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The Changing Shape of Magnetic Refrigeration: an investigation of adaptive magnetic materials

磁制冷形状的变化：自适应磁性材料的研究

基本信息

批准号：
EP/J006750/1
负责人：
Julie Staunton
金额：
$ 41.81万
依托单位：
University of Warwick
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2012
资助国家：
英国
起止时间：
2012 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FJ006750%2F1
关键词：
Changing Shape Magnetic Refrigeration investigation

项目摘要

Modern cooling is based almost entirely on a compression/expansion refrigeration cycle - a technology more or less unchanged since its invention over a century ago. It is a high-energy demand industry which consumes billions of kWh every year. Yet, modern refrigeration is close to its fundamental performance limit which is well below what is thermodynamically possible. Furthermore, the liquid chemicals used as refrigerants, which eventually escape into the environment, are ozone layer depletive and global warming gases, or hazardous chemicals.Recently magnetic refrigeration has emerged as a promising way for a new and environmentally friendly solid state cooling technology. Prototype magnetic fridges have been demonstrated during the last decade. They have been proven to be much more energy efficient than conventional fridges and can span a broad temperature range around room temperature. But most prototypes use expensive rare earth metals such as gadolinium as the refrigerant and alternatives are urgently required. Several families of promising magnetic materials have been discovered but up to now this process has been a heuristic one. In this proposal we intend to establish an ab-initio quantum materials modeling tool to transform this process and to facilitate its application by groups working with magnetic materials. In the most suitable materials the interactions that underpin the magnetic properties have to be delicately poised and our modeling will need to be able to track and indicate their temperature dependence, how they vary with compositional and structural changes and/or when dopants are added. In a magnetic refrigerant randomly oriented magnetic moments in the material align when a magnetic field is applied making the solid warm up. By removing this heat using a heat transfer fluid, like water or air, and then removing the field allows the magnetic material to lower its temperature. The heat from the object being cooled is then extracted with the heat transfer fluid and the cycle completed. The changes in entropy and temperature that happen when a magnetic field is applied to a material describe the magnetocaloric effect and this proposal will determine it and the magnetic interactions behind it on a quantitative basis. Our results for several classes of materials will be tested against the extensive experimental data available. A particularly novel and ambitious part of the work will be to investigate how to nanostructure a large magnetocaloric effect. To this end we will study some rare earth - transition metal heterostructures and optimise the effect.This physics which produces a strong warming effect when a magnetic field is applied has another intriguing facet. It can explain how some of the most promising materials also change their shape significantly in the presence of a magnetic field. Such magnetoplastic, 'magnetic shape memory' effects have diverse potential technological applications, such as micropumps, sonars and magnetomechanical sensors. We will adapt our theoretical nanostructural modeling to investigate the strengths and anisotropies of the magnetic interactions across a boundary defect in the material and how they lead to the defect itself moving as a magnetic field is applied. A test case of a Ni-Mn-Ga Heusler alloy will be undertaken and the effect will be optimised as the composition of the alloy is varied.

现代冷却几乎完全基于压缩/膨胀制冷循环--自一个世纪前发明以来，这项技术或多或少没有改变。这是一个高能耗行业，每年消耗数十亿千瓦时。然而，现代制冷接近其基本性能极限，这远低于物理上可能的极限。此外，作为制冷剂的液体化学品，最终会逃逸到环境中，是破坏臭氧层和全球变暖的气体，或者是危险的化学品。最近，磁制冷已经成为一种新的和环境友好的固态冷却技术的有前途的方式。在过去的十年里，磁冰箱的原型已经得到了展示。它们已被证明比传统冰箱更节能，并且可以跨越室温附近的广泛温度范围。但大多数原型使用昂贵的稀土金属，如钆作为制冷剂，迫切需要替代品。已经发现了几个有前途的磁性材料家族，但到目前为止，这一过程一直是一个启发性的。在这个提议中，我们打算建立一个从头算量子材料建模工具来改变这个过程，并促进磁性材料研究小组的应用。在最合适的材料中，支撑磁性的相互作用必须保持微妙的平衡，我们的建模将需要能够跟踪和指示它们的温度依赖性，它们如何随着成分和结构的变化和/或添加掺杂剂而变化。在磁性制冷剂中，当施加磁场时，材料中随机取向的磁矩对齐，使固体升温。通过使用传热流体（如水或空气）去除这种热量，然后去除磁场，可以使磁性材料降低其温度。然后用传热流体从被冷却的物体提取热量，并完成循环。当磁场施加到材料上时，熵和温度发生的变化描述了磁热效应，该提案将定量地确定它及其背后的磁相互作用。我们的几类材料的结果将进行测试，对广泛的实验数据。这项工作的一个特别新颖和雄心勃勃的部分将是研究如何纳米结构化一个大的磁热效应。为此，我们将研究一些稀土-过渡金属异质结构并优化其效果。这种当施加磁场时产生强烈升温效应的物理学还有另一个有趣的方面。它可以解释一些最有前途的材料如何在磁场的存在下显着改变它们的形状。这种磁塑性的“磁性形状记忆”效应具有多种潜在的技术应用，例如微型泵、声纳和磁力传感器。我们将调整我们的理论纳米结构建模，以研究材料中边界缺陷的磁相互作用的强度和各向异性，以及它们如何导致缺陷本身在施加磁场时移动。将进行Ni-Mn-Ga Heusler合金的测试案例，随着合金成分的变化，效果将得到优化。