Spin supercurrents in ferromagnetic and antiferromagnetic films

非技术摘要：手机和电脑等电子设备中的电流通常会因为设备发热而损失很大一部分电源能量。然而，如果材料的温度足够低，一些材料中的电流可以流动而不产生热量。例如，这种被称为超导体的材料被用于磁共振成像扫描仪中，以产生巨大的磁场。这个研究项目的目的是发现一种与超导电性类似的磁性物质，称为自旋超流，并研究它在室温下的稳定性。自旋超流体可以像超导体中的电流一样，以最小的损耗传输磁流。这种近乎无损的磁流可能会用在使用磁性材料进行信息存储和处理的下一代计算机中。本研究的主要研究人员和参与研究的研究生为中学生开发了关于磁学和超导的动手演示，激发了学生对科学和工程的兴趣。技术摘要这项研究的主要目标是在实验上实现一种称为自旋超流的新的磁性物质状态，这种物质被预测存在于铁磁体和反铁磁体中，具有容易的平面磁各向异性。自旋超流体的名字源于它与超流液氦和超导体中的库珀对凝聚体的性质相似。特别是，自旋超流体有望支持自旋超流，这种超流将自旋角动量的传输距离比自旋波的传输距离长几个数量级。这个项目的目标是通过注入垂直于磁各向异性易平面极化的纯自旋电流，在铁磁和反铁磁体的薄膜和纳米线中诱导自旋超流态。自旋超流状态可以通过一种独特的低频超流模式在电学上探测到，这种模式预计会在易平面磁性材料中传播到微观距离。工作范围还包括对铁磁纳米线中Dzyaloshinskii-Moriya相互作用诱导的手性自旋超流状态的研究。通过实验和大规模微磁模拟研究了自旋超流态对热致磁涡形成的稳定性。

Nontechnical abstract:Electric currents in electronic devices such as cell phones and computers typically lose a large fraction of their power supply's energy to the device heating. However, electric currents in some materials can flow without generating heat if the material's temperature is low enough. Such materials called superconductors are used, for example, in magnetic resonance imaging scanners to create large magnetic fields. The aim of this research project is to discover a magnetic analog of superconductivity, which is called spin superfluidity, and to study its stability at room temperature. Spin superfluids can transport magnetic currents with minimal losses similar to electric currents in superconductors. The nearly lossless magnetic currents may find use in the next generation of computers that employ magnetic materials for information storage and processing. The principal investigator and the graduate students involved in this research develop hands-on demonstrations on magnetism and superconductivity for middle school students that stimulate the students' interest in science and engineering. Technical abstractThe main goal of the proposed research is to experimentally realize a new state of magnetic matter called spin superfluid, which has been predicted to exist in ferromagnets and antiferromagnets with easy plane magnetic anisotropy. The name "spin superfluid" stems from the similarity of its properties to those of superfluid liquid helium and Cooper pair condensate in superconductors. In particular, the spin superfluid is expected to support spin supercurrents that transport spin angular momentum over distances orders of magnitude longer than those achievable with spin waves. The goal of this project is to induce the spin superfluid state in thin films and nanowires of ferromagnets and antiferromagnet via injection of pure spin currents polarized perpendicular to the easy plane of magnetic anisotropy. The spin superfluid state can be detected electrically via a unique low-frequency supercurrent mode predicted to propagate over microscopic distances in easy-plane magnetic materials. The scope of work also includes studies of a chiral spin superfluid state induced by Dzyaloshinskii-Moriya interaction in ferromagnetic nanowires. Stability of the spin superfluid state against thermally induced magnetic vortex formation is investigated both experimentally and via large-scale micromagnetic simulations.