Propagating Low-Energy 4f Paramagnons

自旋波及其量子磁振子的概念是由F·布洛赫在1930年提出的。今天，研究自旋波和磁子并利用它们进行数据处理的科学领域被称为磁振子。用于研究磁子的典型材料是低于临界温度(居里温度或尼尔温度)的磁性有序铁磁体和反铁磁体(FM和AFM)。在这些温度以上，磁序丢失，但导致自发磁序的交换刚度虽然降低，但仍然有限。这一现象使得通过非弹性中子散射也可以在准磁网(PM)中观测到高能(&gt；10 mev)磁子。这些磁子被称为准磁子。在“ParaMagnon”项目中，我们将施加一个强大的外磁场，降低PM的温度，以实现磁矩的基本有序化。这些准独立的力矩仍将被剩余的交换刚度和/或偶极-偶极相互作用所耦合。利用材料、温度和外加磁场的变化，我们将证明在临界温度以上的PM、FM和AFM中存在传播低能(&lt；0.5 meV)偶极和交换顺子。因此，我们将研究它们的色散、衰减和传播特性。我们的假设是，4f离子携带的顺子应该具有最低的阻尼值，因为它们与晶格隔离。最后，我们将利用自旋轨道力矩(SOT)现象来激发、放大和探测弹道和扩散的顺子。我们将使用不同的PM和特别是FM和AFM性质的Eu-硫化物家族。用低温微波和布里渊光散射谱对顺子进行探测和表征。电学测量和SOT现象将被用来理解扩散的顺子自旋输运的性质，以及激发和放大它们。准磁振子具有非常高的原创性，因为传播的低能量顺子从未被实验观察到，它们具有比普通磁振子更广泛的一系列优势：用于磁振子的非常广泛的PM材料，低阻尼，对顺磁子性质的灵敏控制和这种控制的新的自由度，以及一个新的量子磁振子工具箱。

The concept of spin waves and their quanta magnons was introduced by F. Bloch in 1930. Today, the field of science investigating spin waves and magnons and utilizing them for data processing is known as magnonics. The typical materials used to investigate magnons are the magnetically ordered ferro- and anti-ferromagnets (FMs and AFMs) at temperatures below the critical (Curie or Neel) temperature. Above these temperatures, the magnetic order is lost, but the exchange stiffness, responsible for the spontaneous magnetic ordering, although decreases, remains finite. This phenomenon allowed for the observation of high-energy (> 10 meV) magnons also in the paramagnets (PMs) by inelastic neutron scattering. These magnons are called paramagnons. In the project "ParaMagnonics", we will apply a strong external magnetic field and will decrease the temperature of the PMs, to achieve the essential ordering of the magnetic moments. These quasi-independent moments will still be coupled by the remaining exchange-stiffness and/or by the dipole-dipolar interaction. Exploiting the variation of the materials, temperature and applied magnetic fields, we will prove the existence of propagating low-energy (< 0.5 meV) dipolar and exchange paramagnons in PMs and in FMs and AFMs above the critical temperatures. Consequently, we will investigate their dispersions, damping, and propagation characteristics. Our hypothesis is that paramagnons carried by 4f ions should have the fundamentally lowest damping values due to their isolation from the crystal lattice. Finally, we will exploit spin-orbit torque (SOT) phenomena to excite, amplify, and detect ballistic and diffusive paramagnons. We will use different PM and the family of Eu-chalcogenides of FM and AFM nature in particular. The paramagnons will be detected and characterized by low-temperature microwave and Brillouin Light Scattering spectroscopy. Electrical measurements and SOT phenomena will be utilized to understand the nature of the diffusive paramagnons spin transport as well as to excite and amplify them. ParaMagnonics has a very high degree of originality, as propagating low-energy paramagnons have never been observed experimentally and they have a whole range of advantages over ordinary magnons: a very broad class of PM materials for magnonics, low damping, sensitive control of paramagnon properties and new degrees of freedom for this control, and a novel toolbox for quantum magnonics.