Spin physics in Two-Dimensional Layered Ferromagnets

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For the last several decades, the development of currently available electronic devices has relied heavily on the downsizing of the transistor, allowing the technology for the small, powerful computers that are the basis of our modern information society. Moore's Law, effectively describing the growth of the number of transistors per unit area (and computing power), has continued ever since, but the end of that trend - the moment when transistors are as small as atoms, and cannot be shrunk any further - will approaching very rapidly. The characteristic feature length of transistors in latest smart phones is 7 nm, within which we can only fit about 14 lattices of silicon crystals. Electronic devices uses the charge of electrons to manipulate them for data-processing. This fundamental concept needs to be revisited now and radically new computing concepts have to be pursued and examined to sustain the further growth of computation efficiency. The concept of spintronics that creates a "spin"-based electronic technology holds potential to replace the charge-based technology of semiconductors and scientists have begun to examine the spin degree of freedom for new electronics. At the heart of the development of spintronic technologies are new discoveries and understanding of magnetic materials at the nanoscale. Magnetic materials can store digital information by the direction of their dipoles (arrows pointing from South to North poles). Hard disk drives have a vast number of tiny magnets (magnetic domains to be precise) which act as data storages to secure our digital information reliably and cheaply. The reliability of data storage in magnets has been achieved by enormous efforts of understanding magnetic properties (so-called anisotropies) and reversal switching of the recording media as well as developing the controllability of thin-film multi-layers. Spintronics has taken it further to build more functional and active memory devices where local data-processing by flipping magnetic dipoles is performed. Reversing the dipole at a very low power consumption is a key to develop commercially-viable spintronic devices. To do so, continued efforts of discovering new magnetic materials, together with an understanding of their materials properties, is a valid and effective approach. In this project, we will study a new class of magnetic materials, the van der Waals 2D layered ferromagnets. They are a magnetic version of graphene, and graphene is a single layer of graphite. A pencil is made out of graphite and the reason that we can write words on a paper with a pencil is because we break a bonding between sheets of graphene while writing and a broken piece of graphite (sheets of graphene) is left over on the paper. Scientists in the UK discovered that it is possible to make a single layer of graphene when we carefully break graphite sheets. And most importantly, graphene shows remarkable electronic properties which do not show up in the form of graphite. After the discovery of graphene, many van der Waals materials have been actively studied at the monolayer limit, forming the active research field of 2D materials. In 2017, the discovery of a magnetic version of graphene was made in two different materials and by two independent research groups, which attract a great deal of interest but yet not much is so far known about these materials. We will on this project study fundamental properties of magnetic 2D layered materials to answer important questions such as "are they different from normal 3D magnets?", "If so, how useful are they for our spintronic technologies?". We have specific workplans to answer these questions as much as possible and also to explore new discoveries with the novel class of nano-materials. Answering these questions allows us to advance the current understanding of ferromagnetism at 2D and spin transport therein, potentially leading to the creation of highly efficient spintronic memories.