室温磁性斯格明子材料及其应用研究进展

Research progress of room temperature magnetic skyrmion and its application

磁性斯格明子是一种具有涡旋状非共线自旋结构的准粒子,具有独特的拓扑保护特性,可在极低电流驱动下运动,有望在信息技术领域获得广泛应用.从2015年开始,科学家已经发现了多种室温磁性斯格明子材料,例如斯格明子多层膜、人工斯格明子材料、β-Mn型单晶材料、中心对称材料(铁氧体、六方Ni2In型)等.其中多层膜材料由于其制备工艺简单、可通过调节各膜层厚度优化性能、器件集成度高等优点而备受关注.这些室温磁性斯格明子材料具有涌生电动势、拓扑霍尔效应、斯格明子霍尔效应等特性,有望用来制备多种新型自旋电子器件,例如赛道存储器、微波探测器、纳米振荡器等,其中赛道存储器有望成为下一代非易失性、低能耗和高密度的存储器.本文首先介绍了磁性斯格明子的基本特性,然后综述了近年来室温磁性斯格明子材料的研究进展、制备技术及表征方法,最后简单介绍了用室温磁性斯格明子材料研制赛道存储器、微波探测器等原型器件的研究进展,展望了室温磁性斯格明子材料的未来发展趋势.

It has been found that many magnetic materials possess the properties arising from skyrmions at room temperature. In addition to the common interaction energy, chiral interaction is also needed to form the skyrmion in magnetic material. There are four chiral magnetic interactions, namely: 1) DzyaloshinskiiMoriya(DM) interaction;2) long-ranged magnetic dipolar interaction;3) four-spin exchange interaction;4) frustrated exchanged interaction. Through the competition between exchange interaction and chiral interaction, magnetic skyrmion can be realized in magnetic material subject to a certain magnetic field and temperature. The skyrmion generated by the DM interaction features small size(5–100 nm), which is easy to adjust. The skyrmion can be driven by magnetic field or ultralow current density. The magnetic materials with skyrmion can exhibit the properties related to the skyrmion Hall effect, the topological Hall effect and the emergent electrodynamics, which are closely related to the skyrmion number. The existence of skyrmion in the magnetic material can be indirectly measured by topological Hall effect. The movement of skyrmion can be driven by spin polarized current in the direction either parallel or perpendicular to the current direction. The movement of the skyrmion driven by spin polarized currents will continue when the current is present, and will disappear when the current disappears.In previous studies, magnetic skyrmions were realized in a variety of materials. However magnetic skyrmions were found only in very limited types of single crystal materials at room temperature or near room temperature. In recent years, scientists have discovered a variety of magnetic skyrmion materials at room temperature, including film materials(such as multilayer materials, artificial skyrmion materials) and crystal materialssuch as b-Mn-type Co10–x/2Zn10–x/2Mnx, Fe3Sn2. Among all kinds of room temperature magnetic skyrmion materials, the most valuable one is the multilayer film material. The Skyrmion multilayer film has the advantages of small size, adjustable material type, simple preparation, good temperature stability, good device integration,etc. At the same time, skyrmion multilayer film is very easy to optimize by adjusting and constructing a special structure that has the wanted types of materials each with a certain thickness. Artificial skyrmion material obtains artificial skyrmion by constructing a micro-nano structure, therefore the artificial skyrmion with high-temperature stability can be realized by choosing high Curie temperature materials. There are a variety of materials which can realize the skyrmion above room temperature, such as Co9Zn9Mn2(300–390 K)and Fe3Sn2(100–400 K). These room temperature materials further widen the temperature application range of skyrmion. The room temperature materials can be prepared or characterized by a variety of techniques including sputtering for fabrication and X-ray magnetic circular dichroism-photoemission electron microscopy(XMCD-PEEM) for characterization.The discovery of the magnetic skyrmion materials at room temperature not only enriches the research content of materials science, but also makes the skyrmion widely applicable in novel electronic devices(such as racetrack memory, microwave detector, oscillators). Because the skyrmion has the advantages of small size,ultra-low driving current density, and topological stability, it is expected to produce racetrack memory based on the skyrmion with low energy consumption, non-volatile and high density. The MTJ microwave detector based on skyrmion can be achieved with no external magnetic field nor bias current but with low power input(<1.0 μW);the sensitivity of the microwave detector can reach 2000 V·W–1. The frequency of the oscillator based on skyrmion can be tuned by magnetic field or current, and moreover, the oscillato is very easy to integrate with IC. In this paper, first, the basic characteristic of magnetic skyrmion is introduced;and then room temperature magnetic skyrmion is reviewed;finally the advances of the racetrack memory, microwave detectors and oscillators are introduced, highlighting the development trend of room temperature magnetic skyrmion.