Investigation of the physics underlying the principles of design of rare earth - transition metal permanent magnets.

永磁体在现有和发展中的技术中都很普遍。用于电机和发电机、换能器、磁机械设备、磁场和成像系统，它们在全球有数十亿英镑的市场。在基础材料物理学方面，它们既迷人又具有挑战性。随着节能技术、可再生能源供应和设备进一步小型化的发展，对更强、更便宜的磁性材料的需求不断增长。大多数强磁体由稀土（RE）和过渡金属（TM）原子组成，排列成特定的晶体结构。TM元素，如铁或钴，有助于铁磁性在高温下保持不变，而RE元素，如钕或钐，则产生很大的磁化，很难从晶体结构指定的“容易”方向重新定向。nd2fe14b基磁体最初是在20世纪80年代开发的，是非常广泛使用的例子，但它们的磁性在T=100℃以上迅速恶化，因此它们在许多应用中掺杂了关键的稀土金属，如Dy。这不可避免地会导致环境和地缘政治供应问题。另一个著名的RE-TM冠军永磁类，sm - co5为基础，开发于20世纪70年代，具有更好的高温性能，但钴的成本和可用性可能是一个问题。现在，全世界都在共同努力，开发新的永磁材料，提高磁性，减少对关键元素的依赖。然而，这种搜索在很大程度上是启发式的。因此，我们提出的从头开始磁性材料建模，与最先进的样品合成，表征和实验研究并行应用和测试，将有一个极好的机会产生影响。这项工作旨在了解RE-TM磁体的内在磁性和改进设计原则。磁体中的每个稀土原子都有一个磁矩，这个磁矩是由它的近局域化的f电子建立的。这些瞬间沉浸在来自所有稀土原子和TM原子的数以千万计的价电子的粘合剂中。与TM原子相关的局部磁矩也可以从这种复杂的电子流体中产生。磁特性源于RE和TM局部矩如何相互影响和相互影响以及电子胶，原子如何排列以及对外加场的总体响应。我们将建立并应用一个理论，该理论提供了价电子的无参数精确描述，并通过对它们进行平均来结合局部矩的影响，以便可以描述与温度相关的效应。通过引入电子的自旋轨道耦合，对RE-TM磁体的温度、成分和结构依赖性进行预测建模是可行的。为了实现这一目标，在每个阶段，我们将通过与实验室和中心设施的详细实验测量相比较来测试和改进理论。我们将研究许多RE-TM组合形成的三种相对简单的晶体结构，并推动每项研究朝着解决技术相关主题的方向发展，同时规划工作，以最好地提取对基础材料物理学的见解。面临的挑战是：(1)如何通过成分调谐来改进sm - co5基磁铁在高温下的使用；(2)研究nd - fe12基磁体是否可以设计出比dy掺杂Nd2Fe14B具有更好（更便宜）永磁体性能的磁体；(3)找到Tb(1-x)Dy(x)-Fe2金属间化合物的最佳温度和组成范围，用于开发新型磁致伸缩材料。合适的高温磁铁也将被内置到试验传感器中，并在一定温度范围内进行测试。

Permanent magnets are pervasive in both established and developing technologies. Found in motors and generators, transducers, magnetomechanical devices and magnetic field and imaging systems, there is a multi-billion pound worldwide market for them. They are also both fascinating and challenging in terms of their fundamental materials physics.With the drive towards more energy efficient technologies, renewable energy supplies and further miniaturisation of devices, there is a growing demand for stronger and cheaper magnetic materials. Most strong magnets are comprised of rare earth (RE) and transition metal (TM) atoms arranged in specific crystal structures. The TM element, such as iron or cobalt, helps the ferromagnetism to persist to high temperatures and the RE component, such as neodymium or samarium, is there to generate a large magnetisation which is hard to reorientate away from an 'easy' direction specified by the crystal structure. Nd2Fe14B-based magnets, originally developed back in the 1980's, are very widely used examples but their magnetic performance deteriorates rapidly above T=100 C and for this reason they are doped with critical rare earth metals like Dy for many applications. This inevitably leads to environmental and geopolitical supply issues. The other well-known RE-TM champion permanent magnet class, Sm-Co5-based, developed in the 1970's, has better high temperature performance but the cost and availability of cobalt can be a problem. There is now a concerted effort worldwide to come up with new permanent magnetic materials with improved magnetic characteristics and reduced dependence on critical elements. However much of this search is being conducted heuristically. There is therefore an excellent opportunity for our proposed ab-initio magnetic materials modelling, applied and tested in parallel with state-of-the-art sample synthesis, characterisation and experimental investigation to have an impact. This work is aimed understanding intrinsic magnetic properties and refining the design principles of RE-TM magnets. Each RE atom in the magnet has a magnetic moment which is set up by its nearly localised f-electrons. These moments are immersed in a glue of septillions of valence electrons coming from all the RE and TM atoms. Local magnetic moments associated with the TM atoms can also emerge from this complex electron fluid. The magnetic properties stem from how the RE and TM local moments affect and are affected by each other and the electron glue, on how the atoms are arranged and on the overall response to applied fields. We will establish and apply a theory which provides a parameter-free accurate account of the valence electrons and which incorporates the effects of the local moments by averaging over them so that temperature dependent effects can be described. With inclusion of spin-orbit coupling of the electrons, predictive modelling of the temperature, compositional and structural dependence of the magnetic hardness of the RE-TM magnets is feasible. To bring this to fruition, at each stage, we will test and improve the theory by comparison with detailed experimental measurements, both laboratory-based and at central facilities. We will study three relatively simple crystal structures which many RE-TM combinations form and drive each study towards addressing a technologically relevant topic whilst planning the work to best extract insight into the fundamental materials physics. The challenges are: (1) Find out how to improve Sm-Co5-based magnets for use at high temperatures by compositional tuning; (2) Investigate if a Nd-Fe12-based magnet can be designed with better (cheaper) permanent magnet properties than Dy-doped Nd2Fe14B; (3) Find the optimal ranges of temperature and composition for Tb(1-x)Dy(x)-Fe2 intermetallics for the development of new magnetostrictive materials. Suitable high temperature magnets will also be built into trial sensors and tested over a range of temperatures.