant on the starting point of the measurement. MTH was observed in thin film Dy samples at low values of constant external magnetic field strengths using a Superconducting Quantum Interference Device (SQUID magnetometer). The temperature is changed from 20K to 300K back to 20K under a constant field. In these temperature sweeps differences in magnetic moment were observed near the low end of the temperature range starting around 150K. However, when starting at the high end of the temperature scale and making the same measurements this separation is not observed. The large difference in moment at low temperature can also be controlled by the magnitude of the external field strength. In the Dy films the existence of Alternate Helicity (AH-state) a shifting of the easy magnetization axis and a Helical (H-state) are the primary causes for the existence of the observed MTH. In Gd helical magnetization states do not exist but to a small extent the Gd films also show thermal hysteresis, over a smaller temperature range. Measurements of three layer systems which consist of a Dy film between two Gd films showed noticeable differences in the forward and return paths of the moment vs. temperature M(T) graphs consistent with the effects seen in the individual films. The effects of the individual films are easily distinguished in the three layer system. This cumulative effect can be controlled by modifying the layer thickness and therefore changing the shape and size of the observed magnetic thermal hysteresis. In addition to this a series of measurements was done to find a simplified means for calculating otherwise difficult thermodynamic properties of a system such heat capacity and entropy. A dataset consisting of multiple field hysteresis M(H) loops was made and by using the well known Maxwell relationships, for a magnetic system, the necessary calculations are done to find these otherwise intricate functions.
机译：当材料的温度相关磁性能依赖于测量的起点时，会观察到磁热滞（MTH）。使用超导量子干涉仪（SQUID磁力计）在薄膜Dy样品中以恒定外部磁场强度的低值观察到MTH。在恒定磁场下，温度从20K变为300K，再回到20K。在这些温度扫描中，在大约150K左右的温度范围的低端附近观察到了磁矩差异。但是，当从温度标尺的高端开始并进行相同的测量时，不会观察到这种分离。低温下的大力矩差也可以通过外部场强的大小来控制。在Dy薄膜中，交替螺旋（AH状态）的存在，易磁化轴的移动和螺旋（H状态）的存在是观察到的MTH存在的主要原因。在Gd中不存在螺旋磁化状态，但在较小的温度范围内，Gd膜在较小程度上也显示出热磁滞现象。由两片Gd薄膜之间的Dy薄膜组成的三层系统的测量结果显示，力矩与温度的M（T）曲线的前向和返回路径存在明显差异，这与各个薄膜中看到的效果一致。在三层系统中，可以轻松地区分各个胶片的效果。可以通过修改层的厚度并因此更改观察到的磁热滞后的形状和大小来控制这种累积效应。除此之外，还进行了一系列测量，以找到简化的方法来计算系统的其他困难的热力学性质，例如热容和熵。制作了一个由多个磁场磁滞M（H）回路组成的数据集，并通过使用众所周知的麦克斯韦关系，对一个磁系统进行了必要的计算，以找到这些其他复杂的函数。

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  • 作者

    Ross, Ajani Luister Walden.;

  • 作者单位

    The University of Texas at Arlington.;

  • 授予单位 The University of Texas at Arlington.;
  • 学科 Physics General.;Engineering Materials Science.;Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 148 p.
  • 总页数 148
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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